diff options
| author | Allen Byrne <50328838+byrnHDF@users.noreply.github.com> | 2021-05-04 22:46:10 (GMT) |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2021-05-04 22:46:10 (GMT) |
| commit | 021d7c7278fd9c182802f2d5419438716beb37bc (patch) | |
| tree | 772b610158e3c771e575a5d7095ebfa589480240 /doxygen/examples | |
| parent | 0801e83615713d95174ed936462310cea32328c7 (diff) | |
| download | hdf5-021d7c7278fd9c182802f2d5419438716beb37bc.zip hdf5-021d7c7278fd9c182802f2d5419438716beb37bc.tar.gz hdf5-021d7c7278fd9c182802f2d5419438716beb37bc.tar.bz2 | |
Hdf5 1 12 doxygen merge (#615)
* OESS-98 fix tools test for plugins
* sync fork
* Merge of changes from dev
* Move problem option to bottom of the list until fixed
* HDFFV-11106 - fix parsing optional args
* HDFFV-11106 add note
* grammer fix
* Whitespace after clang formatting
* Undo format version 11 changes
* Update check to working version
* Merge workflow and minor changes from develop
* Update supported platforms
* PR#3 merge from develop
* Merge gcc 10 diagnostics option from develop
* Merge #318 OSX changes from develop
* Merge serval small changes from dev
* fix typo
* Minor non-space formatting changes
* GH #386 copyright corrections for java folder
* revert because logic requires false return
* Merges from develop
#358 patches from vtk
#361 fix header guard spelling
* Remove case statement for H5I_EVENTSET
* Correct call with versioning
* Remove tabs
* Double underscore change
* Merges from develop
#340 clang -Wformat-security warnings
#360 Fixed uninitialized warnings
Remove more underscores from header guards
* Merge #380 from develop
* Correct date entry
* Split format source and commit changes on repo push
* remove pre-split setting
* Change windows TS to use older VS.
* HDFFV-11212 JNI export util and Javadoc
* Suggested review changes
* Another change found
* Committing clang-format changes
* Some Javadoc warning fixes
* Committing clang-format changes
* Updated javadoc fixes
* HDFFV-11228/9 merges from develop
* remove obsolete debug comment
* Fix conflict
* HDFFV-11229 merge changes from develop
* HDFFV-11229 merge second compare from develop
* HDFFV-11229 fix reference file
* HDFFV-11229 update autotools test script for two ref files
* HDFFV-11229 merge dev changes for long double display in tools
* Committing clang-format changes
* Update with changes from develop
* Add "option" command for clang options
* Rework CMake add_custom to use the BYPRODUCTS argument
Update pkgconfig scripts for parallel builds.
Fix install COPYING file reference.
Remove unused round defines.
Change CMake default setting of BUILD_CPP to off.
* Whitespace changes
* Rework CMake add_custom to use the BYPRODUCTS argument
* Revert CMake configure checks for round defines
* With VS 2015 minimum strdup is supported
* Doxygen comments merged from develop
* doxygen build updates
* Correct version string for map functions
Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>
Diffstat (limited to 'doxygen/examples')
22 files changed, 50331 insertions, 0 deletions
diff --git a/doxygen/examples/FF-IH_FileGroup.gif b/doxygen/examples/FF-IH_FileGroup.gif Binary files differnew file mode 100644 index 0000000..b0d76f5 --- /dev/null +++ b/doxygen/examples/FF-IH_FileGroup.gif diff --git a/doxygen/examples/FF-IH_FileObject.gif b/doxygen/examples/FF-IH_FileObject.gif Binary files differnew file mode 100644 index 0000000..8eba623 --- /dev/null +++ b/doxygen/examples/FF-IH_FileObject.gif diff --git a/doxygen/examples/FileFormatSpecChunkDiagram.jpg b/doxygen/examples/FileFormatSpecChunkDiagram.jpg Binary files differnew file mode 100644 index 0000000..03fd90a --- /dev/null +++ b/doxygen/examples/FileFormatSpecChunkDiagram.jpg diff --git a/doxygen/examples/H5.format.1.0.html b/doxygen/examples/H5.format.1.0.html new file mode 100644 index 0000000..2d3ffbe --- /dev/null +++ b/doxygen/examples/H5.format.1.0.html @@ -0,0 +1,4050 @@ +<html> + <head> + <title> + HDF5 File Format Specification + </title> + </head> + <body bgcolor="#FFFFFF"> + + <center> + <table border=0 width=90%> + <tr> + <td valign=top> + <ol type=I> + <li><a href="#Intro">Introduction</a> + <li><a href="#BootBlock">Disk Format Level 0 - File Signature and Super Block</a> + <li><a href="#Group">Disk Format Level 1 - File Infrastructure</a> + <font size=-2> + <ol type=A> + <li><a href="#Btrees">Disk Format Level 1A - B-link Trees and B-tree Nodes</a> + <li><a href="#SymbolTable">Disk Format Level 1B - Group</a> + <li><a href="#SymbolTableEntry">Disk Format Level 1C - Group Entry</a> + <li><a href="#LocalHeap">Disk Format Level 1D - Local Heaps</a> + <li><a href="#GlobalHeap">Disk Format Level 1E - Global Heap</a> + <li><a href="#FreeSpaceIndex">Disk Format Level 1F - Free-space Index</a> + </ol> + </font> + <li><a href="#DataObject">Disk Format Level 2 - Data Objects</a> + <font size=-2> + <ol type=A> + <li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a> + <ol type=1> + <li><a href="#NILMessage">Name: NIL</a> <!-- 0x0000 --> + <li><a href="#SimpleDataSpace">Name: Simple Dataspace</a> <!-- 0x0001 --> +<!-- + <li><a href="#DataSpaceMessage">Name: Complex Dataspace</a> --> <!-- 0x0002 --> + <li><a href="#DataTypeMessage">Name: Datatype</a> <!-- 0x0003 --> + <li><a href="#FillValueMessage">Name: Data Storage - Fill Value</a> <!-- 0x0004 --> + <li><a href="#ReservedMessage_0005">Name: Reserved - not assigned yet</a> <!-- 0x0005 --> + </ol> + </ol> + </font> + </ol> + </td><td> </td><td valign=top> + <ol type=I> + + <li><a href="#DataObject">Disk Format Level 2 - Data Objects</a> + <font size=-2><i>(Continued)</i> + <ol type=A> + <li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a><i>(Continued)</i> + <ol type=1> + <li><a href="#CompactDataStorageMessage">Name: Data Storage - Compact</a> <!-- 0x0006 --> + <li><a href="#ExternalFileListMessage">Name: Data Storage - External Data Files</a> <!-- 0x0007 --> + <li><a href="#LayoutMessage">Name: Data Storage - Layout</a> <!-- 0x0008 --> + <li><a href="#ReservedMessage_0009">Name: Reserved - not assigned yet</a> <!-- 0x0009 --> + <li><a href="#ReservedMessage_000A">Name: Reserved - not assigned yet</a> <!-- 0x000a --> + <li><a href="#FilterMessage">Name: Data Storage - Filter Pipeline</a> <!-- 0x000b --> + <li><a href="#AttributeMessage">Name: Attribute</a> <!-- 0x000c --> + <li><a href="#NameMessage">Name: Object Name</a> <!-- 0x000d --> + <li><a href="#ModifiedMessage">Name: Object Modification Date and Time</a> <!-- 0x000e --> + <li><a href="#SharedMessage">Name: Shared Object Message</a> <!-- 0x000f --> + <li><a href="#ContinuationMessage">Name: Object Header Continuation</a> <!-- 0x0010 --> + <li><a href="#SymbolTableMessage">Name: Group Message</a> <!-- 0x0011 --> + </ol> + <li><a href="#SharedObjectHeader">Disk Format: Level 2b - Shared Data Object Headers</a> + <li><a href="#DataStorage">Disk Format: Level 2c - Data Object Data Storage</a> + </ol> + </font> + </ol> +</td></tr> +</table> +</center> + +<br><br> + + + <h2>Introduction</h2> + + <table align=right width=100> + <tr><td> </td><td align=center> + <hr> + <img src="FF-IH_FileGroup.gif" alt="HDF5 Groups" hspace=15 vspace=15> + </td><td> </td></tr> + <tr><td> </td><td align=center> + <strong>Figure 1:</strong> Relationships among the HDF5 root group, other groups, and objects + <hr> + </td><td> </td></tr> + + <tr><td> </td><td align=center> + <img src="FF-IH_FileObject.gif" alt="HDF5 Objects" hspace=15 vspace=15> + </td><td> </td></tr> + <tr><td> </td><td align=center> + <strong>Figure 2:</strong> HDF5 objects -- datasets, datatypes, or dataspaces + <hr> + </td><td> </td></tr> + </table> + + + <P>The format of an HDF5 file on disk encompasses several + key ideas of the HDF4 and AIO file formats as well as + addressing some shortcomings therein. The new format is + more self-describing than the HDF4 format and is more + uniformly applied to data objects in the file. + + <P>An HDF5 file appears to the user as a directed graph. + The nodes of this graph are the higher-level HDF5 objects + that are exposed by the HDF5 APIs: + + <ul> + <li>Groups + <li>Datasets + <li>Datatypes + <li>Dataspaces + </ul> + + <P>At the lowest level, as information is actually written to the disk, + an HDF5 file is made up of the following objects: + <ul> + <li>A super block + <li>B-tree nodes (containing either symbol nodes or raw data chunks) + <li>Object headers + + <li>Collections + <li>Local heaps + <li>Free space + </ul> + + The HDF5 library uses these lower-level objects to represent the + higher-level objects that are then presented to the user or + to applications through the APIs. + For instance, a group is an object header that contains a message that + points to a local heap and to a B-tree which points to symbol nodes. + A dataset is an object header that contains messages that describe + datatype, space, layout, filters, external files, fill value, etc + with the layout message pointing to either a raw data chunk or to a + B-tree that points to raw data chunks. + + + <h3>This Document</h3> + + <p>This document describes the lower-level data objects; + the higher-level objects and their properties are described + in the <a href="H5.user.html"><cite>HDF5 User's Guide</cite></a>. + + +<!-- +<blockquote> +<pre> + +Elena> NOTE: give reference to the detailed discussion of the B-trees +Elena> when needed. Right now we do not have specification (only general one) +Elena> for the Symbol Table B-trees and B-trees used to manage chunked datasets. +Elena> B-trees +Elena> General Discussion +Elena> Object related discussions +Elena> Symbol Tables +Elena> Global heap +Elena> "Free-space object" + + +</pre> +</blockquote> +--> + + + + <P>Three levels of information comprise the file format. + Level 0 contains basic information for identifying and + defining information about the file. Level 1 information contains + the group information (stored as a B-tree) and is used as the + index for all the objects in the file. Level 2 is the rest + of the file and contains all of the data objects, with each object + partitioned into header information, also known as + <em>meta information</em>, and data. + + <p>The sizes of various fields in the following layout tables are + determined by looking at the number of columns the field spans + in the table. There are three exceptions: (1) The size may be + overridden by specifying a size in parentheses, (2) the size of + addresses is determined by the <em>Size of Offsets</em> field + in the super block, and (3) the size of size fields is determined + by the <em>Size of Lengths</em> field in the super block. + + + +<br><br> +<br><br> + + + <h2><a name="BootBlock"> + Disk Format: Level 0 - File Signature and Super Block</a></h2> + + <P>The super block may begin at certain predefined offsets within + the HDF5 file, allowing a block of unspecified content for + users to place additional information at the beginning (and + end) of the HDF5 file without limiting the HDF5 library's + ability to manage the objects within the file itself. This + feature was designed to accommodate wrapping an HDF5 file in + another file format or adding descriptive information to the + file without requiring the modification of the actual file's + information. The super block is located by searching for the + HDF5 file signature at byte offset 0, byte offset 512 and at + successive locations in the file, each a multiple of two of + the previous location, i.e. 0, 512, 1024, 2048, etc. + + <P>The super block is composed of a file signature, followed by + super block and group version numbers, information + about the sizes of offset and length values used to describe + items within the file, the size of each group page, + and a group entry for the root object in the file. + + <p> + <center> + <table border align=center cellpadding=4 width="80%"> + <caption align=top> + <B>HDF5 Super Block Layout</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4><br>HDF5 File Signature (8 bytes)<br><br></td> + </tr> + + <tr align=center> + <td>Version # of Super Block</td> + <td>Version # of Global Free-space Storage</td> + <td>Version # of Group</td> + <td>Reserved</td> + </tr> + + <tr align=center> + <td>Version # of Shared Header Message Format</td> + <td>Size of Offsets</td> + <td>Size of Lengths</td> + <td>Reserved (zero)</td> + </tr> + + <tr align=center> + <td colspan=2>Group Leaf Node K</td> + <td colspan=2>Group Internal Node K</td> + </tr> + + <tr align=center> + <td colspan=4>File Consistency Flags</td> + </tr> + + <tr align=center> + <td colspan=4>Base Address*</td> + </tr> + + <tr align=center> + <td colspan=4>Address of Global Free-space Heap*</td> + </tr> + + <tr align=center> + <td colspan=4>End of File Address*</td> + </tr> + + <tr align=center> + <td colspan=4>Driver Information Block Address*</td> + </tr> + + <tr align=center> + <td colspan=4>Root Group Address*</td> + </tr> + </table> + + <table width="80%" border=0> + <tr><td> + <div align=right> + (Items marked with an asterisk (*) in the above table + <br> + are of the size specified in "Size of Offsets.") + </div> + </td></tr> + </table> + </center> + + <p> + <center> + <table width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>File Signature</td> + <td>This field contains a constant value and can be used to + quickly identify a file as being an HDF5 file. The + constant value is designed to allow easy identification of + an HDF5 file and to allow certain types of data corruption + to be detected. The file signature of an HDF5 file always + contains the following values: + + <br><br><center> + <table border align=center cellpadding=4 width="100%"> + <tr align=center> + <td>decimal</td> + <td width="8%">137</td> + <td width="8%">72</td> + <td width="8%">68</td> + <td width="8%">70</td> + <td width="8%">13</td> + <td width="8%">10</td> + <td width="8%">26</td> + <td width="8%">10</td> + </tr> + + <tr align=center> + <td>hexadecimal</td> + <td width="8%">89</td> + <td width="8%">48</td> + <td width="8%">44</td> + <td width="8%">46</td> + <td width="8%">0d</td> + <td width="8%">0a</td> + <td width="8%">1a</td> + <td width="8%">0a</td> + </tr> + + <tr align=center> + <td>ASCII C Notation</td> + <td width="8%">\211</td> + <td width="8%">H</td> + <td width="8%">D</td> + <td width="8%">F</td> + <td width="8%">\r</td> + <td width="8%">\n</td> + <td width="8%">\032</td> + <td width="8%">\n</td> + </tr> + </table> + </center> + <br> + + This signature both identifies the file as an HDF5 file + and provides for immediate detection of common + file-transfer problems. The first two bytes distinguish + HDF5 files on systems that expect the first two bytes to + identify the file type uniquely. The first byte is + chosen as a non-ASCII value to reduce the probability + that a text file may be misrecognized as an HDF5 file; + also, it catches bad file transfers that clear bit + 7. Bytes two through four name the format. The CR-LF + sequence catches bad file transfers that alter newline + sequences. The control-Z character stops file display + under MS-DOS. The final line feed checks for the inverse + of the CR-LF translation problem. (This is a direct + descendent of the PNG file signature.)</td> + </tr> + + <tr valign=top> + <td>Version Number of the Super Block</td> + <td>This value is used to determine the format of the + information in the super block. When the format of the + information in the super block is changed, the version number + is incremented to the next integer and can be used to + determine how the information in the super block is + formatted.</td> + </tr> + + <tr valign=top> + <td>Version Number of the Global Free-space Heap</td> + <td>This value is used to determine the format of the + information in the Global Free-space Heap.</td> + </tr> + + <tr valign=top> + <td>Version Number of the Group</td> + <td>This value is used to determine the format of the + information in the Group. When the format of + the information in the Group is changed, the + version number is incremented to the next integer and can be + used to determine how the information in the Group + is formatted.</td> + </tr> + + <tr valign=top> + <td>Version Number of the Shared Header Message Format</td> + <td>This value is used to determine the format of the + information in a shared object header message, which is + stored in the global small-data heap. Since the format + of the shared header messages differs from the private + header messages, a version number is used to identify changes + in the format.</td> + </tr> + + <tr valign=top> + <td>Size of Offsets</td> + <td>This value contains the number of bytes used to store + addresses in the file. The values for the addresses of + objects in the file are offsets relative to a base address, + usually the address of the super block signature. This + allows a wrapper to be added after the file is created + without invalidating the internal offset locations.</td> + </tr> + + <tr valign=top> + <td>Size of Lengths</td> + <td>This value contains the number of bytes used to store + the size of an object.</td> + </tr> + + <tr valign=top> + <td>Group Leaf Node K</td> + <td>Each leaf node of a group B-tree will have at + least this many entries but not more than twice this + many. If a group has a single leaf node then it + may have fewer entries.</td> + </tr> + + <tr valign=top> + <td>Group Internal Node K</td> + <td>Each internal node of a group B-tree will have + at least K pointers to other nodes but not more than 2K + pointers. If the group has only one internal + node then it might have fewer than K pointers.</td> + </tr> + + <tr valign=top> + <td>Bytes per B-tree Page</td> + <td>This value contains the number of bytes used for symbol + pairs per page of the B-trees used in the file. All + B-tree pages will have the same size per page. + <br> + For 32-bit file offsets, 340 objects is the maximum + per 4KB page; for 64-bit file offset, 254 objects will fit + per 4KB page. In general, the equation is: + <br> + <code> <<i>number of objects</i>> = + <br> + FLOOR((<<i>page size</i>> - <<i>offset size</i>>) / + <br> + (<<i>Symbol size</i>> + <<i>offset size</i>>)) + - 1 </code></td> + </tr> + + <tr valign=top> + <td>File Consistency Flags</td> + <td>This value contains flags to indicate information + about the consistency of the information contained + within the file. Currently, the following bit flags are + defined: + <ul> + <li>Bit 0 set indicates that the file is opened for + write-access. + <li>Bit 1 set indicates that the file has + been verified for consistency and is guaranteed to be + consistent with the format defined in this document. + <li>Bits 2-31 are reserved for future use. + </ul> + Bit 0 should be + set as the first action when a file is opened for write + access and should be cleared only as the final action + when closing a file. Bit 1 should be cleared during + normal access to a file and only set after the file's + consistency is guaranteed by the library or a + consistency utility.</td> + </tr> + + <tr valign=top> + <td>Base Address</td> + <td>This is the absolute file address of the first byte of + the HDF5 data within the file. The library currently + constrains this value to be the absolute file address + of the super block itself when creating new files; + future versions of the library may provide greater + flexibility. Unless otherwise noted, + all other file addresses are relative to this base + address.</td> + </tr> + + <tr valign=top> + <td>Address of Global Free-space Heap</td> + <td>Free-space management is not yet defined in the HDF5 + file format and is not handled by the library. + Currently this field always contains the + undefined address <code>0xfff...ff</code>. +<!-- + <td>This value contains the relative address of the B-tree + used to manage the blocks of data which are unused in the + file currently. The free-space heap is used to manage the + blocks of bytes at the file-level which become unused when + objects are moved within the file.</td> +--> + </tr> + + <tr valign=top> + <td>End of File Address</td> + <td>This is the relative file address of the first byte past + the end of all HDF5 data. It is used to determine whether a + file has been accidently truncated and as an address where + file data allocation can occur if the free list is not + used.</td> + </tr> + + <tr valign=top> + <td>Driver Information Block Address</td> + <td>This is the relative file address of the file driver + information block which contains driver-specific + information needed to reopen the file. If there is no + driver information block then this entry should be the + undefined address (all bits set).</td> + </tr> + + <tr valign=top> + <td>Root Group Address</td> + <td>This is the address of the root group (described later + in this document), which serves as the entry point into + the group graph.</td> + </tr> + </table> + </center> + + + <p>The <em>file driver information block</em> is an optional region of the + file which contains information needed by the file driver in + order to reopen a file. The format of the file driver information + block is: + + <p> + <center> + <table border align=center cellpadding=4 width="80%"> + <caption align=top> + <B>Driver Information Block</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Version</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr align=center> + <td colspan=4>Driver Information Size (4 bytes)</td> + </tr> + + <tr align=center> + <td colspan=4><br>Driver Identification (8 bytes)<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br><br>Driver Information<br><br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version</td> + <td>The version number of the driver information block. The + file format documented here is version zero.</td> + </tr> + + <tr valign=top> + <td>Driver Information Size</td> + <td>The size in bytes of the Driver Information part of this + structure.</td> + </tr> + + <tr valign=top> + <td>Driver Identification</td> + <td>This is an eight-byte ASCII string without null + termination which identifies the driver and version number + of the Driver Information block. The predefined drivers + supplied with the HDF5 library are identified by the + letters <code>NCSA</code> followed by the first four characters of + the driver name. If the Driver Information block is not + the original version then the last letter(s) of the + identification will be replaced by a version number in + ASCII. + For example, the various versions of the <em>family driver</em> + will be identified by <code>NCSAfami</code>, <code>NCSAfam0</code>, + <code>NCSAfam1</code>, etc. + (<code>NCSAfami</code> is simply <code>NCSAfamily</code> truncated + to eight characters. Subsequent identifiers will be created by + substituting sequential numerical values for the final character, + starting with zero.) + <p> + Identification for user-defined drivers + is arbitrary but should be unique.</td> + </tr> + + <tr valign=top> + <td>Driver Information</td> + <td>Driver information is stored in a format defined by the + file driver and encoded/decoded by the driver callbacks + invoked from the <code>H5FD_sb_encode</code> and + <code>H5FD_sb_decode</code> functions.</td> + </tr> + </table> + </center> + + + <br><br> + <br><br> + + + <h2><a name="Group"> + Disk Format: Level 1 - File Infrastructure</a></h2> + <h3><a name="Btrees">Disk Format: Level 1A - B-link Trees and B-tree Nodes</a></h3> + + <p>B-link trees allow flexible storage for objects which tend to grow + in ways that cause the object to be stored discontiguously. B-trees + are described in various algorithms books including "Introduction to + Algorithms" by Thomas H. Cormen, Charles E. Leiserson, and Ronald + L. Rivest. The B-link tree, in which the sibling nodes at a + particular level in the tree are stored in a doubly-linked list, + is described in the "Efficient Locking for Concurrent Operations + on B-trees" paper by Phillip Lehman and S. Bing Yao as published + in the <em>ACM Transactions on Database Systems</em>, Vol. 6, + No. 4, December 1981. + + <p>The B-link trees implemented by the file format contain one more + key than the number of children. In other words, each child + pointer out of a B-tree node has a left key and a right key. + The pointers out of internal nodes point to sub-trees while + the pointers out of leaf nodes point to symbol nodes and + raw data chunks. + Aside from that difference, internal nodes and leaf nodes + are identical. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>B-tree Nodes</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Node Signature</td> + + <tr align=center> + <td>Node Type</td> + <td>Node Level</td> + <td colspan=2>Entries Used</td> + + <tr align=center> + <td colspan=4>Address of Left Sibling</td> + + <tr align=center> + <td colspan=4>Address of Right Sibling</td> + + <tr align=center> + <td colspan=4>Key 0 (variable size)</td> + + <tr align=center> + <td colspan=4>Address of Child 0</td> + + <tr align=center> + <td colspan=4>Key 1 (variable size)</td> + + <tr align=center> + <td colspan=4>Address of Child 1</td> + + <tr align=center> + <td colspan=4>...</td> + + <tr align=center> + <td colspan=4>Key 2<em>K</em> (variable size)</td> + + <tr align=center> + <td colspan=4>Address of Child 2<em>K</em></td> + + <tr align=center> + <td colspan=4>Key 2<em>K</em>+1 (variable size)</td> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Node Signature</td> + <td>The ASCII character string <code>TREE</code> is + used to indicate the + beginning of a B-link tree node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file.</td> + </tr> + + <tr valign=top> + <td>Node Type</td> + <td>Each B-link tree points to a particular type of data. + This field indicates the type of data as well as + implying the maximum degree <em>K</em> of the tree and + the size of each Key field. + <br> + <dl compact> + <dt>0 + <dd>This tree points to group nodes. + <dt>1 + <dd>This tree points to a new data chunk. + </dl> + </td> + </tr> + + <tr valign=top> + <td>Node Level</td> + <td>The node level indicates the level at which this node + appears in the tree (leaf nodes are at level zero). Not + only does the level indicate whether child pointers + point to sub-trees or to data, but it can also be used + to help file consistency checking utilities reconstruct + damanged trees.</td> + </tr> + + <tr valign=top> + <td>Entries Used</td> + <td>This determines the number of children to which this + node points. All nodes of a particular type of tree + have the same maximum degree, but most nodes will point + to less than that number of children. The valid child + pointers and keys appear at the beginning of the node + and the unused pointers and keys appear at the end of + the node. The unused pointers and keys have undefined + values.</td> + </tr> + + <tr valign=top> + <td>Address of Left Sibling</td> + <td>This is the file address of the left sibling of the + current node relative to the super block. If the current + node is the left-most node at this level then this field + is the undefined address (all bits set).</td> + </tr> + + <tr valign=top> + <td>Address of Right Sibling</td> + <td>This is the file address of the right sibling of the + current node relative to the super block. If the current + node is the right-most node at this level then this + field is the undefined address (all bits set).</td> + </tr> + + <tr valign=top> + <td>Keys and Child Pointers</td> + <td>Each tree has 2<em>K</em>+1 keys with 2<em>K</em> + child pointers interleaved between the keys. The number + of keys and child pointers actually containing valid + values is determined by the <em>Entries Used</em> field. If + that field is <em>N</em> then the B-link tree contains + <em>N</em> child pointers and <em>N</em>+1 keys.</td> + </tr> + + <tr valign=top> + <td>Key</td> + <td>The format and size of the key values is determined by + the type of data to which this tree points. The keys are + ordered and are boundaries for the contents of the child + pointer; that is, the key values represented by child + <em>N</em> fall between Key <em>N</em> and Key + <em>N</em>+1. Whether the interval is open or closed on + each end is determined by the type of data to which the + tree points. + <p> + The format of the key depends on the node type. + For nodes of node type 1, the key is formatted as follows: + <center> + <table> + <tr valign=top align=left> + <td width=40%>Bytes 1-4</td> + <td>Size of chunk in bytes.</td> + <tr valign=top align=left></tr> + <td>Bytes 4-8</td> + <td>Filter mask, a 32-bit bitfield indicating which + filters have been applied to that chunk.</td> + </tr><tr valign=top align=left> + <td><i>N</i> fields of 8 bytes each</td> + <td>A 64-bit index indicating the offset of the + chunk within the dataset where <i>N</i> is the number + of dimensions of the dataset. For example, if + a chunk in a 3-dimensional dataset begins at the + position <code>[5,5,5]</code>, there will be three + such 8-bit indices, each with the value of + <code>5</code>.</td> + </tr> + </table> + </center> + <p> + For nodes of node type 0, the key is formatted as follows: + <center> + <table> + <tr valign=top align=left> + <td width=40%>A single field of <i>Size of Lengths</i> + bytes</td> + <td>Indicates the byte offset into the local heap + for the first object name in the subtree which + that key describes.</td> + </tr> + </table> + </center> + </td> + </tr> + + <tr valign=top> + <td>Child Pointers</td> + <td>The tree node contains file addresses of subtrees or + data depending on the node level. Nodes at Level 0 point + to data addresses, either data chunk or group nodes. + Nodes at non-zero levels point to other nodes of the + same B-tree.</td> + </tr> + </table> + </center> + +<p> + Each B-tree node looks like this: + + <center> + <table> + <tr valign=top align=center> + <td>key[0]</td><td> </td> + <td>child[0]</td><td> </td> + <td>key[1]</td><td> </td> + <td>child[1]</td><td> </td> + <td>key[2]</td><td> </td> + <td>...</td><td> </td> + <td>...</td><td> </td> + <td>key[<i>N</i>-1]</td><td> </td> + <td>child[<i>N</i>-1]</td><td> </td> + <td>key[<i>N</i>]</td> + </tr> + </table> + </center> + + where child[<i>i</i>] is a pointer to a sub-tree (at a level + above Level 0) or to data (at Level 0). + Each key[<i>i</i>] describes an <i>item</i> stored by the B-tree + (a chunk or an object of a group node). The range of values + represented by child[<i>i</i>] are indicated by key[<i>i</i>] + and key[<i>i</i>+1]. + + + <p>The following question must next be answered: + "Is the value described by key[<i>i</i>] contained in + child[<i>i</i>-1] or in child[<i>i</i>]?" + The answer depends on the type of tree. + In trees for groups (node type 0) the object described by + key[<i>i</i>] is the greatest object contained in + child[<i>i</i>-1] while in chunk trees (node type 1) the + chunk described by key[<i>i</i>] is the least chunk in + child[<i>i</i>]. + + <p>That means that key[0] for group trees is sometimes unused; + it points to offset zero in the heap, which is always the + empty string and compares as "less-than" any valid object name. + + <p>And key[<i>N</i>] for chunk trees is sometimes unused; + it contains a chunk offset which compares as "greater-than" + any other chunk offset and has a chunk byte size of zero + to indicate that it is not actually allocated. + + + <h3><a name="SymbolTable">Disk Format: Level 1B - Group and Symbol Nodes</a></h3> + + <p>A group is an object internal to the file that allows + arbitrary nesting of objects (including other groups). + A group maps a set of names to a set of file + address relative to the base address. Certain meta data + for an object to which the group points can be duplicated + in the group symbol table in addition to the object header. + + <p>An HDF5 object name space can be stored hierarchically by + partitioning the name into components and storing each + component in a group. The group entry for a + non-ultimate component points to the group containing + the next component. The group entry for the last + component points to the object being named. + + <p>A group is a collection of group nodes pointed + to by a B-link tree. Each group node contains entries + for one or more symbols. If an attempt is made to add a + symbol to an already full group node containing + 2<em>K</em> entries, then the node is split and one node + contains <em>K</em> symbols and the other contains + <em>K</em>+1 symbols. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Group Node (A Leaf of a B-tree)</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Node Signature</td> + + <tr align=center> + <td>Version Number</td> + <td>Reserved for Future Use</td> + <td colspan=2>Number of Symbols</td> + + <tr align=center> + <td colspan=4><br><br>Group Entries<br><br><br></td> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Node Signature</td> + <td>The ASCII character string <code>SNOD</code> is + used to indicate the + beginning of a group node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file.</td> + </tr> + + <tr valign=top> + <td>Version Number</td> + <td>The version number for the group node. This + document describes version 1.</td> + </tr> + + <tr valign=top> + <td>Number of Symbols</td> + <td>Although all group nodes have the same length, + most contain fewer than the maximum possible number of + symbol entries. This field indicates how many entries + contain valid data. The valid entries are packed at the + beginning of the group node while the remaining + entries contain undefined values.</td> + </tr> + + <tr valign=top> + <td>Group Entries</td> + <td>Each symbol has an entry in the group node. + The format of the entry is described below.</td> + </tr> + </table> + </center> + + <h3><a name="SymbolTableEntry"> + Disk Format: Level 1C - Group Entry </a></h3> + + <p>Each group entry in a group node is designed + to allow for very fast browsing of stored objects. + Toward that design goal, the group entries + include space for caching certain constant meta data from the + object header. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Group Entry</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4>Name Offset (<size> bytes)</td> + </tr> + + <tr align=center> + <td colspan=4>Object Header Address</td> + </tr> + + <tr align=center> + <td colspan=4>Cache Type</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4><br><br>Scratch-pad Space (16 bytes)<br><br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Name Offset</td> + <td>This is the byte offset into the group local + heap for the name of the object. The name is null + terminated.</td> + </tr> + + <tr valign=top> + <td>Object Header Address</td> + <td>Every object has an object header which serves as a + permanent location for the object's meta data. In addition + to appearing in the object header, some meta data can be + cached in the scratch-pad space.</td> + </tr> + + <tr valign=top> + <td>Cache Type</td> + <td>The cache type is determined from the object header. + It also determines the format for the scratch-pad space. + <br> + <dl compact> + <dt>0 + <dd>No data is cached by the group entry. This + is guaranteed to be the case when an object header + has a link count greater than one. + + <dt>1 + <dd>Object header meta data is cached in the group + entry. This implies that the group + entry refers to another group. + + <dt>2 + <dd>The entry is a symbolic link. The first four bytes + of the scratch-pad space are the offset into the local + heap for the link value. The object header address + will be undefined. + + <dt><em>N</em> + <dd>Other cache values can be defined later and + libraries that do not understand the new values will + still work properly. + </dl> + </td> + </tr> + + <tr valign=top> + <td>Reserved</td> + <td>These four bytes are present so that the scratch-pad + space is aligned on an eight-byte boundary. They are + always set to zero.</td> + </tr> + + <tr valign=top> + <td>Scratch-pad Space</td> + <td>This space is used for different purposes, depending + on the value of the Cache Type field. Any meta-data + about a dataset object represented in the scratch-pad + space is duplicated in the object header for that + dataset. This meta data can include the datatype + and the size of the dataspace for a dataset whose datatype + is atomic and whose dataspace is fixed and less than + four dimensions. + Furthermore, no data is cached in the group + entry scratch-pad space if the object header for + the group entry has a link count greater than + one.</td> + </tr> + </table> + </center> + + <h4>Format of the Scratch-pad Space</h4> + + <p>The group entry scratch-pad space is formatted + according to the value in the Cache Type field. + + <p>If the Cache Type field contains the value zero + (<code>0</code>) then no information is + stored in the scratch-pad space. + + <p>If the Cache Type field contains the value one + (<code>1</code>), then the scratch-pad space + contains cached meta data for another object header + in the following format: + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Object Header Scratch-pad Format</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Address of B-tree</td> + + <tr align=center> + <td colspan=4>Address of Name Heap</td> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Address of B-tree</td> + <td>This is the file address for the root of the + group's B-tree.</td> + </tr> + + <tr valign=top> + <td>Address of Name Heap</td> + <td>This is the file address for the group's local + heap, in which are stored the symbol names.</td> + </tr> + </table> + </center> + + + <p>If the Cache Type field contains the value two + (<code>2</code>), then the scratch-pad space + contains cached meta data for another symbolic link + in the following format: + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Symbolic Link Scratch-pad Format</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4>Offset to Link Value</td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Offset to Link Value</td> + <td>The value of a symbolic link (that is, the name of the + thing to which it points) is stored in the local heap. + This field is the 4-byte offset into the local heap for + the start of the link value, which is null terminated.</td> + </tr> + </table> + </center> + + <h3><a name="LocalHeap">Disk Format: Level 1D - Local Heaps</a></h3> + + <p>A heap is a collection of small heap objects. Objects can be + inserted and removed from the heap at any time. + The address of a heap does not change once the heap is created. + References to objects are stored in the group table; + the names of those objects are stored in the local heap. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Local Heaps</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4>Heap Signature</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved (zero)</td> + </tr> + + <tr align=center> + <td colspan=4>Data Segment Size</td> + </tr> + + <tr align=center> + <td colspan=4>Offset to Head of Free-list (<size> bytes)</td> + </tr> + + <tr align=center> + <td colspan=4>Address of Data Segment</td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Heap Signature</td> + <td>The ASCII character string <code>HEAP</code> + is used to indicate the + beginning of a heap. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file.</td> + </tr> + + <tr valign=top> + <td>Data Segment Size</td> + <td>The total amount of disk memory allocated for the heap + data. This may be larger than the amount of space + required by the object stored in the heap. The extra + unused space holds a linked list of free blocks.</td> + </tr> + + <tr valign=top> + <td>Offset to Head of Free-list</td> + <td>This is the offset within the heap data segment of the + first free block (or all 0xff bytes if there is no free + block). The free block contains <size> bytes that + are the offset of the next free chunk (or all 0xff bytes + if this is the last free chunk) followed by <size> + bytes that store the size of this free chunk.</td> + </tr> + + <tr valign=top> + <td>Address of Data Segment</td> + <td>The data segment originally starts immediately after + the heap header, but if the data segment must grow as a + result of adding more objects, then the data segment may + be relocated, in its entirety, to another part of the + file.</td> + </tr> + </table> + </center> + + <p>Objects within the heap should be aligned on an 8-byte boundary. + + <h3><a name="GlobalHeap">Disk Format: Level 1E - Global Heap</a></h3> + + <p>Each HDF5 file has a global heap which stores various types of + information which is typically shared between datasets. The + global heap was designed to satisfy these goals: + + <ol type="A"> + <li>Repeated access to a heap object must be efficient without + resulting in repeated file I/O requests. Since global heap + objects will typically be shared among several datasets, it is + probable that the object will be accessed repeatedly. + + <br><br> + <li>Collections of related global heap objects should result in + fewer and larger I/O requests. For instance, a dataset of + void pointers will have a global heap object for each + pointer. Reading the entire set of void pointer objects + should result in a few large I/O requests instead of one small + I/O request for each object. + + <br><br> + <li>It should be possible to remove objects from the global heap + and the resulting file hole should be eligible to be reclaimed + for other uses. + <br><br> + </ol> + + <p>The implementation of the heap makes use of the memory + management already available at the file level and combines that + with a new top-level object called a <em>collection</em> to + achieve Goal B. The global heap is the set of all collections. + Each global heap object belongs to exactly one collection and + each collection contains one or more global heap objects. For + the purposes of disk I/O and caching, a collection is treated as + an atomic object. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>A Global Heap Collection</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4>Magic Number</td> + </tr> + + <tr align=center> + <td>Version</td> + <td colspan=3>Reserved</td> + </td> + + <tr align=center> + <td colspan=4>Collection Size</td> + </tr> + + <tr align=center> + <td colspan=4><br>Global Heap Object 1 + <i>(described below)</i><br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Global Heap Object 2<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>...<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Global Heap Object <em>N</em><br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Global Heap Object 0 (free space)<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Magic Number</td> + <td>The magic number for global heap collections are the + four bytes <code>G</code>, <code>C</code>, <code>O</code>, + and <code>L</code>.</td> + </tr> + + <tr valign=top> + <td>Version</td> + <td>Each collection has its own version number so that new + collections can be added to old files. This document + describes version zero of the collections. + </tr> + + <tr valign=top> + <td>Collection Data Size</td> + <td>This is the size in bytes of the entire collection + including this field. The default (and minimum) + collection size is 4096 bytes which is a typical file + system block size and which allows for 170 16-byte heap + objects plus their overhead.</td> + </tr> + + <tr valign=top> + <td>Object 1 through <em>N</em></td> + <td>The objects are stored in any order with no + intervening unused space.</td> + </tr> + + <tr valign=top> + <td>Object 0</td> + <td>Object 0 (zero), when present, represents the free space in + the collection. Free space always appears at the end of + the collection. If the free space is too small to store + the header for Object 0 (described below) then the + header is implied and the collection contains no free space. + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Global Heap Object</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=2>Object ID</td> + <td colspan=2>Reference Count</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Object Data Size</td> + </tr> + + <tr align=center> + <td colspan=4><br>Object Data<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Object ID</td> + <td>Each object has a unique identification number within a + collection. The identification numbers are chosen so that + new objects have the smallest value possible with the + exception that the identifier <code>0</code> always refers to the + object which represents all free space within the + collection.</td> + </tr> + + <tr valign=top> + <td>Reference Count</td> + <td>All heap objects have a reference count field. An + object which is referenced from some other part of the + file will have a positive reference count. The reference + count for Object 0 is always zero.</td> + </tr> + + <tr valign=top> + <td>Reserved</td> + <td>Zero padding to align next field on an 8-byte + boundary.</td> + </tr> + + <tr valign=top> + <td>Object Size</td> <td>This is the size of the the fields + above plus the object data stored for the object. The + actual storage size is rounded up to a multiple of + eight.</td> + </tr> + + <tr valign=top> + <td>Object Data</td> + <td>The object data is treated as a one-dimensional array + of bytes to be interpreted by the caller.</td> + </tr> + </table> + </center> + + <h3><a name="FreeSpaceIndex">Disk Format: Level 1F - Free-space Heap</a></h3> + + <p>The Free-space Index is a collection of blocks of data, + dispersed throughout the file, which are currently not used by + any file objects. + + <p>The super block contains a pointer to root of the free-space description; + that pointer is currently (i.e., in HDF5 Release 1.2) required + to be the undefined address <code>0xfff...ff</code>. + + <p>The free-sapce index is not otherwise publicly defined at this time. + + + <!-- + <p>The Free-space Index is a collection of blocks of data, + dispersed throughout the file, which are currently not used by + any file objects. The blocks of data are indexed by a B-tree of + their length within the file. + + + <p>Each B-tree page is composed of the following entries and + B-tree management information, organized as follows: + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Free-space Heap Page</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Free-space Heap Signature</td> + <tr align=center> + <td colspan=4>B-tree Left-link Offset</td> + <tr align=center> + <td colspan=4><br>Length of Free-block #1<br> <br></td> + <tr align=center> + <td colspan=4><br>Offset of Free-block #1<br> <br></td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4><br>Length of Free-block #n<br> <br></td> + <tr align=center> + <td colspan=4><br>Offset of Free-block #n<br> <br></td> + <tr align=center> + <td colspan=4>"High" Offset</td> + <tr align=center> + <td colspan=4>Right-link Offset</td> + </table> + </center> + + <p> + <dl> + <dt> The elements of the free-space heap page are described below: + <dd> + <dl> + <dt>Free-space Heap Signature: (4 bytes) + <dd>The ASCII character string <code>FREE</code> + is used to indicate the + beginning of a free-space heap B-tree page. This gives + file consistency checking utilities a better chance of + reconstructing a damaged file. + + <dt>B-tree Left-link Offset: (<offset> bytes) + <dd>This value is used to indicate the offset of all offsets + in the B-link-tree which are smaller than the value of the + offset in entry #1. This value is also used to indicate a + leaf node in the B-link-tree by being set to all ones. + + <dt>Length of Free-block #n: (<length> bytes) + <dd>This value indicates the length of an unused block in + the file. + + <dt>Offset of Free-block #n: (<offset> bytes) + <dd>This value indicates the offset in the file of an + unused block in the file. + + <dt>"High" Offset: (4-bytes) + <dd>This offset is used as the upper bound on offsets + contained within a page when the page has been split. + + <dt>Right-link Offset: (<offset> bytes) + <dd>This value is used to indicate the offset of the next + child to the right of the parent of this group + page. When there is no node to the right, this value is + all zeros. + </dl> + </dl> + + <p>The algorithms for searching and inserting objects in the + B-tree pages are described fully in the Lehman and Yao paper, + which should be read to provide a full description of the + B-tree's usage. +--> + + +<br><br> +<br><br> + + + <h2><a name="DataObject">Disk Format: Level 2 - Data Objects </a></h2> + + <p>Data objects contain the real information in the file. These + objects compose the scientific data and other information which + are generally thought of as "data" by the end-user. All the + other information in the file is provided as a framework for + these data objects. + + <p>A data object is composed of header information and data + information. The header information contains the information + needed to interpret the data information for the data object as + well as additional "meta-data" or pointers to additional + "meta-data" used to describe or annotate each data object. + + <h3><a name="ObjectHeader"> + Disk Format: Level 2a - Data Object Headers</a></h3> + + <p>The header information of an object is designed to encompass + all the information about an object which would be desired to be + known, except for the data itself. This information includes + the dimensionality, number-type, information about how the data + is stored on disk (in external files, compressed, broken up in + blocks, etc.), as well as other information used by the library + to speed up access to the data objects or maintain a file's + integrity. The header of each object is not necessarily located + immediately prior to the object's data in the file and in fact + may be located in any position in the file. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Object Headers</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=1 width="25%">Version # of Object Header</td> + <td colspan=1 width="25%">Reserved</td> + <td colspan=2 width="50%">Number of Header Messages</td> + </tr> + <tr align=center> + <td colspan=4>Object Reference Count</td> + </tr> + <tr align=center> + <td colspan=4><br>Total Object Header Size<br><br></td> + </tr> + <tr align=center> + <td colspan=2>Header Message Type #1</td> + <td colspan=2>Size of Header Message Data #1</td> + </tr> + <tr align=center> + <td>Flags</td> + <td colspan=3>Reserved</td> + </tr> + <tr align=center> + <td colspan=4><br>Header Message Data #1<br><br></td> + </tr> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + </tr> + <tr align=center> + <td colspan=2>Header Message Type #n</td> + <td colspan=2>Size of Header Message Data #n</td> + </tr> + <tr align=center> + <td>Flags</td> + <td colspan=3>Reserved</td> + </tr> + <tr align=center> + <td colspan=4><br>Header Message Data #n<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version number of the object header</td> + <td>This value is used to determine the format of the + information in the object header. When the format of the + information in the object header is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted.</td> + </tr> + + <tr valign=top> + <td>Reserved</td> + <td>Always set to zero.</td> + </tr> + + <tr valign=top> + <td>Number of header messages</td> + <td>This value determines the number of messages listed in + this object header. This provides a fast way for software + to prepare storage for the messages in the header.</td> + </tr> + + <tr valign=top> + <td>Object Reference Count</td> + <td>This value specifies the number of references to this + object within the current file. References to the + data object from external files are not tracked.</td> + </tr> + + <tr valign=top> + <td>Total Object Header Size</td> + <td>This value specifies the total number of bytes of header + message data following this length field for the current + message as well as any continuation data located elsewhere + in the file.</td> + </tr> + + <tr valign=top> + <td>Header Message Type</td> + <td>The header message type specifies the type of + information included in the header message data following + the type along with a small amount of other information. + Bit 15 of the message type is set if the message is + constant (constant messages cannot be changed since they + may be cached in group entries throughout the + file). The header message types for the pre-defined + header messages will be included in further discussion + below.</td> + </tr> + + <tr valign=top> + <td>Size of Header Message Data</td> + <td>This value specifies the number of bytes of header + message data following the header message type and length + information for the current message. The size includes + padding bytes to make the message a multiple of eight + bytes.</td> + </tr> + + <tr valign=top> + <td>Flags</td> + <td>This is a bit field with the following definition: + <dl> + <dt><code>0</code> + <dd>If set, the message data is constant. This is used + for messages like the datatype message of a dataset. + <dt><code>1</code> + <dd>If set, the message is stored in the global heap and + the Header Message Data field contains a Shared Object + message and the Size of Header Message Data field + contains the size of that Shared Object message. + <dt><code>2-7</code> + <dd>Reserved + </dl> + </td> + + <tr valign=top> + <td>Header Message Data</td> + <td>The format and length of this field is determined by the + header message type and size respectively. Some header + message types do not require any data and this information + can be eliminated by setting the length of the message to + zero. The data is padded with enough zeros to make the + size a multiple of eight.</td> + </tr> + </table> + </center> + + <p>The header message types and the message data associated with + them compose the critical "meta-data" about each object. Some + header messages are required for each object while others are + optional. Some optional header messages may also be repeated + several times in the header itself, the requirements and number + of times allowed in the header will be noted in each header + message description below. + + <P>The following is a list of currently defined header messages: + + <hr> + <h4><a name="NILMessage">Name: NIL</a></h4> + <b>Type: </b>0x0000<br> + <b>Length:</b> varies<br> + <b>Status:</b> Optional, may be repeated.<br> + <b>Purpose and Description:</b> The NIL message is used to + indicate a message + which is to be ignored when reading the header messages for a data object. + [Probably one which has been deleted for some reason.]<br> + <b>Format of Data:</b> Unspecified.<br> + +<!-- Delete examples throughout doc + <b>Examples:</b> None. +--> + + + <hr> + <h4><a name="SimpleDataSpace">Name: Simple Dataspace</a></h4> + + <b>Type: </b>0x0001<br> + <b>Length:</b> Varies according to the number of dimensions, + as described in the following table<br> + <b>Status:</b> The <em>Simple Dataspace</em> message is required + and may not be repeated. This message is currently used with + datasets and named dataspaces.<br> + + <p>The <em>Simple Dataspace</em> message describes the number + of dimensions and size of each dimension that the data object + has. This message is only used for datasets which have a + simple, rectilinear grid layout; datasets requiring a more + complex layout (irregularly structured or unstructured grids, etc.) + must use the <em>Complex Dataspace</em> message for expressing + the space the dataset inhabits. + <i>(Note: The <em>Complex Dataspace</em> functionality is + not yet implemented (as of HDF5 Release 1.2). It is not described + in this document.)</i> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Simple Dataspace Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Version</td> + <td>Dimensionality</td> + <td>Flags</td> + <td>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Dimension Size #1 (<size> bytes)</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Dimension Size #n (<size> bytes)</td> + <tr align=center> + <td colspan=4>Dimension Maximum #1 (<size> bytes)</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Dimension Maximum #n (<size> bytes)</td> + <tr align=center> + <td colspan=4>Permutation Index #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Permutation Index #n</td> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version </td> + <td>This value is used to determine the format of the + Simple Dataspace Message. When the format of the + information in the message is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted.</td> + </tr> + + <tr valign=top> + <td>Dimensionality</td> + <td>This value is the number of dimensions that the data + object has.</td> + </tr> + + <tr valign=top> + <td>Flags</td> + <td>This field is used to store flags to indicate the + presence of parts of this message. Bit 0 (the least + significant bit) is used to indicate that maximum + dimensions are present. Bit 1 is used to indicate that + permutation indices are present for each dimension.</td> + </tr> + + <tr valign=top> + <td>Dimension Size #n (<size> bytes)</td> + <td>This value is the current size of the dimension of the + data as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension.</td> + </tr> + + <tr valign=top> + <td>Dimension Maximum #n (<size> bytes)</td> + <td>This value is the maximum size of the dimension of the + data as stored in the file. This value may be the special + value <UNLIMITED> (all bits set) which indicates + that the data may expand along this dimension + indefinitely. If these values are not stored, the maximum + value of each dimension is assumed to be the same as the + current size value.</td> + </tr> + + <tr valign=top> + <td>Permutation Index #n (4 bytes)</td> + <td>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. If these values are + not stored, the first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension.</td> + </tr> + </table> + </center> + +<!-- Delete examples throughout doc + <h4>Examples</h4> + <dl> + <dt> Example #1 + <dd>A sample 640 horizontally by 480 vertically raster image + dimension header. The number of dimensions would be set to 2 + and the first dimension's size and maximum would both be set + to 480. The second dimension's size and maximum would both be + set to 640 +. + <dt>Example #2 + <dd>A sample 4 dimensional scientific dataset which is composed + of 30x24x3 slabs of data being written out in an unlimited + series every several minutes as timestep data (currently there + are five slabs). The number of dimensions is 4. The first + dimension size is 5 and its maximum is <UNLIMITED>. The + second through fourth dimension's size and maximum value are + set to 3, 24, and 30 respectively. + + <dt>Example #3 + <dd>A sample unlimited length text string, currently of length + 83. The number of dimensions is 1, the size of the first + dimension is 83 and the maximum of the first dimension is set + to <UNLIMITED>, allowing further text data to be + appended to the string or possibly the string to be replaced + with another string of a different size. (This could also be + stored as a scalar dataset with number-type set to "string") + </dl> +--> + +<!-- DELETE ENTIRE DATASPACE SECTION --> +<!-- + <hr> + <h4><a name="DataSpaceMessage">Name: Complex Dataspace (Fiber Bundle?)</a></h4> + <b>Type: </b>0x0002<br> + <b>Length:</b> varies<br> + + <b>Status:</b> One of the <em>Simple Dataspace</em> or + <em>Complex Dataspace</em> messages is required (but not both) and may + not be repeated.<br> <b>Purpose and Description:</b> The + <em>Dataspace</em> message describes space that the dataset is + mapped onto in a more comprehensive way than the <em>Simple + Dimensionality</em> message is capable of handling. The + dataspace of a dataset encompasses the type of coordinate system + used to locate the dataset's elements as well as the structure and + regularity of the coordinate system. The dataspace also + describes the number of dimensions which the dataset inhabits as + well as a possible higher dimensional space in which the dataset + is located within. + + <br> + <b>Format of Data:</b> + + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Message Layout</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Mesh Type</td> + <tr align=center> + <td colspan=4>Logical Dimensionality</td> + </table> + </center> + + <p> + <dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Mesh Type: (unsigned 32-bit integer) + <dd>This value indicates whether the grid is + polar/spherical/cartesion, + structured/unstructured and regular/irregular. <br> + The mesh type value is broken up as follows: <br> + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Mesh-type Layout</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=1>Mesh Embedding</td> + <td colspan=1>Coordinate System</td> + <td colspan=1>Structure</td> + <td colspan=1>Regularity</td> + </table> + </center> + The following are the definitions of mesh-type bytes: + <dl> + <dt>Mesh Embedding + <dd>This value indicates whether the dataset dataspace + is located within + another dataspace or not: + <dl> <dl> + <dt><STANDALONE> + <dd>The dataset mesh is self-contained and is not + embedded in another mesh. + <dt><EMBEDDED> + <dd>The dataset's dataspace is located within + another dataspace, as + described in information below. + </dl> </dl> + <dt>Coordinate System + <dd>This value defines the type of coordinate system + used for the mesh: + <dl> <dl> + <dt><POLAR> + <dd>The last two dimensions are in polar + coordinates, higher dimensions are + cartesian. + <dt><SPHERICAL> + <dd>The last three dimensions are in spherical + coordinates, higher dimensions + are cartesian. + <dt><CARTESIAN> + <dd>All dimensions are in cartesian coordinates. + </dl> </dl> + <dt>Structure + <dd>This value defines the locations of the grid-points + on the axes: + <dl> <dl> + <dt><STRUCTURED> + <dd>All grid-points are on integral, sequential + locations, starting from 0. + <dt><UNSTRUCTURED> + <dd>Grid-points locations in each dimension are + explicitly defined and + may be of any numeric datatype. + </dl> </dl> + <dt>Regularity + <dd>This value defines the locations of the dataset + points on the grid: + <dl> <dl> + <dt><REGULAR> + <dd>All dataset elements are located at the + grid-points defined. + <dt><IRREGULAR> + <dd>Each dataset element has a particular + grid-location defined. + </dl> </dl> + </dl> + <p>The following grid combinations are currently allowed: + <dl> <dl> + <dt><POLAR-STRUCTURED-REGULAR> + <dt><SPHERICAL-STRUCTURED-REGULAR> + <dt><CARTESIAN-STRUCTURED-REGULAR> + <dt><POLAR-UNSTRUCTURED-REGULAR> + <dt><SPHERICAL-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-IRREGULAR> + </dl> </dl> + All of the above grid types can be embedded within another + dataspace. + <br> <br> + <dt>Logical Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions that the dataset occupies. + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Embedded Dimensionality Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Embedded Dimensionality</td> + <tr align=center> + <td colspan=4>Embedded Dimension Size #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Embedded Dimension Size #n</td> + <tr align=center> + <td colspan=4>Embedded Origin Location #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Embedded Origin Location #n</td> + </table> + </center> + + <dt>Embedded Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions of the space the + dataset is located + within. i.e. a planar dataset located within a 3-D space, + or a 3-D dataset + which is a subset of another 3-D space, etc. + <dt>Embedded Dimension Size: (unsigned 32-bit integer) + <dd>These values are the sizes of the dimensions of the + embedded dataspace + that the dataset is located within. + <dt>Embedded Origin Location: (unsigned 32-bit integer) + <dd>These values comprise the location of the dataset's + origin within the embedded dataspace. + </dl> + </dl> + [Comment: need some way to handle different orientations of the + dataset dataspace + within the embedded dataspace]<br> + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Structured/Regular Grid Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Logical Dimension Size #1</td> + <tr align=center> + <td colspan=4>Logical Dimension Maximum #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Logical Dimension Size #n</td> + <tr align=center> + <td colspan=4>Logical Dimension Maximum #n</td> + </table> + </center> + + <p> + <dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Logical Dimension Size #n: (unsigned 32-bit integer) + <dd>This value is the current size of the dimension of the + data as stored in + the file. The first dimension stored in the list of + dimensions is the slowest + changing dimension and the last dimension stored is the + fastest changing + dimension. + <dt>Logical Dimension Maximum #n: (unsigned 32-bit integer) + <dd>This value is the maximum size of the dimension of the + data as stored in + the file. This value may be the special value + <UNLIMITED> which + indicates that the data may expand along this dimension + indefinitely. + </dl> + </dl> + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Structured/Irregular Grid Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4># of Grid Points in Dimension #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4># of Grid Points in Dimension #n</td> + <tr align=center> + <td colspan=4>Datatype of Grid Point Locations</td> + <tr align=center> + <td colspan=4>Location of Grid Points in Dimension #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Location of Grid Points in Dimension #n</td> + </table> + </center> + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Unstructured Grid Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4># of Grid Points</td> + <tr align=center> + <td colspan=4>Datatype of Grid Point Locations</td> + <tr align=center> + <td colspan=4>Grid Point Locations<br>.<br>.<br></td> + </table> + </center> + + <h4><a name="DataSpaceExample">Examples:</a></h4> + Need some good examples, this is complex! +--> + + + <hr> + <h4><a name="DataTypeMessage">Name: Datatype</a></h4> + + <b>Type:</b> 0x0003<br> + <b>Length:</b> variable<br> + <b>Status:</b> One required per dataset or named datatype<br> + + <p>The datatype message defines the datatype for each data point + of a dataset. A datatype can describe an atomic type like a + fixed- or floating-point type or a compound type like a C + struct. A datatype does not, however, describe how data points + are combined to produce a dataset. Datatypes are stored on disk + as a datatype message, which is a list of datatype classes and + their associated properties. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Datatype Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Type Class and Version</td> + <td colspan=3>Class Bit Field</td> + </tr> + + <tr align=center> + <td colspan=4>Size in Bytes (4 bytes)</td> + </tr> + + <tr align=center> + <td colspan=4><br><br>Properties<br><br><br></td> + </tr> + </table> + </center> + + <p>The Class Bit Field and Properties fields vary depending + on the Type Class, which is the low-order four bits of the Type + Class and Version field (the high-order four bits are the + version, which should be set to the value one). The type class + is one of 0 (fixed-point number), 1 (floating-point number), + 2 (date and time), 3 (text string), 4 (bit field), 5 (opaque), + 6 (compound), 7 (reference), 8 (enumeration), or 9 (variable-length). + The Class Bit Field is zero and the size of the + Properties field is zero except for the cases noted here. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Fixed-point Numbers (Class 0)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr valign=top> + <td>1, 2</td> + <td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2 + is the hi_pad type. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</td> + </tr> + + <tr valign=top> + <td>3</td> + <td><b>Signed.</b> If this bit is set then the fixed-point + number is in 2's complement form.</td> + </tr> + + <tr valign=top> + <td>4-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Fixed-point Numbers (Class 0)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=2>Bit Offset</td> + <td colspan=2>Bit Precision</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Floating-point Numbers (Class 1)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr valign=top> + <td>1, 2, 3</td> + <td><b>Padding type.</b> Bit 1 is the low bits pad type, bit 2 + is the high bits pad type, and bit 3 is the internal bits + pad type. If a datum has unused bits at either or between + the sign bit, exponent, or mantissa, then the value of bit + 1, 2, or 3 is copied to those locations.</td> + </tr> + + <tr valign=top> + <td>4-5</td> + <td><b>Normalization.</b> The value can be 0 if there is no + normalization, 1 if the most significant bit of the + mantissa is always set (except for 0.0), and 2 if the most + signficant bit of the mantissa is not stored but is + implied to be set. The value 3 is reserved and will not + appear in this field.</td> + </tr> + + <tr valign=top> + <td>6-7</td> + <td>Reserved (zero).</td> + </tr> + + <tr valign=top> + <td>8-15</td> + <td><b>Sign.</b> This is the bit position of the sign + bit.</td> + </tr> + + <tr valign=top> + <td>16-23</td> + <td>Reserved (zero).</td> + </tr> + + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Floating-point Numbers (Class 1)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=2>Bit Offset</td> + <td colspan=2>Bit Precision</td> + </tr> + + <tr align=center> + <td>Exponent Location</td> + <td>Exponent Size in Bits</td> + <td>Mantissa Location</td> + <td>Mantissa Size in Bits</td> + </tr> + + <tr align=center> + <td colspan=4>Exponent Bias</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Strings (Class 3)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0-3</td> + <td><b>Padding type.</b> This four-bit value determines the + type of padding to use for the string. The values are: + + <dl> + <dt><code>0</code> Null terminate. + <dd>A zero byte marks the end of the string and is + guaranteed to be present after converting a long + string to a short string. When converting a short + string to a long string the value is padded with + additional null characters as necessary. + + <br><br> + <dt><code>1</code> Null pad. + <dd>Null characters are added to the end of the value + during conversions from short values to long values + but conversion in the opposite direction simply + truncates the value. + + <br><br> + <dt><code>2</code> Space pad. + <dd>Space characters are added to the end of the value + during conversions from short values to long values + but conversion in the opposite direction simply + truncates the value. This is the Fortran + representation of the string. + + <br><br> + <dt><code>3-15</code> Reserved. + <dd>These values are reserved for future use. + </dl> + </tr> + + <tr valign=top> + <td>4-7</td> + <td><b>Character Set.</b> The character set to use for + encoding the string. The only character set supported is + the 8-bit ASCII (zero) so no translations have been defined + yet.</td> + </tr> + + <tr valign=top> + <td>8-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Bitfield Types (Class 4)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr valign=top> + <td>1, 2</td> + <td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2 + is the hi_pad type. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</td> + </tr> + + <tr valign=top> + <td>3-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Bitfield Types (Class 4)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=2>Bit Offset</td> + <td colspan=2>Bit Precision</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Opaque Types (Class 5)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Opaque Types (Class 5)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=4><br>Null-terminated ASCII Tag<br> + (multiple of 8 bytes)<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Compound Types (Class 6)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0-15</td> + <td><b>Number of Members.</b> This field contains the number + of members defined for the compound datatype. The member + definitions are listed in the Properties field of the data + type message. + </tr> + + <tr valign=top> + <td>15-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p>The Properties field of a compound datatype is a list of the + member definitions of the compound datatype. The member + definitions appear one after another with no intervening bytes. + The member types are described with a recursive datatype + message. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Compound Types (Class 6)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=4><br><br>Name (null terminated, multiple of + eight bytes)<br><br><br></td> + </tr> + + <tr align=center> + <td colspan=4>Byte Offset of Member in Compound Instance</td> + </tr> + + <tr align=center> + <td>Dimensionality</td> + <td colspan=3>reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Dimension Permutation</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Size of Dimension 0 (required)</td> + </tr> + + <tr align=center> + <td colspan=4>Size of Dimension 1 (required)</td> + </tr> + + <tr align=center> + <td colspan=4>Size of Dimension 2 (required)</td> + </tr> + + <tr align=center> + <td colspan=4>Size of Dimension 3 (required)</td> + </tr> + + <tr align=center> + <td colspan=4><br><br>Member Type Message<br><br><br></td> + </tr> + + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Enumeration Types (Class 8)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0-15</td> + <td><b>Number of Members.</b> The number of name/value + pairs defined for the enumeration type.</td> + </tr> + + <tr valign=top> + <td>16-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Enumeration Types (Class 8)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=4><br>Parent Type<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Names<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Values<br><br></td> + </tr> + + </table> + </center> + + <center> + <table border=0 cellpadding=4 width="80%"> + <tr align=left valign=top> + <td valign=top width=20%>Parent Type:</td> + <td valign=top>Each enumeration type is based on some parent type, + usually an integer. The information for that parent type is + described recursively by this field.</td> + </tr><tr align=left valign=top> + <td valign=top>Names:</td> + <td valign=top>The name for each name/value pair. Each name is + stored as a null terminated ASCII string in a multiple of + eight bytes. The names are in no particular order.</td> + </tr><tr align=left valign=top> + <td valign=top>Values:</td> + <td valign=top>The list of values in the same order as the names. + The values are packed (no inter-value padding) and the + size of each value is determined by the parent type.</td> + </tr> + </table> + </center> + + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Bit Field for Variable-length Types (Class 9)</b> + </caption> + + <tr align=center> + <th width="10%">Bits</th> + <th width="90%">Meaning</th> + </tr> + + <tr valign=top> + <td>0-3</td> + <td><dl><dt><b>Type</b></dt> + <dt>0 Variable-length sequence</dt> + <dd>This variable-length datatype can be of any sequence + of data. Variable-length sequences do not have padding + or character set information.</dd> + <dt>1 Variable-length string</dt> + <dd>This variable-length datatype is composed of a series of + characters. Variable-length strings have padding and + character set information.</dd></dl> + </td> + </tr> + + <tr valign=top> + <td>4-7</td> + <td><dl><dt><b>Padding type</b> (variable-length string only)</dt> + <dd>This four-bit value determines the type of padding + used for variable-length strings. The values are the same + as for the string padding type, as follows:</dd> + <dt>0 Null terminate</dt> + <dd>A zero byte marks the end of a string and is guaranteed + to be present after converting a long string to a short + string. When converting a short string to a long string, + the value is padded with additional null characters + as necessary. + <dt>1 Null pad</dt> + <dd>Null characters are added to the end of the value + during conversion from a short string to a longer string. + Conversion from a long string to a shorter string + simply truncates the value.</dd> + <dt>2 Space pad</dt> + <dd>Space characters are added to the end of the value + during conversion from a short string to a longer string. + Conversion from a long string to a shorter string simply + truncates the value. + This is the Fortran representation of the string. + </dd> + <dt>3-15 Reserved</dt> + <dd>These values are reserved for future use.</dd></dl> + </td> + </tr> + + <tr valign=top> + <td>8-11</td> + <td><dl><dt><b>Character set</b> (variable-length string only)</dt> + <dd>This four-bit value specifies the character set + to be used for encoding the string.</dd> + <dt>0 8-bit ASCII</dt> + <dd>As of this writing (July 2002, Release 1.4.4), + 8-bit ASCII is the only character set supported. + Therefore, no translations have been defined.</dd></dl> + </td> + </tr> + + <tr valign=top> + <td>12-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Properties for Variable-length Types (Class 9)</b> + </caption> + + <tr align=center> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr align=center> + <td colspan=4><br>Parent Type<br><br></td> + </tr> + + </table> + </center> + + <center> + <table border=0 cellpadding=4 width="80%"> + <tr align=left valign=top> + <td valign=top width=20%>Parent Type:</td> + <td valign=top>Each variable-length type is based on + some parent type. The information for that parent type is + described recursively by this field.</td> + </tr> + </table> + </center> + + + + <p> + +<!-- + <p>Datatype examples are <a href="Datatypes.html">here</a>. +--> + + + <hr> + <h4><a name="FillValueMessage">Name: Data Storage - Fill Value</a></h4> + <b>Type:</b> 0x0004<br> + <b>Length:</b> varies<br> + <b>Status:</b> Optional, may not be repeated.<br> + + <p>The fill value message stores a single data point value which + is returned to the application when an uninitialized data point + is read from the dataset. The fill value is interpretted with + the same datatype as the dataset. If no fill value message is + present then a fill value of all zero is assumed. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Fill Value Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4>Size (4 bytes)</td> + </tr> + + <tr align=center> + <td colspan=4><br>Fill Value<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Size (4 bytes)</td> + <td>This is the size of the Fill Value field in bytes.</td> + </tr> + + <tr valign=top> + <td>Fill Value</td> + <td>The fill value. The bytes of the fill value are + interpreted using the same datatype as for the dataset.</td> + </tr> + </table> + </center> + + <hr> + <h4><a name="ReservedMessage_0005">Name: Reserved - Not Assigned Yet</a></h4> + <b>Type:</b> 0x0005<br> + <b>Length:</b> N/A<br> + <b>Status:</b> N/A<br> + + + + <hr> + <h4><a name="CompactDataStorageMessage">Name: Data Storage - Compact</a></h4> + + <b>Type:</b> 0x0006<br> + <b>Length:</b> varies<br> + <b>Status:</b> Optional, may not be repeated.<br> + + <p>This message indicates that the data for the data object is + stored within the current HDF file by including the actual + data as the header data for this message. The data is + stored internally in + the <em>normal format</em>, i.e. in one chunk, uncompressed, etc. + + <P>Note that one and only one of the <em>Data Storage</em> headers can be + stored for each data object. + + <P><b>Format of Data:</b> The message data is actually composed + of dataset data, so the format will be determined by the dataset + format. + +<!-- Delete examples throughout doc + <h4><a name="CompactDataStorageExample">Examples:</a></h4> + [very straightforward] +--> + + <hr> + <h4><a name="ExternalFileListMessage">Name: Data Storage - + External Data Files</a></h4> + <b>Type:</b> 0x0007<BR> + <b>Length:</b> varies<BR> + <b>Status:</b> Optional, may not be repeated.<BR> + + <p><b>Purpose and Description:</b> The external object message + indicates that the data for an object is stored outside the HDF5 + file. The filename of the object is stored as a Universal + Resource Location (URL) of the actual filename containing the + data. An external file list record also contains the byte offset + of the start of the data within the file and the amount of space + reserved in the file for that data. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>External File List Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Version</td> + <td colspan=3>Reserved</td> + </tr> + + <tr align=center> + <td colspan=2>Allocated Slots</td> + <td colspan=2>Used Slots</td> + </tr> + + <tr align=center> + <td colspan=4><br>Heap Address<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Slot Definitions...<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version </td> + <td>This value is used to determine the format of the + External File List Message. When the format of the + information in the message is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted.</td> + </tr> + + <tr valign=top> + <td>Reserved</td> + <td>This field is reserved for future use.</td> + </tr> + + <tr valign=top> + <td>Allocated Slots</td> + <td>The total number of slots allocated in the message. Its + value must be at least as large as the value contained in + the Used Slots field.</td> + </tr> + + <tr valign=top> + <td>Used Slots</td> + <td>The number of initial slots which contain valid + information. The remaining slots are zero filled.</td> + </tr> + + <tr valign=top> + <td>Heap Address</td> + <td>This is the address of a local name heap which contains + the names for the external files. The name at offset zero + in the heap is always the empty string.</td> + </tr> + + <tr valign=top> + <td>Slot Definitions</td> + <td>The slot definitions are stored in order according to + the array addresses they represent. If more slots have + been allocated than what has been used then the defined + slots are all at the beginning of the list.</td> + </tr> + </table> + </center> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>External File List Slot</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4><br>Name Offset (<size> bytes)<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>File Offset (<size> bytes)<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Size<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Name Offset (<size> bytes)</td> + <td>The byte offset within the local name heap for the name + of the file. File names are stored as a URL which has a + protocol name, a host name, a port number, and a file + name: + <code><em>protocol</em>:<em>port</em>//<em>host</em>/<em>file</em></code>. + If the protocol is omitted then "file:" is assumed. If + the port number is omitted then a default port for that + protocol is used. If both the protocol and the port + number are omitted then the colon can also be omitted. If + the double slash and host name are omitted then + "localhost" is assumed. The file name is the only + mandatory part, and if the leading slash is missing then + it is relative to the application's current working + directory (the use of relative names is not + recommended).</td> + </tr> + + <tr valign=top> + <td>File Offset (<size> bytes)</td> + <td>This is the byte offset to the start of the data in the + specified file. For files that contain data for a single + dataset this will usually be zero.</td> + </tr> + + <tr valign=top> + <td>Size</td> + <td>This is the total number of bytes reserved in the + specified file for raw data storage. For a file that + contains exactly one complete dataset which is not + extendable, the size will usually be the exact size of the + dataset. However, by making the size larger one allows + HDF5 to extend the dataset. The size can be set to a value + larger than the entire file since HDF5 will read zeros + past the end of the file without failing.</td> + </tr> + </table> + </center> + + + <hr> + <h4><a name="LayoutMessage">Name: Data Storage - Layout</a></h4> + + <b>Type:</b> 0x0008<BR> + <b>Length:</b> varies<BR> + <b>Status:</b> Required for datasets, may not be repeated. + + <p><b>Purpose and Description:</b> Data layout describes how the + elements of a multi-dimensional array are arranged in the linear + address space of the file. Two types of data layout are + supported: + + <ol> + <li>The array can be stored in one contiguous area of the file. + The layout requires that the size of the array be constant and + does not permit chunking, compression, checksums, encryption, + etc. The message stores the total size of the array and the + offset of an element from the beginning of the storage area is + computed as in C. + + <li>The array domain can be regularly decomposed into chunks and + each chunk is allocated separately. This layout supports + arbitrary element traversals, compression, encryption, and + checksums, and the chunks can be distributed across external + raw data files (these features are described in other + messages). The message stores the size of a chunk instead of + the size of the entire array; the size of the entire array can + be calculated by traversing the B-tree that stores the chunk + addresses. + </ol> + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <B>Data Layout Message</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Version</td> + <td>Dimensionality</td> + <td>Layout Class</td> + <td>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4><br>Address<br><br></td> + </tr> + + <tr align=center> + <td colspan=4>Dimension 0 (4-bytes)</td> + </tr> + + <tr align=center> + <td colspan=4>Dimension 1 (4-bytes)</td> + </tr> + + <tr align=center> + <td colspan=4>...</td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version</td> + <td>A version number for the layout message. This + documentation describes version one.</td> + </tr> + + <tr valign=top> + <td>Dimensionality</td> + <td>An array has a fixed dimensionality. This field + specifies the number of dimension size fields later in the + message.</td> + </tr> + + <tr valign=top> + <td>Layout Class</td> + <td>The layout class specifies how the other fields of the + layout message are to be interpreted. A value of one + indicates contiguous storage while a value of two + indicates chunked storage. Other values will be defined + in the future.</td> + </tr> + + <tr valign=top> + <td>Address</td> + <td>For contiguous storage, this is the address of the first + byte of storage. For chunked storage this is the address + of the B-tree that is used to look up the addresses of the + chunks.</td> + </tr> + + <tr valign=top> + <td>Dimensions</td> + <td>For contiguous storage the dimensions define the entire + size of the array while for chunked storage they define + the size of a single chunk.</td> + </tr> + </table> + </center> + + + <hr> + <h4><a name="ReservedMessage_0009">Name: Reserved - Not Assigned Yet</a></h4> + <b>Type:</b> 0x0009<BR> + <b>Length:</b> N/A<BR> + <b>Status:</b> N/A<BR> + <b>Purpose and Description:</b> N/A<BR> + <b>Format of Data:</b> N/A + + <hr> + <h4><a name="ReservedMessage_000A">Name: Reserved - Not Assigned Yet</a></h4> + <b>Type:</b> 0x000A<BR> + <b>Length:</b> N/A<BR> + <b>Status:</b> N/A<BR> + <b>Purpose and Description:</b> N/A<BR> + <b>Format of Data:</b> N/A + + <hr> + <h4><a name="FilterMessage">Name: Data Storage - Filter Pipeline</a></h4> + <b>Type:</b> 0x000B<BR> + <b>Length:</b> varies<BR> + <b>Status:</b> Optional, may not be repeated. + + <p><b>Purpose and Description:</b> This message describes the + filter pipeline which should be applied to the data stream by + providing filter identification numbers, flags, a name, an + client data. + + <p> + <center> + <table border align=center cellpadding=4 witdh="80%"> + <caption align=top> + <b>Filter Pipeline Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Version</td> + <td>Number of Filters</td> + <td colspan=2>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4><br>Filter List<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version</td> + <td>The version number for this message. This document + describes version one.</td> + </tr> + + <tr valign=top> + <td>Number of Filters</td> + <td>The total number of filters described by this + message. The maximum possible number of filters in a + message is 32.</td> + </tr> + + <tr valign=top> + <td>Filter List</td> + <td>A description of each filter. A filter description + appears in the next table.</td> + </tr> + </table> + </center> + + <p> + <center> + <table border align=center cellpadding=4 witdh="80%"> + <caption align=top> + <b>Filter Pipeline Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=2>Filter Identification</td> + <td colspan=2>Name Length</td> + </tr> + + <tr align=center> + <td colspan=2>Flags</td> + <td colspan=2>Client Data Number of Values</td> + </tr> + + <tr align=center> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Client Data<br><br></td> + </tr> + + <tr align=center> + <td colspan=4>Padding</td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Filter Identification</td> + <td>This is a unique (except in the case of testing) + identifier for the filter. Values from zero through 255 + are reserved for filters defined by the NCSA HDF5 + library. Values 256 through 511 have been set aside for + use when developing/testing new filters. The remaining + values are allocated to specific filters by contacting the + <a href="mailto:hdf5dev@ncsa.uiuc.edu">HDF5 Development + Team</a>.</td> + </tr> + + <tr valign=top> + <td>Name Length</td> + <td>Each filter has an optional null-terminated ASCII name + and this field holds the length of the name including the + null termination padded with nulls to be a multiple of + eight. If the filter has no name then a value of zero is + stored in this field.</td> + </tr> + + <tr valign=top> + <td>Flags</td> + <td>The flags indicate certain properties for a filter. The + bit values defined so far are: + + <dl> + <dt><code>bit 1</code> + <dd>If set then the filter is an optional filter. + During output, if an optional filter fails it will be + silently removed from the pipeline. + </dl> + </tr> + + <tr valign=top> + <td>Client Data Number of Values</td> + <td>Each filter can store a few integer values to control + how the filter operates. The number of entries in the + Client Data array is stored in this field.</td> + </tr> + + <tr valign=top> + <td>Name</td> + <td>If the Name Length field is non-zero then it will + contain the size of this field, a multiple of eight. This + field contains a null-terminated, ASCII character + string to serve as a comment/name for the filter.</td> + </tr> + + <tr valign=top> + <td>Client Data</td> + <td>This is an array of four-byte integers which will be + passed to the filter function. The Client Data Number of + Values determines the number of elements in the + array.</td> + </tr> + + <tr valign=top> + <td>Padding</td> + <td>Four bytes of zeros are added to the message at this + point if the Client Data Number of Values field contains + an odd number.</td> + </tr> + </table> + </center> + + <hr> + <h4><a name="AttributeMessage">Name: Attribute</a></h4> + <b>Type:</b> 0x000C<BR> + <b>Length:</b> varies<BR> + <b>Status:</b> Optional, may be repeated.<BR> + + <p><b>Purpose and Description:</b> The <em>Attribute</em> + message is used to list objects in the HDF file which are used + as attributes, or "meta-data" about the current object. An + attribute is a small dataset; it has a name, a datatype, a data + space, and raw data. Since attributes are stored in the object + header they must be relatively small (<64kb) and can be + associated with any type of object which has an object header + (groups, datasets, named types and spaces, etc.). + + <p> + <center> + <table border align=center cellpadding=4 width="80%"> + <caption align=top> + <b>Attribute Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td>Version</td> + <td>Reserved</td> + <td colspan=2>Name Size</td> + </tr> + + <tr align=center> + <td colspan=2>Type Size</td> + <td colspan=2>Space Size</td> + </tr> + + <tr align=center> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Type<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Space<br><br></td> + </tr> + + <tr align=center> + <td colspan=4><br>Data<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version</td> + <td>Version number for the message. This document describes + version 1 of attribute messages.</td> + </tr> + + <tr valign=top> + <td>Reserved</td> + <td>This field is reserved for later use and is set to + zero.</td> + </tr> + + <tr valign=top> + <td>Name Size</td> + <td>The length of the attribute name in bytes including the + null terminator. Note that the Name field below may + contain additional padding not represented by this + field.</td> + </tr> + + <tr valign=top> + <td>Type Size</td> + <td>The length of the datatype description in the Type + field below. Note that the Type field may contain + additional padding not represented by this field.</td> + </tr> + + <tr valign=top> + <td>Space Size</td> + <td>The length of the dataspace description in the Space + field below. Note that the Space field may contain + additional padding not represented by this field.</td> + </tr> + + <tr valign=top> + <td>Name</td> + <td>The null-terminated attribute name. This field is + padded with additional null characters to make it a + multiple of eight bytes.</td> + </tr> + + <tr valign=top> + <td>Type</td> + <td>The datatype description follows the same format as + described for the datatype object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</td> + </tr> + + <tr valign=top> + <td>Space</td> + <td>The dataspace description follows the same format as + described for the dataspace object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</td> + </tr> + + <tr valign=top> + <td>Data</td> + <td>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. This + field is <em>not</em> padded with additional zero + bytes.</td> + </tr> + </table> + </center> + + <hr> + <h4><a name="NameMessage">Name: Object Name</a></h4> + + <p><b>Type:</b> 0x000D<br> + <b>Length:</b> varies<br> + <b>Status:</b> Optional, may not be repeated. + + <p><b>Purpose and Description:</b> The object name or comment is + designed to be a short description of an object. An object name + is a sequence of non-zero (<code>\0</code>) ASCII characters with no other + formatting included by the library. + + <p> + <center> + <table border align=center cellpadding=4 width="80%"> + <caption align=top> + <b>Name Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4><br>Name<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Name</td> + <td>A null terminated ASCII character string.</td> + </tr> + </table> + </center> + + <hr> + <h4><a name="ModifiedMessage">Name: Object Modification Date & Time</a></h4> + + <p><b>Type:</b> 0x000E<br> + <b>Length:</b> fixed<br> + <b>Status:</b> Optional, may not be repeated. + + <p><b>Purpose and Description:</b> The object modification date + and time is a timestamp which indicates (using ISO-8601 date and + time format) the last modification of an object. The time is + updated when any object header message changes according to the + system clock where the change was posted. + + <p> + <center> + <table border align=center cellpadding=4 width="80%"> + <caption align=top> + <b>Modification Time Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align=center> + <td colspan=4>Year</td> + </tr> + + <tr align=center> + <td colspan=2>Month</td> + <td colspan=2>Day of Month</td> + </tr> + + <tr align=center> + <td colspan=2>Hour</td> + <td colspan=2>Minute</td> + </tr> + + <tr align=center> + <td colspan=2>Second</td> + <td colspan=2>Reserved</td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Year</td> + <td>The four-digit year as an ASCII string. For example, + <code>1998</code>. All fields of this message should be interpreted + as coordinated universal time (UTC)</td> + </tr> + + <tr valign=top> + <td>Month</td> + <td>The month number as a two digit ASCII string where + January is <code>01</code> and December is <code>12</code>.</td> + </tr> + + <tr valign=top> + <td>Day of Month</td> + <td>The day number within the month as a two digit ASCII + string. The first day of the month is <code>01</code>.</td> + </tr> + + <tr valign=top> + <td>Hour</td> + <td>The hour of the day as a two digit ASCII string where + midnight is <code>00</code> and 11:00pm is <code>23</code>.</td> + </tr> + + <tr valign=top> + <td>Minute</td> + <td>The minute of the hour as a two digit ASCII string where + the first minute of the hour is <code>00</code> and + the last is <code>59</code>.</td> + </tr> + + <tr valign=top> + <td>Second</td> + <td>The second of the minute as a two digit ASCII string + where the first second of the minute is <code>00</code> + and the last is <code>59</code>.</td> + </tr> + + <tr valign=top> + <td>Reserved</td> + <td>This field is reserved and should always be zero.</td> + </tr> + </table> + </center> + + <hr> + <h4><a name="SharedMessage">Name: Shared Object Message</a></h4> + <b>Type:</b> 0x000F<br> + <b>Length:</b> 4 Bytes<br> + <b>Status:</b> Optional, may be repeated. + + <p>A constant message can be shared among several object headers + by writing that message in the global heap and having the object + headers all point to it. The pointing is accomplished with a + Shared Object message which is understood directly by the object + header layer of the library. It is also possible to have a + message of one object header point to a message in some other + object header, but care must be exercised to prevent cycles. + + <p>If a message is shared, then the message appears in the global + heap and its message ID appears in the Header Message Type + field of the object header. Also, the Flags field in the object + header for that message will have bit two set (the + <code>H5O_FLAG_SHARED</code> bit). The message body in the + object header will be that of a Shared Object message defined + here and not that of the pointed-to message. + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=top> + <b>Shared Message Message</b> + </caption> + + <tr align=center> + <th width="25%">byte</td> + <th width="25%">byte</td> + <th width="25%">byte</td> + <th width="25%">byte</td> + </tr> + + <tr align=center> + <td>Version</td> + <td>Flags</td> + <td colspan=2>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4>Reserved</td> + </tr> + + <tr align=center> + <td colspan=4><br>Pointer<br><br></td> + </tr> + </table> + </center> + + <p> + <center> + <table align=center width="80%"> + <tr> + <th width="30%">Field Name</th> + <th width="70%">Description</th> + </tr> + + <tr valign=top> + <td>Version</td> + <td>The version number for the message. This document + describes version one of shared messages.</td> + </tr> + + <tr valign=top> + <td>Flags</td> + <td>The Shared Message message points to a message which is + shared among multiple object headers. The Flags field + describes the type of sharing: + + <dl> + <dt><code>Bit 0</code> + <dd>If this bit is clear then the actual message is the + first message in some other object header; otherwise + the actual message is stored in the global heap. + + <dt><code>Bits 2-7</code> + <dd>Reserved (always zero) + </dl> + </tr> + + <tr valign=top> + <td>Pointer</td> + <td>This field points to the actual message. The format of + the pointer depends on the value of the Flags field. If + the actual message is in the global heap then the pointer + is the file address of the global heap collection that + holds the message, and a four-byte index into that + collection. Otherwise the pointer is a group entry + that points to some other object header.</td> + </tr> + </table> + </center> + + +<hr> +<h4><a name="ContinuationMessage">Name: Object Header Continuation</a></h4> +<b>Type:</b> 0x0010<BR> +<b>Length:</b> fixed<BR> +<b>Status:</b> Optional, may be repeated.<BR> +<b>Purpose and Description:</b> The object header continuation is the location +in the file of more header messages for the current data object. This can be +used when header blocks are large, or likely to change over time.<BR> +<b>Format of Data:</b><p> + The object header continuation is formatted as follows (assuming a 4-byte +length & offset are being used in the current file): + +<P> +<center> +<table border cellpadding=4 width=60%> +<caption align=bottom> +<B>HDF5 Object Header Continuation Message Layout</B> +</caption> + +<tr align=center> +<th width=25%>byte</th> +<th width=25%>byte</th> +<th width=25%>byte</th> +<th width=25%>byte</th> + +<tr align=center> +<td colspan=4>Header Continuation Offset</td> +<tr align=center> +<td colspan=4>Header Continuation Length</td> +</table> +</center> + +<P> +<dl> +<dt>The elements of the Header Continuation Message are described below: +<dd> +<dl> +<dt>Header Continuation Offset: (<offset> bytes) +<dd>This value is the offset in bytes from the beginning of the file where the +header continuation information is located. +<dt>Header Continuation Length: (<length> bytes) +<dd>This value is the length in bytes of the header continuation information in +the file. +</dl> +</dl> + +<!-- Delete examples throughout doc +<h4><a name="ContinuationExample">Examples:</a></h4> + [straightforward] +--> + +<hr> +<h4><a name="SymbolTableMessage">Name: Group Message</a></h4> +<b>Type:</b> 0x0011<BR> +<b>Length:</b> fixed<BR> +<b>Status:</b> Required for groups, may not be repeated.<BR> +<b>Purpose and Description:</b> Each group has a B-tree and a +name heap which are pointed to by this message.<BR> +<b>Format of data:</b> +<p>The group message is formatted as follows: + +<p> +<center> +<table border cellpadding=4 width="80%"> +<caption align=bottom> +<b>HDF5 Object Header Group Message Layout</b> +</caption> + +<tr align=center> +<th width="25%">byte</th> +<th width="25%">byte</th> +<th width="25%">byte</th> +<th width="25%">byte</th> + +<tr align=center> +<td colspan=4>B-tree Address</td> + +<tr align=center> +<td colspan=4>Heap Address</td> +</table> +</center> + +<P> +<dl> +<dt>The elements of the Group Message are described below: +<dd> +<dl> +<dt>B-tree Address (<offset> bytes) +<dd>This value is the offset in bytes from the beginning of the file +where the B-tree is located. +<dt>Heap Address (<offset> bytes) +<dd>This value is the offset in bytes from the beginning of the file +where the group name heap is located. +</dl> +</dl> + +<h3><a name="SharedObjectHeader">Disk Format: Level 2b - Shared Data Object Headers</a></h3> +<P>In order to share header messages between several dataset objects, object +header messages may be placed into the global heap. Since these +messages require additional information beyond the basic object header message +information, the format of the shared message is detailed below. + +<BR> <BR> +<center> +<table border cellpadding=4 width=60%> +<caption align=bottom> +<B>HDF5 Shared Object Header Message</B> +</caption> + +<tr align=center> +<th width=25%>byte</th> +<th width=25%>byte</th> +<th width=25%>byte</th> +<th width=25%>byte</th> + +<tr align=center> +<td colspan=4>Reference Count of Shared Header Message</td> +<tr align=center> +<td colspan=4><br> Shared Object Header Message<br> <br></td> +</table> +</center> + +<p> +<dl> +<dt> The elements of the shared object header message are described below: +<dd> +<dl> +<dt>Reference Count of Shared Header Message: (32-bit unsigned integer) +<dd>This value is used to keep a count of the number of dataset objects which +refer to this message from their dataset headers. When this count reaches zero, +the shared message header may be removed from the global heap. +<dt>Shared Object Header Message: (various lengths) +<dd>The data stored for the shared object header message is formatted in the +same way as the private object header messages described in the object header +description earlier in this document and begins with the header message Type. +</dl> +</dl> + + +<h3><a name="DataStorage">Disk Format: Level 2c - Data Object Data Storage</a></h3> +<P>The data for an object is stored separately from the header +information in the file and may not actually be located in the HDF5 file +itself if the header indicates that the data is stored externally. The +information for each record in the object is stored according to the +dimensionality of the object (indicated in the dimensionality header message). +Multi-dimensional data is stored in C order [same as current scheme], i.e. the +"last" dimension changes fastest. +<P>Data whose elements are composed of simple number-types are stored in +native-endian IEEE format, unless they are specifically defined as being stored +in a different machine format with the architecture-type information from the +number-type header message. This means that each architecture will need to +[potentially] byte-swap data values into the internal representation for that +particular machine. +<P> Data with a "variable" sized number-type is stored in a data heap +internal to the HDF5 file. Global heap identifiers are stored in the +data object storage. +<P>Data whose elements are composed of pointer number-types are stored in several +different ways depending on the particular pointer type involved. Simple +pointers are just stored as the dataset offset of the object being pointed to with the +size of the pointer being the same number of bytes as offsets in the file. +Partial-object pointers are stored as a heap-ID which points to the following +information within the file-heap: an offset of the object pointed to, number-type +information (same format as header message), dimensionality information (same +format as header message), sub-set start and end information (i.e. a coordinate +location for each), and field start and end names (i.e. a [pointer to the] +string indicating the first field included and a [pointer to the] string name +for the last field). + +<P>Data of a compound datatype is stored as a contiguous stream of the items +in the structure, with each item formatted according to its datatype. + +</body> +</html> diff --git a/doxygen/examples/H5.format.1.1.html b/doxygen/examples/H5.format.1.1.html new file mode 100644 index 0000000..ebbbe8e --- /dev/null +++ b/doxygen/examples/H5.format.1.1.html @@ -0,0 +1,6439 @@ +<html> + <head> + <title> + HDF5 File Format Specification Version 1.1 + </title> + +<STYLE TYPE="text/css"> + +P { text-indent: 2em} +P.item { margin-left: 2em; text-indent: -2em} +P.item2 { margin-left: 2em; text-indent: 2em} + +TABLE.format { border:solid; border-collapse:collapse; caption-side:top; text-align:center; width:80%;} +TABLE.format TH { border:ridge; padding:4px; width:25%;} +TABLE.format TD { border:ridge; padding:4px; } +TABLE.format CAPTION { font-weight:bold; font-size:larger;} + +TABLE.note {border:none; text-align:right; width:80%;} + +TABLE.desc { border:solid; border-collapse:collapse; caption-size:top; text-align:left; width:80%;} +TABLE.desc TR { vertical-align:top;} +TABLE.desc TH { border-style:ridge; font-size:larger; padding:4px; text-decoration:underline;} +TABLE.desc TD { border-style:ridge; padding:4px; } +TABLE.desc CAPTION { font-weight:bold; font-size:larger;} + +TABLE.list { border:none; } +TABLE.list TR { vertical-align:top;} +TABLE.list TH { border:none; text-decoration:underline;} +TABLE.list TD { border:none; } + +</STYLE> +</head> + <body> + + <center> + <table border=0 width=90%> + <tr> + <td valign=top> + <ol type=I> + <li><a href="#Intro">Introduction</a> + <li><a href="#FileMetaData">Disk Format Level 0 - File Metadata</a> + <font size=-2> + <ol type=A> + <li><a href="#SuperBlock">Disk Format Level 0A - File Signature and Super Block</a> + <li><a href="#DriverInfo">Disk Format Level 0B - File Driver Info</a> + </ol> + </font> + <li><a href="#FileInfra">Disk Format Level 1 - File Infrastructure</a> + <font size=-2> + <ol type=A> + <li><a href="#Btrees">Disk Format Level 1A - B-link Trees and B-tree Nodes</a> + <li><a href="#SymbolTable">Disk Format Level 1B - Group</a> + <li><a href="#SymbolTableEntry">Disk Format Level 1C - Group Entry</a> + <li><a href="#LocalHeap">Disk Format Level 1D - Local Heaps</a> + <li><a href="#GlobalHeap">Disk Format Level 1E - Global Heap</a> + <li><a href="#FreeSpaceIndex">Disk Format Level 1F - Free-space Index</a> + </ol> + </font> + <li><a href="#DataObject">Disk Format Level 2 - Data Objects</a> + <font size=-2> + <ol type=A> + <li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a> + <ol type=1> + <li><a href="#NILMessage">Name: NIL</a> <!-- 0x0000 --> + <li><a href="#SimpleDataSpace">Name: Simple Dataspace</a> <!-- 0x0001 --> +<!-- <li><a href="#DataSpaceMessage">Name: Complex Dataspace</a> --> <!-- 0x0002 --> + <li><a href="#ReservedMessage_0002">Name: Reserved - not assigned yet</a> <!-- 0x0002 --> + <li><a href="#DataTypeMessage">Name: Datatype</a> <!-- 0x0003 --> + <li><a href="#OldFillValueMessage">Name: Data Storage - Fill Value (Old)</a> <!-- 0x0004 --> + <li><a href="#FillValueMessage">Name: Data Storage - Fill Value</a> <!-- 0x0005 --> + </ol> + </ol> + </font> + </ol> + </td><td> </td><td valign=top> + <ol type=I start=4> + + <li><a href="#DataObject">Disk Format Level 2 - Data Objects</a> + <font size=-2><i>(Continued)</i> + <ol type=A> + <li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a><i>(Continued)</i> + <ol type=1 start=6> +<!-- <li><a href="#CompactDataStorageMessage">Name: Data Storage - Compact</a> --> <!-- 0x0006 --> + <li><a href="#ReservedMessage_0006">Name: Reserved - not assigned yet</a> <!-- 0x0006 --> + <li><a href="#ExternalFileListMessage">Name: Data Storage - External Data Files</a> <!-- 0x0007 --> + <li><a href="#LayoutMessage">Name: Data Storage - Layout</a> <!-- 0x0008 --> + <li><a href="#ReservedMessage_0009">Name: Reserved - not assigned yet</a> <!-- 0x0009 --> + <li><a href="#ReservedMessage_000A">Name: Reserved - not assigned yet</a> <!-- 0x000a --> + <li><a href="#FilterMessage">Name: Data Storage - Filter Pipeline</a> <!-- 0x000b --> + <li><a href="#AttributeMessage">Name: Attribute</a> <!-- 0x000c --> + <li><a href="#CommentMessage">Name: Object Comment</a> <!-- 0x000d --> + <li><a href="#OldModifiedMessage">Name: Object Modification Date and Time (Old)</a> <!-- 0x000e --> + <li><a href="#SharedMessage">Name: Shared Object Message</a> <!-- 0x000f --> + <li><a href="#ContinuationMessage">Name: Object Header Continuation</a> <!-- 0x0010 --> + <li><a href="#SymbolTableMessage">Name: Group Message</a> <!-- 0x0011 --> + <li><a href="#ModifiedMessage">Name: Object Modification Date and Time</a> <!-- 0x0012 --> + </ol> + <li><a href="#DataStorage">Disk Format: Level 2b - Data Object Data Storage</a> + </ol> + </font> + <LI><A href="#Appendix">Appendix</A> + </ol> +</td></tr> +</table> +</center> + + <BR> + <HR> + + + <h2>Introduction</h2> + + <table align=right width=100> + <tr><td> </td><td align=center> + <hr> + <img src="FF-IH_FileGroup.gif" alt="HDF5 Groups" hspace=15 vspace=15> + </td><td> </td></tr> + <tr><td> </td><td align=center> + <strong>Figure 1:</strong> Relationships among the HDF5 root group, other groups, and objects + <hr> + </td><td> </td></tr> + + <tr><td> </td><td align=center> + <img src="FF-IH_FileObject.gif" alt="HDF5 Objects" hspace=15 vspace=15> + </td><td> </td></tr> + <tr><td> </td><td align=center> + <strong>Figure 2:</strong> HDF5 objects -- datasets, datatypes, or dataspaces + <hr> + </td><td> </td></tr> + </table> + + + <P>The format of an HDF5 file on disk encompasses several + key ideas of the HDF4 and AIO file formats as well as + addressing some shortcomings therein. The new format is + more self-describing than the HDF4 format and is more + uniformly applied to data objects in the file. + + <P>An HDF5 file appears to the user as a directed graph. + The nodes of this graph are the higher-level HDF5 objects + that are exposed by the HDF5 APIs: + + <ul> + <li>Groups + <li>Datasets + <li>Named datatypes + </ul> + + <P>At the lowest level, as information is actually written to the disk, + an HDF5 file is made up of the following objects: + <ul> + <li>A super block + <li>B-tree nodes (containing either symbol nodes or raw data chunks) + <li>Object headers + <li>A global heap + <li>Local heaps + <li>Free space + </ul> + + <P>The HDF5 library uses these low-level objects to represent the + higher-level objects that are then presented to the user or + to applications through the APIs. + For instance, a group is an object header that contains a message that + points to a local heap and to a B-tree which points to symbol nodes. + A dataset is an object header that contains messages that describe + datatype, space, layout, filters, external files, fill value, etc + with the layout message pointing to either a raw data chunk or to a + B-tree that points to raw data chunks. + + + <h3>This Document</h3> + + <p>This document describes the lower-level data objects; + the higher-level objects and their properties are described + in the <a href="H5.user.html"><cite>HDF5 User's Guide</cite></a>. + + <P>Three levels of information comprise the file format. + Level 0 contains basic information for identifying and + defining information about the file. Level 1 information contains + the information about the pieces of a file shared by many objects + in the file (such as a B-trees and heaps). Level 2 is the rest + of the file and contains all of the data objects, with each object + partitioned into header information, also known as + <em>metadata</em>, and data. + + <p>The sizes of various fields in the following layout tables are + determined by looking at the number of columns the field spans + in the table. There are three exceptions: (1) The size may be + overridden by specifying a size in parentheses, (2) the size of + addresses is determined by the <em>Size of Offsets</em> field + in the super block and is indicated in this document with a + superscripted 'O', and (3) the size of length fields is determined + by the <em>Size of Lengths</em> field in the super block and is + indicated in this document with a superscripted 'L'. + + <P>Values for all fields in this document should be treated as unsigned + integers, unless otherwise noted in the description of a field. + Additionally, all metadata fields are stored in little-endian byte + order. + </P> + + <BR> + <HR> + + <h2><a name="FileMetaData"> + Disk Format: Level 0 - File Metadata</a></h2> + + <H3><A name="SuperBlock"> + Disk Format: Level 0A - File Signature and Super Block</A></H3> + + <P>The super block may begin at certain predefined offsets within + the HDF5 file, allowing a block of unspecified content for + users to place additional information at the beginning (and + end) of the HDF5 file without limiting the HDF5 library's + ability to manage the objects within the file itself. This + feature was designed to accommodate wrapping an HDF5 file in + another file format or adding descriptive information to the + file without requiring the modification of the actual file's + information. The super block is located by searching for the + HDF5 file signature at byte offset 0, byte offset 512 and at + successive locations in the file, each a multiple of two of + the previous location, i.e. 0, 512, 1024, 2048, etc. + + <P>The super block is composed of a file signature, followed by + super block and group version numbers, information + about the sizes of offset and length values used to describe + items within the file, the size of each group page, + and a group entry for the root object in the file. + + <br> + <div align=center> + <table class=format> + <caption> + HDF5 Super Block Layout + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan=4><br>HDF5 File Signature (8 bytes)<br><br></td> + </tr> + + <tr> + <td>Version # of Super Block</td> + <td>Version # of Global Free-space Storage</td> + <td>Version # of Root Group Symbol Table Entry</td> + <td>Reserved (zero)</td> + </tr> + + <tr> + <td>Version # of Shared Header Message Format</td> + <td>Size of Offsets</td> + <td>Size of Lengths</td> + <td>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=2>Group Leaf Node K</td> + <td colspan=2>Group Internal Node K</td> + </tr> + + <tr> + <td colspan=4>File Consistency Flags</td> + </tr> + + <tr> + <td colspan=2 style="border:dotted;">Indexed Storage Internal Node K<sup>1</sup></td> + <td colspan=2 style="border:dotted;">Reserved (zero)<sup>1</sup></td> + </tr> + + <tr> + <td colspan=4>Base Address<sup>O</sup></td> + </tr> + + <tr> + <td colspan=4>Address of Global Free-space Heap<sup>O</sup></td> + </tr> + + <tr> + <td colspan=4>End of File Address<sup>O</sup></td> + </tr> + + <tr> + <td colspan=4>Driver Information Block Address<sup>O</sup></td> + </tr> + + <tr> + <td colspan=4>Root Group Symbol Table Entry</td> + </tr> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'O' the above table are + <br> + of the size specified in "Size of Offsets.") + </td></tr> + <tr><td> + (Items marked with an '1' the above table are + <br> + new in version 1 of the superblock) + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>HDF5 File Signature</td> + <td> + <P>This field contains a constant value and can be used to + quickly identify a file as being an HDF5 file. The + constant value is designed to allow easy identification of + an HDF5 file and to allow certain types of data corruption + to be detected. The file signature of an HDF5 file always + contains the following values: + </P> + + <center> + <table border align=center cellpadding=4> + <tr align=center> + <td align=right>Decimal:</td> + <td width="8%">137</td> + <td width="8%">72</td> + <td width="8%">68</td> + <td width="8%">70</td> + <td width="8%">13</td> + <td width="8%">10</td> + <td width="8%">26</td> + <td width="8%">10</td> + </tr> + + <tr align=center> + <td align=right>Hexadecimal:</td> + <td>89</td> + <td>48</td> + <td>44</td> + <td>46</td> + <td>0d</td> + <td>0a</td> + <td>1a</td> + <td>0a</td> + </tr> + + <tr align=center> + <td align=right>ASCII C Notation:</td> + <td>\211</td> + <td>H</td> + <td>D</td> + <td>F</td> + <td>\r</td> + <td>\n</td> + <td>\032</td> + <td>\n</td> + </tr> + </table> + </center> + <br> + + <P>This signature both identifies the file as an HDF5 file + and provides for immediate detection of common + file-transfer problems. The first two bytes distinguish + HDF5 files on systems that expect the first two bytes to + identify the file type uniquely. The first byte is + chosen as a non-ASCII value to reduce the probability + that a text file may be misrecognized as an HDF5 file; + also, it catches bad file transfers that clear bit + 7. Bytes two through four name the format. The CR-LF + sequence catches bad file transfers that alter newline + sequences. The control-Z character stops file display + under MS-DOS. The final line feed checks for the inverse + of the CR-LF translation problem. (This is a direct + descendent of the <A href="http://www.libpng.org/pub/png/spec/PNG-Rationale.html#R.PNG-file-signature">PNG</A> file + signature.) + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Version Number of the Super Block</td> + <td> + <P>This value is used to determine the format of the + information in the super block. When the format of the + information in the super block is changed, the version number + is incremented to the next integer and can be used to + determine how the information in the super block is + formatted. + </P> + + <P>Values of 0 and 1 are defined for this field. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Version Number of the File Free-space Information</td> + <td> + <P>This value is used to determine the format of the + information in the File Free-space Information. + </P> + <P>The only value currently valid in this field is '0', which + indicates that the free space index is formatted as described + <A href="#FreeSpaceIndex">below</A>. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Version Number of the Root Group Symbol Table Entry</td> + <td> + <P>This value is used to determine the format of the + information in the Root Group Symbol Table Entry. When the + format of the information in that field is changed, the + version number is incremented to the next integer and can be + used to determine how the information in the field + is formatted. + </P> + <P>The only value currently valid in this field is '0', which + indicates that the root group symbol table entry is formatted as + described <A href="#SymbolTableEntry">below</A>. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Version Number of the Shared Header Message Format</td> + <td> + <P>This value is used to determine the format of the + information in a shared object header message. Since the format + of the shared header messages differs from the other private + header messages, a version number is used to identify changes + in the format. + </P> + <P>The only value currently valid in this field is '0', which + indicates that shared header messages are formatted as + described <A href="#SharedMessage">below</A>. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Size of Offsets</td> + <td> + <P>This value contains the number of bytes used to store + addresses in the file. The values for the addresses of + objects in the file are offsets relative to a base address, + usually the address of the super block signature. This + allows a wrapper to be added after the file is created + without invalidating the internal offset locations. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Size of Lengths</td> + <td> + <P>This value contains the number of bytes used to store + the size of an object. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Group Leaf Node K</td> + <td> + <P>Each leaf node of a group B-tree will have at + least this many entries but not more than twice this + many. If a group has a single leaf node then it + may have fewer entries. + </P> + <P>This value must be greater than zero. + </P> + <P>See the <A href="#Btrees">description</A> of B-trees below. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Group Internal Node K</td> + <td> + <P>Each internal node of a group B-tree will have at + least this many entries but not more than twice this + many. If the group has only one internal + node then it might have fewer entries. + </P> + <P>This value must be greater than zero. + </P> + <P>See the <A href="#Btrees">description</A> of B-trees below. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>File Consistency Flags</td> + <td> + <P>This value contains flags to indicate information + about the consistency of the information contained + within the file. Currently, the following bit flags are + defined: + <ul> + <li>Bit 0 set indicates that the file is opened for + write-access. + <li>Bit 1 set indicates that the file has + been verified for consistency and is guaranteed to be + consistent with the format defined in this document. + <li>Bits 2-31 are reserved for future use. + </ul> + Bit 0 should be + set as the first action when a file is opened for write + access and should be cleared only as the final action + when closing a file. Bit 1 should be cleared during + normal access to a file and only set after the file's + consistency is guaranteed by the library or a + consistency utility. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Indexed Storage Internal Node K</td> + <td> + <P>Each internal node of a indexed storage B-tree will have at + least this many entries but not more than twice this + many. If the group has only one internal + node then it might have fewer entries. + </P> + <P>This value must be greater than zero. + </P> + <P>See the <A href="#Btrees">description</A> of B-trees below. + </P> + + <P><EM>This field is present in version 1+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Base Address</td> + <td> + <P>This is the absolute file address of the first byte of + the HDF5 data within the file. The library currently + constrains this value to be the absolute file address + of the super block itself when creating new files; + future versions of the library may provide greater + flexibility. When opening an existing file and this address does + not match the offset of the superblock, the library assumes + that the entire contents of the HDF5 file have been adjusted in + the file and adjusts the base address and end of file address to + reflect their new positions in the file. Unless otherwise noted, + all other file addresses are relative to this base + address. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Address of Global Free-space Index</td> + <td> + <P>Free-space management is not yet defined in the HDF5 + file format and is not handled by the library. + Currently this field always contains the + <A href="#UndefinedAddress">undefined address</A>. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>End of File Address</td> + <td> + <P>This is the absolute file address of the first byte past + the end of all HDF5 data. It is used to determine whether a + file has been accidently truncated and as an address where + file data allocation can occur if space from the free list is + not used. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Driver Information Block Address</td> + <td> + <P>This is the relative file address of the file driver + information block which contains driver-specific + information needed to reopen the file. If there is no + driver information block then this entry should be the + <A href="#UndefinedAddress">undefined address</A>. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + + <tr> + <td>Root Group Symbol Table Entry</td> + <td> + <P>This is the <A href="#SymbolTableEntry">symbol table entry</A> + of the root group, which serves as the entry point into + the group graph for the file. + </P> + + <P><EM>This field is present in version 0+ of the superblock.</EM> + </P> + </td> + </tr> + </table> + </div> + + <H3><A name="DriverInfo"> + Disk Format: Level 0B - File Driver Info</A></H3> + + <p>The <em>file driver information block</em> is an optional region of the + file which contains information needed by the file driver in + order to reopen a file. The format of the file driver information + block is: + + <br> + <div align=center> + <table class=format> + <caption> + Driver Information Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4>Driver Information Size (4 bytes)</td> + </tr> + + <tr> + <td colspan=4><br>Driver Identification (8 bytes)<br><br></td> + </tr> + + <tr> + <td colspan=4><br><br>Driver Information (<em>n</em> bytes)<br><br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>The version number of the driver information block. The + file format documented here is version zero. + </P> + </td> + </tr> + + <tr> + <td>Driver Information Size</td> + <td> + <P>The size in bytes of the Driver Information part of this + structure. + </P> + </td> + </tr> + + <tr> + <td>Driver Identification</td> + <td> + <P>This is an eight-byte ASCII string without null + termination which identifies the driver and version number + of the Driver Information block. The predefined drivers + supplied with the HDF5 library are identified by the + letters <code>NCSA</code> followed by the first four characters of + the driver name. If the Driver Information block is not + the original version then the last letter(s) of the + identification will be replaced by a version number in + ASCII. + </P> + <P> + For example, the various versions of the <em>multi driver</em> + will be identified by <code>NCSAmult</code>. + (<code>NCSAmult</code> is simply <code>NCSAmulti</code> truncated + to eight characters. Subsequent identifiers will be created by + substituting sequential numerical values for the final character, + starting with zero.) <em>multi driver</em> is the only default driver that + is encoded in this field. + </P> + <P> + Identification for user-defined drivers + is eight-byte long and arbitrary but should be unique and avoid + the four character prefix "NCSA". + </P> + </td> + </tr> + + <tr valign=top> + <td>Driver Information</td> + <td>Driver information is encoded/decoded in a format defined by the + file driver. <em>multi driver</em> is the only default driver that has driver + information stored in this field. Its format is explained in the + following block.</td> + </tr> + </table> + </div> + + <BR> + <P><em>Multi driver</em> has the following format:</P> + + <div align=center> + <table class=format> + <caption> + Multi Driver Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Member Mapping</td> + </tr> + + <tr> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Reserved</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan=4><br>Address of Member File 1<br><br></td> + </tr> + + <tr> + <td colspan=4><br>End of Address for Member File 1<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Address of Member File 2<br><br></td> + </tr> + + <tr> + <td colspan=4><br>End of Address for Member File 2<br><br></td> + </tr> + + <tr> + <td colspan=4><br>... ...<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Name of Member File 1<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Name of Member File 2<br><br></td> + </tr> + + <tr> + <td colspan=4><br>... ...<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Member Mapping</td> + <td><P><em>Multi driver</em> enables different types of HDF5 data and + metadata to be written to separate files. These files are viewed by the + library as a single virtual HDF5 file with a single file address. + It allows maximal 6 files to be created. + In sequence, these <em>Member Mapping</em> fields are for super block, + B-tree, raw data, global heap, local heap, + and object header. More than one type of data can be written to the + same file.</P> + <P>These <em>Member Mapping</em> fields are integer values from 1 to 6 + indicating how the data can be mapped to or merged with another type of + data. + <table class=list> + <tr> + <th width="30%">Member Mapping</th> + <th align=left>Description</th> + </tr> + <tr> + <td align=center>1</td> + <td>The super block data.</td> + </tr> + <tr> + <td align=center>2</td> + <td>The B-tree data.</td> + </tr> + <tr> + <td align=center>3</td> + <td>The raw data.</td> + </tr> + <tr> + <td align=center>4</td> + <td>The global heap data.</td> + </tr> + <tr> + <td align=center>5</td> + <td>The local heap data.</td> + </tr> + <tr> + <td align=center>6</td> + <td>The object header data.</td> + </tr> + </table></P> + For example, if the third field has the value 3 and all the rest have the + value 1, it means there are two files, one for raw data, one for super block, + B-tree, global heap, local heap, and object header. + </td> + </tr> + + <tr> + <td>Reserved</td> + <td><P>These fields are reserved and should always be zero.</P></td> + </tr> + + <tr> + <td>Address of Member File</td> + <td><P>Specifies the virtual address. A normally eight-byte integer with + the value from <em>0</em> (zero) to maximal value, + at which the member file starts.</P></td> + </tr> + + <tr> + <td>End of Address for Member File</td> + <td><P>The end of allocated address for the member file. A normally eight-byte + integer value.</P></td> + </tr> + + <tr> + <td>Name of Member File</td> + <td><P>The null-terminated name of member file. Its length should be multiples of + 8 bytes. Additional bytes will be padded with <em>NULL</em>s. The default naming + convention is <em>%%s-X.h5</em>, where <em>X</em> is one of the letters + <em>s</em> (for super block), <em>b</em> (for B-tree), <em>r</em> (for raw data), + <em>g</em> (for global heap), <em>l</em> (for local heap), and <em>o</em> (for + object header). The name for the whole HDF5 file will substitute the <em>%s</em> + in the string. + </P> + </td> + </tr> + </table> + </div> + + <BR> + <HR> + + <h2><a name="FileInfra"> + Disk Format: Level 1 - File Infrastructure</a></h2> + <h3><a name="Btrees">Disk Format: Level 1A - B-link Trees and B-tree Nodes</a></h3> + + <p>B-link trees allow flexible storage for objects which tend to grow + in ways that cause the object to be stored discontiguously. B-trees + are described in various algorithms books including "Introduction to + Algorithms" by Thomas H. Cormen, Charles E. Leiserson, and Ronald + L. Rivest. The B-link tree, in which the sibling nodes at a + particular level in the tree are stored in a doubly-linked list, + is described in the "Efficient Locking for Concurrent Operations + on B-trees" paper by Phillip Lehman and S. Bing Yao as published + in the <cite>ACM Transactions on Database Systems</cite>, Vol. 6, + No. 4, December 1981. + + <p>The B-link trees implemented by the file format contain one more + key than the number of children. In other words, each child + pointer out of a B-tree node has a left key and a right key. + The pointers out of internal nodes point to sub-trees while + the pointers out of leaf nodes point to symbol nodes and + raw data chunks. + Aside from that difference, internal nodes and leaf nodes + are identical. + + <br> + <div align=center> + <table class=format> + <caption> + B-tree Nodes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + + <tr> + <td colspan=4>Signature</td> + + <tr> + <td>Node Type</td> + <td>Node Level</td> + <td colspan=2>Entries Used</td> + + <tr> + <td colspan=4>Address of Left Sibling<sup>O</sup></td> + + <tr> + <td colspan=4>Address of Right Sibling<sup>O</sup></td> + + <tr> + <td colspan=4>Key 0 (variable size)</td> + + <tr> + <td colspan=4>Address of Child 0<sup>O</sup></td> + + <tr> + <td colspan=4>Key 1 (variable size)</td> + + <tr> + <td colspan=4>Address of Child 1<sup>O</sup></td> + + <tr> + <td colspan=4>...</td> + + <tr> + <td colspan=4>Key 2<em>K</em> (variable size)</td> + + <tr> + <td colspan=4>Address of Child 2<em>K</em><sup>O</sup></td> + + <tr> + <td colspan=4>Key 2<em>K</em>+1 (variable size)</td> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'O' the above table are + <br> + of the size specified in "Size of Offsets.") + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Signature</td> + <td> + <P>The ASCII character string "<code>TREE</code>" is + used to indicate the + beginning of a B-link tree node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file. + </P> + </td> + </tr> + + <tr> + <td>Node Type</td> + <td> + <P>Each B-link tree points to a particular type of data. + This field indicates the type of data as well as + implying the maximum degree <em>K</em> of the tree and + the size of each Key field. + </P> + + <table class=list> + <tr> + <th width="30%">Node Type</th> + <th align=left>Description</th> + </tr> + <tr> + <td align=center>0</td> + <td>This tree points to group nodes.</td> + </tr> + <tr> + <td align=center>1</td> + <td>This tree points to raw data chunk nodes.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Node Level</td> + <td> + <P>The node level indicates the level at which this node + appears in the tree (leaf nodes are at level zero). Not + only does the level indicate whether child pointers + point to sub-trees or to data, but it can also be used + to help file consistency checking utilities reconstruct + damanged trees. + </P> + </td> + </tr> + + <tr valign=top> + <td>Entries Used</td> + <td> + <P>This determines the number of children to which this + node points. All nodes of a particular type of tree + have the same maximum degree, but most nodes will point + to less than that number of children. The valid child + pointers and keys appear at the beginning of the node + and the unused pointers and keys appear at the end of + the node. The unused pointers and keys have undefined + values. + </P> + </td> + </tr> + + <tr valign=top> + <td>Address of Left Sibling</td> + <td> + <P>This is the relative file address of the left sibling of + the current node. If the current + node is the left-most node at this level then this field + is the <A href="#UndefinedAddress">undefined address</A>. + </P> + </td> + </tr> + + <tr valign=top> + <td>Address of Right Sibling</td> + <td> + <P>This is the relative file address of the right sibling of + the current node. If the current + node is the right-most node at this level then this + field is the <A href="#UndefinedAddress">undefined address</A>. + </P> + </td> + </tr> + + <tr valign=top> + <td>Keys and Child Pointers</td> + <td> + <P>Each tree has 2<em>K</em>+1 keys with 2<em>K</em> + child pointers interleaved between the keys. The number + of keys and child pointers actually containing valid + values is determined by the node's <em>Entries Used</em> field. + If that field is <em>N</em> then the B-link tree contains + <em>N</em> child pointers and <em>N</em>+1 keys. + </P> + </td> + </tr> + + <tr valign=top> + <td>Key</td> + <td> + <P>The format and size of the key values is determined by + the type of data to which this tree points. The keys are + ordered and are boundaries for the contents of the child + pointer; that is, the key values represented by child + <em>N</em> fall between Key <em>N</em> and Key + <em>N</em>+1. Whether the interval is open or closed on + each end is determined by the type of data to which the + tree points. + </P> + + <P> + The format of the key depends on the node type. + For nodes of node type 0 (group nodes), the key is formatted as + follows: + <center> + <table class=list> + <tr> + <td width=30%>A single field of <i>Size of Lengths</i> + bytes:</td> + <td>Indicates the byte offset into the local heap + for the first object name in the subtree which + that key describes. + </td> + </tr> + </table> + </center> + </P> + + <P> + For nodes of node type 1 (chunked raw data nodes), the key is + formatted as follows: + <center> + <table class=list> + <tr> + <td width=30%>Bytes 1-4:</td> + <td>Size of chunk in bytes.</td> + </tr> + <tr> + <td>Bytes 4-8:</td> + <td>Filter mask, a 32-bit bitfield indicating which + filters have been skipped for this chunk. Each filter + has an index number in the pipeline (starting at 0, with + the first filter to apply) and if that filter is skipped, + the bit corresponding to it's index is set.</td> + </tr> + <tr> + <td><em>N</em> 64-bit fields:</td> + <td>A 64-bit index indicating the offset of the + chunk within the dataset where <i>N</i> is the number + of dimensions of the dataset. For example, if + a chunk in a 3-dimensional dataset begins at the + position <code>[5,5,5]</code>, there will be three + such 64-bit indices, each with the value of + <code>5</code>.</td> + </tr> + </table> + </center> + </P> + </td> + </tr> + + <tr valign=top> + <td>Child Pointer</td> + <td> + <P>The tree node contains file addresses of subtrees or + data depending on the node level. Nodes at Level 0 point + to data addresses, either raw data chunk or group nodes. + Nodes at non-zero levels point to other nodes of the + same B-tree. + </P> + <P>For raw data chunk nodes, the child pointer is the address + of a single raw data chunk. For group nodes, the child pointer + points to a <A href="#SymbolTable">symbol table</A>, which contains + information for multiple symbol table entries. + </P> + </td> + </tr> + </table> + </div> + + <p> + Conceptually, each B-tree node looks like this: + <center> + <table> + <tr valign=top align=center> + <td>key[0]</td><td> </td> + <td>child[0]</td><td> </td> + <td>key[1]</td><td> </td> + <td>child[1]</td><td> </td> + <td>key[2]</td><td> </td> + <td>...</td><td> </td> + <td>...</td><td> </td> + <td>key[<i>N</i>-1]</td><td> </td> + <td>child[<i>N</i>-1]</td><td> </td> + <td>key[<i>N</i>]</td> + </tr> + </table> + </center> + <br> + + where child[<i>i</i>] is a pointer to a sub-tree (at a level + above Level 0) or to data (at Level 0). + Each key[<i>i</i>] describes an <i>item</i> stored by the B-tree + (a chunk or an object of a group node). The range of values + represented by child[<i>i</i>] is indicated by key[<i>i</i>] + and key[<i>i</i>+1]. + + + <p>The following question must next be answered: + "Is the value described by key[<i>i</i>] contained in + child[<i>i</i>-1] or in child[<i>i</i>]?" + The answer depends on the type of tree. + In trees for groups (node type 0) the object described by + key[<i>i</i>] is the greatest object contained in + child[<i>i</i>-1] while in chunk trees (node type 1) the + chunk described by key[<i>i</i>] is the least chunk in + child[<i>i</i>]. + + <p>That means that key[0] for group trees is sometimes unused; + it points to offset zero in the heap, which is always the + empty string and compares as "less-than" any valid object name. + + <p>And key[<i>N</i>] for chunk trees is sometimes unused; + it contains a chunk offset which compares as "greater-than" + any other chunk offset and has a chunk byte size of zero + to indicate that it is not actually allocated. + + + <h3><a name="SymbolTable">Disk Format: Level 1B - Group and Symbol Nodes</a></h3> + + <p>A group is an object internal to the file that allows + arbitrary nesting of objects within the file (including other groups). + A group maps a set of names in the group to a set of relative + file addresses where objects with those names are located in + the file. Certain metadata for an object to which the group points + can be cached in the group's symbol table in addition to the + object's header. + + <p>An HDF5 object name space can be stored hierarchically by + partitioning the name into components and storing each + component in a group. The group entry for a + non-ultimate component points to the group containing + the next component. The group entry for the last + component points to the object being named. + + <p>A group is a collection of group nodes pointed + to by a B-link tree. Each group node contains entries + for one or more symbols. If an attempt is made to add a + symbol to an already full group node containing + 2<em>K</em> entries, then the node is split and one node + contains <em>K</em> symbols and the other contains + <em>K</em>+1 symbols. + + <br> + <div align=center> + <table class=format> + <caption> + Group Node (A Leaf of a B-tree) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + + <tr> + <td colspan=4>Signature</td> + + <tr> + <td>Version Number</td> + <td>Reserved (0)</td> + <td colspan=2>Number of Symbols</td> + + <tr> + <td colspan=4><br><br>Group Entries<br><br><br></td> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Signature</td> + <td> + <P>The ASCII character string "<code>SNOD</code>" is + used to indicate the + beginning of a group node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file. + </P> + </td> + </tr> + + <tr> + <td>Version Number</td> + <td> + <P>The version number for the group node. This + document describes version 1. (There is no version '0' + of the group node) + </P> + </td> + </tr> + + <tr> + <td>Number of Symbols</td> + <td> + <P>Although all group nodes have the same length, + most contain fewer than the maximum possible number of + symbol entries. This field indicates how many entries + contain valid data. The valid entries are packed at the + beginning of the group node while the remaining + entries contain undefined values. + </P> + </td> + </tr> + + <tr> + <td>Group Entries</td> + <td> + <P>Each symbol has an entry in the group node. + The format of the entry is described below. + There are 2<EM>K</EM> entries in each group node, where + <EM>K</EM> is the "Group Leaf Node K" value from the + <A href="#SuperBlock">super block</A>. + </P> + </td> + </tr> + </table> + </div> + + <h3><a name="SymbolTableEntry"> + Disk Format: Level 1C - Group Entry </a></h3> + + <p>Each group entry in a group node is designed + to allow for very fast browsing of stored objects. + Toward that design goal, the group entries + include space for caching certain constant metadata from the + object header. + + <br> + <div align=center> + <table class=format> + <caption> + Group Entry + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan=4>Name Offset<sup>O</sup></td> + </tr> + + <tr> + <td colspan=4>Object Header Address<sup>O</sup></td> + </tr> + + <tr> + <td colspan=4>Cache Type</td> + </tr> + + <tr> + <td colspan=4>Reserved</td> + </tr> + + <tr> + <td colspan=4><br><br>Scratch-pad Space (16 bytes)<br><br><br></td> + </tr> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'O' the above table are + <br> + of the size specified in "Size of Offsets.") + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Name Offset</td> + <td> + <P>This is the byte offset into the group local + heap for the name of the object. The name is null + terminated. + </P> + </td> + </tr> + + <tr> + <td>Object Header Address</td> + <td> + <P>Every object has an object header which serves as a + permanent location for the object's metadata. In addition + to appearing in the object header, some metadata can be + cached in the scratch-pad space. + </P> + </td> + </tr> + + <tr> + <td>Cache Type</td> + <td> + <P>The cache type is determined from the object header. + It also determines the format for the scratch-pad space: + <br> + <table class=list> + <tr align=left> + <th>Type:</th> + <th>Description:</th> + </tr> + <tr> + <td width="10%" align=center>0</td> + <td>No data is cached by the group entry. This + is guaranteed to be the case when an object header + has a link count greater than one. + </td> + </tr> + <tr> + <td align=center>1</td> + <td>Object header metadata is cached in the group + entry. This implies that the group + entry refers to another group. + </td> + </tr> + <tr> + <td align=center>2</td> + <td>The entry is a symbolic link. The first four bytes + of the scratch-pad space are the offset into the local + heap for the link value. The object header address + will be undefined. + </td> + </tr> + <tr> + <td align=center><em>N</em></td> + <td>Other cache values can be defined later and + libraries that do not understand the new values will + still work properly. + </td> + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Reserved</td> + <td> + <P>These four bytes are present so that the scratch-pad + space is aligned on an eight-byte boundary. They are + always set to zero. + </P> + </td> + </tr> + + <tr> + <td>Scratch-pad Space</td> + <td> + <P>This space is used for different purposes, depending + on the value of the Cache Type field. Any metadata + about a dataset object represented in the scratch-pad + space is duplicated in the object header for that + dataset. This metadata can include the datatype + and the size of the dataspace for a dataset whose datatype + is atomic and whose dataspace is fixed and less than + four dimensions. + </P> + <P> + Furthermore, no data is cached in the group + entry scratch-pad space if the object header for + the group entry has a link count greater than + one. + </P> + </td> + </tr> + </table> + </div> + + <h4>Format of the Scratch-pad Space</h4> + + <p>The group entry scratch-pad space is formatted + according to the value in the Cache Type field. + + <p>If the Cache Type field contains the value zero + <code>(0)</code> then no information is + stored in the scratch-pad space. + + <p>If the Cache Type field contains the value one + <code>(1)</code>, then the scratch-pad space + contains cached metadata for another object header + in the following format: + + <br> + <div align=center> + <table class=format> + <caption> + Object Header Scratch-pad Format + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + + <tr> + <td colspan=4>Address of B-tree<sup>O</sup></td> + + <tr> + <td colspan=4>Address of Name Heap<sup>O</sup></td> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'O' the above table are + <br> + of the size specified in "Size of Offsets.") + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Address of B-tree</td> + <td> + <P>This is the file address for the root of the + group's B-tree. + </P> + </td> + </tr> + + <tr> + <td>Address of Name Heap</td> + <td> + <P>This is the file address for the group's local + heap, in which are stored the group's symbol names. + </P> + </td> + </tr> + </table> + </div> + + + <P>If the Cache Type field contains the value two + <code>(2)</code>, then the scratch-pad space + contains cached metadata for another symbolic link + in the following format: + + <br> + <div align=center> + <table class=format> + <caption> + Symbolic Link Scratch-pad Format + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan=4>Offset to Link Value</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Offset to Link Value</td> + <td> + <P>The value of a symbolic link (that is, the name of the + thing to which it points) is stored in the local heap. + This field is the 4-byte offset into the local heap for + the start of the link value, which is null terminated. + </P> + </td> + </tr> + </table> + </div> + + <h3><a name="LocalHeap">Disk Format: Level 1D - Local Heaps</a></h3> + + <P>A heap is a collection of small heap objects. Objects can be + inserted and removed from the heap at any time. + The address of a heap does not change once the heap is created. + References to objects are stored in the group table; + the names of those objects are stored in the local heap. + </P> + + <br> + <div align=center> + <table class=format> + <caption> + Local Heap + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan=4>Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4>Data Segment Size<sup>L</sup></td> + </tr> + + <tr> + <td colspan=4>Offset to Head of Free-list<sup>L</sup></td> + </tr> + + <tr> + <td colspan=4>Address of Data Segment<sup>O</sup></td> + </tr> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'L' the above table are + <br> + of the size specified in "Size of Lengths.") + </td></tr> + <tr><td> + (Items marked with an 'O' the above table are + <br> + of the size specified in "Size of Offsets.") + </td></tr> + </table> + </div> + + <p> + <center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Signature</td> + <td> + <P>The ASCII character string "<code>HEAP</code>" + is used to indicate the + beginning of a heap. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </P> + </td> + </tr> + + <tr> + <td>Version</td> + <td> + <P>Each local heap has its own version number so that new + heaps can be added to old files. This document + describes version zero (0) of the local heap. + </P> + </td> + </tr> + + <tr> + <td>Data Segment Size</td> + <td> + <P>The total amount of disk memory allocated for the heap + data. This may be larger than the amount of space + required by the objects stored in the heap. The extra + unused space in the heap holds a linked list of free blocks. + </P> + </td> + </tr> + + <tr> + <td>Offset to Head of Free-list</td> + <td> + <P>This is the offset within the heap data segment of the + first free block (or the + <A href="#UndefinedAddress">undefined address</A> if there is no + free block). The free block contains "Size of Lengths" bytes that + are the offset of the next free block (or the + value '1' if this is the + last free block) followed by "Size of Lengths" bytes that store + the size of this free block. The size of the free block includes + the space used to store the offset of the next free block and + the of the current block, making the minimum size of a free block + 2 * "Size of Lengths". + </P> + </td> + </tr> + + <tr> + <td>Address of Data Segment</td> + <td> + <P>The data segment originally starts immediately after + the heap header, but if the data segment must grow as a + result of adding more objects, then the data segment may + be relocated, in its entirety, to another part of the + file. + </P> + </td> + </tr> + </table> + </center> + + <p>Objects within the heap should be aligned on an 8-byte boundary. + + <h3><a name="GlobalHeap">Disk Format: Level 1E - Global Heap</a></h3> + + <P>Each HDF5 file has a global heap which stores various types of + information which is typically shared between datasets. The + global heap was designed to satisfy these goals: + + <ol type="A"> + <li>Repeated access to a heap object must be efficient without + resulting in repeated file I/O requests. Since global heap + objects will typically be shared among several datasets, it is + probable that the object will be accessed repeatedly. + <li>Collections of related global heap objects should result in + fewer and larger I/O requests. For instance, a dataset of + object references will have a global heap object for each + reference. Reading the entire set of object references + should result in a few large I/O requests instead of one small + I/O request for each reference. + <li>It should be possible to remove objects from the global heap + and the resulting file hole should be eligible to be reclaimed + for other uses. + </ol> + </P> + + <P>The implementation of the heap makes use of the memory + management already available at the file level and combines that + with a new top-level object called a <em>collection</em> to + achieve Goal B. The global heap is the set of all collections. + Each global heap object belongs to exactly one collection and + each collection contains one or more global heap objects. For + the purposes of disk I/O and caching, a collection is treated as + an atomic object. + </P> + + <P>The HDF5 library creates global heap collections as needed, so there may + be multiple collections throughout the file. The set of all of them is + abstractly called the "global heap", although they don't actually link + to each other, and there is no global place in the file where you can + discover all of the collections. The collections are found simply by + finding a reference to one through another object in the file (eg. + variable-length datatype elements, etc). + </P> + + <br> + <div align=center> + <table class=format> + <caption> + A Global Heap Collection + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan=4>Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4>Collection Size<sup>L</sup></td> + </tr> + + <tr> + <td colspan=4><br>Global Heap Object 1<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Global Heap Object 2<br><br></td> + </tr> + + <tr> + <td colspan=4><br>...<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Global Heap Object <em>N</em><br><br></td> + </tr> + + <tr> + <td colspan=4><br>Global Heap Object 0 (free space)<br><br></td> + </tr> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'L' the above table are + <br> + of the size specified in "Size of Lengths.") + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Signature</td> + <td> + <P>The ASCII character string "<code>GCOL</code>" + is used to indicate the + beginning of a collection. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </P> + </td> + </tr> + + <tr> + <td>Version</td> + <td> + <P>Each collection has its own version number so that new + collections can be added to old files. This document + describes version one (1) of the collections (there is no + version zero (0)). + </P> + </td> + </tr> + + <tr> + <td>Collection Size</td> + <td> + <P>This is the size in bytes of the entire collection + including this field. The default (and minimum) + collection size is 4096 bytes which is a typical file + system block size. This allows for 127 16-byte heap + objects plus their overhead (the collection header of 16 bytes + and the 16 bytes of information about each heap object). + </P> + </td> + </tr> + + <tr> + <td>Global Heap Object 1 through <em>N</em></td> + <td> + <P>The objects are stored in any order with no + intervening unused space. + </P> + </td> + </tr> + + <tr> + <td>Global Heap Object 0</td> + <td> + <P>Global Heap Object 0 (zero), when present, represents the free + space in the collection. Free space always appears at the end of + the collection. If the free space is too small to store the header + for Object 0 (described below) then the header is implied and the + collection contains no free space. + </P> + </td> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Global Heap Object + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan=2>Heap Object ID</td> + <td colspan=2>Reference Count</td> + </tr> + + <tr> + <td colspan=4>Reserved</td> + </tr> + + <tr> + <td colspan=4>Object Size<sup>L</sup></td> + </tr> + + <tr> + <td colspan=4><br>Object Data<br><br></td> + </tr> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'L' the above table are + <br> + of the size specified in "Size of Lengths.") + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Heap Object ID</td> + <td> + <P>Each object has a unique identification number within a + collection. The identification numbers are chosen so that + new objects have the smallest value possible with the + exception that the identifier <code>0</code> always refers to the + object which represents all free space within the + collection. + </P> + </td> + </tr> + + <tr> + <td>Reference Count</td> + <td> + <P>All heap objects have a reference count field. An + object which is referenced from some other part of the + file will have a positive reference count. The reference + count for Object 0 is always zero. + </P> + </td> + </tr> + + <tr> + <td>Reserved</td> + <td> + <P>Zero padding to align next field on an 8-byte boundary. + </P> + </td> + </tr> + + <tr> + <td>Object Size</td> + <td> + <P>This is the size of the object data stored for the object. + The actual storage space allocated for the object data is rounded + up to a multiple of eight. + </P> + </td> + </tr> + + <tr> + <td>Object Data</td> + <td> + <P>The object data is treated as a one-dimensional array + of bytes to be interpreted by the caller. + </P> + </td> + </tr> + </table> + </div> + + <h3><a name="FreeSpaceIndex">Disk Format: Level 1F - Free-space Index</a></h3> + + <p>The free-space index is a collection of blocks of data, + dispersed throughout the file, which are currently not used by + any file objects. + + <p>The super block contains a pointer to root of the free-space description; + that pointer is currently required to be the + <A href="#UndefinedAddress">undefined address</A>. + + <p>The format of the free-space index is not defined at this time. + +<!-- + <p>The Free-space Index is a collection of blocks of data, + dispersed throughout the file, which are currently not used by + any file objects. The blocks of data are indexed by a B-tree of + their length within the file. + + + <p>Each B-tree page is composed of the following entries and + B-tree management information, organized as follows: + + <p> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Free-space Heap Page</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Signature</td> + <tr align=center> + <td colspan=4>B-tree Left-link Offset</td> + <tr align=center> + <td colspan=4><br>Length of Free-block #1<br> <br></td> + <tr align=center> + <td colspan=4><br>Offset of Free-block #1<br> <br></td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4><br>Length of Free-block #n<br> <br></td> + <tr align=center> + <td colspan=4><br>Offset of Free-block #n<br> <br></td> + <tr align=center> + <td colspan=4>"High" Offset</td> + <tr align=center> + <td colspan=4>Right-link Offset</td> + </table> + </center> + + <p> + <dl> + <dt> The elements of the free-space heap page are described below: + <dd> + <dl> + <dt>Signature: (4 bytes) + <dd>The ASCII character string <code>FREE</code> + is used to indicate the + beginning of a free-space heap B-tree page. This gives + file consistency checking utilities a better chance of + reconstructing a damaged file. + + <dt>B-tree Left-link Offset: (<offset> bytes) + <dd>This value is used to indicate the offset of all offsets + in the B-link-tree which are smaller than the value of the + offset in entry #1. This value is also used to indicate a + leaf node in the B-link-tree by being set to all ones. + + <dt>Length of Free-block #n: (<length> bytes) + <dd>This value indicates the length of an unused block in + the file. + + <dt>Offset of Free-block #n: (<offset> bytes) + <dd>This value indicates the offset in the file of an + unused block in the file. + + <dt>"High" Offset: (4-bytes) + <dd>This offset is used as the upper bound on offsets + contained within a page when the page has been split. + + <dt>Right-link Offset: (<offset> bytes) + <dd>This value is used to indicate the offset of the next + child to the right of the parent of this group + page. When there is no node to the right, this value is + all zeros. + </dl> + </dl> + + <p>The algorithms for searching and inserting objects in the + B-tree pages are described fully in the Lehman and Yao paper, + which should be read to provide a full description of the + B-tree's usage. +--> + + <BR> + <HR> + + <h2><a name="DataObject">Disk Format: Level 2 - Data Objects </a></h2> + + <P>Data objects contain the real information in the file. These + objects compose the scientific data and other information which + are generally thought of as "data" by the end-user. All the + other information in the file is provided as a framework for + these data objects. + </P> + + <P>A data object is composed of header information and data + information. The header information contains the information + needed to interpret the data information for the data object as + well as additional "metadata" or pointers to additional + "metadata" used to describe or annotate each data object. + </P> + + <h3><a name="ObjectHeader"> + Disk Format: Level 2A - Data Object Headers</a></h3> + + <P>The header information of an object is designed to encompass + all the information about an object, except for the data itself. + This information includes + the dataspace, datatype, information about how the data + is stored on disk (in external files, compressed, broken up in + blocks, etc.), as well as other information used by the library + to speed up access to the data objects or maintain a file's + integrity. Information stored by user applications as attributes + is also stored in the object's header. The header of each object is + not necessarily located immediately prior to the object's data in the + file and in fact may be located in any position in the file. The order + of the messages in an object header is not significant. + </P> + + <P>Header messages are aligned on 8-byte boundaries. + </P> + + <br> + <div align=center> + <table class=format> + <caption> + Object Headers + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Reserved (zero)</td> + <td colspan=2>Number of Header Messages</td> + </tr> + + <tr> + <td colspan=4>Object Reference Count</td> + </tr> + + <tr> + <td colspan=4>Object Header Size</td> + </tr> + + <tr> + <td colspan=2>Header Message Type #1</td> + <td colspan=2>Size of Header Message Data #1</td> + </tr> + + <tr> + <td>Header Message #1 Flags</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4><br>Header Message Data #1<br><br></td> + </tr> + + <tr> + <td colspan=4>.<br>.<br>.<br></td> + </tr> + + <tr> + <td colspan=2>Header Message Type #n</td> + <td colspan=2>Size of Header Message Data #n</td> + </tr> + + <tr> + <td>Header Message #n Flags</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4><br>Header Message Data #n<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>This value is used to determine the format of the + information in the object header. When the format of the + information in the object header is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted. This + document describes version one (1) (there was no version + zero (0)). + </P> + </td> + </tr> + + <tr> + <td>Number of Header Messages</td> + <td> + <P>This value determines the number of messages listed in + object headers for this object. This value includes the messages + in continuation messages for this object. + </P> + </td> + </tr> + + <tr> + <td>Object Reference Count</td> + <td> + <P>This value specifies the number of "hard links" to this object + within the current file. References to the object from external + files, "soft links" in this file and object references in this + file are not tracked. + </P> + </td> + </tr> + + <tr> + <td>Object Header Size</td> + <td> + <P>This value specifies the number of bytes of header message data + following this length field that contain object header messages + for this object header. This value does not include the size of + object header continuation blocks for this object elsewhere in the + file. + </P> + </td> + </tr> + + <tr> + <td>Header Message Type</td> + <td> + <P>This value specifies the type of information included in the + following header message data. The header message types for the + pre-defined header messages are included in sections below. + </P> + </td> + </tr> + + <tr> + <td>Size of Header Message Data</td> + <td> + <P>This value specifies the number of bytes of header + message data following the header message type and length + information for the current message. The size includes + padding bytes to make the message a multiple of eight + bytes. + </P> + </td> + </tr> + + <tr> + <td>Header Message Flags</td> + <td> + <P>This is a bit field with the following definition: + <table class=list> + <tr> + <th width="30%">Bit</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>If set, the message data is constant. This is used + for messages like the datatype message of a dataset. + </td> + </tr> + <tr> + <td align=center><code>1</code></td> + <td>If set, the message is stored in the global heap. + The Header Message Data field contains a Shared Object + message and the Size of Header Message Data field + contains the size of that Shared Object message. + </td> + </tr> + <tr> + <td align=center><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Header Message Data</td> + <td> + <P>The format and length of this field is determined by the + header message type and size respectively. Some header + message types do not require any data and this information + can be eliminated by setting the length of the message to + zero. The data is padded with enough zeros to make the + size a multiple of eight. + </P> + </td> + </tr> + </table> + </div> + + <P>The header message types and the message data associated with + them compose the critical "metadata" about each object. Some + header messages are required for each object while others are + optional. Some optional header messages may also be repeated + several times in the header itself, the requirements and number + of times allowed in the header will be noted in each header + message description below. + </P> + + <P>The following is a list of currently defined header messages: + </P> + + <hr> + <h4><a name="NILMessage">Name: NIL</a></h4> + + <P class=item><B>Header Message Type: </B>0x0000 + </P> + <P class=item><B>Length:</B> varies + </P> + <P class=item><B>Status:</B> Optional, may be repeated. + </P> + <P class=item><B>Purpose and Description:</B> The NIL message is used to indicate a + message which is to be ignored when reading the header messages for a + data object. [Possibly one which has been deleted for some reason.] + </P> + <P class=item><B>Format of Data:</B> Unspecified. + </P> + + <hr> + <h4><a name="SimpleDataSpace">Name: Simple Dataspace</a></h4> + + <P class=item><B>Header Message Type: </B>0x0001 + </P> + <P class=item><B>Length:</B> Varies according to the number of dimensions, + as described in the following table. + </P> + <P class=item><B>Status:</B> Required for dataset objects, may not be + repeated. + </P> + <P class=item><B>Description:</B> The simple dataspace message describes the + number of dimensions (i.e. "rank") and size of each dimension that the + data object has. This message is only used for datasets which have a + simple, rectilinear grid layout; datasets requiring a more complex + layout (irregularly structured or unstructured grids, etc.) must use + the <em>Complex Dataspace</em> message for expressing the space the + dataset inhabits. <i>(Note: The <em>Complex Dataspace</em> + functionality is not yet implemented and it is not described in this + document.)</i> + </P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Simple Dataspace Message + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Flags</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan=4>Reserved</td> + </tr> + + <tr> + <td colspan=4>Dimension #1 Size<sup>L</sup></td> + <tr> + <td colspan=4>.<br>.<br>.<br></td> + <tr> + <td colspan=4>Dimension #n Size<sup>L</sup></td> + <tr> + <td colspan=4>Dimension #1 Maximum Size<sup>L</sup></td> + <tr> + <td colspan=4>.<br>.<br>.<br></td> + <tr> + <td colspan=4>Dimension #n Maximum Size<sup>L</sup></td> + <tr> + <td colspan=4>Permutation Index #1<sup>L</sup></td> + <tr> + <td colspan=4>.<br>.<br>.<br></td> + <tr> + <td colspan=4>Permutation Index #n<sup>L</sup></td> + </table> + + <table class=note> + <tr><td> + (Items marked with an 'L' the above table are + <br> + of the size specified in "Size of Lengths.") + </td></tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>This value is used to determine the format of the + Simple Dataspace Message. When the format of the + information in the message is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted. This + document describes version one (1) (there was no version + zero (0)). + </P> + </td> + </tr> + + <tr> + <td>Dimensionality</td> + <td> + <P>This value is the number of dimensions that the data + object has. + </P> + </td> + </tr> + + <tr> + <td>Flags</td> + <td> + <P>This field is used to store flags to indicate the + presence of parts of this message. Bit 0 (the least + significant bit) is used to indicate that maximum + dimensions are present. Bit 1 is used to indicate that + permutation indices are present. + </P> + </td> + </tr> + + <tr> + <td>Dimension #n Size</td> + <td> + <P>This value is the current size of the dimension of the + data as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </P> + </td> + </tr> + + <tr> + <td>Dimension #n Maximum Size</td> + <td> + <P>This value is the maximum size of the dimension of the + data as stored in the file. This value may be the special + "<A href="#UnlimitedDim">unlimited</A>" size which indicates + that the data may expand along this dimension indefinitely. + If these values are not stored, the maximum size of each + dimension is assumed to be the dimension's current size. + </P> + </td> + </tr> + + <tr> + <td>Permutation Index #n</td> + <td> + <P>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. If these values are + not stored, the first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </P> + </td> + </tr> + </table> + </div> + + </P> + +<!-- + <hr> + <h4><a name="DataSpaceMessage">Name: Complex Dataspace (Fiber Bundle?)</a></h4> + <b>Header Message Type: </b>0x0002<br> + <b>Length:</b> varies<br> + + <b>Status:</b> One of the <em>Simple Dataspace</em> or + <em>Complex Dataspace</em> messages is required (but not both) and may + not be repeated.<br> <b>Purpose and Description:</b> The + <em>Dataspace</em> message describes space that the dataset is + mapped onto in a more comprehensive way than the <em>Simple + Dimensionality</em> message is capable of handling. The + dataspace of a dataset encompasses the type of coordinate system + used to locate the dataset's elements as well as the structure and + regularity of the coordinate system. The dataspace also + describes the number of dimensions which the dataset inhabits as + well as a possible higher dimensional space in which the dataset + is located within. + + <br> + <b>Format of Data:</b> + + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Message Layout</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Mesh Type</td> + <tr align=center> + <td colspan=4>Logical Dimensionality</td> + </table> + </center> + + <p> + <dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Mesh Type: (unsigned 32-bit integer) + <dd>This value indicates whether the grid is + polar/spherical/cartesion, + structured/unstructured and regular/irregular. <br> + The mesh type value is broken up as follows: <br> + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Mesh-type Layout</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=1>Mesh Embedding</td> + <td colspan=1>Coordinate System</td> + <td colspan=1>Structure</td> + <td colspan=1>Regularity</td> + </table> + </center> + The following are the definitions of mesh-type bytes: + <dl> + <dt>Mesh Embedding + <dd>This value indicates whether the dataset dataspace + is located within + another dataspace or not: + <dl> <dl> + <dt><STANDALONE> + <dd>The dataset mesh is self-contained and is not + embedded in another mesh. + <dt><EMBEDDED> + <dd>The dataset's dataspace is located within + another dataspace, as + described in information below. + </dl> </dl> + <dt>Coordinate System + <dd>This value defines the type of coordinate system + used for the mesh: + <dl> <dl> + <dt><POLAR> + <dd>The last two dimensions are in polar + coordinates, higher dimensions are + cartesian. + <dt><SPHERICAL> + <dd>The last three dimensions are in spherical + coordinates, higher dimensions + are cartesian. + <dt><CARTESIAN> + <dd>All dimensions are in cartesian coordinates. + </dl> </dl> + <dt>Structure + <dd>This value defines the locations of the grid-points + on the axes: + <dl> <dl> + <dt><STRUCTURED> + <dd>All grid-points are on integral, sequential + locations, starting from 0. + <dt><UNSTRUCTURED> + <dd>Grid-points locations in each dimension are + explicitly defined and + may be of any numeric datatype. + </dl> </dl> + <dt>Regularity + <dd>This value defines the locations of the dataset + points on the grid: + <dl> <dl> + <dt><REGULAR> + <dd>All dataset elements are located at the + grid-points defined. + <dt><IRREGULAR> + <dd>Each dataset element has a particular + grid-location defined. + </dl> </dl> + </dl> + <p>The following grid combinations are currently allowed: + <dl> <dl> + <dt><POLAR-STRUCTURED-REGULAR> + <dt><SPHERICAL-STRUCTURED-REGULAR> + <dt><CARTESIAN-STRUCTURED-REGULAR> + <dt><POLAR-UNSTRUCTURED-REGULAR> + <dt><SPHERICAL-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-IRREGULAR> + </dl> </dl> + All of the above grid types can be embedded within another + dataspace. + <br> <br> + <dt>Logical Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions that the dataset occupies. + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Embedded Dimensionality Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Embedded Dimensionality</td> + <tr align=center> + <td colspan=4>Embedded Dimension Size #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Embedded Dimension Size #n</td> + <tr align=center> + <td colspan=4>Embedded Origin Location #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Embedded Origin Location #n</td> + </table> + </center> + + <dt>Embedded Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions of the space the + dataset is located + within. i.e. a planar dataset located within a 3-D space, + or a 3-D dataset + which is a subset of another 3-D space, etc. + <dt>Embedded Dimension Size: (unsigned 32-bit integer) + <dd>These values are the sizes of the dimensions of the + embedded dataspace + that the dataset is located within. + <dt>Embedded Origin Location: (unsigned 32-bit integer) + <dd>These values comprise the location of the dataset's + origin within the embedded dataspace. + </dl> + </dl> + [Comment: need some way to handle different orientations of the + dataset dataspace + within the embedded dataspace]<br> + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Structured/Regular Grid Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4>Logical Dimension Size #1</td> + <tr align=center> + <td colspan=4>Logical Dimension Maximum #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Logical Dimension Size #n</td> + <tr align=center> + <td colspan=4>Logical Dimension Maximum #n</td> + </table> + </center> + + <p> + <dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Logical Dimension Size #n: (unsigned 32-bit integer) + <dd>This value is the current size of the dimension of the + data as stored in + the file. The first dimension stored in the list of + dimensions is the slowest + changing dimension and the last dimension stored is the + fastest changing + dimension. + <dt>Logical Dimension Maximum #n: (unsigned 32-bit integer) + <dd>This value is the maximum size of the dimension of the + data as stored in + the file. This value may be the special value + <UNLIMITED> which + indicates that the data may expand along this dimension + indefinitely. + </dl> + </dl> + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Structured/Irregular Grid Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4># of Grid Points in Dimension #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4># of Grid Points in Dimension #n</td> + <tr align=center> + <td colspan=4>Datatype of Grid Point Locations</td> + <tr align=center> + <td colspan=4>Location of Grid Points in Dimension #1</td> + <tr align=center> + <td colspan=4>.<br>.<br>.<br></td> + <tr align=center> + <td colspan=4>Location of Grid Points in Dimension #n</td> + </table> + </center> + + <P> + <center> + <table border cellpadding=4 width="80%"> + <caption align=bottom> + <B>HDF5 Dataspace Unstructured Grid Information</B> + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + + <tr align=center> + <td colspan=4># of Grid Points</td> + <tr align=center> + <td colspan=4>Datatype of Grid Point Locations</td> + <tr align=center> + <td colspan=4>Grid Point Locations<br>.<br>.<br></td> + </table> + </center> +--> + + <hr> + <h4><a name="ReservedMessage_0002">Name: Reserved - Not Assigned Yet</a></h4> + <b>Header Message Type:</b> 0x0002<BR> + <b>Length:</b> N/A<BR> + <b>Status:</b> N/A<BR> + <b>Format of Data:</b> N/A<BR> + + <p><b>Purpose and Description:</b> This message type was skipped during + the initial specification of the file format and may be used in a + future expansion to the format. + + + <hr> + <h4><a name="DataTypeMessage">Name: Datatype</a></h4> + + <P class=item><B>Header Message Type:</B> 0x0003 + </P> + <P class=item><B>Length:</B> variable + </P> + <P class=item><B>Status:</B> Required for dataset or named datatype objects, + may not be repeated. + </P> + + <P class=item><B>Description:</B> The datatype message defines the datatype + for each element of a dataset. A datatype can describe an atomic type + like a fixed- or floating-point type or a compound type like a C + struct. + Datatypes messages are stored + as a list of datatype classes and + their associated properties. + </P> + + <P class=item2>Datatype messages that are part of a dataset object, + do not describe how elements are related to one another, the dataspace + message is used for that purpose. Datatype messages that are part of + a named datatype message describe an "abstract" datatype that can be + used by other objects in the file. + </P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Datatype Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Class and Version</td> + <td>Class Bit Field, Bits 0-7</td> + <td>Class Bit Field, Bits 8-15</td> + <td>Class Bit Field, Bits 16-23</td> + </tr> + + <tr> + <td colspan=4>Size</td> + </tr> + + <tr> + <td colspan=4><br><br>Properties<br><br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Class and Version</td> + <td> + <P>The version of the datatype message and the datatype's class + information are packed together in this field. The version + number is packed in the top 4 bits of the field and the class + is contained in the bottom 4 bits. + </P> + <P>The version number information is used for changes in the + format of the datatype message and is described here: + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align=center><code>1</code></td> + <td>Used by early versions of the library to encode + compound datatypes with explicit array fields. + See the compound datatype description below for + further details. + </td> + </tr> + <tr> + <td align=center><code>2</code></td> + <td>The current version used by the library. + </td> + </tr> + </table> + </P> + <P>The class of the datatype determines the format for the class + bit field and properties portion of the datatype message, which + are described below. The + following classes are currently defined: + <table width=100% class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Fixed-Point</td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Floating-Point</td> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Time</td> + </tr> + + <tr> + <td align=center><code>3</code></td> + <td>String</td> + </tr> + + <tr> + <td align=center><code>4</code></td> + <td>Bitfield</td> + </tr> + + <tr> + <td align=center><code>5</code></td> + <td>Opaque</td> + </tr> + + <tr> + <td align=center><code>6</code></td> + <td>Compound</td> + </tr> + + <tr> + <td align=center><code>7</code></td> + <td>Reference</td> + </tr> + + <tr> + <td align=center><code>8</code></td> + <td>Enumerated</td> + </tr> + + <tr> + <td align=center><code>9</code></td> + <td>Variable-Length</td> + </tr> + + <tr> + <td align=center><code>10</code></td> + <td>Array</td> + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Class Bit Fields</td> + <td> + <P>The information in these bit fields is specific to each datatype + class and is described below. All bits not defined for a + datatype class are set to zero. + </P> + </td> + </tr> + + <tr> + <td>Size</td> + <td> + <P>The size of the datatype in bytes. + </P> + </td> + </tr> + + <tr> + <td>Properties</td> + <td> + <P>This variable-sized field encodes information specific to each + datatype class and is described below. If there is no + property information specified for a datatype class, the size + of this field is zero. + </P> + </td> + </tr> + + </table> + </div> + </P> + + <P>Class specific information for Fixed-Point Numbers (Class 0): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr> + <td>1, 2</td> + <td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2 + is the hi_pad type. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</td> + </tr> + + <tr> + <td>3</td> + <td><b>Signed.</b> If this bit is set then the fixed-point + number is in 2's complement form.</td> + </tr> + + <tr> + <td>4-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Descriptions + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=2>Bit Offset</td> + <td colspan=2>Bit Precision</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Bit Offset</td> + <td> + <P>The bit offset of the first significant bit of the fixed-point + value within the datatype. The bit offset specifies the number + of bits "to the right of" the value. + </P> + </td> + </tr> + + <tr> + <td>Bit Precision</td> + <td> + <P>The number of bits of precision of the fixed-point value + within the datatype. + </P> + </td> + </tr> + + </table> + </div> + </P> + + <P>Class specific information for Floating-Point Numbers (Class 1): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr> + <td>1, 2, 3</td> + <td><b>Padding type.</b> Bit 1 is the low bits pad type, bit 2 + is the high bits pad type, and bit 3 is the internal bits + pad type. If a datum has unused bits at either end or between + the sign bit, exponent, or mantissa, then the value of bit + 1, 2, or 3 is copied to those locations.</td> + </tr> + + <tr> + <td>4-5</td> + <td><b>Normalization.</b> The value can be 0 if there is no + normalization, 1 if the most significant bit of the + mantissa is always set (except for 0.0), and 2 if the most + signficant bit of the mantissa is not stored but is + implied to be set. The value 3 is reserved and will not + appear in this field.</td> + </tr> + + <tr> + <td>6-7</td> + <td>Reserved (zero).</td> + </tr> + + <tr> + <td>8-15</td> + <td><b>Sign Location.</b> This is the bit position of the sign + bit. Bits are numbered with the least significant bit zero.</td> + </tr> + + <tr> + <td>16-23</td> + <td>Reserved (zero).</td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Descriptions + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=2>Bit Offset</td> + <td colspan=2>Bit Precision</td> + </tr> + + <tr> + <td>Exponent Location</td> + <td>Exponent Size</td> + <td>Mantissa Location</td> + <td>Mantissa Size</td> + </tr> + + <tr> + <td colspan=4>Exponent Bias</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Bit Offset</td> + <td> + <P>The bit offset of the first significant bit of the floating-point + value within the datatype. The bit offset specifies the number + of bits "to the right of" the value. + </P> + </td> + </tr> + + <tr> + <td>Bit Precision</td> + <td> + <P>The number of bits of precision of the floating-point value + within the datatype. + </P> + </td> + </tr> + + <tr> + <td>Exponent Location</td> + <td> + <P>The bit position of the exponent field. Bits are numbered with + the least significant bit number zero. + </P> + </td> + </tr> + + <tr> + <td>Exponent Size</td> + <td> + <P>The size of the exponent field in bits. + </P> + </td> + </tr> + + <tr> + <td>Mantissa Location</td> + <td> + <P>The bit position of the mantissa field. Bits are numbered with + the least significant bit number zero. + </P> + </td> + </tr> + + <tr> + <td>Mantissa Size</td> + <td> + <P>The size of the mantissa field in bits. + </P> + </td> + </tr> + + <tr> + <td>Exponent Bias</td> + <td> + <P>The bias of the exponent field. + </P> + </td> + </tr> + + </table> + </div> + </P> + + <P>Class specific information for Time (Class 2): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr> + <td>1-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Descriptions + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=2>Bit Precision</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Bit Precision</td> + <td> + <P>The number of bits of precision of the time value. + </P> + </td> + </tr> + + </table> + </div> + </P> + + <P>Class specific information for Strings (Class 3): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0-3</td> + <td><b>Padding type.</b> This four-bit value determines the + type of padding to use for the string. The values are: + + <table width=100% class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Null Terminate: A zero byte marks the end of the + string and is guaranteed to be present after + converting a long string to a short string. When + converting a short string to a long string the value is + padded with additional null characters as necessary. + </td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Null Pad: Null characters are added to the end of + the value during conversions from short values to long + values but conversion in the opposite direction simply + truncates the value. + </td> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Space Pad: Space characters are added to the end of + the value during conversions from short values to long + values but conversion in the opposite direction simply + truncates the value. This is the Fortran + representation of the string. + </td> + </tr> + + <tr> + <td align=center><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table> + </tr> + + <tr> + <td>4-7</td> + <td><b>Character Set.</b> The character set to use for + encoding the string. The only character set supported is + the 8-bit ASCII (zero) so no translations have been defined + yet.</td> + </tr> + + <tr> + <td>8-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <P>There are no properties defined for the string class. + </P> + </P> + + <P>Class specific information for Bitfields (Class 4): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0</td> + <td><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</td> + </tr> + + <tr> + <td>1, 2</td> + <td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2 + is the hi_pad type. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</td> + </tr> + + <tr> + <td>3-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=2>Bit Offset</td> + <td colspan=2>Bit Precision</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Bit Offset</td> + <td> + <P>The bit offset of the first significant bit of the bitfield + within the datatype. The bit offset specifies the number + of bits "to the right of" the value. + </P> + </td> + </tr> + + <tr> + <td>Bit Precision</td> + <td> + <P>The number of bits of precision of the bitfield + within the datatype. + </P> + </td> + </tr> + </table> + </div> + </P> + + <P>Class specific information for Opaque (Class 5): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0-7</td> + <td>Length of ASCII tag in bytes.</td> + </tr> + + <tr> + <td>8-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=4><br>ASCII Tag<br> + <br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>ASCII Tag</td> + <td> + <P>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </P> + </td> + </tr> + </table> + </div> + </P> + + <P>Class specific information for Compound (Class 6): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0-15</td> + <td><b>Number of Members.</b> This field contains the number + of members defined for the compound datatype. The member + definitions are listed in the Properties field of the data + type message. + </tr> + + <tr> + <td>15-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + </P> + + <P>The Properties field of a compound datatype is a list of the + member definitions of the compound datatype. The member + definitions appear one after another with no intervening bytes. + The member types are described with a recursive datatype + message. + + <P>Note that the property descriptions are different for different + versions of the datatype version. Additionally note that the version + 0 properties are deprecated and have been replaced with the version + 1 properties in versions of the HDF5 library from the 1.4 release + onward. + + <br> + <div align=center> + <table class=format> + <caption> + Properties Description for Datatype Version 1 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr> + <td colspan=4>Byte Offset of Member</td> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4>Dimension Permutation</td> + </tr> + + <tr> + <td colspan=4>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4>Dimension #1 Size (required)</td> + </tr> + + <tr> + <td colspan=4>Dimension #2 Size (required)</td> + </tr> + + <tr> + <td colspan=4>Dimension #3 Size (required)</td> + </tr> + + <tr> + <td colspan=4>Dimension #4 Size (required)</td> + </tr> + + <tr> + <td colspan=4><br>Member Type Message<br><br></td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Name</td> + <td> + <P>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </P> + </td> + </tr> + + <tr> + <td>Byte Offset of Member</td> + <td> + <P>This is the byte offset of the member within the datatype. + </P> + </td> + </tr> + + <tr> + <td>Dimensionality</td> + <td> + <P>If set to zero, this field indicates a scalar member. If set + to a value greater than zero, this field indicates that the + member is an array of values. For array members, the size of + the array is indicated by the 'Size of Dimension n' field in + this message. + </P> + </td> + </tr> + + <tr> + <td>Dimension Permutation</td> + <td> + <P>This field was intended to allow an array field to have + it's dimensions permuted, but this was never implemented. + This field should always be set to zero. + </P> + </td> + </tr> + + <tr> + <td>Dimension #n Size</td> + <td> + <P>This field is the size of a dimension of the array field as + stored in the file. The first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </P> + </td> + </tr> + + <tr> + <td>Member Type Message</td> + <td> + <P>This field is a datatype message describing the datatype of + the member. + </P> + </td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Properties Description for Datatype Version 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr> + <td colspan=4>Byte Offset of Member</td> + </tr> + + <tr> + <td colspan=4><br>Member Type Message<br><br></td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Name</td> + <td> + <P>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </P> + </td> + </tr> + + <tr> + <td>Byte Offset of Member</td> + <td> + <P>This is the byte offset of the member within the datatype. + </P> + </td> + </tr> + + <tr> + <td>Member Type Message</td> + <td> + <P>This field is a datatype message describing the datatype of + the member. + </P> + </td> + </tr> + + </table> + </div> + </P> + + <P>Class specific information for Reference (Class 7): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0-3</td> + <td><b>Type.</b> This four-bit value contains the type of reference + described. The values defined are: + + <table width=100% class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Object Reference: A reference to another object in this + HDF5 file. + </td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Dataset Region Reference: A reference to a region within + a dataset in this HDF5 file. + </td> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Internal Reference: A reference to a region within the + current dataset. (Not currently implemented) + </td> + </tr> + + <tr> + <td align=center><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table> + + </td> + </tr> + + <tr> + <td>15-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <P>There are no properties defined for the reference class. + </P> + </P> + + <P>Class specific information for Enumeration (Class 8): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0-15</td> + <td><b>Number of Members.</b> The number of name/value + pairs defined for the enumeration type.</td> + </tr> + + <tr> + <td>16-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=4><br>Base Type<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Names<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Values<br><br></td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Base Type</td> + <td> + <P>Each enumeration type is based on some parent type, usually an + integer. The information for that parent type is described + recursively by this field. + </P> + </td> + </tr> + + <tr> + <td>Names</td> + <td> + <P>The name for each name/value pair. Each name is stored as a null + terminated ASCII string in a multiple of eight bytes. The names + are in no particular order. + </P> + </td> + </tr> + + <tr> + <td>Values</td> + <td> + <P>The list of values in the same order as the names. The values + are packed (no inter-value padding) and the size of each value + is determined by the parent type. + </P> + </td> + </tr> + + </table> + </div> + </P> + + + <P>Class specific information for Variable-Length (Class 9): + + <br> + <div align=center> + <table class=desc> + <caption> + Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td>0-3</td> + <td><b>Type.</b> This four-bit value contains the type of + variable-length datatype described. The values defined are: + + <table width=100% class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Sequence: A variable-length sequence of any sequence of + data. Variable-length sequences do not have padding or + character set information. + </td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>String: A variable-length sequence of characters. + Variable-length strings have padding and character set + information. + </td> + </tr> + + <tr> + <td align=center><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table> + + </td> + </tr> + + <tr> + <td>4-7</td> + <td><b>Padding type.</b> (variable-length string only) + This four-bit value determines the type of padding + used for variable-length strings. The values are the same + as for the string padding type, as follows: + <table width=100% class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Null terminate: A zero byte marks the end of a string + and is guaranteed to be present after converting a long + string to a short string. When converting a short string + to a long string, the value is padded with additional null + characters as necessary. + </td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Null pad: Null characters are added to the end of the + value during conversion from a short string to a longer + string. Conversion from a long string to a shorter string + simply truncates the value. + </td> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Space pad: Space characters are added to the end of the + value during conversion from a short string to a longer + string. Conversion from a long string to a shorter string + simply truncates the value. This is the Fortran + representation of the string. + </td> + </tr> + + <tr> + <td align=center><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table> + + This value is set to zero for variable-length sequences. + + </td> + </tr> + + <tr> + <td>8-11</td> + <td><b>Character Set.</b> (variable-length string only) + This four-bit value specifies the character set + to be used for encoding the string: + <table width=100% class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>ASCII: As of this writing (July 2003, Release 1.6.0), + 8-bit ASCII is the only character set supported. Therefore, + no translations have been defined. + </td> + </tr> + + <tr> + <td align=center><code>1-15</code></td> + <td>Reserved + </td> + </tr> + </table> + + This value is set to zero for variable-length sequences. + + </td> + </tr> + + <tr> + <td>12-23</td> + <td>Reserved (zero).</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan=4><br>Base Type<br><br></td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Base Type</td> + <td> + <P>Each variable-length type is based on some parent type. The + information for that parent type is described recursively by + this field. + </P> + </td> + </tr> + + </table> + </div> + </P> + + <P>Class specific information for Array (Class 10): + + <P>There are no bit fields defined for the array class. + </P> + + <P>Note that the dimension information defined in the property for this + datatype class is independent of dataspace information for a dataset. + The dimension information here describes the dimensionality of the + information within a data element (or a component of an element, if the + array datatype is nested within another datatype) and the dataspace for a + dataset describes the location of the elements in a dataset. + </P> + + <br> + <div align=center> + <table class=format> + <caption> + Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan=3>Reserved (zero)</td> + </tr> + + <tr> + <td colspan=4>Dimension #1 Size</td> + </tr> + <tr> + <td colspan=4>.<br>.<br>.<br></td> + </tr> + <tr> + <td colspan=4>Dimension #n Size</td> + </tr> + + <tr> + <td colspan=4>Permutation Index #1</td> + </tr> + <tr> + <td colspan=4>.<br>.<br>.<br></td> + </tr> + <tr> + <td colspan=4>Permutation Index #n</td> + </tr> + + <tr> + <td colspan=4><br>Base Type<br><br></td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td> + <P>This value is the number of dimensions that the array has. + </P> + </td> + </tr> + + <tr> + <td>Dimension #n Size</td> + <td> + <P>This value is the size of the dimension of the array + as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </P> + </td> + </tr> + + <tr> + <td>Permutation Index #n</td> + <td> + <P>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. Currently, dimension + permutations are not supported and these indices should be set + to the index position minus one (i.e. the first dimension should + be set to 0, the second dimension should be set to 1, etc.) + </P> + </td> + </tr> + + <tr> + <td>Base Type</td> + <td> + <P>Each array type is based on some parent type. The + information for that parent type is described recursively by + this field. + </P> + </td> + </tr> + + </table> + </div> + + </P> + + <hr> + <h4><a name="OldFillValueMessage">Name: Data Storage - Fill Value (Old)</a></h4> + + <P class=item><B>Header Message Type:</B> 0x0004 + </P> + <P class=item><B>Length:</B> varies + </P> + <P class=item><B>Status:</B> Optional, may not be repeated. + </P> + + <P class=item><B>Description:</B> The fill value message stores a single + data value which is returned to the application when an uninitialized + data element is read from a dataset. The fill value is interpreted + with the same datatype as the dataset. If no fill value message is + present then a fill value of all zero bytes is assumed. + </P> + + <P class=item2>This fill value message is deprecated in favor of the "new" + fill value message (Message Type 0x0005) and is only written to the + file for forward compatibility with versions of the HDF5 library before + the 1.6.0 version. Additionally, it only appears for datasets with a + user defined fill value (as opposed to the library default fill value + or an explicitly set "undefined" fill value). + </P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Fill Value Message (Old) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=4>Size</td> + </tr> + + <tr> + <td colspan=4><br>Fill Value<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Size</td> + <td> + <P>This is the size of the Fill Value field in bytes. + </P> + </td> + </tr> + + <tr> + <td>Fill Value</td> + <td> + <P>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. + </P> + </td> + </tr> + </table> + </div> + </P> + + <hr> + <h4><a name="FillValueMessage">Name: Data Storage - Fill Value </a></h4> + + <P class=item><B>Header Message Type:</B> 0x0005 + </P> + <P class=item><B>Length:</B> varies + </P> + <P class=item><B>Status:</B> Required for dataset objects, may not be repeated. + </P> + + <P class=item><B>Description:</B> The fill value message stores a single + data value which is returned to the application when an uninitialized + data element is read from a dataset. The fill value is interpreted + with the same datatype as the dataset. + </P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Fill Value Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Space Allocation Time</td> + <td>Fill Value Write Time</td> + <td>Fill Value Defined</td> + </tr> + + <tr> + <td colspan=4>Size</td> + </tr> + + <tr> + <td colspan=4><br>Fill Value<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>The version number information is used for changes in the + format of the fill value message and is described here: + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align=center><code>1</code></td> + <td>Used by version 1.6.x of the library to encode + fill values. In this version, the Size field is + always present. + </td> + </tr> + <tr> + <td align=center><code>2</code></td> + <td>The current version used by the library (version + 1.7.3 or later). In this version, the Size and + Fill Value fields are + only present if the Fill Value Defined field is set + to 1. + </td> + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Space Allocation Time</td> + <td> + <P>When the storage space for the dataset's raw data will be + allocated. The allowed values are: + <table class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Early allocation. Storage space for the entire dataset + should be allocated in the file when the dataset is + created. + </td> + </tr> + <tr> + <td align=center><code>2</code></td> + <td>Late allocation. Storage space for the entire dataset + should not be allocated until the dataset is written + to. + </td> + </tr> + <tr> + <td align=center><code>3</code></td> + <td>Incremental allocation. Storage space for the + dataset should not be allocated until the portion + of the dataset is written to. This is currently + used in conjunction with chunked data storage for + datasets. + </td> + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Fill Value Write Time</td> + <td> + <P>At the time that storage space for the dataset's raw data is + allocated, this value indicates whether the fill value should + be written to the raw data storage elements. The allowed values + are: + <table class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>On allocation. The fill value is always written to + the raw data storage when the storage space is allocated. + </td> + </tr> + <tr> + <td align=center><code>1</code></td> + <td>Never. The fill value should never be written to + the raw data storage. + </td> + </tr> + <tr> + <td align=center><code>2</code></td> + <td>Fill value written if set by user. The fill value + will be written to the raw data storage when the storage + space is allocated only if the user explicitly set + the fill value. If the fill value is the library + default or is undefined, it will not be written to + the raw data storage. + </td> + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Fill Value Defined</td> + <td> + <P>This value indicates if a fill value is defined for this + dataset. If this value is 0, the fill value is undefined. + If this value is 1, a fill value is defined for this dataset. + For version 2 or later of the fill value message, this value + controls the presence of the Size field. + </P> + </td> + </tr> + + <tr> + <td>Size</td> + <td> + <P>This is the size of the Fill Value field in bytes. This field + is not present if the Version field is >1 and the Fill Value + Defined field is set to 0. + </P> + </td> + </tr> + + <tr> + <td>Fill Value</td> + <td> + <P>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. This field is + not present if the Version field is >1 and the Fill Value + Defined field is set to 0. + </P> + </td> + </tr> + </table> + </div> + </P> + +<!-- + <hr> + <h4><a name="CompactDataStorageMessage">Name: Data Storage - Compact</a></h4> + + <b>Header Message Type:</b> 0x0006<br> + <b>Length:</b> varies<br> + <b>Status:</b> Optional, may not be repeated.<br> + + <p>This message indicates that the data for the data object is + stored within the current HDF file by including the actual + data as the header data for this message. The data is + stored internally in + the <em>normal format</em>, i.e. in one chunk, uncompressed, etc. + + <P>Note that one and only one of the <em>Data Storage</em> headers can be + stored for each data object. + + <P><b>Format of Data:</b> The message data is actually composed + of dataset data, so the format will be determined by the dataset + format. +--> + + <hr> + <h4><a name="ReservedMessage_0006">Name: Reserved - Not Assigned Yet</a></h4> + <P class=item><B>Header Message Type:</B> 0x0006</P> + <P class=item><B>Length:</B> N/A</P> + <P class=item><B>Status:</B> N/A</P> + <P class=item><B>Format of Data:</B> N/A</P> + + <P class=item><B>Purpose and Description:</B> This message type was skipped during + the initial specification of the file format and may be used in a + future expansion to the format.</P> + + <hr> + <h4><a name="ExternalFileListMessage">Name: Data Storage - + External Data Files</a></h4> + <P class=item><B>Header Message Type:</B> 0x0007 </P> + <P class=item><B>Length:</B> varies</P> + <P class=item><B>Status:</B> Optional, may not be repeated.</P> + + <P class=item><B>Purpose and Description:</B> The external object message + indicates that the data for an object is stored outside the HDF5 + file. The filename of the object is stored as a Universal + Resource Location (URL) of the actual filename containing the + data. An external file list record also contains the byte offset + of the start of the data within the file and the amount of space + reserved in the file for that data.</P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + External File List Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan=3>Reserved</td> + </tr> + + <tr> + <td colspan=2>Allocated Slots</td> + <td colspan=2>Used Slots</td> + </tr> + + <tr> + <td colspan=4><br>Heap Address<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Slot Definitions...<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>The version number information is used for changes in the format of External File + List Message and is described here: + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + <tr> + <td align=center><code>0</code></td> + <td>Never used. + </tr> + <tr> + <td align=center><code>1</code></td> + <td>The current version used by the library. + </tr> + </table> + </P> + </td> + </tr> + + <tr> + <td>Reserved</td> + <td> + <P>This field is reserved for future use.</P> + </td> + </tr> + + <tr> + <td>Allocated Slots</td> + <td> + <P>The total number of slots allocated in the message. Its value must be at least as + large as the value contained in the Used Slots field. (The current library simply + uses the number of Used Slots for this message)</P> + </td> + </tr> + + <tr> + <td>Used Slots</td> + <td> + <P>The number of initial slots which contains valid information.</P> + </td> + </tr> + + <tr> + <td>Heap Address</td> + <td> + <P>This is the address of a local heap which contains the names for the external + files (The local heap information can be found in Disk Format Level 1D in this + document). The name at offset zero in the heap is always the empty string.</P> + </td> + </tr> + + <tr> + <td>Slot Definitions</td> + <td> + <P>The slot definitions are stored in order according to the array addresses they + represent.</P> + </td> + </tr> + + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + External File List Slot + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=4><br>Name Offset(<size> bytes)<br><br></td> + </tr> + + <tr> + <td colspan=4><br>File Offset(<size> bytes)<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Size<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Name Offset(<size> bytes)</td> + <td> + <P>The byte offset within the local name heap for the name + of the file. File names are stored as a URL which has a + protocol name, a host name, a port number, and a file + name: + <code><em>protocol</em>:<em>port</em>//<em>host</em>/<em>file</em></code>. + If the protocol is omitted then "file:" is assumed. If + the port number is omitted then a default port for that + protocol is used. If both the protocol and the port + number are omitted then the colon can also be omitted. If + the double slash and host name are omitted then + "localhost" is assumed. The file name is the only + mandatory part, and if the leading slash is missing then + it is relative to the application's current working + directory (the use of relative names is not + recommended).</P> + </td> + </tr> + + <tr> + <td>File Offset(<size> bytes)</td> + <td> + <P>This is the byte offset to the start of the data in the + specified file. For files that contain data for a single + dataset this will usually be zero.</P> + </td> + </tr> + + <tr> + <td>Size</td> + <td> + <P>This is the total number of bytes reserved in the + specified file for raw data storage. For a file that + contains exactly one complete dataset which is not + extendable, the size will usually be the exact size of the + dataset. However, by making the size larger one allows + HDF5 to extend the dataset. The size can be set to a value + larger than the entire file since HDF5 will read zeros + past the end of the file without failing.</P> + </td> + </tr> + </table> + </div> + + + <hr> + <h4><a name="LayoutMessage">Name: Data Storage - Layout</a></h4> + + <P class=item><B>Header Message Type:</B> 0x0008</P> + <P class=item><B>Length:</B> varies</P> + <P class=item><B>Status:</B> Required for datasets, may not be repeated.</P> + + <P class=item><B>Purpose and Description:</B> Data layout describes how the + elements of a multi-dimensional array are arranged in the linear + address space of the file. Three types of data layout are + supported: + + <ol> + <li>Contiguous: The array can be stored in one contiguous area of the file. + The layout requires that the size of the array be constant and + does not permit chunking, compression, checksums, encryption, + etc. The message stores the total size of the array and the + offset of an element from the beginning of the storage area is + computed as in C. + + <li>Chunked: The array domain can be regularly decomposed into chunks and + each chunk is allocated separately. This layout supports + arbitrary element traversals, compression, encryption, and + checksums, and the chunks can be distributed across external + raw data files (these features are described in other + messages). The message stores the size of a chunk instead of + the size of the entire array; the size of the entire array can + be calculated by traversing the B-tree that stores the chunk + addresses. + + <li>Compact: The array can be stored in one contiguous block, as part of + this object header message (this is called "compact" storage below). + </ol> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Data Layout Message (Versions 1 and 2) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Layout Class</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan=4>Reserved</td> + </tr> + + <tr> + <td colspan=4><br>Address<br><br></td> + </tr> + + <tr> + <td colspan=4>Dimension 0 (4-bytes)</td> + </tr> + + <tr> + <td colspan=4>Dimension 1 (4-bytes)</td> + </tr> + + <tr> + <td colspan=4>...</td> + </tr> + + <tr> + <td colspan=4>Dataset Element Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan=4>Compact Data Size (4-bytes)</td> + </tr> + + <tr> + <td colspan=4><br>Compact Data...<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>The version number information is used for changes in the format of the data + layout message and is described here:</P> + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Used by version 1.4 and before of the library to encode layout information. + Data space is always allocated when the data set is created.</td> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Used by version 1.6.x of the library to encode layout information. + Data space is allocated only when it is necessary.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Dimensionality</td> + <td><P>An array has a fixed dimensionality. This field + specifies the number of dimension size fields later in the + message.</P></td> + </tr> + + <tr> + <td>Layout Class</td> + <td><P>The layout class specifies how the other fields of the + layout message are to be interpreted. A value of one + indicates contiguous storage, a value of two indicates chunked storage, + while a value of zero indicates compact storage. Other values will be defined + in the future.</P></td> + </tr> + + <tr> + <td>Address</td> + <td><P>For contiguous storage, this is the address of the first + byte of storage. For chunked storage this is the address + of the B-tree that is used to look up the addresses of the + chunks. This field is not present for compact storage. + If the version for this message is set to 2, the address + may have the "undefined address" value, to indicate that + storage has not yet been allocated for this array.</P></td> + </tr> + + <tr> + <td>Dimensions</td> + <td><P>For contiguous and compact storage the dimensions define + the entire size of the array while for chunked storage they define + the size of a single chunk. In all cases, they are in units of + array elements (not bytes). The first dimension stored in the list + of dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </P> + </td> + </tr> + + <tr> + <td>Dataset Element Size</td> + <td><P>The size of a dataset element, in bytes. This field is only + present for chunked storage. + </P> + </td> + </tr> + + <tr> + <td>Compact Data Size</td> + <td><P>This field is only present for compact data storage. + It contains the size of the raw data for the dataset array.</P></td> + + <tr> + <td>Compact Data</td> + <td><P>This field is only present for compact data storage. + It contains the raw data for the dataset array.</P></td> + </tr> + </table> + </div> + + <br> + <P>Version 3 of this message re-structured the format into specific + properties that are required for each layout class. + + <br> + <div align=center> + <table class=format> + <caption> + <B>Data Layout Message (Version 3)</B> + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Layout Class</td> + <td colspan=2 bgcolor=#DDDDDD> </td> + </tr> + + <tr> + <td colspan=4><br>Properties<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td> + <P>The version number information is used for changes in the format of layout message + and is described here:</P> + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>3</code></td> + <td>Used by the version 1.6.3 and later of the library to store properties + for each layout class.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Layout Class</td> + <td><P>The layout class specifies how the other fields of the layout message are to be + interpreted. A value of one indicates contiguous storage, a value of two + indicates chunked storage, while a value of zero indicates compact storage.</P></td> + </tr> + + <tr> + <td>Properties</td> + <td><P>This variable-sized field encodes information specific to each + layout class and is described below. If there is no property + information specified for a layout class, the size of this field + is zero bytes.</P></td> + </tr> + </table> + </div> + + <br> + <P>Class-specific information for compact layout (Class 0): (Note: The dimensionality information + is in the Dataspace message) + + <br> + <div align=center> + <table class=format> + <caption> + Property Descriptions + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=2>Size</td> + <td colspan=2 bgcolor=#DDDDDD> </td> + </tr> + + <tr> + <td colspan=4><br>Raw Data...<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Size</td> + <td><P>This field contains the size of the raw data for the dataset array.</P></td> + </tr> + + <tr> + <td>Raw Data</td> + <td><P>This field contains the raw data for the dataset array.</P></td> + </tr> + </table> + </div> + + <br> + <P>Class-specific information for contiguous layout (Class 1): (Note: The dimensionality information + is in the Dataspace message) + + <br> + <div align=center> + <table class=format> + <caption> + Property Descriptions + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=4><br>Address<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Size<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Address</td> + <td><P>This is the address of the first byte of raw data storage. + The address may have the "undefined address" value, to indicate + that storage has not yet been allocated for this array.</P></td> + </tr> + + <tr> + <td>Size</td> + <td><P>This field contains the size allocated to store the raw data.</P></td> + </tr> + </table> + </div> + + <br> + <P>Class-specific information for chunked layout (Class 2): + + <br> + <div align=center> + <table class=format> + <caption> + Property Descriptions + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan=3 bgcolor=#DDDDDD> </td> + </tr> + + <tr> + <td colspan=4><br>Address<br><br></td> + </tr> + + <tr> + <td colspan=4>Dimension 0 (4-bytes)</td> + </tr> + + <tr> + <td colspan=4>Dimension 1 (4-bytes)</td> + </tr> + + <tr> + <td colspan=4>...</td> + </tr> + + <tr> + <td colspan=4>Dataset Element Size</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td><P>A chunk has a fixed dimensionality. This field specifies + the number of dimension size fields later in the message.</P></td> + </tr> + + <tr> + <td>Address</td> + <td><P>This is the address of the B-tree that is used to look up the addresses of the + chunks. The address may have the "undefined address" value, to indicate that + storage has not yet been allocated for this array.</P></td> + </tr> + + <tr> + <td>Dimensions</td> + <td><P>These values define the dimension size of a single chunk, in + units of array elements (not bytes). The first dimension stored in + the list of dimensions is the slowest changing dimension and the + last dimension stored is the fastest changing dimension. + </P> + </td> + </tr> + + <tr> + <td>Dataset Element Size</td> + <td><P>The size of a dataset element, in bytes. + </P> + </td> + </tr> + </table> + </div> + + <hr> + <h4><a name="ReservedMessage_0009">Name: Reserved - Not Assigned Yet</a></h4> + <P class=item><B>Header Message Type:</B> 0x0009</P> + <P class=item><B>Length:</B> N/A</P> + <P class=item><B>Status:</B> N/A</P> + <P class=item><B>Format of Data:</B> N/A</P> + + <P class=item><B>Purpose and Description:</B> This message type was skipped during the initial + specification of the file format and may be used in a future expansion to the format. + + <hr> + <h4><a name="ReservedMessage_000A">Name: Reserved - Not Assigned Yet</a></h4> + <P class=item><B>Header Message Type:</B> 0x0009</P> + <P class=item><B>Length:</B> N/A</P> + <P class=item><B>Status:</B> N/A</P> + <P class=item><B>Format of Data:</B> N/A</P> + + <P class=item><B>Purpose and Description:</B> This message type was skipped during the initial + specification of the file format and may be used in a future expansion to the format. + + <hr> + <h4><a name="FilterMessage">Name: Data Storage - Filter Pipeline</a></h4> + <P class=item><B>Header Message Type:</B> 0x000B</P> + <P class=item><B>Length:</B> varies</P> + <P class=item><B>Status:</B> Optional, may not be repeated.</P> + + <P class=item><B>Description:</B> This message describes the + filter pipeline which should be applied to the data stream by + providing filter identification numbers, flags, a name, and + client data.</P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Filter Pipeline Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Number of Filters</td> + <td colspan=2>Reserved</td> + </tr> + + <tr> + <td colspan=4>Reserved</td> + </tr> + + <tr> + <td colspan=4><br>Filter List<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td><P>The version number for this message. This document + describes version 1.</P></td> + </tr> + + <tr> + <td>Number of Filters</td> + <td><P>The total number of filters described by this + message. The maximum possible number of filters in a + message is 32.</P></td> + </tr> + + <tr> + <td>Filter List</td> + <td><P>A description of each filter. A filter description + appears in the next table.</P></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Filter Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=2>Filter Identification</td> + <td colspan=2>Name Length</td> + </tr> + + <tr> + <td colspan=2>Flags</td> + <td colspan=2>Number of Values for Client Data</td> + </tr> + + <tr> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Client Data<br><br></td> + </tr> + + <tr> + <td colspan=4>Padding</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Filter Identification</td> + <td> + <p> + This value, often referred to as a filter identifier, + is designed to be a unique identifier for the filter. + Values from zero through 32,767 are reserved for filters + supported by The HDF Group in the HDF5 library and for + filters requested and supported by third parties. + Filters supported by The HDF Group are documented immediately + below. Information on 3rd-party filters can be found at + <a href="/services/contributions.html#filters"> + <code>https://support.hdfgroup.org/services/contributions.html#filters</code></a>. + <a href="#Footnote1Change"><sup><small>1</small></sup></a> + <p> + To request a filter identifier, please contact + The HDF Group’s Help Desk at + <img src="Graphics/help.png" valign="center" height=14>. + You will be asked to provide the following information: + <ol> + <li>Contact information for the developer requesting the + new identifier + <li>A short description of the new filter + <li>Links to any relevant information, including licensing + information + </ol> + <p> + Values from 32768 to 65535 are reserved for non-distributed uses + (for example, internal company usage) or for application usage + when testing a feature. The HDF Group does not track or document + the use of the filters with identifiers from this range. + + <p> + The filters currently in library version 1.6.5 are + listed below: + <table class=list> + <tr> + <th width="30%">Identification</th> + <th align=left>Name</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>deflate</td> + <td>GZIP deflate compression</td> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>shuffle</td> + <td>Data element shuffling</td> + </tr> + + <tr> + <td align=center><code>3</code></td> + <td>fletcher32</td> + <td>Fletcher32 checksum</td> + </tr> + + <tr> + <td align=center><code>4</code></td> + <td>szip</td> + <td>SZIP compression</td> + </tr> + </table> + </P></td> + </tr> + + <tr> + <td>Name Length</td> + <td><P>Each filter has an optional null-terminated ASCII name + and this field holds the length of the name including the + null termination padded with nulls to be a multiple of + eight. If the filter has no name then a value of zero is + stored in this field.</P></td> + </tr> + + <tr> + <td>Flags</td> + <td><P>The flags indicate certain properties for a filter. The + bit values defined so far are:</P> + <table class=list> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>bit 1</code></td> + <td>If set then the filter is an optional filter. + During output, if an optional filter fails it will be + silently removed from the pipeline.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Client Data Number of Values</td> + <td><P>Each filter can store a few integer values to control + how the filter operates. The number of entries in the + Client Data array is stored in this field.</P></td> + </tr> + + <tr> + <td>Name</td> + <td><P>If the Name Length field is non-zero then it will + contain the size of this field, a multiple of eight. This + field contains a null-terminated, ASCII character + string to serve as a comment/name for the filter.</P></td> + </tr> + + <tr> + <td>Client Data</td> + <td><P>This is an array of four-byte integers which will be + passed to the filter function. The Client Data Number of + Values determines the number of elements in the array.</P></td> + </tr> + + <tr> + <td>Padding</td> + <td><P>Four bytes of zeros are added to the message at this + point if the Client Data Number of Values field contains + an odd number.</P></td> + </tr> + </table> + </div> + <p> + <hr align="left" width="50"> + <a name="Footnote1Change"><sup>1</sup></a>If you are reading + an earlier version of this document, this link may have changed. + If the link does not work, use the latest version of this document + on <a href="https://support.hdfgroup.org">The HDF Group</a>’s website, + <a href="/HDF5/doc/H5.format.html"> + <code>https://support.hdfgroup.org/HDF5/doc/H5.format.html</code></a>; + the link there will always be correct. + <small><a href="#FilterMessage">(Return)</a> + </P> + + <hr> + <h4><a name="AttributeMessage">Name: Attribute</a></h4> + <P class=item><B>Header Message Type:</B> 0x000C + <P class=item><B>Length:</B> varies + <P class=item><B>Status:</B> Optional, may be repeated. + + <P class=item><B>Description:</B> The <em>Attribute</em> + message is used to list objects in the HDF file which are used + as attributes, or "metadata" about the current object. An + attribute is a small dataset; it has a name, a datatype, a data + space, and raw data. Since attributes are stored in the object + header they must be relatively small (<64KB) and can be + associated with any type of object which has an object header + (groups, datasets, named types and spaces, etc.). + + <P class=item2>Note: Attributes on an object must have unique names. (The HDF5 library + currently enforces this by causing the creation of an attribute with + a duplicate name to fail). Attributes on different objects may have the + same name, however. + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Attribute Message (Version 1) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Reserved</td> + <td colspan=2>Name Size</td> + </tr> + + <tr> + <td colspan=2>Datatype Size</td> + <td colspan=2>Dataspace Size</td> + </tr> + + <tr> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Datatype<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Dataspace<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Data<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td><P>The version number information is used for changes in the format of the + attribute message and is described here:</P> + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Used by the library before version 1.6 to encode attribute message. + This version does not support shared data type.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Reserved</td> + <td><P>This field is reserved for later use and is set to + zero.</P></td> + </tr> + + <tr> + <td>Name Size</td> + <td><P>The length of the attribute name in bytes including the + null terminator. Note that the Name field below may + contain additional padding not represented by this + field.</P></td> + </tr> + + <tr> + <td>Datatype Size</td> + <td><P>The length of the datatype description in the Datatype + field below. Note that the Datatype field may contain + additional padding not represented by this field.</P></td> + </tr> + + <tr> + <td>Dataspace Size</td> + <td><P>The length of the dataspace description in the Dataspace + field below. Note that the Dataspace field may contain + additional padding not represented by this field.</P></td> + </tr> + + <tr> + <td>Name</td> + <td><P>The null-terminated attribute name. This field is + padded with additional null characters to make it a + multiple of eight bytes.</P></td> + </tr> + + <tr> + <td>Datatype</td> + <td><P>The datatype description follows the same format as + described for the datatype object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</P></td> + </tr> + + <tr> + <td>Dataspace</td> + <td><P>The dataspace description follows the same format as + described for the dataspace object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</P></td> + </tr> + + <tr> + <td>Data</td> + <td><P>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. This + field is <em>not</em> padded with additional bytes.</P></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Attribute Message (Version 2) + </caption> + + <tr align=center> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flag</td> + <td colspan=2>Name Size</td> + </tr> + + <tr> + <td colspan=2>Type Size</td> + <td colspan=2>Space Size</td> + </tr> + + <tr> + <td colspan=4><br>Name<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Type<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Space<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Data<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td><P>The version number information is used for changes in the format of the + attribute message and is described here:</P> + <table class=list width="90%"> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Used by the library of version 1.6.x and after to encode attribute message. + This version supports shared data type. The fields of name, type, and space + are not padded with additional bytes of zero.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Flag</td> + <td><P>This field indicates whether the data type of this attribute is shared:</P> + <table class=list width="90%"> + <tr> + <th width="30%">Value</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Datatype is <em>not</em> shared.</td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Datatype is shared.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Name Size</td> + <td><P>The length of the attribute name in bytes including the + null terminator.</P></td> + </tr> + + <tr> + <td>Datatype Size</td> + <td><P>The length of the datatype description in the Datatype + field below.</P></td> + </tr> + + <tr> + <td>Dataspace Size</td> + <td><P>The length of the dataspace description in the Dataspace + field below.</P></td> + </tr> + + <tr> + <td>Name</td> + <td><P>The null-terminated attribute name. This field is <em>not</em> + padded with additional bytes.</P></td> + </tr> + + <tr> + <td>Datatype</td> + <td><P>The datatype description follows the same format as + described for the datatype object header message. This + field is <em>not</em> padded with additional bytes.</P></td> + </tr> + + <tr> + <td>Dataspace</td> + <td><P>The dataspace description follows the same format as + described for the dataspace object header message. This + field is <em>not</em> padded with additional bytes.</P></td> + </tr> + + <tr> + <td>Data</td> + <td><P>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. This + field is <em>not</em> padded with additional zero + bytes.</P></td> + </tr> + </table> + </div> + + <hr> + <h4><a name="CommentMessage">Name: Object Comment</a></h4> + + <P class=item><B>Header Message Type:</B> 0x000D</P> + <P class=item><B>Length:</B> varies</P> + <P class=item><B>Status:</B> Optional, may not be repeated.</P> + + <P class=item><B>Description:</B> The object comment is + designed to be a short description of an object. An object comment + is a sequence of non-zero (<code>\0</code>) ASCII characters with no other + formatting included by the library.</P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Name Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=4><br>Comment<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Name</td> + <td>A null terminated ASCII character string.</td> + </tr> + </table> + </div> + + <hr> + <h4><a name="OldModifiedMessage">Name: Object Modification Date & Time (Old)</a></h4> + + <P class=item><B>Header Message Type:</B> 0x000E</P> + <P class=item><B>Length:</B> fixed</P> + <P class=item><B>Status:</B> Optional, may not be repeated.</P> + + <P class=item><B>Description:</B> The object modification date + and time is a timestamp which indicates (using ISO-8601 date and + time format) the last modification of an object. The time is + updated when any object header message changes according to the + system clock where the change was posted. + + <br><br>This modification time message is deprecated in favor of the "new" + modification time message (Message Type 0x0012) and is no longer written + to the file in versions of the HDF5 library after the 1.6.0 version. + </P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Modification Time Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=4>Year</td> + </tr> + + <tr> + <td colspan=2>Month</td> + <td colspan=2>Day of Month</td> + </tr> + + <tr> + <td colspan=2>Hour</td> + <td colspan=2>Minute</td> + </tr> + + <tr> + <td colspan=2>Second</td> + <td colspan=2>Reserved</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Year</td> + <td><P>The four-digit year as an ASCII string. For example, + <code>1998</code>. All fields of this message should be interpreted + as coordinated universal time (UTC)</P></td> + </tr> + + <tr> + <td>Month</td> + <td><P>The month number as a two digit ASCII string where + January is <code>01</code> and December is <code>12</code>.</P></td> + </tr> + + <tr> + <td>Day of Month</td> + <td><P>The day number within the month as a two digit ASCII + string. The first day of the month is <code>01</code>.</P></td> + </tr> + + <tr> + <td>Hour</td> + <td><P>The hour of the day as a two digit ASCII string where + midnight is <code>00</code> and 11:00pm is <code>23</code>.</P></td> + </tr> + + <tr> + <td>Minute</td> + <td><P>The minute of the hour as a two digit ASCII string where + the first minute of the hour is <code>00</code> and + the last is <code>59</code>.</P></td> + </tr> + + <tr> + <td>Second</td> + <td><P>The second of the minute as a two digit ASCII string + where the first second of the minute is <code>00</code> + and the last is <code>59</code>.</P></td> + </tr> + + <tr> + <td>Reserved</td> + <td><P>This field is reserved and should always be zero.</P></td> + </tr> + </table> + </div> + + <hr> + <h4><a name="SharedMessage">Name: Shared Object Message</a></h4> + <P class=item><B>Header Message Type:</B> 0x000F</P> + <P class=item><B>Length:</B> Fixed</P> + <P class=item><B>Status:</B> Optional, may be repeated.</P> + + <P class=item><B>Description:</B> A constant message can be shared among + several object headers. A <em>Shared Object</em> Message contains the address of + the object message to be shared. Care must be exercised to prevent cycles when a + message of one object header points to a message in some other object header. + Starting from Version 2 of the Shared Object Message, the <em>Flags</em> + field becomes unused. + </P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Shared Object Message (Version 1) + </caption> + + <tr> + <th width="25%">byte</td> + <th width="25%">byte</td> + <th width="25%">byte</td> + <th width="25%">byte</td> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan=2>Reserved</td> + </tr> + + <tr> + <td colspan=4>Reserved</td> + </tr> + + <tr> + <td colspan=4><br>Pointer<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td><P>The version number is used when there are changes in the format + of a shared object message and is described here:</P> + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Used by the library before version 1.6.1. In this version, + the Flags field is used to indicate whether the actual message is + stored in the global heap (never implemented). The Pointer field + either contains the the header message address in the global heap + (never implemented) or the address of the shared object header.</td> + </tr> + </table> + </tr> + + <tr> + <td>Flags</td> + <td><P>The Shared Message message points to a message which is + shared among multiple object headers. The Flags field + describes the type of sharing:</P> + <table class=list> + <tr> + <th width="30%">Bit</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>If this bit is clear then the actual message is the + first message in some other object header; otherwise + the actual message is stored in the global heap (never + implemented).</td> + </tr> + + <tr> + <td align=center><code>2-7</code></td> + <td>Reserved (always zero)</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Pointer</td> + <td><P>The address of the object header + containing the message to be shared.</P></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=format> + <caption> + Shared Object Message (Version 2) + </caption> + + <tr> + <th width="25%">byte</td> + <th width="25%">byte</td> + <th width="25%">byte</td> + <th width="25%">byte</td> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan=2 bgcolor=#DDDDDD> </td> + </tr> + + <tr> + <td colspan=4><br>Pointer<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td><P>The version number is used when there are changes in the format + of a shared object message and is described here:</P> + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>2</code></td> + <td>Used by the library of version 1.6.1 and after. In this version, + The Flags field is not used and the Pointer field contains the address + of the object header containing the message to be shared. </td> + </tr> + </table> + </tr> + + <tr> + <td>Flags</td> + <td><P>Unused.</P></td> + </tr> + + <tr> + <td>Pointer</td> + <td><P>The address of the object header + containing the message to be shared.</P></td> + </tr> + </table> + </div> + + + <hr> + <h4><a name="ContinuationMessage">Name: Object Header Continuation</a></h4> + <P class=item><B>Header Message Type:</B> 0x0010</P> + <P class=item><B>Length:</B> fixed</P> + <P class=item><B>Status:</B> Optional, may be repeated.</P> + <P class=item><B>Description:</B> The object header continuation is the location + in the file of more header messages for the current data object. This can be + used when header blocks become too large or are likely to change over time.</P> + + <P class=item><B>Format of Data:</B> + <br> + <div align=center> + <table class=format> + <caption> + Object Header Continuation Message + </caption> + + <tr> + <th width=25%>byte</th> + <th width=25%>byte</th> + <th width=25%>byte</th> + <th width=25%>byte</th> + </tr> + + <tr> + <td colspan=4><br>Offset<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Length<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width=30%>Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Offset</td> + <td><P>This value is the offset in bytes from the beginning of the file where the + header continuation information is located.</P></td> + </tr> + + <tr> + <td>Length</td> + <td><P>This value is the length in bytes of the header continuation information in + the file.</P></td> + </tr> + </table> + </div> + + <hr> + <h4><a name="SymbolTableMessage">Name: Group Message</a></h4> + <P class=item><B>Header Message Type:</B> 0x0011</P> + <P class=item><B>Length:</B> fixed</P> + <P class=item><B>Status:</B> Required for groups, may not be repeated.</P> + <P class=item><B>Description:</B> Each group has a B-tree and a + name heap which are pointed to by this message.</P> + <P class=item><B>Format of data:</B> + + <br> + <div align=center> + <table class=format> + <caption> + <B>Group Message</B> + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan=4><br>B-tree Address<br><br></td> + </tr> + + <tr> + <td colspan=4><br>Heap Address<br><br></td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width=30%>Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>B-tree Address</td> + <td><P>This value is the offset in bytes from the beginning of the file + where the B-tree is located.</P></td> + </tr> + + <tr> + <td>Heap Address</td> + <td><P>This value is the offset in bytes from the beginning of the file + where the group name heap is located.</P></td> + </tr> + </table> + </div> + + <hr> + <h4><a name="ModifiedMessage">Name: Object Modification Date & Time</a></h4> + + <P class=item><B>Header Message Type:</B> 0x0012 </P> + <P class=item><B>Length:</B> Fixed </P> + <P class=item><B>Status:</B> Optional, may not be repeated. </P> + + <P class=item><B>Description:</B> The object modification date + and time is a timestamp which indicates the last modification of an object. + The time is updated when any object header message changes according to the + system clock where the change was posted. + </P> + + <P class=item><B>Format of Data:</B> + <div align=center> + <table class=format> + <caption> + Modification Time Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan=3>Reserved</td> + </tr> + + <tr> + <td colspan=4>Seconds After Epoch</td> + </tr> + </table> + </div> + + <br> + <div align=center> + <table class=desc> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td>Version</td> + <td><P>The version number is used for changes in the format of Object Modification Time + and is described here:</P> + <table class=list> + <tr> + <th width="30%">Version</th> + <th align=left>Description</th> + </tr> + + <tr> + <td align=center><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align=center><code>1</code></td> + <td>Used by Version 1.6.1 and after of the library to encode time. In + this version, the time is the seconds after Epoch.</td> + </tr> + </table> + </td> + </tr> + + <tr> + <td>Reserved</td> + <td><P>This field is reserved and should always be zero.</P></td> + </tr> + + <tr> + <td>Seconds After Epoch</td> + <td><P>The number of seconds since 0 hours, 0 minutes, 0 seconds, + January 1, 1970, Coordinated Universal Time.</P></td> + </tr> + </table> + </div> + +<hr> +<h3><a name="DataStorage">Disk Format: Level 2b - Data Object Data Storage</a></h3> +<P>The data for an object is stored separately from the header +information in the file and may not actually be located in the HDF5 file +itself if the header indicates that the data is stored externally. The +information for each record in the object is stored according to the +dimensionality of the object (indicated in the dimensionality header message). +Multi-dimensional data is stored in C order [same as current scheme], i.e. the +"last" dimension changes fastest. +<P>Data whose elements are composed of simple number-types are stored in +native-endian IEEE format, unless they are specifically defined as being stored +in a different machine format with the architecture-type information from the +number-type header message. This means that each architecture will need to +[potentially] byte-swap data values into the internal representation for that +particular machine. +<P> Data with a variable-length datatype is stored in the global heap +of the HDF5 file. Global heap identifiers are stored in the +data object storage. +<P>Data whose elements are composed of pointer number-types are stored in several +different ways depending on the particular pointer type involved. Simple +pointers are just stored as the dataset offset of the object being pointed to with the +size of the pointer being the same number of bytes as offsets in the file. +Dataset region references are stored as a heap-ID which points to the following +information within the file-heap: an offset of the object pointed to, number-type +information (same format as header message), dimensionality information (same +format as header message), sub-set start and end information (i.e. a coordinate +location for each), and field start and end names (i.e. a [pointer to the] +string indicating the first field included and a [pointer to the] string name +for the last field). + +<P>Data of a compound datatype is stored as a contiguous stream of the items +in the structure, with each item formatted according to its datatype.</p> + +<hr> +<h3><a name="Appendix">Appendix</a></h3> +<P>Definitions of various terms used in this document. +</P> +<P>The <A name="UndefinedAddress">"undefined address"</A> for a file is a +file address with all bits set, i.e. <code>0xffff...ff</code>. +<P>The <A name="UnlimitedDim">"unlimited size"</A> for a size is a +value with all bits set, i.e. <code>0xffff...ff</code>. + +</body> +</html> diff --git a/doxygen/examples/H5.format.2.0.html b/doxygen/examples/H5.format.2.0.html new file mode 100644 index 0000000..3653489 --- /dev/null +++ b/doxygen/examples/H5.format.2.0.html @@ -0,0 +1,14902 @@ +<!DOCTYPE HTML> +<html> + <head> + <title> + HDF5 File Format Specification Version 2.0 + </title> + +<style> +h1 { display: block; + margin-top: 24px; + margin-bottom: 24px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + } + +h2 { display: block; + margin-top: 8x; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + } +<!-- A horizontal rule (<hr />) should be placed on the line above +each h2 tag. The h2 tags are used on the main sections along with +the hr tags. --> + +h3 { display: block; + margin-top: 8px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + } + +h4 { display: block; + margin-top: 8px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + } + +p { display: block; + margin-top: 8px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + } +<!-- +p.item { margin-left: 2em; + text-indent: -2em + } --> +<!-- p.item2 { margin-left: 2em; text-indent: 2em} --> + +table.format { border:solid; + border-collapse:collapse; + caption-side:top; + text-align:center; + width:80%; + } +table.format th { border:ridge; + padding:4px; + width:25%; + } +table.format td { border:ridge; + padding:4px; + } +table.format caption { font-weight:bold; + font-size:larger; + } + +table.note {border:none; + text-align:right; + width:80%; + } + +table.desc { border:solid; + border-collapse:collapse; + caption-size:top; + text-align:left; + width:80%; + } +table.desc tr { vertical-align:top; + } +table.desc th { border-style:ridge; + font-size:larger; + padding:4px; + <!-- text-decoration:underline; --> + } +table.desc td { border-style:ridge; + <!-- padding: 4px; --> + vertical-align:text-top; + } +table.desc caption { font-weight:bold; + font-size:larger; + } + +table.list { border:none; + width:100% + } +table.list tr { vertical-align:text-top; + } +table.list th { border:none; + text-decoration:underline; + vertical-align:text-top; + } +table.list td { border:none; + vertical-align:text-top; + } + +table.msgdesc { border:none; + text-align:left; + width: 80% + } +table.msgdesc tr { vertical-align:text-top; + border-spacing:0; + padding:0; } +table.msgdesc th { border:none; + text-decoration:underline; + vertical-align:text-top; } +table.msgdesc td { border:none; + vertical-align:text-top; + } + +table.list80 { border:none; + width:80% + } +table.list80 tr { vertical-align:text-top; + } +table.list80 th { border:none; + text-decoration:underline; + vertical-align:text-top; + } +table.list80 td { border:none; + vertical-align:text-top; + } + +table.glossary { border:none; + text-align:left; + width: 80% + } +table.glossary tr { vertical-align:text-top; + border-spacing:0; + padding:0; } +table.glossary th { border:none; + text-align:left; + text-decoration:underline; + vertical-align:text-top; } +table.glossary td { border:none; + text-align:left; + vertical-align:text-top; + } + +div { page-break-inside:avoid; + page-break-after:auto + } + +</style> + + <center> + <table border="0" width="90%"> + <tr> + <td valign="top"> + <ol type="I"> + <li><a href="#Intro">Introduction</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#ThisDocument">This Document</a></li> + <li><a href="#ChangesForHdf5_1_10">Changes for HDF5 1.10</a></li> + </ol> + </font> + + <li><a href="#FileMetaData">Disk Format: Level 0 - File Metadata</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#Superblock">Disk Format: Level 0A - Format Signature and Superblock</a></li> + <li><a href="#DriverInfo">Disk Format: Level 0B - File Driver Info</a></li> + <li><a href="#SuperblockExt">Disk Format: Level 0C - Superblock Extension</a></li> + </ol> + </font> + <li><a href="#FileInfra">Disk Format: Level 1 - File Infrastructure</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#Btrees">Disk Format: Level 1A - B-trees and B-tree + Nodes</a></li> + <ol type="1"> + <li><a href="#V1Btrees">Disk Format: Level 1A1 - Version 1 + B-trees (B-link Trees)</a></li> + <li><a href="#V2Btrees">Disk Format: Level 1A2 - Version 2 + B-trees</a></li> + </ol> + <li><a href="#SymbolTable">Disk Format: Level 1B - Group Symbol Table Nodes</a></li> + <li><a href="#SymbolTableEntry">Disk Format: Level 1C - Symbol Table Entry</a></li> + <li><a href="#LocalHeap">Disk Format: Level 1D - Local Heaps</a></li> + <li><a href="#GlobalHeap">Disk Format: Level 1E - Global Heap</a></li> + <li><a href="#FractalHeap">Disk Format: Level 1F - Fractal Heap</a></li> + <li><a href="#FreeSpaceManager">Disk Format: Level 1G - Free-space Manager</a></li> + <li><a href="#SOHMTable">Disk Format: Level 1H - Shared Object Header Message Table</a></li> + </ol> + </font> + <li><a href="#DataObject">Disk Format: Level 2 - Data Objects</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#ObjectHeader">Disk Format: Level 2A - Data Object Headers</a></li> + <ol type="1"> + <li><a href="#ObjectHeaderPrefix">Disk Format: Level 2A1 - Data Object Header Prefix</a></li> + <ol type="a"> + <li><a href="#V1ObjectHeaderPrefix">Version 1 Data Object Header Prefix</a></li> + <li><a href="#V2ObjectHeaderPrefix">Version 2 Data Object Header Prefix</a></li> + </ol> + <li><a href="#ObjectHeaderMessages">Disk Format: Level 2A2 - Data Object Header Messages</a></li> + <ol type="a"> + <li><a href="#NILMessage">The NIL Message</a></li> <!-- 0x0000 --> + <li><a href="#DataspaceMessage">The Dataspace Message</a></li> <!-- 0x0001 --> + <li><a href="#LinkInfoMessage">The Link Info Message</a></li> <!-- 0x0002 --> + </ol> + </ol> + </ol> + </font> + </ol> + </td> + + <td> </td> + + <td valign="top"> + <ol type="I" start="4"> + <li><a href="#DataObject">Disk Format: Level 2 - Data + Objects</a><font size="-1"><i> (Continued)</i></li> + <ol type="A"> + <li><a href="#ObjectHeader">Disk Format: Level 2A - Data Object + Headers</a><i> (Continued)</i></li> + <ol type="1" start="2"> + <li><a href="#ObjectHeaderMessages">Disk Format: Level 2A2 - + Data Object Header Messages</a><i> (Continued)</i></li> + <ol type="a" start="4"> + <li><a href="#DatatypeMessage">The Datatype Message</a></li> <!-- 0x0003 --> + <li><a href="#OldFillValueMessage">The Data Storage - + Fill Value (Old) Message</a></li> <!-- 0x0004 --> + <li><a href="#FillValueMessage">The Data Storage - + Fill Value Message</a></li> <!-- 0x0005 --> + <li><a href="#LinkMessage">The Link Message</a></li> <!-- 0x0006 --> + <li><a href="#ExternalFileListMessage">The Data Storage - + External Data Files Message</a></li> <!-- 0x0007 --> + <li><a href="#LayoutMessage">The Data Storage - + Layout Message</a></li> <!-- 0x0008 --> + <li><a href="#BogusMessage">The Bogus Message</a></li> <!-- 0x0009 --> + <li><a href="#GroupInfoMessage">The Group Info + Message</a></li> <!-- 0x000a --> + <li><a href="#FilterMessage">The Data Storage - + Filter Pipeline Message</a></li> <!-- 0x000b --> + <li><a href="#AttributeMessage">The Attribute + Message</a></li> <!-- 0x000c --> + <li><a href="#CommentMessage">The Object Comment + Message</a></li> <!-- 0x000d --> + <li><a href="#OldModificationTimeMessage">The Object + Modification Time (Old) Message</a></li> <!-- 0x000e --> + <li><a href="#SOHMTableMessage">The Shared Message + Table Message</a></li> <!-- 0x000f --> + <li><a href="#ContinuationMessage">The Object Header + Continuation Message</a></li> <!-- 0x0010 --> + <li><a href="#SymbolTableMessage">The Symbol + Table Message</a></li> <!-- 0x0011 --> + <li><a href="#ModificationTimeMessage">The Object + Modification Time Message</a></li> <!-- 0x0012 --> + <li><a href="#BtreeKValuesMessage">The B-tree + ‘K’ Values Message</a></li> <!-- 0x0013 --> + <li><a href="#DrvInfoMessage">The Driver Info + Message</a></li> <!-- 0x0014 --> + <li><a href="#AinfoMessage">The Attribute Info + Message</a></li> <!-- 0x0015 --> + <li><a href="#RefCountMessage">The Object Reference + Count Message</a></li> <!-- 0x0016 --> + <li><a href="#FsinfoMessage">The File Space Info + Message</a></li> <!-- 0x0018 --> + </ol> + </ol> + <li><a href="#DataStorage">Disk Format: Level 2B - Data Object Data Storage</a></li> + </ol> + </font> + <li><a href="#AppendixA">Appendix A: Definitions</a></li> + <li><a href="#AppendixB">Appendix B: File Memory Allocation Types</a></li> + </ol> +</td></tr> +</table> +</center> + + + +<br /> +<br /> +<hr /> +<a name="Intro"><h2>I. Introduction</h2></a> + + <table align="right" width="100"> + <tr><td> </td><td align="center"> + <hr /> + <img src="FF-IH_FileGroup.gif" alt="HDF5 Groups" hspace="15" vspace="15"> + </td><td> </td></tr> + <tr><td> </td><td align="center"> + <strong>Figure 1:</strong> Relationships among the HDF5 root group, other groups, and objects + <hr /> + </td><td> </td></tr> + + <tr><td> </td><td align="center"> + <img src="FF-IH_FileObject.gif" alt="HDF5 Objects" hspace="15" vspace="15"> + </td><td> </td></tr> + <tr><td> </td><td align="center"> + <strong>Figure 2:</strong> HDF5 objects -- datasets, datatypes, or dataspaces + <hr /> + </td><td> </td></tr> + </table> + + + <p>The format of an HDF5 file on disk encompasses several + key ideas of the HDF4 and AIO file formats as well as + addressing some shortcomings therein. The new format is + more self-describing than the HDF4 format and is more + uniformly applied to data objects in the file.</p> + + <p>An HDF5 file appears to the user as a directed graph. + The nodes of this graph are the higher-level HDF5 objects + that are exposed by the HDF5 APIs:</p> + + <ul> + <li>Groups</li> + <li>Datasets</li> + <li>Committed (formerly Named) datatypes</li> + </ul> + + <p>At the lowest level, as information is actually written to the disk, + an HDF5 file is made up of the following objects:</p> + <ul> + <li>A superblock</li> + <li>B-tree nodes</li> + <li>Heap blocks</li> + <li>Object headers</li> + <li>Object data</li> + <li>Free space</li> + </ul> + + <p>The HDF5 Library uses these low-level objects to represent the + higher-level objects that are then presented to the user or + to applications through the APIs. For instance, a group is an + object header that contains a message that points to a local + heap (for storing the links to objects in the group) and to a + B-tree (which indexes the links). A dataset is an object header + that contains messages that describe datatype, dataspace, layout, + filters, external files, fill value, and other elements with the + layout message pointing to either a raw data chunk or to a + B-tree that points to raw data chunks.</p> + + +<br /> +<a name="ThisDocument"><h3>I.A. This Document</h3></a> + + <p>This document describes the lower-level data objects; + the higher-level objects and their properties are described + in the <a href="UG/HDF5_Users_Guide-Responsive HTML5/index.html"><cite>HDF5 User’s Guide</cite></a>.</p> + + <p>Three levels of information comprise the file format. + Level 0 contains basic information for identifying and + defining information about the file. Level 1 information contains + the information about the pieces of a file shared by many objects + in the file (such as a B-trees and heaps). Level 2 is the rest + of the file and contains all of the data objects, with each object + partitioned into header information, also known as + <em>metadata</em>, and data.</p> + + <p>The sizes of various fields in the following layout tables are + determined by looking at the number of columns the field spans + in the table. There are three exceptions: (1) The size may be + overridden by specifying a size in parentheses, (2) the size of + addresses is determined by the <em>Size of Offsets</em> field + in the superblock and is indicated in this document with a + superscripted ‘O’, and (3) the size of length fields is determined + by the <em>Size of Lengths</em> field in the superblock and is + indicated in this document with a superscripted ‘L’.</p> + + <p>Values for all fields in this document should be treated as unsigned + integers, unless otherwise noted in the description of a field. + Additionally, all metadata fields are stored in little-endian byte + order. + </p> + + <p>All checksums used in the format are computed with the + <a href="http://www.burtleburtle.net/bob/hash/doobs.html">Jenkins’ + lookup3</a> algorithm. + </p> + + <p>Whenever a bit flag or field is mentioned for an entry, bits are + numbered from the lowest bit position in the entry. + </p> + + <p>Various tables in this document aligned with “This space inserted + only to align table nicely”. These entries in the table are just + to make the table presentation nicer and do not represent any values + or padding in the file. + </p> + + +<br /> +<a name="ChangesForHdf5_1_10"><h3>I.B. Changes for HDF5 1.10</h3></a> + + <p>As of October 2015, changes in the file format for HDF5 1.10 + have not yet been finalized.</p> + + + +<br /> +<br /> +<hr /> +<h2><a name="FileMetaData"> +II. Disk Format: Level 0 - File Metadata</a></h2> + +<br /> +<h3><a name="Superblock"> +II.A. Disk Format: Level 0A - Format Signature and Superblock</a></h3> + + <p>The superblock may begin at certain predefined offsets within + the HDF5 file, allowing a block of unspecified content for + users to place additional information at the beginning (and + end) of the HDF5 file without limiting the HDF5 Library’s + ability to manage the objects within the file itself. This + feature was designed to accommodate wrapping an HDF5 file in + another file format or adding descriptive information to an HDF5 + file without requiring the modification of the actual file’s + information. The superblock is located by searching for the + HDF5 format signature at byte offset 0, byte offset 512, and at + successive locations in the file, each a multiple of two of + the previous location; in other words, at these byte offsets: + 0, 512, 1024, 2048, and so on.</p> + + <p>The superblock is composed of the format signature, followed by a + superblock version number and information that is specific to each + version of the superblock. + Currently, there are three versions of the superblock format. + Version 0 is the default format, while version 1 is basically the same + as version 0 with additional information when a non-default B-tree ‘K’ + value is stored. Version 2 is the latest format, with some fields + eliminated or compressed and with superblock extension and checksum + support.</p> + + <p>Version 0 and 1 of the superblock are described below:</p> + + + <div align="center"> + <table class="format"> + <caption> + Superblock (Versions 0 and 1) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Format Signature (8 bytes)<br /><br /></td> + </tr> + + <tr> + <td>Version # of Superblock</td> + <td>Version # of File’s Free Space Storage</td> + <td>Version # of Root Group Symbol Table Entry</td> + <td>Reserved (zero)</td> + </tr> + + <tr> + <td>Version # of Shared Header Message Format</td> + <td>Size of Offsets</td> + <td>Size of Lengths</td> + <td>Reserved (zero)</td> + </tr> + + <tr> + <td colspan="2">Group Leaf Node K</td> + <td colspan="2">Group Internal Node K</td> + </tr> + + <tr> + <td colspan="4">File Consistency Flags</td> + </tr> + + <tr> + <td colspan="2" style="border:dotted;">Indexed Storage Internal Node K<sup>1</sup></td> + <td colspan="2" style="border:dotted;">Reserved (zero)<sup>1</sup></td> + </tr> + + <tr> + <td colspan="4"><br />Base Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of File Free space Info<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of File Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Driver Information Block Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Root Group Symbol Table Entry</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in “Size of Offsets.”) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with a ‘1’ in the above table are + new in version 1 of the superblock) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Format Signature</p></td> + <td><p>This field contains a constant value and can be used to + quickly identify a file as being an HDF5 file. The + constant value is designed to allow easy identification of + an HDF5 file and to allow certain types of data corruption + to be detected. The file signature of an HDF5 file always + contains the following values:</p> + <center> + <table border align="center" cellpadding="4"> + <tr align="center"> + <td align="right">Decimal:</td> + <td width="8%">137</td> + <td width="8%">72</td> + <td width="8%">68</td> + <td width="8%">70</td> + <td width="8%">13</td> + <td width="8%">10</td> + <td width="8%">26</td> + <td width="8%">10</td> + </tr> + + <tr align="center"> + <td align="right">Hexadecimal:</td> + <td>89</td> + <td>48</td> + <td>44</td> + <td>46</td> + <td>0d</td> + <td>0a</td> + <td>1a</td> + <td>0a</td> + </tr> + + <tr align="center"> + <td align="right">ASCII C Notation:</td> + <td>\211</td> + <td>H</td> + <td>D</td> + <td>F</td> + <td>\r</td> + <td>\n</td> + <td>\032</td> + <td>\n</td> + </tr> + </table> + </center> + <p>This signature both identifies the file as an HDF5 file + and provides for immediate detection of common + file-transfer problems. The first two bytes distinguish + HDF5 files on systems that expect the first two bytes to + identify the file type uniquely. The first byte is + chosen as a non-ASCII value to reduce the probability + that a text file may be misrecognized as an HDF5 file; + also, it catches bad file transfers that clear bit + 7. Bytes two through four name the format. The CR-LF + sequence catches bad file transfers that alter newline + sequences. The control-Z character stops file display + under MS-DOS. The final line feed checks for the inverse + of the CR-LF translation problem. (This is a direct + descendent of the + <a href="http://www.libpng.org/pub/png/spec/iso/index-object.html#5PNG-file-signature">PNG</a> file + signature.)</p> + <p><em>This field is present in version 0+ of the superblock.</em> + </p></td> + </tr> + + <tr> + <td><p>Version Number of the Superblock</p></td> + <td><p>This value is used to determine the format of the + information in the superblock. When the format of the + information in the superblock is changed, the version number + is incremented to the next integer and can be used to + determine how the information in the superblock is + formatted.</p> + + <p>Values of 0, 1 and 2 are defined for this field. (The format + of version 2 is described below, not here) + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Version Number of the File’s Free Space + Information</p></td> + <td> + <p>This value is used to determine the format of the + file’s free space information. + </p> + <p>The only value currently valid in this field is ‘0’, which + indicates that the file’s free space is as described + <a href="#FreeSpaceManager">below</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Version Number of the Root Group Symbol Table + Entry</p></td> + <td><p>This value is used to determine the format of the + information in the Root Group Symbol Table Entry. When the + format of the information in that field is changed, the + version number is incremented to the next integer and can be + used to determine how the information in the field + is formatted.</p> + <p>The only value currently valid in this field is ‘0’, + which indicates that the root group symbol table entry is + formatted as described <a href="#SymbolTableEntry">below</a>.</p> + <p><em>This field is present in version 0 and 1 of the + superblock.</em></p> + </td> + </tr> + + <tr> + <td><p>Version Number of the Shared Header Message Format</p></td> + <td><p>This value is used to determine the format of the + information in a shared object header message. Since the format + of the shared header messages differs from the other private + header messages, a version number is used to identify changes + in the format. + </p> + <p>The only value currently valid in this field is ‘0’, which + indicates that shared header messages are formatted as + described <a href="#ObjectHeaderMessages">below</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Size of Offsets</p></td> + <td><p>This value contains the number of bytes used to store + addresses in the file. The values for the addresses of + objects in the file are offsets relative to a base address, + usually the address of the superblock signature. This + allows a wrapper to be added after the file is created + without invalidating the internal offset locations. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Size of Lengths</p></td> + <td><p>This value contains the number of bytes used to store + the size of an object. + </p> + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Group Leaf Node K</p></td> + <td> + <p>Each leaf node of a group B-tree will have at + least this many entries but not more than twice this + many. If a group has a single leaf node then it + may have fewer entries. + </p> + <p>This value must be greater than zero. + </p> + <p>See the <a href="#Btrees">description</a> of B-trees below. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Group Internal Node K</p></td> + <td> + <p>Each internal node of a group B-tree will have at + least this many entries but not more than twice this + many. If the group has only one internal + node then it might have fewer entries. + </p> + <p>This value must be greater than zero. + </p> + <p>See the <a href="#Btrees">description</a> of B-trees below. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>File Consistency Flags</p></td> + <td> + <p>This value contains flags to indicate information + about the consistency of the information contained + within the file. Currently, the following bit flags are + defined: + <ul> + <li>Bit 0 set indicates that the file is opened for + write-access.</li> + <li>Bit 1 set indicates that the file has + been verified for consistency and is guaranteed to be + consistent with the format defined in this document.</li> + <li>Bits 2-31 are reserved for future use.</li> + </ul> + Bit 0 should be + set as the first action when a file is opened for write + access and should be cleared only as the final action + when closing a file. Bit 1 should be cleared during + normal access to a file and only set after the file’s + consistency is guaranteed by the library or a + consistency utility. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Indexed Storage Internal Node K</p></td> + <td> + <p>Each internal node of an indexed storage B-tree will have at + least this many entries but not more than twice this + many. If the index storage B-tree has only one internal + node then it might have fewer entries. + </p> + <p>This value must be greater than zero. + </p> + <p>See the <a href="#Btrees">description</a> of B-trees below. + </p> + + <p><em>This field is present in version 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Base Address</p></td> + <td> + <p>This is the absolute file address of the first byte of + the HDF5 data within the file. The library currently + constrains this value to be the absolute file address + of the superblock itself when creating new files; + future versions of the library may provide greater + flexibility. When opening an existing file and this address does + not match the offset of the superblock, the library assumes + that the entire contents of the HDF5 file have been adjusted in + the file and adjusts the base address and end of file address to + reflect their new positions in the file. Unless otherwise noted, + all other file addresses are relative to this base + address. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Address of Global Free-space Index</p></td> + <td> + <p>The file’s free space is not persistent for version 0 and 1 of + the superblock. + Currently this field always contains the + <a href="#UndefinedAddress">undefined address</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>End of File Address</p></td> + <td> + <p>This is the absolute file address of the first byte past + the end of all HDF5 data. It is used to determine whether a + file has been accidently truncated and as an address where + file data allocation can occur if space from the free list is + not used. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Driver Information Block Address</p></td> + <td> + <p>This is the relative file address of the file driver + information block which contains driver-specific + information needed to reopen the file. If there is no + driver information block then this entry should be the + <a href="#UndefinedAddress">undefined address</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Root Group Symbol Table Entry</p></td> + <td> + <p>This is the <a href="#SymbolTableEntry">symbol table entry</a> + of the root group, which serves as the entry point into + the group graph for the file. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + </table> + </div> + + <br /> + <p>Version 2 of the superblock is described below:</p> + + <div align="center"> + <table class="format"> + <caption> + Superblock (Version 2) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Format Signature (8 bytes)<br /><br /></td> + </tr> + + <tr> + <td>Version # of Superblock</td> + <td>Size of Offsets</td> + <td>Size of Lengths</td> + <td>File Consistency Flags</td> + </tr> + + <tr> + <td colspan="4"><br />Base Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Superblock Extension Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of File Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Root Group Object Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Superblock Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in “Size of Offsets.”) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Format Signature</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p></td> + </tr> + + <tr> + <td><p>Version Number of the Superblock</p></td> + <td> + <p>This field has a value of 2 and has the same meaning as for + versions 0 and 1. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Offsets</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Lengths</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>File Consistency Flags</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 except + that it is smaller (the number of reserved bits has been reduced + from 30 to 6). + </p> + </td> + </tr> + + <tr> + <td><p>Base Address</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Superblock Extension Address</p></td> + <td> + <p>The field is the address of the object header for the + <a href="#SuperblockExt">superblock extension</a>. + If there is no extension then this entry should be the + <a href="#UndefinedAddress">undefined address</a>. + </p> + </td> + </tr> + + <tr> + <td><p>End of File Address</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Root Group Object Header Address</p></td> + <td> + <p>This is the address of + the <a href="#DataObject">root group object header</a>, + which serves as the entry point into the group graph for the file. + </p> + </td> + </tr> + + <tr> + <td><p>Superblock Checksum</p></td> + <td> + <p>The checksum for the superblock. + </p> + </td> + </tr> + + </table> + </div> + +<br /> +<h3><a name="DriverInfo"> +II.B. Disk Format: Level 0B - File Driver Info</a></h3> + + <p>The <b>driver information block</b> is an optional region of the + file which contains information needed by the file driver + to reopen a file. The format is described below:</p> + + + <div align="center"> + <table class="format"> + <caption> + Driver Information Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved</td> + </tr> + + <tr> + <td colspan="4">Driver Information Size</td> + </tr> + + <tr> + <td colspan="4"><br />Driver Identification (8 bytes)<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Driver Information (<em>variable size</em>)<br /><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number of the Driver Information Block. + This document describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Driver Information Size</p></td> + <td> + <p>The size in bytes of the <em>Driver Information</em> field. + </p> + </td> + </tr> + + <tr> + <td><p>Driver Identification</p></td> + <td> + <p>This is an eight-byte ASCII string without null + termination which identifies the driver and/or version number + of the Driver Information Block. The predefined driver encoded + in this field by the HDF5 Library is identified by the + letters <code>NCSA</code> followed by the first four characters of + the driver name. If the Driver Information block is not + the original version then the last letter(s) of the + identification will be replaced by a version number in + ASCII, starting with 0. + </p> + <p> + Identification for user-defined drivers is also eight-byte long. + It can be arbitrary but should be unique to avoid + the four character prefix “NCSA”. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Driver Information</p></td> + <td>Driver information is stored in a format defined by the + file driver (see description below).</td> + </tr> + </table> + </div> + + <br /> + The two drivers encoded in the <em>Driver Identification</em> field are as follows: + <ul> + <li> + Multi driver: + <p> + The identifier for this driver is “NCSAmulti”. + This driver provides a mechanism for segregating raw data and different types of metadata + into multiple files. + These files are viewed by the library as a single virtual HDF5 file with a single file address. + A maximum of 6 files will be created for the following data: + superblock, B-tree, raw data, global heap, local heap, and object header. + More than one type of data can be written to the same file. + </p></li> + <li> + Family driver + <p> + The identifier for this driver is “NCSAfami” and is encoded in this field for library version 1.8 and after. + This driver is designed for systems that do not support files larger than 2 gigabytes + by splitting the HDF5 file address space across several smaller files. + It does nothing to segregate metadata and raw data; + they are mixed in the address space just as they would be in a single contiguous file. + </p></li> + </ul> + <p>The format of the <em>Driver Information</em> field for the + above two drivers are described below:</p> + + <div align="center"> + <table class="format"> + <caption> + Multi Driver Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Member Mapping</td> + </tr> + + <tr> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Reserved</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Member File 1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of Address for Member File 1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Member File 2<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of Address for Member File 2<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />... ...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Member File N<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of Address for Member File N<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Name of Member File 1 <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Name of Member File 2 <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />... ...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Name of Member File N <em>(variable size)</em><br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Member Mapping</p></td> + <td><p>These fields are integer values from 1 to 6 + indicating how the data can be mapped to or merged with another type of + data. + <table class="list"> + <tr> + <th width="20%" align="center">Member Mapping</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">1</td> + <td>The superblock data.</td> + </tr> + <tr> + <td align="center">2</td> + <td>The B-tree data.</td> + </tr> + <tr> + <td align="center">3</td> + <td>The raw data.</td> + </tr> + <tr> + <td align="center">4</td> + <td>The global heap data.</td> + </tr> + <tr> + <td align="center">5</td> + <td>The local heap data.</td> + </tr> + <tr> + <td align="center">6</td> + <td>The object header data.</td> + </tr> + </table></p> + <p>For example, if the third field has the value 3 and all the rest have the + value 1, it means there are two files: one for raw data, and one for superblock, + B-tree, global heap, local heap, and object header.</p> + </td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td><p>These fields are reserved and should always be zero.</p></td> + </tr> + + <tr> + <td><p>Address of Member File N</p></td> + <td><p>This field Specifies the virtual address at which the member file starts.</p> + <p>N is the number of member files.</p> + </td> + </tr> + + <tr> + <td><p>End of Address for Member File N</p></td> + <td><p>This field is the end of the allocated address for the member file. + </p></td> + </tr> + + <tr> + <td><p>Name of Member File N</p></td> + <td><p>This field is the null-terminated name of the member file and + its length should be multiples of 8 bytes. + Additional bytes will be padded with <em>NULL</em>s. The default naming + convention is <em>%s-X.h5</em>, where <em>X</em> is one of the letters + <em>s</em> (for superblock), <em>b</em> (for B-tree), <em>r</em> (for raw data), + <em>g</em> (for global heap), <em>l</em> (for local heap), and <em>o</em> (for + object header). The name of the whole HDF5 file will substitute the <em>%s</em> + in the string. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Family Driver Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="8"><br />Size of Member File<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size of Member File</p></td> + <td><p>This field is the size of the member file in the family of files.</p></td> + </tr> + </table> + </div> + +<br /> +<h3><a name="SuperblockExt"> +II.C. Disk Format: Level 0C - Superblock Extension</a></h3> + + <p>The <em>superblock extension</em> is used to store superblock metadata + which is either optional, or added after the version of the superblock + was defined. Superblock extensions may only exist when version 2+ of + superblock is used. A superblock extension is an object header which may + hold the following messages:</p> + <ul> + <li> + <a href="#SOHMTableMessage">Shared Message Table message</a> containing + information to locate the master table of shared object header message + indices.</li> + <li> + <a href="#BtreeKValuesMessage">B-tree ‘K’ Values message</a> containing + non-default B-tree ‘K’ values.</li> + <li> + <a href="#DrvInfoMessage">Driver Info message</a> containing information + needed by the file driver in order to reopen a file. + See also the + <a href="#DriverInfo">“Disk Format: Level 0B - File Driver + Info”</a> section above.</li> + <li> + <a href="#FsinfoMessage">File Space Info message</a> containing + information about file space handling in the file.</li> + </ul> + + + +<br /> +<br /> +<hr /> +<h2><a name="FileInfra"> +III. Disk Format: Level 1 - File Infrastructure</a></h2> + +<br /> +<h3><a name="Btrees"> +III.A. Disk Format: Level 1A - B-trees and B-tree Nodes</a></h3> + + <p>B-trees allow flexible storage for objects which tend to grow + in ways that cause the object to be stored discontiguously. B-trees + are described in various algorithms books including “Introduction to + Algorithms” by Thomas H. Cormen, Charles E. Leiserson, and Ronald + L. Rivest. B-trees are used in several places in the HDF5 file format, + when an index is needed for another data structure.</p> + + <p>The version 1 B-tree structure described below is the original index + structure, but are limited by some bugs in our implementation (mainly in + how they handle deleting records). The version 1 B-trees are being phased + out in favor of the version 2 B-trees described below, although both + types of structures may be found in the same file, depending on + application settings when creating the file.</p> + +<br /> +<h4><a name="V1Btrees"> +III.A.1. Disk Format: Level 1A1 - Version 1 B-trees (B-link Trees)</a></h4> + + <p>Version 1 B-trees in HDF5 files an implementation of the B-link tree, + in which the sibling nodes at a particular level in the tree are stored + in a doubly-linked list, is described in the “Efficient Locking for + Concurrent Operations on B-trees” paper by Phillip Lehman and S. Bing Yao + as published in the <cite>ACM Transactions on Database Systems</cite>, + Vol. 6, No. 4, December 1981.</p> + + <p>The B-link trees implemented by the file format contain one more + key than the number of children. In other words, each child + pointer out of a B-tree node has a left key and a right key. + The pointers out of internal nodes point to sub-trees while + the pointers out of leaf nodes point to symbol nodes and + raw data chunks. + Aside from that difference, internal nodes and leaf nodes + are identical.</p> + + <div align="center"> + <table class="format"> + <caption> + B-link Tree Nodes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Node Type</td> + <td>Node Level</td> + <td colspan="2">Entries Used</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Left Sibling<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Right Sibling<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Key 0 (variable size)</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Child 0<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Key 1 (variable size)</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Child 1<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Key 2<em>K</em> (variable size)</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Child 2<em>K</em><sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Key 2<em>K</em>+1 (variable size)</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>TREE</code>” is + used to indicate the + beginning of a B-link tree node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Node Type</p></td> + <td> + <p>Each B-link tree points to a particular type of data. + This field indicates the type of data as well as + implying the maximum degree <em>K</em> of the tree and + the size of each Key field. + + + <table class="list"> + <tr> + <th width="20%" align="center">Node Type</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>This tree points to group nodes.</td> + </tr> + <tr> + <td align="center">1</td> + <td>This tree points to raw data chunk nodes.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Node Level</p></td> + <td> + <p>The node level indicates the level at which this node + appears in the tree (leaf nodes are at level zero). Not + only does the level indicate whether child pointers + point to sub-trees or to data, but it can also be used + to help file consistency checking utilities reconstruct + damaged trees. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Entries Used</p></td> + <td> + <p>This determines the number of children to which this + node points. All nodes of a particular type of tree + have the same maximum degree, but most nodes will point + to less than that number of children. The valid child + pointers and keys appear at the beginning of the node + and the unused pointers and keys appear at the end of + the node. The unused pointers and keys have undefined + values. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Address of Left Sibling</p></td> + <td> + <p>This is the relative file address of the left sibling of + the current node. If the current + node is the left-most node at this level then this field + is the <a href="#UndefinedAddress">undefined address</a>. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Address of Right Sibling</p></td> + <td> + <p>This is the relative file address of the right sibling of + the current node. If the current + node is the right-most node at this level then this + field is the <a href="#UndefinedAddress">undefined address</a>. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Keys and Child Pointers</p></td> + <td> + <p>Each tree has 2<em>K</em>+1 keys with 2<em>K</em> + child pointers interleaved between the keys. The number + of keys and child pointers actually containing valid + values is determined by the node’s <em>Entries Used</em> field. + If that field is <em>N</em> then the B-link tree contains + <em>N</em> child pointers and <em>N</em>+1 keys. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Key</p></td> + <td> + <p>The format and size of the key values is determined by + the type of data to which this tree points. The keys are + ordered and are boundaries for the contents of the child + pointer; that is, the key values represented by child + <em>N</em> fall between Key <em>N</em> and Key + <em>N</em>+1. Whether the interval is open or closed on + each end is determined by the type of data to which the + tree points. + </p> + + <p> + The format of the key depends on the node type. + For nodes of node type 0 (group nodes), the key is formatted as + follows: + + <table class="list"> + <tr> + <td width="20%">A single field of <i>Size of Lengths</i> + bytes:</td> + <td width="80%">Indicates the byte offset into the local heap + for the first object name in the subtree which + that key describes. + </td> + </tr> + </table> + </p> + + + <p> + For nodes of node type 1 (chunked raw data nodes), the key is + formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-4:</td> + <td width="80%">Size of chunk in bytes.</td> + </tr> + <tr> + <td>Bytes 4-8:</td> + <td>Filter mask, a 32-bit bit field indicating which + filters have been skipped for this chunk. Each filter + has an index number in the pipeline (starting at 0, with + the first filter to apply) and if that filter is skipped, + the bit corresponding to its index is set.</td> + </tr> + <tr> + <td>(<em>D + 1</em>) 64-bit fields:</td> + <td>The offset of the + chunk within the dataset where <i>D</i> is the number + of dimensions of the dataset, and the last value is the + offset within the dataset’s datatype and should always be + zero. For example, if + a chunk in a 3-dimensional dataset begins at the + position <code>[5,5,5]</code>, there will be three + such 64-bit values, each with the value of + <code>5</code>, followed by a <code>0</code> value.</td> + </tr> + </table> + </p> + + </td> + </tr> + + <tr valign="top"> + <td><p>Child Pointer</p></td> + <td> + <p>The tree node contains file addresses of subtrees or + data depending on the node level. Nodes at Level 0 point + to data addresses, either raw data chunks or group nodes. + Nodes at non-zero levels point to other nodes of the + same B-tree. + </p> + <p>For raw data chunk nodes, the child pointer is the address + of a single raw data chunk. For group nodes, the child pointer + points to a <a href="#SymbolTable">symbol table</a>, which contains + information for multiple symbol table entries. + </p> + </td> + </tr> + </table> + </div> + + <p> + Conceptually, each B-tree node looks like this:</p> + <center> + <table> + <tr valign="top" align="center"> + <td>key[0]</td><td> </td> + <td>child[0]</td><td> </td> + <td>key[1]</td><td> </td> + <td>child[1]</td><td> </td> + <td>key[2]</td><td> </td> + <td>...</td><td> </td> + <td>...</td><td> </td> + <td>key[<i>N</i>-1]</td><td> </td> + <td>child[<i>N</i>-1]</td><td> </td> + <td>key[<i>N</i>]</td> + </tr> + </table> + </center> + <br /> + + where child[<i>i</i>] is a pointer to a sub-tree (at a level + above Level 0) or to data (at Level 0). + Each key[<i>i</i>] describes an <i>item</i> stored by the B-tree + (a chunk or an object of a group node). The range of values + represented by child[<i>i</i>] is indicated by key[<i>i</i>] + and key[<i>i</i>+1]. + + + <p>The following question must next be answered: + “Is the value described by key[<i>i</i>] contained in + child[<i>i</i>-1] or in child[<i>i</i>]?” + The answer depends on the type of tree. + In trees for groups (node type 0) the object described by + key[<i>i</i>] is the greatest object contained in + child[<i>i</i>-1] while in chunk trees (node type 1) the + chunk described by key[<i>i</i>] is the least chunk in + child[<i>i</i>].</p> + + <p>That means that key[0] for group trees is sometimes unused; + it points to offset zero in the heap, which is always the + empty string and compares as “less-than” any valid object name.</p> + + <p>And key[<i>N</i>] for chunk trees is sometimes unused; + it contains a chunk offset which compares as “greater-than” + any other chunk offset and has a chunk byte size of zero + to indicate that it is not actually allocated.</p> + +<br /> +<h4><a name="V2Btrees"> +III.A.2. Disk Format: Level 1A2 - Version 2 B-trees</a></h4> + + <p>Version 2 B-trees are “traditional” B-trees, with one major difference. + Instead of just using a simple pointer (or address in the file) to a + child of an internal node, the pointer to the child node contains two + additional pieces of information: the number of records in the child + node itself, and the total number of records in the child node and + all its descendants. Storing this additional information allows fast + array-like indexing to locate the n<sup>th</sup> record in the B-tree.</p> + + <p>The entry into a version 2 B-tree is a header which contains global + information about the structure of the B-tree. The <em>root node + address</em> + field in the header points to the B-tree root node, which is either an + internal or leaf node, depending on the value in the header’s + <em>depth</em> field. An internal node consists of records plus + pointers to further leaf or internal nodes in the tree. A leaf node + consists of solely of records. The format of the records depends on + the B-tree type (stored in the header).</p> + + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Node Size</td> + </tr> + <tr> + <td colspan="2">Record Size</td> + <td colspan="2">Depth</td> + </tr> + <tr> + <td>Split Percent</td> + <td>Merge Percent</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Root Node Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="2">Number of Records in Root Node</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Total Number of Records in B-tree<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>BTHD</code>” is + used to indicate the header of a version 2 B-link tree node. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this B-tree header. This document + describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field indicates the type of B-tree: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>A “testing” B-tree, this value should <em>not</em> be + used for storing records in actual HDF5 files. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>This B-tree is used for indexing indirectly accessed, + non-filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">2</td> + <td>This B-tree is used for indexing indirectly accessed, + filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">3</td> + <td>This B-tree is used for indexing directly accessed, + non-filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">4</td> + <td>This B-tree is used for indexing directly accessed, + filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">5</td> + <td>This B-tree is used for indexing the ‘name’ field for + links in indexed groups. + </td> + </tr> + <tr> + <td align="center">6</td> + <td>This B-tree is used for indexing the ‘creation order’ + field for links in indexed groups. + </td> + </tr> + <tr> + <td align="center">7</td> + <td>This B-tree is used for indexing shared object header + messages. + </td> + </tr> + <tr> + <td align="center">8</td> + <td>This B-tree is used for indexing the ‘name’ field for + indexed attributes. + </td> + </tr> + <tr> + <td align="center">9</td> + <td>This B-tree is used for indexing the ‘creation order’ + field for indexed attributes. + </td> + </tr> + </table></p> + <p>The format of records for each type is described below.</p> + </td> + </tr> + + <tr valign="top"> + <td><p>Node Size</p></td> + <td> + <p>This is the size in bytes of all B-tree nodes. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Record Size</p></td> + <td> + <p>This field is the size in bytes of the B-tree record. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Depth</p></td> + <td> + <p>This is the depth of the B-tree. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Split Percent</p></td> + <td> + <p>The percent full that a node needs to increase above before it + is split. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Merge Percent</p></td> + <td> + <p>The percent full that a node needs to be decrease below before it + is split. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Root Node Address</p></td> + <td> + <p>This is the address of the root B-tree node. A B-tree with + no records will have the <a href="#UndefinedAddress">undefined + address</a> in this field. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Number of Records in Root Node</p></td> + <td> + <p>This is the number of records in the root node. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Total Number of Records in B-tree</p></td> + <td> + <p>This is the total number of records in the entire B-tree. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the B-tree header. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree Internal Node + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2">Records 0, 1, 2...N-1 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Child Node Pointer 0<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Number of Records N<sub>0</sub> for Child Node 0 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Total Number of Records for Child Node 0 <em>(optional, variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Child Node Pointer 1<sup>O</sup><br /><br /></td> + </tr> + <td colspan="4"><br />Number of Records N<sub>1</sub> for Child Node 1 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Total Number of Records for Child Node 1 <em>(optional, variable size)</em></td> + </tr> + <tr> + <td colspan="4">...</td> + </tr> + <tr> + <td colspan="4"><br />Child Node Pointer N<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Number of Records N<sub>n</sub> for Child Node N <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Total Number of Records for Child Node N <em>(optional, variable size)</em></td> + </tr> + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + </div> + + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>BTIN</code>” is + used to indicate the internal node of a B-link tree. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this B-tree internal node. + This document describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field is the type of the B-tree node. It should always + be the same as the B-tree type in the header. + </p> + </td> + </tr> + + <tr> + <td><p>Records</p></td> + <td> + <p>The size of this field is determined by the number of records + for this node and the record size (from the header). The format + of records depends on the type of B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Child Node Pointer</p></td> + <td> + <p>This field is the address of the child node pointed to by the + internal node. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Records in Child Node</p></td> + <td> + <p>This is the number of records in the child node pointed to by + the corresponding <em>Node Pointer</em>. + </p> + <p>The number of bytes used to store this field is determined by + the maximum possible number of records able to be stored in the + child node. + </p> + <p> + The maximum number of records in a child node is computed + in the following way: + + <ul> + <li>Subtract the fixed size overhead for + the child node (for example, its signature, version, + checksum, and so on and <em>one</em> pointer triplet + of information for the child node (because there is one + more pointer triplet than records in each internal node)) + from the size of nodes for the B-tree. </li> + <li>Divide that result by the size of a record plus the + pointer triplet of information stored to reach each + child node from this node. + </ul> + + </p> + <p> + Note that leaf nodes do not encode any + child pointer triplets, so the maximum number of records in a + leaf node is just the node size minus the leaf node overhead, + divided by the record size. + </p> + <p> + Also note that the first level of internal nodes above the + leaf nodes do not encode the <em>Total Number of Records in Child + Node</em> value in the child pointer triplets (since it is the + same as the <em>Number of Records in Child Node</em>), so the + maximum number of records in these nodes is computed with the + equation above, but using (<em>Child Pointer</em>, <em>Number of + Records in Child Node</em>) pairs instead of triplets. + </p> + <p> + The number of + bytes used to encode this field is the least number of bytes + required to encode the maximum number of records in a child + node value for the child nodes below this level + in the B-tree. + </p> + <p> + For example, if the maximum number of child records is + 123, one byte will be used to encode these values in this + node; if the maximum number of child records is + 20000, two bytes will be used to encode these values in this + node; and so on. The maximum number of bytes used to + encode these values is 8 (in other words, an unsigned + 64-bit integer). + </p> + </td> + </tr> + + <tr> + <td><p>Total Number of Records in Child Node</p></td> + <td> + <p>This is the total number of records for the node pointed to by + the corresponding <em>Node Pointer</em> and all its children. + This field exists only in nodes whose depth in the B-tree node + is greater than 1 (in other words, the “twig” + internal nodes, just above leaf nodes, do not store this + field in their child node pointers). + </p> + <p>The number of bytes used to store this field is determined by + the maximum possible number of records able to be stored in the + child node and its descendants. + </p> + <p> + The maximum possible number of records able to be stored in a + child node and its descendants is computed iteratively, in the + following way: The maximum number of records in a leaf node + is computed, then that value is used to compute the maximum + possible number of records in the first level of internal nodes + above the leaf nodes. Multiplying these two values together + determines the maximum possible number of records in child node + pointers for the level of nodes two levels above leaf nodes. + This process is continued up to any level in the B-tree. + </p> + <p> + The number of bytes used to encode this value is computed in + the same way as for the <em>Number of Records in Child Node</em> + field. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for this node. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree Leaf Node + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2">Record 0, 1, 2...N-1 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>BTLF</code>“ is + used to indicate the leaf node of a version 2 B-link tree. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this B-tree leaf node. + This document describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field is the type of the B-tree node. It should always + be the same as the B-tree type in the header. + </p> + </td> + </tr> + + <tr> + <td><p>Records</p></td> + <td> + <p>The size of this field is determined by the number of records + for this node and the record size (from the header). The format + of records depends on the type of B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for this node. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <p>The record layout for each stored (in other words, non-testing) + B-tree type is as follows:</p> + + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 1 Record Layout - Indirectly Accessed, Non-Filtered, + ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object ID<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Huge Object Address</p></td> + <td> + <p>The address of the huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object Length</p></td> + <td> + <p>The length of the huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object ID</p></td> + <td> + <p>The heap ID for the huge object. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 2 Record Layout - Indirectly Accessed, Filtered, + ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Filtered Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask</td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Memory Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object ID<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filtered Huge Object Address</p></td> + <td> + <p>The address of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Length</p></td> + <td> + <p>The length of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td> + <p>A 32-bit bit field indicating which filters have been skipped for + this chunk. Each filter has an index number in the pipeline + (starting at 0, with the first filter to apply) and if that + filter is skipped, the bit corresponding to its index is set. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Memory Size</p></td> + <td> + <p>The size of the de-filtered huge object in memory. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object ID</p></td> + <td> + <p>The heap ID for the huge object. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 3 Record Layout - Directly Accessed, Non-Filtered, + ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Huge Object Address</p></td> + <td> + <p>The address of the huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object Length</p></td> + <td> + <p>The length of the huge object in the file. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 4 Record Layout - Directly Accessed, Filtered, + ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Filtered Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask</td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Memory Size<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filtered Huge Object Address</p></td> + <td> + <p>The address of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Length</p></td> + <td> + <p>The length of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td> + <p>A 32-bit bit field indicating which filters have been skipped for + this chunk. Each filter has an index number in the pipeline + (starting at 0, with the first filter to apply) and if that + filter is skipped, the bit corresponding to its index is set. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Memory Size</p></td> + <td> + <p>The size of the de-filtered huge object in memory. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 5 Record Layout - Link Name for Indexed Group + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Hash of Name</td> + </tr> + <tr> + <td colspan="4">ID <em>(bytes 1-4)</em></td> + </tr> + + <tr> + <td colspan="3">ID <em>(bytes 5-7)</em></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the name for the link. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the link’s name. + </p> + </td> + </tr> + + <tr> + <td><p>ID</p></td> + <td> + <p>This is a 7-byte sequence of bytes and is the heap ID for the + link record in the group’s fractal heap.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 6 Record Layout - Creation Order for Indexed Group + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Creation Order <em>(8 bytes)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">ID <em>(bytes 1-4)</em></td> + </tr> + <tr> + <td colspan="3">ID <em>(bytes 5-7)</em></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td> + <p>This field is the creation order value for the link. + </p> + </td> + </tr> + + <tr> + <td><p>ID</p></td> + <td> + <p>This is a 7-byte sequence of bytes and is the heap ID for the + link record in the group’s fractal heap.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 7 Record Layout - Shared Object Header Messages (Sub-Type 0 - Message in Heap) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Hash</td> + </tr> + <tr> + <td colspan="4">Reference Count</td> + </tr> + <tr> + <td colspan="4"><br />Heap ID <em>(8 bytes)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This field Indicates the location where the message is stored: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>Shared message is stored in shared message index heap. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>Shared message is stored in object header. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the shared message. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the shared message.</p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td> + <p>The number of objects which reference this message.</p> + </td> + </tr> + + <tr> + <td><p>Heap ID</p></td> + <td> + <p>This is an 8-byte sequence of bytes and is the heap ID for the + shared message in the shared message index’s fractal heap.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 7 Record Layout - Shared Object Header Messages (Sub-Type 1 - Message in Object Header) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Hash</td> + </tr> + <tr> + <td>Reserved (zero)</td> + <td>Message Type</td> + <td colspan="2">Object Header Index</td> + </tr> + <tr> + <td colspan="4"><br />Object Header Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This field Indicates the location where the message is stored: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>Shared message is stored in shared message index heap. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>Shared message is stored in object header. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the shared message. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the shared message.</p> + </td> + </tr> + + <tr> + <td><p>Message Type</p></td> + <td> + <p>The object header message type of the shared message.</p> + </td> + </tr> + + <tr> + <td><p>Object Header Index</p></td> + <td> + <p>This field indicates that the shared message is the n<sup>th</sup> message + of its type in the specified object header.</p> + </td> + </tr> + + <tr> + <td><p>Object Header Address</p></td> + <td> + <p>The address of the object header containing the shared message.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 8 Record Layout - Attribute Name for Indexed Attributes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Heap ID <em>(8 bytes)</em><br /><br /></td> + </tr> + <tr> + <td colspan>Message Flags</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Creation Order</td> + </tr> + <tr> + <td colspan="4">Hash of Name</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Heap ID</p></td> + <td> + <p>This is an 8-byte sequence of bytes and is the heap ID for the + attribute in the object’s attribute fractal heap.</p> + </td> + </tr> + + <tr> + <td><p>Message Flags</p></td> + <td><p>The object header message flags for the attribute message.</p> + </td> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td> + <p>This field is the creation order value for the attribute. + </p> + </td> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the name for the attribute. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the attribute’s name. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Version 2 B-tree, Type 9 Record Layout- Creation Order for Indexed Attributes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Heap ID <em>(8 bytes)</em><br /><br /></td> + </tr> + <tr> + <td colspan>Message Flags</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Creation Order</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Heap ID</p></td> + <td> + <p>This is an 8-byte sequence of bytes and is the heap ID for the + attribute in the object’s attribute fractal heap.</p> + </td> + </tr> + + <tr> + <td><p>Message Flags</p></td> + <td> + <p>The object header message flags for the attribute message.</p> + </td> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td> + <p>This field is the creation order value for the attribute. + </p> + </td> + </tr> + + </table> + </div> + + +<br /> +<h3><a name="SymbolTable"> +III.B. Disk Format: Level 1B - Group Symbol Table Nodes</a></h3> + + <p>A group is an object internal to the file that allows + arbitrary nesting of objects within the file (including other groups). + A group maps a set of link names in the group to a set of relative + file addresses of objects in the file. Certain metadata for an object to + which the group points can be cached in the group’s symbol table entry in + addition to being in the object’s header.</p> + + <p>An HDF5 object name space can be stored hierarchically by + partitioning the name into components and storing each + component as a link in a group. The link for a + non-ultimate component points to the group containing + the next component. The link for the last + component points to the object being named.</p> + + <p>One implementation of a group is a collection of symbol table nodes + indexed by a B-link tree. Each symbol table node contains entries + for one or more links. If an attempt is made to add a link to an already + full symbol table node containing 2<em>K</em> entries, then the node is + split and one node contains <em>K</em> symbols and the other contains + <em>K</em>+1 symbols.</p> + + <div align="center"> + <table class="format"> + <caption> + Symbol Table Node (A Leaf of a B-link tree) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version Number</td> + <td>Reserved (zero)</td> + <td colspan="2">Number of Symbols</td> + </tr> + + <tr> + <td colspan="4"><br /><br />Group Entries<br /><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>SNOD</code>” is + used to indicate the + beginning of a symbol table node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version Number</p></td> + <td> + <p>The version number for the symbol table node. This + document describes version 1. (There is no version ‘0’ + of the symbol table node) + </p> + </td> + </tr> + + <tr> + <td><p>Number of Entries</p></td> + <td> + <p>Although all symbol table nodes have the same length, + most contain fewer than the maximum possible number of + link entries. This field indicates how many entries + contain valid data. The valid entries are packed at the + beginning of the symbol table node while the remaining + entries contain undefined values. + </p> + </td> + </tr> + + <tr> + <td><p>Symbol Table Entries</p></td> + <td> + <p>Each link has an entry in the symbol table node. + The format of the entry is described below. + There are 2<em>K</em> entries in each group node, where + <em>K</em> is the “Group Leaf Node K” value from the + <a href="#Superblock">superblock</a>. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h3><a name="SymbolTableEntry"> +III.C. Disk Format: Level 1C - Symbol Table Entry </a></h3> + + <p>Each symbol table entry in a symbol table node is designed + to allow for very fast browsing of stored objects. + Toward that design goal, the symbol table entries + include space for caching certain constant metadata from the + object header.</p> + + <div align="center"> + <table class="format"> + <caption> + Symbol Table Entry + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Link Name Offset<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Object Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Cache Type</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br /><br />Scratch-pad Space (16 bytes)<br /><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Link Name Offset</p></td> + <td> + <p>This is the byte offset into the group’s local + heap for the name of the link. The name is null + terminated. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Address</p></td> + <td> + <p>Every object has an object header which serves as a + permanent location for the object’s metadata. In addition + to appearing in the object header, some of the object’s metadata + can be cached in the scratch-pad space. + </p> + </td> + </tr> + + <tr> + <td><p>Cache Type</p></td> + <td> + <p>The cache type is determined from the object header. + It also determines the format for the scratch-pad space: + + <table class="list"> + <tr> + <th width="20%" align="center">Type</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>No data is cached by the group entry. This + is guaranteed to be the case when an object header + has a link count greater than one. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>Group object header metadata is cached in the + scratch-pad space. This implies that the symbol table + entry refers to another group. + </td> + </tr> + <tr> + <td align="center">2</td> + <td>The entry is a symbolic link. The first four bytes + of the scratch-pad space are the offset into the local + heap for the link value. The object header address + will be undefined. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td> + <p>These four bytes are present so that the scratch-pad + space is aligned on an eight-byte boundary. They are + always set to zero. + </p> + </td> + </tr> + + <tr> + <td><p>Scratch-pad Space</p></td> + <td> + <p>This space is used for different purposes, depending + on the value of the Cache Type field. Any metadata + about an object represented in the scratch-pad + space is duplicated in the object header for that + object. + </p> + <p> + Furthermore, no data is cached in the group + entry scratch-pad space if the object header for + the object has a link count greater than one. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h4>Format of the Scratch-pad Space</h4> + + <p>The symbol table entry scratch-pad space is formatted + according to the value in the Cache Type field.</p> + + <p>If the Cache Type field contains the value zero + <code>(0)</code> then no information is + stored in the scratch-pad space.</p> + + <p>If the Cache Type field contains the value one + <code>(1)</code>, then the scratch-pad space + contains cached metadata for another object header + in the following format:</p> + + <div align="center"> + <table class="format"> + <caption> + Object Header Scratch-pad Format + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address of B-tree<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Name Heap<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address of B-tree</p></td> + <td> + <p>This is the file address for the root of the + group’s B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Name Heap</p></td> + <td> + <p>This is the file address for the group’s local + heap, in which are stored the group’s symbol names. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <p>If the Cache Type field contains the value two + <code>(2)</code>, then the scratch-pad space + contains cached metadata for a symbolic link + in the following format:</p> + + <div align="center"> + <table class="format"> + <caption> + Symbolic Link Scratch-pad Format + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Offset to Link Value</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Offset to Link Value</p></td> + <td> + <p>The value of a symbolic link (that is, the name of the + thing to which it points) is stored in the local heap. + This field is the 4-byte offset into the local heap for + the start of the link value, which is null terminated. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h3><a name="LocalHeap"> +III.D. Disk Format: Level 1D - Local Heaps</a></h3> + + <p>A local heap is a collection of small pieces of data that are particular + to a single object in the HDF5 file. Objects can be + inserted and removed from the heap at any time. + The address of a heap does not change once the heap is created. + For example, a group stores addresses of objects in symbol table nodes + with the names of links stored in the group’s local heap. + </p> + + <div align="center"> + <table class="format"> + <caption> + Local Heap + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Data Segment Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Offset to Head of Free-list<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Data Segment<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>HEAP</code>” + is used to indicate the + beginning of a heap. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>Each local heap has its own version number so that new + heaps can be added to old files. This document + describes version zero (0) of the local heap. + </p> + </td> + </tr> + + <tr> + <td><p>Data Segment Size</p></td> + <td> + <p>The total amount of disk memory allocated for the heap + data. This may be larger than the amount of space + required by the objects stored in the heap. The extra + unused space in the heap holds a linked list of free blocks. + </p> + </td> + </tr> + + <tr> + <td><p>Offset to Head of Free-list</p></td> + <td> + <p>This is the offset within the heap data segment of the + first free block (or the + <a href="#UndefinedAddress">undefined address</a> if there is no + free block). The free block contains “Size of Lengths” bytes that + are the offset of the next free block (or the + value ‘1’ if this is the + last free block) followed by “Size of Lengths” bytes that store + the size of this free block. The size of the free block includes + the space used to store the offset of the next free block and + the size of the current block, making the minimum size of a free + block 2 * “Size of Lengths”. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Data Segment</p></td> + <td> + <p>The data segment originally starts immediately after + the heap header, but if the data segment must grow as a + result of adding more objects, then the data segment may + be relocated, in its entirety, to another part of the + file. + </p> + </td> + </tr> + </table> + </div> + + <p>Objects within a local heap should be aligned on an 8-byte boundary.</p> + +<br /> +<h3><a name="GlobalHeap"> +III.E. Disk Format: Level 1E - Global Heap</a></h3> + + <p>Each HDF5 file has a global heap which stores various types of + information which is typically shared between datasets. The + global heap was designed to satisfy these goals:</p> + + <ol type="A"> + <li>Repeated access to a heap object must be efficient without + resulting in repeated file I/O requests. Since global heap + objects will typically be shared among several datasets, it is + probable that the object will be accessed repeatedly.</li> + <li>Collections of related global heap objects should result in + fewer and larger I/O requests. For instance, a dataset of + object references will have a global heap object for each + reference. Reading the entire set of object references + should result in a few large I/O requests instead of one small + I/O request for each reference.</li> + <li>It should be possible to remove objects from the global heap + and the resulting file hole should be eligible to be reclaimed + for other uses.</li> + </ol> + + + <p>The implementation of the heap makes use of the memory management + already available at the file level and combines that with a new + object called a <em>collection</em> to achieve goal B. The global heap + is the set of all collections. Each global heap object belongs to + exactly one collection and each collection contains one or more global + heap objects. For the purposes of disk I/O and caching, a collection is + treated as an atomic object, addressing goal A. + </p> + + <p>When a global heap object is deleted from a collection (which occurs + when its reference count falls to zero), objects located after the + deleted object in the collection are packed down toward the beginning + of the collection and the collection’s global heap object 0 is created + (if possible) or its size is increased to account for the recently + freed space. There are no gaps between objects in each collection, + with the possible exception of the final space in the collection, if + it is not large enough to hold the header for the collection’s global + heap object 0. These features address goal C. + </p> + + <p>The HDF5 Library creates global heap collections as needed, so there may + be multiple collections throughout the file. The set of all of them is + abstractly called the “global heap”, although they do not actually link + to each other, and there is no global place in the file where you can + discover all of the collections. The collections are found simply by + finding a reference to one through another object in the file. For + example, data of variable-length datatype elements is stored in the + global heap and is accessed via a global heap ID. The format for + global heap IDs is described at the end of this section. + </p> + + <div align="center"> + <table class="format"> + <caption> + A Global Heap Collection + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Collection Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object 1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object 2<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object <em>N</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object 0 (free space)<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>GCOL</code>” + is used to indicate the + beginning of a collection. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>Each collection has its own version number so that new + collections can be added to old files. This document + describes version one (1) of the collections (there is no + version zero (0)). + </p> + </td> + </tr> + + <tr> + <td><p>Collection Size</p></td> + <td> + <p>This is the size in bytes of the entire collection + including this field. The default (and minimum) + collection size is 4096 bytes which is a typical file + system block size. This allows for 127 16-byte heap + objects plus their overhead (the collection header of 16 bytes + and the 16 bytes of information about each heap object). + </p> + </td> + </tr> + + <tr> + <td><p>Global Heap Object 1 through <em>N</em></p></td> + <td> + <p>The objects are stored in any order with no + intervening unused space. + </p> + </td> + </tr> + + <tr> + <td><p>Global Heap Object 0</p></td> + <td> + <p>Global Heap Object 0 (zero), when present, represents the free + space in the collection. Free space always appears at the end of + the collection. If the free space is too small to store the header + for Object 0 (described below) then the header is implied and the + collection contains no free space. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Global Heap Object + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="2">Heap Object Index</td> + <td colspan="2">Reference Count</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Object Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Object Data<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Heap Object Index</p></td> + <td> + <p>Each object has a unique identification number within a + collection. The identification numbers are chosen so that + new objects have the smallest value possible with the + exception that the identifier <code>0</code> always refers to the + object which represents all free space within the + collection. + </p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td> + <p>All heap objects have a reference count field. An + object which is referenced from some other part of the + file will have a positive reference count. The reference + count for Object 0 is always zero. + </p> + </td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td> + <p>Zero padding to align next field on an 8-byte boundary. + </p> + </td> + </tr> + + <tr> + <td><p>Object Size</p></td> + <td> + <p>This is the size of the object data stored for the object. + The actual storage space allocated for the object data is rounded + up to a multiple of eight. + </p> + </td> + </tr> + + <tr> + <td><p>Object Data</p></td> + <td> + <p>The object data is treated as a one-dimensional array + of bytes to be interpreted by the caller. + </p> + </td> + </tr> + </table> + + </div> + + <br /> + <p> + The format for the ID used to locate an object in the global heap is + described here:</p> + + <div align="center"> + <table class="format"> + <caption> + Global Heap ID + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Collection Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Object Index</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Collection Address</p></td> + <td> + <p>This field is the address of the global heap collection + where the data object is stored. + </p> + </td> + </tr> + + <tr> + <td><p>ID</p></td> + <td> + <p>This field is the index of the data object within the + global heap collection. + </p> + </td> + </tr> + + </table> + </div> + + +<br /> +<h3><a name="FractalHeap"> +III.F. Disk Format: Level 1F - Fractal Heap</a></h3> + + <p> + Each fractal heap consists of a header and zero or more direct and + indirect blocks (described below). The header contains general + information as well as + initialization parameters for the doubling table. The <em>Root + Block Address</em> in the header points to the first direct or + indirect block in the heap. + </p> + + <p> + Fractal heaps are based on a data structure called a <em>doubling + table</em>. A doubling table provides a mechanism for quickly + extending an array-like data structure that minimizes the number of + empty blocks in the heap, while retaining very fast lookup of any + element within the array. More information on fractal heaps and + doubling tables can be found in the RFC + “<a href="Supplements/FractalHeap/PrivateHeap.pdf">Private + Heaps in HDF5</a>.” + </p> + + <p> + The fractal heap implements the doubling table structure with + indirect and direct blocks. + Indirect blocks in the heap do not actually contain data for + objects in the heap, their “size” is abstract - + they represent the indexing structure for locating the + direct blocks in the doubling table. + Direct blocks + contain the actual data for objects stored in the heap. + </p> + + <p> + All indirect blocks have a constant number of block entries in each + row, called the <em>width</em> of the doubling table (stored in + the heap header). + + The number + of rows for each indirect block in the heap is determined by the + size of the block that the indirect block represents in the + doubling table (calculation of this is shown below) and is + constant, except for the “root” + indirect block, which expands and shrinks its number of rows as + needed. + </p> + + <p> + Blocks in the first <em>two</em> rows of an indirect block + are <em>Starting Block Size</em> number of bytes in size, + and the blocks in each subsequent row are twice the size of + the blocks in the previous row. In other words, blocks in + the third row are twice the <em>Starting Block Size</em>, + blocks in the fourth row are four times the + <em>Starting Block Size</em>, and so on. Entries for + blocks up to the <em>Maximum Direct Block Size</em> point to + direct blocks, and entries for blocks greater than that size + point to further indirect blocks (which have their own + entries for direct and indirect blocks). + </p> + + <p> + The number of rows of blocks, <em>nrows</em>, in an + indirect block of size <em>iblock_size</em> is given by the + following expression: + <br /> <br /> + <em>nrows</em> = (log<sub>2</sub>(<em>iblock_size</em>) - + log<sub>2</sub>(<em><Starting Block Size></em> * + <em><Width></em>)) + 1 + </p> + + <p> + The maximum number of rows of direct blocks, <em>max_dblock_rows</em>, + in any indirect block of a fractal heap is given by the + following expression: + <br /> <br /> + <em>max_dblock_rows</em> = + (log<sub>2</sub>(<em><Max. Direct Block Size></em>) - + log<sub>2</sub>(<em><Starting Block Size></em>)) + 2 + </p> + + <p> + Using the computed values for <em>nrows</em> and + <em>max_dblock_rows</em>, along with the <em>Width</em> of the + doubling table, the number of direct and indirect block entries + (<em>K</em> and <em>N</em> in the indirect block description, below) + in an indirect block can be computed: + <br /> <br /> + <em>K</em> = MIN(<em>nrows</em>, <em>max_dblock_rows</em>) * + <em>Width</em> + + <br /> <br /> + If <em>nrows</em> is less than or equal to <em>max_dblock_rows</em>, + <em>N</em> is 0. Otherwise, <em>N</em> is simply computed: + <br /> <br /> + <em>N</em> = <em>K</em> - (<em>max_dblock_rows</em> * + <em>Width</em>) + </p> + + <p> + The size indirect blocks on disk is determined by the number + of rows in the indirect block (computed above). The size of direct + blocks on disk is exactly the size of the block in the doubling + table. + </p> + + <div align="center"> + <table class="format"> + <caption> + Fractal Heap Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="2">Heap ID Length</td> + <td colspan="2">I/O Filters’ Encoded Length</td> + </tr> + + <tr> + <td>Flags</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Maximum Size of Managed Objects</td> + </tr> + + <tr> + <td colspan="4"><br />Next Huge Object ID<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />v2 B-tree Address of Huge Objects<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Amount of Free Space in Managed Blocks<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Managed Block Free Space Manager<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Amount of Managed Space in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Amount of Allocated Managed Space in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Offset of Direct Block Allocation Iterator in Managed Space<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Managed Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Huge Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Huge Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Tiny Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Tiny Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Table Width</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Starting Block Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Maximum Direct Block Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Maximum Heap Size</td> + <td colspan="2">Starting # of Rows in Root Indirect Block</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Root Block<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Current # of Rows in Root Indirect Block</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Filtered Root Direct Block <em>(optional)</em><sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">I/O Filter Mask<em> (optional)</em></td> + </tr> + + <tr> + <td colspan="4">I/O Filter Information<em> (optional, variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FRHP</code>” + is used to indicate the + beginning of a fractal heap header. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Heap ID Length</p></td> + <td> + <p>This is the length in bytes of heap object IDs for this heap.</p> + </td> + </tr> + + <tr> + <td><p>I/O Filters’ Encoded Length</p></td> + <td> + <p>This is the size in bytes of the encoded <em>I/O Filter Information</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is the heap status flag and is a bit field + indicating additional information about the fractal heap. + <table class="list"> + <tr> + <th width="20%" align="center">Bit(s)</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the ID value to use for huge object has wrapped + around. If the value for the <em>Next Huge Object ID</em> + has wrapped around, each new huge object inserted into the + heap will require a search for an ID value. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the direct blocks in the heap are checksummed. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Maximum Size of Managed Objects</p></td> + <td> + <p>This is the maximum size of managed objects allowed in the heap. + Objects greater than this this are ‘huge’ objects and will be + stored in the file directly, rather than in a direct block for + the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Next Huge Object ID</p></td> + <td> + <p>This is the next ID value to use for a huge object in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>v2 B-tree Address of Huge Objects</p></td> + <td> + <p>This is the address of the <a href="#V2Btrees">v2 B-tree</a> + used to track huge objects in the heap. The type of records + stored in the <em>v2 B-tree</em> will + be determined by whether the address & length of a huge object + can fit into a heap ID (if yes, it is a “directly” accessed + huge object) and whether there is a filter used on objects + in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Amount of Free Space in Managed Blocks</p></td> + <td> + <p>This is the total amount of free space in managed direct blocks + (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Address of Managed Block Free Space Manager</p></td> + <td> + <p>This is the address of the + <em><a href="#FreeSpaceManager">Free-space Manager</a></em> for + managed blocks. + </p> + </td> + </tr> + + <tr> + <td><p>Amount of Managed Space in Heap</p></td> + <td> + <p>This is the total amount of managed space in the heap (in bytes), + essentially the upper bound of the heap’s linear address space. + </p> + </td> + </tr> + + <tr> + <td><p>Amount of Allocated Managed Space in Heap</p></td> + <td> + <p>This is the total amount of managed space (in bytes) actually + allocated in + the heap. This can be less than the <em>Amount of Managed Space + in Heap</em> field, if some direct blocks in the heap’s linear + address space are not allocated. + </p> + </td> + </tr> + + <tr> + <td><p>Offset of Direct Block Allocation Iterator in Managed Space</p></td> + <td> + <p>This is the linear heap offset where the next direct + block should be allocated at (in bytes). This may be less than + the <em>Amount of Managed Space in Heap</em> value because the + heap’s address space is increased by a “row” of direct blocks + at a time, rather than by single direct block increments. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Managed Objects in Heap</p></td> + <td> + <p>This is the number of managed objects in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Huge Objects in Heap</p></td> + <td> + <p>This is the total size of huge objects in the heap (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Number of Huge Objects in Heap</p></td> + <td> + <p>This is the number of huge objects in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Tiny Objects in Heap</p></td> + <td> + <p>This is the total size of tiny objects that are packed in heap + IDs (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Number of Tiny Objects in Heap</p></td> + <td> + <p>This is the number of tiny objects that are packed in heap IDs. + </p> + </td> + </tr> + + <tr> + <td><p>Table Width</p></td> + <td> + <p>This is the number of columns in the doubling table for managed + blocks. This value must be a power of two. + </p> + </td> + </tr> + + <tr> + <td><p>Starting Block Size</p></td> + <td> + <p>This is the starting block size to use in the doubling table for + managed blocks (in bytes). This value must be a power of two. + </p> + </td> + </tr> + + <tr> + <td><p>Maximum Direct Block Size</p></td> + <td> + <p>This is the maximum size allowed for a managed direct block. + Objects inserted into the heap that are larger than this value + (less the # of bytes of direct block prefix/suffix) + are stored as ‘huge’ objects. This value must be a power of + two. + </p> + </td> + </tr> + + <tr> + <td><p>Maximum Heap Size</p></td> + <td> + <p>This is the maximum size of the heap’s linear address space for + managed objects (in bytes). The value stored is the log2 of + the actual value, that is: the # of bits of the address space. + ‘Huge’ and ‘tiny’ objects are not counted in this value, since + they do not store objects in the linear address space of the + heap. + </p> + </td> + </tr> + + <tr> + <td><p>Starting # of Rows in Root Indirect Block</p></td> + <td> + <p>This is the starting number of rows for the root indirect block. + A value of 0 indicates that the root indirect block will have + the maximum number of rows needed to address the heap’s <em>Maximum + Heap Size</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Root Block</p></td> + <td> + <p>This is the address of the root block for the heap. It can + be the <a href="#UndefinedAddress">undefined address</a> if + there is no data in the heap. It either points to a direct + block (if the <em>Current # of Rows in the Root Indirect Block</em> + value is 0), or an indirect block. + </p> + </td> + </tr> + + <tr> + <td><p>Current # of Rows in Root Indirect Block</p></td> + <td> + <p>This is the current number of rows in the root indirect block. + A value of 0 indicates that <em>Address of Root Block</em> + points to direct block instead of indirect block. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Filtered Root Direct Block</p></td> + <td> + <p>This is the size of the root direct block, if filters are + applied to heap objects (in bytes). This field is only + stored in the header if the <em>I/O Filters’ Encoded Length</em> + is greater than 0. + </p> + </td> + </tr> + + <tr> + <td><p>I/O Filter Mask</p></td> + <td> + <p>This is the filter mask for the root direct block, if filters + are applied to heap objects. This mask has the same format as + that used for the filter mask in chunked raw data records in a + <a href="#V1Btrees">v1 B-tree</a>. + This field is only + stored in the header if the <em>I/O Filters’ Encoded Length</em> + is greater than 0. + </p> + </td> + </tr> + + <tr> + <td><p>I/O Filter Information</p></td> + <td> + <p>This is the I/O filter information encoding direct blocks and + huge objects, if filters are applied to heap objects. This + field is encoded as a <a href="#FilterMessage">Filter Pipeline</a> + message. + The size of this field is determined by <em>I/O Filters’ + Encoded Length</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the header.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Fractal Heap Direct Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Heap Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Block Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Object Data <em>(variable size)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FHDB</code>” + is used to indicate the + beginning of a fractal heap direct block. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Heap Header Address</p></td> + <td> + <p>This is the address for the fractal heap header that this + block belongs to. This field is principally used for file + integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Block Offset</p></td> + <td> + <p>This is the offset of the block within the fractal heap’s + address space (in bytes). The number of bytes used to encode + this field is the <em>Maximum Heap Size</em> (in the heap’s + header) divided by 8 and rounded up to the next highest integer, + for values that are not a multiple of 8. This value is + principally used for file integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the direct block.</p> + <p>This field is only present if bit 1 of <em>Flags</em> in the + heap’s header is set.</p> + </td> + </tr> + + <tr> + <td><p>Object Data</p></td> + <td> + <p>This section of the direct block stores the actual data for + objects in the heap. The size of this section is determined by + the direct block’s size minus the size of the other fields + stored in the direct block (for example, the <em>Signature</em>, + <em>Version</em>, and others including the <em>Checksum</em> if it is + present). + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Fractal Heap Indirect Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Heap Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Block Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Child Direct Block #0 Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Size of Filtered Direct Block #0 <em>(optional)</em> <sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask for Direct Block #0 <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Child Direct Block #1 Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Size of Filtered Direct Block #1 <em>(optional)</em><sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask for Direct Block #1 <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4"><br />Child Direct Block #K-1 Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Size of Filtered Direct Block #K-1 <em>(optional)</em><sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask for Direct Block #K-1 <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Child Indirect Block #0 Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Child Indirect Block #1 Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4"><br />Child Indirect Block #N-1 Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FHIB</code>” is used to + indicate the beginning of a fractal heap indirect block. This + gives file consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Heap Header Address</p></td> + <td> + <p>This is the address for the fractal heap header that this + block belongs to. This field is principally used for file + integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Block Offset</p></td> + <td> + <p>This is the offset of the block within the fractal heap’s + address space (in bytes). The number of bytes used to encode + this field is the <em>Maximum Heap Size</em> (in the heap’s + header) divided by 8 and rounded up to the next highest integer, + for values that are not a multiple of 8. This value is + principally used for file integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Child Direct Block #K Address</p></td> + <td> + <p>This field is the address of the child direct block. + The size of the [uncompressed] direct block can be computed by + its offset in the heap’s linear address space. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Filtered Direct Block #K</p></td> + <td> + <p>This is the size of the child direct block after passing through + the I/O filters defined for this heap (in bytes). If no I/O + filters are present for this heap, this field is not present. + </p> + </td> + </tr> + <tr> + <td><p>Filter Mask for Direct Block #K</p></td> + <td> + <p>This is the I/O filter mask for the filtered direct block. + This mask has the same format as that used for the filter mask + in chunked raw data records in a <a href="#V1Btrees">v1 B-tree</a>. + If no I/O filters are present for this heap, this field is not + present. + </p> + </td> + </tr> + + <tr> + <td><p>Child Indirect Block #N Address</p></td> + <td> + <p>This field is the address of the child indirect block. + The size of the indirect block can be computed by + its offset in the heap’s linear address space. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the indirect block.</p> + </td> + </tr> + + </table> + + </div> + + <br /> + <p>An object in the fractal heap is identified by means of a fractal heap ID, + which encodes information to locate the object in the heap. + Currently, the fractal heap stores an object in one of three ways, + depending on the object’s size:</p> + + <div align="center"> + <table class="list80"> + <tr> + <th width="20%">Type</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center">Tiny</td> + <td> + <p>When an object is small enough to be encoded in the heap ID, the + object’s data is embedded in the fractal heap ID itself. There are + 2 sub-types for this type of object: normal and extended. The + sub-type for tiny heap IDs depends on whether the heap ID is large + enough to store objects greater than 16 bytes or not. If the + heap ID length is 18 bytes or smaller, the ‘normal’ tiny heap ID + form is used. If the heap ID length is greater than 18 bytes in + length, the “extented” form is used. See format description below + for both sub-types. + </p> + </td> + </tr> + + <tr> + <td align="center">Huge</td> + <td> + <p>When the size of an object is larger than <em>Maximum Size of + Managed Objects</em> in the <em>Fractal Heap Header</em>, the + object’s data is stored on its own in the file and the object + is tracked/indexed via a version 2 B-tree. All huge objects + for a particular fractal heap use the same v2 B-tree. All huge + objects for a particular fractal heap use the same format for + their huge object IDs. + </p> + + <p>Depending on whether the IDs for a heap are large enough to hold + the object’s retrieval information and whether I/O pipeline filters + are applied to the heap’s objects, 4 sub-types are derived for + huge object IDs for this heap:</p> + + <div align="center"> + <table class="list"> + <tr> + <th align="left" width="35%">Sub-type</th> + <th align="left">Description</th> + </tr> + + <tr> + <td align="left">Directly accessed, non-filtered</td> + <td> + <p>The object’s address and length are embedded in the + fractal heap ID itself and the object is directly accessed + from them. This allows the object to be accessed without + resorting to the B-tree. + </p> + </td> + </tr> + + <tr> + <td align="left">Directly accessed, filtered</td> + <td> + <p>The filtered object’s address, length, filter mask and + de-filtered size are embedded in the fractal heap ID itself + and the object is accessed directly with them. This allows + the object to be accessed without resorting to the B-tree. + </p> + </td> + </tr> + + <tr> + <td align="left">Indirectly accessed, non-filtered</td> + <td> + <p>The object is located by using a B-tree key embedded in + the fractal heap ID to retrieve the address and length from + the version 2 B-tree for huge objects. Then, the address + and length are used to access the object. + </p> + </td> + </tr> + + <tr> + <td align="left">Indirectly accessed, filtered</td> + <td> + <p>The object is located by using a B-tree key embedded in + the fractal heap ID to retrieve the filtered object’s + address, length, filter mask and de-filtered size from the + version 2 B-tree for huge objects. Then, this information + is used to access the object. + </p> + </td> + </tr> + </table> + </div> + + </td> + </tr> + + <tr> + <td align="center">Managed</td> + <td> + <p>When the size of an object does not meet the above two + conditions, the object is stored and managed via the direct and + indirect blocks based on the doubling table. + </p> + </td> + </tr> + </table> + </div> + + + <p>The specific format for each type of heap ID is described below: + </p> + + <div align="center"> + <table class="format"> + <caption>Fractal Heap ID for Tiny Objects (sub-type 1 - ‘Normal’) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version, Type & Length</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version, Type & Length</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Tiny objects have a value of <code>2</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>The length of the tiny object. The value stored + is one less than the actual length (since zero-length + objects are not allowed to be stored in the heap). + For example, an object of actual length 1 has an + encoded length of 0, an object of actual length 2 + has an encoded length of 1, and so on. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td> + <p>This is the data for the object. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption>Fractal Heap ID for Tiny Objects (sub-type 2 - ‘Extended’) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version, Type & Length</td> + <td>Extended Length</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Data <em>(variable size)</em></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version, Type & Length</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Tiny objects have a value of <code>2</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>These 4 bits, together with the next byte, form an + unsigned 12-bit integer for holding the length of the + object. These 4-bits are bits 8-11 of the 12-bit integer. + See description for the <em>Extended Length</em> field below. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Extended Length</p></td> + <td> + <p>This byte, together with the 4 bits in the previous byte, + forms an unsigned 12-bit integer for holding the length of + the tiny object. These 8 bits are bits 0-7 of the 12-bit + integer formed. The value stored is one less than the actual + length (since zero-length objects are not allowed to be + stored in the heap). For example, an object of actual length + 1 has an encoded length of 0, an object of actual length + 2 has an encoded length of 1, and so on. + </p> + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td> + <p>This is the data for the object. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption>Fractal Heap ID for Huge Objects (sub-type 1 & 2): indirectly accessed, non-filtered/filtered + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version & Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />v2 B-tree Key<sup>L</sup><em> (variable size)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version & Type</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Huge objects have a value of <code>1</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>v2 B-tree Key</p></td> + <td><p>This field is the B-tree key for retrieving the information + from the version 2 B-tree for huge objects needed to access the + object. See the description of <a href="#V2Btrees">v2 B-tree</a> + records sub-type 1 & 2 for a description of the fields. New key + values are derived from <em>Next Huge Object ID</em> in the + <em>Fractal Heap Header</em>.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption>Fractal Heap ID for Huge Objects (sub-type 3): directly accessed, non-filtered + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version & Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address <sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Length <sup>L</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version & Type</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Huge objects have a value of <code>1</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This field is the address of the object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This field is the length of the object in the file.</p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption>Fractal Heap ID for Huge Objects (sub-type 4): directly accessed, filtered + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version & Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address <sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Length <sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Filter Mask</td> + </tr> + + <tr> + <td colspan="4"><br />De-filtered Size <sup>L</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td> + </tr> + <tr> + <td> </td> + <td>(Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version & Type</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Huge objects have a value of <code>1</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This field is the address of the filtered object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This field is the length of the filtered object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td><p>This field is the I/O pipeline filter mask for the + filtered object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Filtered Size</p></td> + <td><p>This field is the size of the de-filtered object in the file.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption>Fractal Heap ID for Managed Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version & Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Length <em>(variable size)</em></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version & Type</p></td> + <td><p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Managed objects have a value of <code>0</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Offset</p></td> + <td><p>This field is the offset of the object in the heap. + This field’s size is the minimum number of bytes + necessary to encode the <em>Maximum Heap Size</em> value + (from the <em>Fractal Heap Header</em>). For example, if the + value of the <em>Maximum Heap Size</em> is less than 256 bytes, + this field is 1 byte in length, a <em>Maximum Heap Size</em> + of 256-65535 bytes uses a 2 byte length, and so on.</p></td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This field is the length of the object in the heap. It + is determined by taking the minimum value of <em>Maximum + Direct Block Size</em> and <em>Maximum Size of Managed + Objects</em> in the <em>Fractal Heap Header</em>. Again, + the minimum number of bytes needed to encode that value is + used for the size of this field.</p></td> + </tr> + </table> + </div> + +<br /> +<h3><a name="FreeSpaceManager"> +III.G. Disk Format: Level 1G - Free-space Manager</a></h3> + + <p> + Free-space managers are used to describe space within a heap or + the entire HDF5 file that is not currently used for that heap or + file. + </p> + + <p> + The <em>free-space manager header</em> contains metadata information + about the space being tracked, along with the address of the list + of <em>free space sections</em> which actually describes the free + space. The header records information about free-space sections being + tracked, creation parameters for handling free-space sections of a + client, and section information used to locate the collection of + free-space sections. + </p> + + <p> + The <em>free-space section list</em> stores a collection of + free-space sections that is specific to each <em>client</em> of the + free-space manager. + + For example, the fractal heap is a client of the free space manager + and uses it to track unused space within the heap. There are 4 + types of section records for the fractal heap, each of which has + its own format, listed below. + </p> + + <div align="center"> + <table class="format"> + <caption> + Free-space Manager Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Total Space Tracked<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Total Number of Sections<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Serialized Sections<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Un-Serialized Sections<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Number of Section Classes</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="2">Shrink Percent</td> + <td colspan="2">Expand Percent</td> + </tr> + + <tr> + <td colspan="2">Size of Address Space</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Maximum Section Size <sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Serialized Section List<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Serialized Section List Used<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Allocated Size of Serialized Section List<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="35%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FSHD</code>” is used to + indicate the beginning of the Free-space Manager Header. + This gives file consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This is the version number for the Free-space Manager Header + and this document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>This is the client ID for identifying the user of this + free-space manager: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Fractal heap + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>File + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Total Space Tracked</p></td> + <td> + <p>This is the total amount of free space being tracked, in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Total Number of Sections</p></td> + <td> + <p>This is the total number of free-space sections being tracked. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Serialized Sections</p></td> + <td> + <p>This is the number of serialized free-space sections being + tracked. + </p> + </td> + </tr> + <tr> + <td><p>Number of Un-Serialized Sections</p></td> + <td> + <p>This is the number of un-serialized free-space sections being + managed. Un-serialized sections are created by the free-space + client when the list of sections is read in. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Section Classes</p></td> + <td> + <p>This is the number of section classes handled by this free space + manager for the free-space client. + </p> + </td> + </tr> + + <tr> + <td><p>Shrink Percent</p></td> + <td> + <p>This is the percent of current size to shrink the allocated + serialized free-space section list. + </p> + </td> + </tr> + + <tr> + <td><p>Expand Percent</p></td> + <td> + <p>This is the percent of current size to expand the allocated + serialized free-space section list. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Address Space</p></td> + <td> + <p>This is the size of the address space that free-space sections + are within. This is stored as the log<sub>2</sub> of the + actual value (in other words, the number of bits required + to store values within that address space). + </p> + </td> + </tr> + + <tr> + <td><p>Maximum Section Size</p></td> + <td> + <p>This is the maximum size of a section to be tracked. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Serialized Section List</p></td> + <td> + <p>This is the address where the serialized free-space section + list is stored. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Serialized Section List Used</p></td> + <td> + <p>This is the size of the serialized free-space section + list used (in bytes). This value must be less than + or equal to the <em>allocated size of serialized section + list</em>, below. + </p> + </td> + </tr> + + <tr> + <td><p>Allocated Size of Serialized Section List</p></td> + <td> + <p>This is the size of serialized free-space section list + actually allocated (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the free-space manager header.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <p>The free-space sections being managed are stored in a + <em>free-space section list</em>, described below. The sections + in the free-space section list are stored in the following way: + a count of the number of sections describing a particular size of + free space and the size of the free-space described (in bytes), + followed by a list of section description records; then another + section count and size, followed by the list of section + descriptions for that size; and so on.</p> + + + <div align="center"> + <table class="format"> + <caption> + Free-space Section List + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Free-space Manager Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Number of Section Records in Set #0 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Size of Free-space Section Described in Record Set #0 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #0 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #0 Section Record #0 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #0 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #K-1 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #0 Section Record #K-1 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #K-1 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Number of Section Records in Set #1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Size of Free-space Section Described in Record Set #1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #0 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #1 Section Record #0 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #0 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #K-1 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #1 Section Record #K-1 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #K-1 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><strong>...</strong></td> + </tr> + + <tr> + <td colspan="4"><strong>...</strong></td> + </tr> + + <tr> + <td colspan="4">Number of Section Records in Set #N-1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Size of Free-space Section Described in Record Set #N-1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #0 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #N-1 Section Record #0 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #0 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #K-1 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #N-1 Section Record #K-1 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #K-1 Data <em>(variable size)</td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="35%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FSSE</code>” is used to + indicate the beginning of the Free-space Section Information. + This gives file consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This is the version number for the Free-space Section List + and this document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Free-space Manager Header Address</p></td> + <td> + <p>This is the address of the <em>Free-space Manager Header</em>. + This field is principally used for file + integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Section Records for Set #N</p></td> + <td> + <p>This is the number of free-space section records for set #N. + The length of this field is the minimum number of bytes needed + to store the <em>number of serialized sections</em> (from the + <em>free-space manager header</em>). + </p> + + <p> + The number of sets of free-space section records is + determined by the <em>size of serialized section list</em> in + the <em>free-space manager header</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Section Size for Record Set #N</p></td> + <td> + <p>This is the size (in bytes) of the free-space section described + for <em>all</em> the section records in set #N. + </p> + + <p> + The length of this field is the minimum number of bytes needed + to store the <em>maximum section size</em> (from the + <em>free-space manager header</em>). + </p> + </td> + </tr> + + <tr> + <td><p>Record Set #N Section #K Offset</p></td> + <td> + <p>This is the offset (in bytes) of the free-space section within + the client for the free-space manager. + </p> + + <p> + The length of this field is the minimum number of bytes needed + to store the <em>size of address space</em> (from the + <em>free-space manager header</em>). + </p> + </td> + </tr> + + <tr> + <td><p>Record Set #N Section #K Type</p></td> + <td> + <p>This is the type of the section record, used to decode the + <em>record set #N section #K data</em> information. The defined + record type for <em>file</em> client is: + + <table class="list"> + <tr> + <th width="20%" align="center">Type</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>File’s section (a range of actual bytes in file) + </td> + </tr> + <tr> + <td align="center"><code>1+</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + <p>The defined record types for a <em>fractal heap</em> client are: + + <table class="list"> + <tr> + <th width="20%" align="center">Type</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Fractal heap “single” section + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Fractal heap “first row” section + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Fractal heap “normal row” section + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Fractal heap “indirect” section + </td> + </tr> + + <tr> + <td align="center"><code>4+</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Record Set #N Section #K Data</p></td> + <td> + <p>This is the section-type specific information for each record + in the record set, described below. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the <em>Free-space Section List</em>. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <p> + The section-type specific data for each free-space section record is + described below: + </p> + + <div align="center"> + <table class="format"> + <caption> + File’s Section Data Record + </caption> + + <tr> + <td colspan="4"><em>No additional record data stored</em></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Fractal Heap “Single” Section Data Record + </caption> + + <tr> + <td colspan="4"><em>No additional record data stored</em></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Fractal Heap “First Row” Section Data Record + </caption> + + <tr> + <td colspan="4"><em>Same format as “indirect” section data</em></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Fractal Heap “Normal Row” Section Data Record + </caption> + + <tr> + <td colspan="4"><em>No additional record data stored</em></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Fractal Heap “Indirect” Section Data Record + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Fractal Heap Indirect Block Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="2">Block Start Row</td> + <td colspan="2">Block Start Column</td> + </tr> + + <tr> + <td colspan="2">Number of Blocks</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Fractal Heap Block Offset</p></td> + <td> + <p>The offset of the indirect block in the fractal heap’s address + space containing the empty blocks. + </p> + <p> + The number of bytes used to encode this field is the minimum + number of bytes needed to encode values for the <em>Maximum + Heap Size</em> (in the fractal heap’s header). + </p> + </td> + </tr> + + <tr> + <td><p>Block Start Row</p></td> + <td> + <p>This is the row that the empty blocks start in. + </p> + </td> + </tr> + + <tr> + <td><p>Block Start Column</p></td> + <td> + <p>This is the column that the empty blocks start in. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Blocks</p></td> + <td> + <p>This is the number of empty blocks covered by the section. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h3><a name="SOHMTable"> +III.H. Disk Format: Level 1H - Shared Object Header Message Table</a></h3> + + <p> + The <em>shared object header message table</em> is used to locate + object + header messages that are shared between two or more object headers + in the file. Shared object header messages are stored and indexed + in the file in one of two ways: indexed sequentially in a + <em>shared header message list</em> or indexed with a v2 B-tree. + The shared messages themselves are either stored in a fractal + heap (when two or more objects share the message), or remain in an + object’s header (when only one object uses the message currently, + but the message can be shared in the future). + </p> + + <p> + The <em>shared object header message table</em> + contains a list of shared message index headers. Each index header + records information about the version of the index format, the index + storage type, flags for the message types indexed, the number of + messages in the index, the address where the index resides, + and the fractal heap address if shared messages are stored there. + </p> + + <p> + Each index can be either a list or a v2 B-tree and may transition + between those two forms as the number of messages in the index + varies. Each shared message record contains information used to + locate the shared message from either a fractal heap or an object + header. The types of messages that can be shared are: <em>Dataspace, + Datatype, Fill Value, Filter Pipeline and Attribute</em>. + </p> + + <p> + The <em>shared object header message table</em> is pointed to + from a <a href="#SOHMTableMessage">shared message table</a> message + in the superblock extension for a file. This message stores the + version of the table format, along with the number of index headers + in the table. + </p> + + <div align="center"> + <table class="format"> + <caption> + Shared Object Header Message Table + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version for index #0</td> + <td>Index Type for index #0</td> + <td colspan="2">Message Type Flags for index #0</td> + </tr> + + <tr> + <td colspan="4">Minimum Message Size for index #0</td> + </tr> + + <tr> + <td colspan="2">List Cutoff for index #0</td> + <td colspan="2">v2 B-tree Cutoff for index #0</td> + </tr> + + <tr> + <td colspan="2">Number of Messages for index #0</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Index Address<sup>O</sup> for index #0<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup> for index #0<br /><br /></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td>Version for index #N-1</td> + <td>Index Type for index #N-1</td> + <td colspan="2">Message Type Flags for index #N-1</td> + </tr> + + <tr> + <td colspan="4">Minimum Message Size for index #N-1</td> + </tr> + + <tr> + <td colspan="2">List Cutoff for index #N-1</td> + <td colspan="2">v2 B-tree Cutoff for index #N-1</td> + </tr> + + <tr> + <td colspan="2">Number of Messages for index #N-1</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Index Address<sup>O</sup> for index #N-1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup> for index #N-1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="35%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>SMTB</code>” is used to + indicate the beginning of the Shared Object Header Message table. + This gives file consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version for index #N</p></td> + <td> + <p>This is the version number for the list of shared object header message + indexes and this document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Index Type for index #N</p></td> + <td> + <p>The type of index can be an unsorted list or a v2 B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Message Type Flags for index #N</p></td> + <td> + <p>This field indicates the type of messages tracked in the index, + as follows: + <table class="list"> + <tr> + <th width="20%" align="center">Bits</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the index tracks <em>Dataspace Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the message tracks <em>Datatype Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>If set, the message tracks <em>Fill Value Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>If set, the message tracks <em>Filter Pipeline Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>If set, the message tracks <em>Attribute Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>5-15</code></td> + <td>Reserved (zero). + </td> + </tr> + </table></p> + + + <p> + An index can track more than one type of message, but each type + of message can only by in one index. + </p> + </td> + </tr> + + <tr> + <td><p>Minimum Message Size for index #N</p></td> + <td> + <p>This is the message size sharing threshold for the index. + If the encoded size of the message is less than this value, the + message is not shared. + </p> + </td> + </tr> + + <tr> + <td><p>List Cutoff for index #N</p></td> + <td> + <p>This is the cutoff value for the indexing of messages to + switch from a list to a v2 B-tree. If the number of messages + is greater than this value, the index should be a v2 B-tree. + </p> + </td> + </tr> + <tr> + <td><p>v2 B-tree Cutoff for index #N</p></td> + <td> + <p>This is is the cutoff value for the indexing of messages to + switch from a v2 B-tree back to a list. If the number of + messages is less than this value, the index should be a list. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Messages for index #N</p></td> + <td> + <p>The number of shared messages being tracked for the index. + </p> + </td> + </tr> + + <tr> + <td><p>Index Address for index #N</p></td> + <td> + <p>This field is the address of the list or v2 B-tree where the + index nodes reside. + </p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap Address for index #N</p></td> + <td> + <p>This field is the address of the fractal heap if shared messages + are stored there. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the table.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <p> + Shared messages are indexed either with a <em>shared message record + list</em>, described below, or using a v2 B-tree (using record type 7). + The number of records in the <em>shared message record list</em> is + determined in the index’s entry in the <em>shared object header message + table</em>. + </p> + + <div align="center"> + <table class="format"> + <caption> + Shared Message Record List + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td colspan="4">Shared Message Record #0</td> + </tr> + + <tr> + <td colspan="4">Shared Message Record #1</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Shared Message Record #N-1</td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>SMLI</code>” is used to + indicate the beginning of a list of index nodes. + This gives file consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Shared Message Record #N</p></td> + <td> + <p>The record for locating the shared message, either in the + fractal heap for the index, or an object header (see format for + <em>index nodes</em> below). + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the list. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <p> + The record for each shared message in an index is stored in one of the + following forms: + </p> + + <div align="center"> + <table class="format"> + <caption> + Shared Message Record, for messages stored in a fractal heap + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Hash Value</td> + </tr> + + <tr> + <td colspan="4">Reference Count</td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap ID<br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This has a value of 0 indicating that the message is stored in + the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Hash Value</p></td> + <td> + <p>This is the hash value for the message. + </p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td> + <p>This is the number of times the message is used in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap ID</p></td> + <td> + <p>This is an 8-byte fractal heap ID for the message as stored in + the fractal heap for the index. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Shared Message Record, for messages stored in an object header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Hash Value</td> + </tr> + + <tr> + <td>Reserved</td> + <td>Message Type</td> + <td colspan="2">Creation Index</td> + </tr> + + <tr> + <td colspan="4"><br />Object Header Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This has a value of 1 indicating that the message is stored in + an object header. + </p> + </td> + </tr> + + <tr> + <td><p>Hash Value</p></td> + <td> + <p>This is the hash value for the message. + </p> + </td> + </tr> + + <tr> + <td><p>Message Type</p></td> + <td> + <p>This is the message type in the object header. + </p> + </td> + </tr> + + <tr> + <td><p>Creation Index</p></td> + <td> + <p>This is the creation index of the message within the object + header. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Address</p></td> + <td> + <p>This is the address of the object header where the message is + located. + </p> + </td> + </tr> + </table> + </div> + + + +<br /> +<br /> +<hr /> +<h2><a name="DataObject"> +IV. Disk Format: Level 2 - Data Objects </a></h2> + + <p>Data objects contain the “real” user-visible information in the file. + These objects compose the scientific data and other information which + are generally thought of as “data” by the end-user. All the + other information in the file is provided as a framework for + storing and accessing these data objects. + </p> + + <p>A data object is composed of header and data + information. The header information contains the information + needed to interpret the data information for the object as + well as additional “metadata” or pointers to additional + “metadata” used to describe or annotate each object. + </p> + +<br /> +<h3><a name="ObjectHeader"> +IV.A. Disk Format: Level 2A - Data Object Headers</a></h3> + + <p>The header information of an object is designed to encompass + all of the information about an object, except for the data itself. + This information includes the dataspace, the datatype, information + about how the data is stored on disk (in external files, compressed, + broken up in blocks, and so on), as well as other information used + by the library to speed up access to the data objects or maintain + a file’s integrity. Information stored by user applications + as attributes is also stored in the object’s header. The header + of each object is not necessarily located immediately prior to the + object’s data in the file and in fact may be located in any + position in the file. The order of the messages in an object header + is not significant.</p> + + <p>Object headers are composed of a prefix and a set of messages. The + prefix contains the information needed to interpret the messages and + a small amount of metadata about the object, and the messages contain + the majority of the metadata about the object. + </p> + +<br /> +<h3><a name="ObjectHeaderPrefix"> +IV.A.1. Disk Format: Level 2A1 - Data Object Header Prefix</a></h3> + +<br /> +<h4><a name="V1ObjectHeaderPrefix"> +IV.A.1.a. Version 1 Data Object Header Prefix</a></h4> + + <p>Header messages are aligned on 8-byte boundaries for version 1 + object headers. + </p> + + <div align="center"> + <table class="format"> + <caption> + Version 1 Object Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Reserved (zero)</td> + <td colspan="2">Total Number of Header Messages</td> + </tr> + + <tr> + <td colspan="4">Object Reference Count</td> + </tr> + + <tr> + <td colspan="4">Object Header Size</td> + </tr> + + <tr> + <td colspan="2">Header Message Type #1</td> + <td colspan="2">Size of Header Message Data #1</td> + </tr> + + <tr> + <td>Header Message #1 Flags</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td colspan="2">Header Message Type #n</td> + <td colspan="2">Size of Header Message Data #n</td> + </tr> + + <tr> + <td>Header Message #n Flags</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #n<br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This value is used to determine the format of the + information in the object header. When the format of the + object header is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted. This + is version one (1) (there was no version zero (0)) of the + object header. + </p> + </td> + </tr> + + <tr> + <td><p>Total Number of Header Messages</p></td> + <td> + <p>This value determines the total number of messages listed in + object headers for this object. This value includes the messages + in continuation messages for this object. + </p> + </td> + </tr> + + <tr> + <td><p>Object Reference Count</p></td> + <td> + <p>This value specifies the number of “hard links” to this object + within the current file. References to the object from external + files, “soft links” in this file and object references in this + file are not tracked. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Size</p></td> + <td> + <p>This value specifies the number of bytes of header message data + following this length field that contain object header messages + for this object header. This value does not include the size of + object header continuation blocks for this object elsewhere in the + file. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Type</p></td> + <td> + <p>This value specifies the type of information included in the + following header message data. The message types for + header messages are defined in sections below. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Header Message #n Data</p></td> + <td> + <p>This value specifies the number of bytes of header + message data following the header message type and length + information for the current message. The size includes + padding bytes to make the message a multiple of eight + bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Flags</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the message data is constant. This is used + for messages like the datatype message of a dataset. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the message is <em>shared</em> and stored + in another location than the object header. The Header + Message Data field contains a Shared Message + (described in the <a href="#ObjectHeaderMessages">Data Object Header Messages</a> + section below) + and the Size of Header Message Data field + contains the size of that Shared Message. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>If set, the message should not be shared. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>If set, the HDF5 decoder should fail to open this object + if it does not understand the message’s type and the file + is open with permissions allowing write access to the file. + (Normally, unknown messages can just be ignored by HDF5 + decoders) + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>If set, the HDF5 decoder should set bit 5 of this + message’s flags (in other words, this bit field) + if it does not understand the message’s type + and the object is modified in any way. (Normally, + unknown messages can just be ignored by HDF5 + decoders) + </td> + </tr> + <tr> + <td align="center"><code>5</code></td> + <td>If set, this object was modified by software that did not + understand this message. + (Normally, unknown messages should just be ignored by HDF5 + decoders) (Can be used to invalidate an index or a similar + feature) + </td> + </tr> + <tr> + <td align="center"><code>6</code></td> + <td>If set, this message is shareable. + </td> + </tr> + <tr> + <td align="center"><code>7</code></td> + <td>If set, the HDF5 decoder should always fail to open this + object if it does not understand the message’s type (whether + it is open for read-only or read-write access). (Normally, + unknown messages can just be ignored by HDF5 decoders) + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Header Message #n Data</p></td> + <td> + <p>The format and length of this field is determined by the + header message type and size respectively. Some header + message types do not require any data and this information + can be eliminated by setting the length of the message to + zero. The data is padded with enough zeroes to make the + size a multiple of eight. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="V2ObjectHeaderPrefix"> +IV.A.1.b. Version 2 Data Object Header Prefix</a></h4> + + <p>Note that the “total number of messages” field has been dropped from + the data object header prefix in this version. The number of messages + in the data object header is just determined by the messages encountered + in all the object header blocks.</p> + + <p>Note also that the fields and messages in this version of data object + headers have <em>no</em> alignment or padding bytes inserted - they are + stored packed together.</p> + + <div align="center"> + <table class="format"> + <caption> + Version 2 Object Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Access time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Modification Time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Change Time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Birth Time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="2">Maximum # of compact attributes <em>(optional)</em></td> + <td colspan="2">Minimum # of dense attributes <em>(optional)</em></td> + </tr> + + <tr> + <td>Size of Chunk #0 <em>(variable size)</em></td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td>Header Message Type #1</td> + <td colspan="2">Size of Header Message Data #1</td> + <td>Header Message #1 Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #1 Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td>Header Message Type #n</td> + <td colspan="2">Size of Header Message Data #n</td> + <td>Header Message #n Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #n Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #n<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Gap <em>(optional, variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>OHDR</code>” + is used to indicate the + beginning of an object header. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This field has a value of 2 indicating version 2 of the object header. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is a bit field indicating additional information + about the object header. + <table class="list"> + <tr> + <th width="20%" align="center">Bit(s)</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0-1</code></td> + <td>This two bit field determines the size of the + <em>Size of Chunk #0</em> field. The values are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>The <em>Size of Chunk #0</em> field is 1 byte. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The <em>Size of Chunk #0</em> field is 2 bytes. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>The <em>Size of Chunk #0</em> field is 4 bytes. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>The <em>Size of Chunk #0</em> field is 8 bytes. + </td> + </tr> + </table></p> + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>If set, attribute creation order is tracked.</td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>If set, attribute creation order is indexed.</td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>If set, non-default attribute storage phase change + values are stored.</td> + </tr> + <tr> + <td align="center"><code>5</code></td> + <td>If set, access, modification, change and birth times + are stored.</td> + </tr> + <tr> + <td align="center"><code>6-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Access Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after the + UNIX epoch when the object’s raw data was last accessed + (in other words, read or written). + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Modification Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after + the UNIX epoch when the object’s raw data was last + modified (in other words, written). + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Change Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after the + UNIX epoch when the object’s metadata was last changed. + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Birth Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after the + UNIX epoch when the object was created. + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Maximum # of compact attributes</p></td> + <td> + <p>This is the maximum number of attributes to store in the compact + format before switching to the indexed format. + </p> + <p>This field is present if bit 4 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Minimum # of dense attributes</p></td> + <td> + <p>This is the minimum number of attributes to store in the indexed + format before switching to the compact format. + </p> + <p>This field is present if bit 4 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Chunk #0</p></td> + <td> + <p> + This unsigned value specifies the number of bytes of header + message data following this field that contain object header + information. + </p> + <p> + This value does not include the size of object header + continuation blocks for this object elsewhere in the file. + </p> + <p> + The length of this field varies depending on bits 0 and 1 of + the <em>flags</em> field. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Type</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Header Message #n Data</p></td> + <td> + <p>This value specifies the number of bytes of header + message data following the header message type and length + information for the current message. The size of messages + in this version does <em>not</em> include any padding bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Flags</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Creation Order</p></td> + <td> + <p>This field stores the order that a message of a given type + was created in. + </p> + <p>This field is present if bit 2 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Data</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p> + </td> + </tr> + + <tr> + <td><p>Gap</p></td> + <td> + <p>A gap in an object header chunk is inferred by the end of the + messages for the chunk before the beginning of the chunk’s + checksum. Gaps are always smaller than the size of an + object header message prefix (message type + message size + + message flags). + </p> + <p>Gaps are formed when a message (typically an attribute message) + in an earlier chunk is deleted and a message from a later + chunk that does not quite fit into the free space is moved + into the earlier chunk. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the object header chunk. + </p> + </td> + </tr> + </table> + </div> + + <p>The header message types and the message data associated with + them compose the critical “metadata” about each object. Some + header messages are required for each object while others are + optional. Some optional header messages may also be repeated + several times in the header itself, the requirements and number + of times allowed in the header will be noted in each header + message description below. + </p> + + +<br /> +<h3><a name="ObjectHeaderMessages"> +IV.A.2. Disk Format: Level 2A2 - Data Object Header Messages</a></h3> + + <p>Data object header messages are small pieces of metadata that are + stored in the data object header for each object in an HDF5 file. + Data object header messages provide the metadata required to describe + an object and its contents, as well as optional pieces of metadata + that annotate the meaning or purpose of the object. + </p> + + <p>Data object header messages are either stored directly in the data + object header for the object or are shared between multiple objects + in the file. When a message is shared, a flag in the <em>Message Flags</em> + indicates that the actual <em>Message Data</em> + portion of that message is stored in another location (such as another + data object header, or a heap in the file) and the <em>Message Data</em> + field contains the information needed to locate the actual information + for the message. + </p> + + <p> + The format of shared message data is described here:</p> + + <div align="center"> + <table class="format"> + <caption> + Shared Message (Version 1) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number is used when there are changes in the format + of a shared object message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by the library before version 1.6.1. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td><p>The type of shared message location: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Message stored in another object’s header (a <em>committed</em> + message). + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the object header + containing the message to be shared.</p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Shared Message (Version 2) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number is used when there are changes in the format + of a shared object message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Used by the library of version 1.6.1 and after. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td><p>The type of shared message location: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Message stored in another object’s header (a <em>committed</em> + message). + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the object header + containing the message to be shared.</p></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Shared Message (Version 3) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Location <em>(variable size)</em></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number indicates changes in the format of shared + object message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Used by the library of version 1.8 and after. In this + version, the <em>Type</em> field can indicate that + the message is stored in the fractal heap. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td><p>The type of shared message location: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Message is not shared and is not shareable. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Message stored in file’s <em>shared object header message</em> + heap (a <em>shared</em> message). + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Message stored in another object’s header (a <em>committed</em> + message). + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Message stored is not shared, but is sharable. + </td> + </tr> + + </table></p> + </td> + </tr> + + <tr> + <td><p>Location</p></td> + <td><p>This field contains either a <em>Size of Offsets</em>-bytes + address of the object header + containing the message to be shared, or an 8-byte fractal heap ID + for the message in the file’s <em>shared object header message</em> + heap. + </p> + </td> + </tr> + </table> + </div> + + + <p>The following is a list of currently defined header messages: + </p> + +<br /> +<h4><a name="NILMessage">IV.A.2.a. The NIL Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> NIL</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0000</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The NIL message is used to indicate a message which is to be + ignored when reading the header messages for a data object. + [Possibly one which has been deleted for some reason.] + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> Unspecified</td></tr> + </table></center> + <!-- end msgdesc table --> + + +<br /> +<h4><a name="DataspaceMessage">IV.A.2.b. The Dataspace Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Dataspace</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0001</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies according to the number of + dimensions, as described in the following table.</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for dataset objects; + may not be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The dataspace message describes the number of dimensions (in + other words, “rank”) and size of each dimension that + the data object has. This message is only used for datasets which + have a simple, rectilinear, array-like layout; datasets requiring + a more complex layout are not yet supported. + </td> + </tr> + + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Dataspace Message - Version 1 + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Flags</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan="4">Reserved</td> + </tr> + + <tr> + <td colspan="4"><br />Dimension #1 Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #1 Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Permutation Index #1<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Permutation Index #n<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This value is used to determine the format of the + Dataspace Message. When the format of the + information in the message is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted. This + document describes version one (1) (there was no version + zero (0)). + </p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the data + object has. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is used to store flags to indicate the + presence of parts of this message. Bit 0 (the least + significant bit) is used to indicate that maximum + dimensions are present. Bit 1 is used to indicate that + permutation indices are present. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the current size of the dimension of the + data as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Maximum Size</p></td> + <td> + <p>This value is the maximum size of the dimension of the + data as stored in the file. This value may be the special + “<a href="#UnlimitedDim">unlimited</a>” size which indicates + that the data may expand along this dimension indefinitely. + If these values are not stored, the maximum size of each + dimension is assumed to be the dimension’s current size. + </p> + </td> + </tr> + + <tr> + <td><p>Permutation Index #n</p></td> + <td> + <p>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. If these values are + not stored, the first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + </table> + </div> + + + + <br /> + <p>Version 2 of the dataspace message dropped the optional + permutation index value support, as it was never implemented in the + HDF5 Library:</p> + + <div align="center"> + <table class="format"> + <caption> + Dataspace Message - Version 2 + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Flags</td> + <td>Type</td> + </tr> + + <tr> + <td colspan="4"><br />Dimension #1 Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #1 Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This value is used to determine the format of the + Dataspace Message. This field should be ‘2’ for version 2 + format messages. + </p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the data object has. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is used to store flags to indicate the + presence of parts of this message. Bit 0 (the least + significant bit) is used to indicate that maximum + dimensions are present. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field indicates the type of the dataspace: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>A <em>scalar</em> dataspace; in other words, + a dataspace with a single, dimensionless element. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>A <em>simple</em> dataspace; in other words, + a dataspace with a rank > 0 and an appropriate # of + dimensions. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>A <em>null</em> dataspace; in other words, + a dataspace with no elements. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the current size of the dimension of the + data as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Maximum Size</p></td> + <td> + <p>This value is the maximum size of the dimension of the + data as stored in the file. This value may be the special + “<a href="#UnlimitedDim">unlimited</a>” size which indicates + that the data may expand along this dimension indefinitely. + If these values are not stored, the maximum size of each + dimension is assumed to be the dimension’s current size. + </p> + </td> + </tr> + + </table> + </div> + + + +<!-- +<br /> +<h4><a name="DataSpaceMessage">Header Message Name: Complex Dataspace (Fiber Bundle?)</a></h4> + + <!-- start msgdesc table -- + <center> + <table class="msgdesc"> + <p><b>Header Message Name: ???????</b></td></tr> + <b>Header Message Type: </b>0x0002<br /> + <b>Length:</b> Varies</td></tr> + + <b>Status:</b> One of the <em>Simple Dataspace</em> or + <em>Complex Dataspace</em> messages is required (but not both) and may + not be repeated.<br /> <b>Description:</b> The + <em>Dataspace</em> message describes space that the dataset is + mapped onto in a more comprehensive way than the <em>Simple + Dimensionality</em> message is capable of handling. The + dataspace of a dataset encompasses the type of coordinate system + used to locate the dataset’s elements as well as the structure and + regularity of the coordinate system. The dataspace also + describes the number of dimensions which the dataset inhabits as + well as a possible higher dimensional space in which the dataset + is located within. + + <br /> + <p><b>Format of Data:</b></p> + + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Message Layout</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4">Mesh Type</td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimensionality</td> + </tr> + </table> + </center> + + <br /> + <dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Mesh Type: (unsigned 32-bit integer) + <dd>This value indicates whether the grid is + polar/spherical/cartesion, + structured/unstructured and regular/irregular. <br /> + The mesh type value is broken up as follows: <br /> + + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Mesh-type Layout</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="1">Mesh Embedding</td> + <td colspan="1">Coordinate System</td> + <td colspan="1">Structure</td> + <td colspan="1">Regularity</td> + </tr> + </table> + </center> + The following are the definitions of mesh-type bytes: + <dl> + <dt>Mesh Embedding + <dd>This value indicates whether the dataset dataspace + is located within + another dataspace or not: + <dl> <dl> + <dt><STANDALONE> + <dd>The dataset mesh is self-contained and is not + embedded in another mesh. + <dt><EMBEDDED> + <dd>The dataset’s dataspace is located within + another dataspace, as + described in information below. + </dl> </dl> + <dt>Coordinate System + <dd>This value defines the type of coordinate system + used for the mesh: + <dl> <dl> + <dt><POLAR> + <dd>The last two dimensions are in polar + coordinates, higher dimensions are + cartesian. + <dt><SPHERICAL> + <dd>The last three dimensions are in spherical + coordinates, higher dimensions + are cartesian. + <dt><CARTESIAN> + <dd>All dimensions are in cartesian coordinates. + </dl> </dl> + <dt>Structure + <dd>This value defines the locations of the grid-points + on the axes: + <dl> <dl> + <dt><STRUCTURED> + <dd>All grid-points are on integral, sequential + locations, starting from 0. + <dt><UNSTRUCTURED> + <dd>Grid-points locations in each dimension are + explicitly defined and + may be of any numeric datatype. + </dl> </dl> + <dt>Regularity + <dd>This value defines the locations of the dataset + points on the grid: + <dl> <dl> + <dt><REGULAR> + <dd>All dataset elements are located at the + grid-points defined. + <dt><IRREGULAR> + <dd>Each dataset element has a particular + grid-location defined. + </dl> </dl> + </dl> + <p>The following grid combinations are currently allowed:</p> + <dl> <dl> + <dt><POLAR-STRUCTURED-REGULAR> + <dt><SPHERICAL-STRUCTURED-REGULAR> + <dt><CARTESIAN-STRUCTURED-REGULAR> + <dt><POLAR-UNSTRUCTURED-REGULAR> + <dt><SPHERICAL-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-IRREGULAR> + </dl> </dl> + All of the above grid types can be embedded within another + dataspace. + <br /> <br /> + <dt>Logical Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions that the dataset occupies. + + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Embedded Dimensionality Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4">Embedded Dimensionality</td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Dimension Size #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Dimension Size #n</td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Origin Location #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Origin Location #n</td> + </tr> + </table> + </center> + + <dt>Embedded Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions of the space the + dataset is located within: in other words, a planar dataset + located within a 3-D space, a 3-D dataset + which is a subset of another 3-D space, and so on. + <dt>Embedded Dimension Size: (unsigned 32-bit integer) + <dd>These values are the sizes of the dimensions of the + embedded dataspace + that the dataset is located within. + <dt>Embedded Origin Location: (unsigned 32-bit integer) + <dd>These values comprise the location of the dataset’s + origin within the embedded dataspace. + </dl> + </dl> + [Comment: need some way to handle different orientations of the + dataset dataspace + within the embedded dataspace]<br /> + + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Structured/Regular Grid Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4">Logical Dimension Size #1</td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimension Maximum #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimension Size #n</td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimension Maximum #n</td> + </tr> + </table> + </center> + + <br /> + <dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Logical Dimension Size #n: (unsigned 32-bit integer) + <dd>This value is the current size of the dimension of the + data as stored in + the file. The first dimension stored in the list of + dimensions is the slowest + changing dimension and the last dimension stored is the + fastest changing + dimension. + <dt>Logical Dimension Maximum #n: (unsigned 32-bit integer) + <dd>This value is the maximum size of the dimension of the + data as stored in + the file. This value may be the special value + <UNLIMITED> which + indicates that the data may expand along this dimension + indefinitely. + </dl> + </dl> + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Structured/Irregular Grid Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4"># of Grid Points in Dimension #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4"># of Grid Points in Dimension #n</td> + </tr> + <tr align="center"> + <td colspan="4">Datatype of Grid Point Locations</td> + </tr> + <tr align="center"> + <td colspan="4">Location of Grid Points in Dimension #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Location of Grid Points in Dimension #n</td> + </tr> + </table> + </center> + + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Unstructured Grid Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4"># of Grid Points</td> + </tr> + <tr align="center"> + <td colspan="4">Datatype of Grid Point Locations</td> + </tr> + <tr align="center"> + <td colspan="4">Grid Point Locations<br />.<br />.<br /></td> + </tr> + </table> + </center> +--> + +<br /> +<h4><a name="LinkInfoMessage">IV.A.2.c. The Link Info Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Link Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x002 </td></tr> + <tr><td colspan="2"><b>Length:</b> Varies </td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated. </td></tr> + <tr><td><b>Description:</b></td> + <td>The link info message tracks variable information about the + current state of the links for a “new style” + group’s behavior. Variable information will be stored in + this message and constant information will be stored in the + <a href="#GroupInfoMessage">Group Info</a> message. + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Link Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Maximum Creation Index <em>(8 bytes, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of v2 B-tree for Name Index<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of v2 B-tree for Creation Order Index<sup>O</sup> <em>(optional)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This field determines various optional aspects of the link + info message: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, creation order for the links is tracked. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, creation order for the links is indexed. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Maximum Creation Index</p></td> + <td><p>This 64-bit value is the maximum creation order index value + stored for a link in this group.</p> + <p>This field is present if bit 0 of <em>flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap Address</p></td> + <td> + <p> + This is the address of the fractal heap to store dense links. + Each link stored in the fractal heap is stored as a + <a href="#LinkMessage">Link Message</a>. + </p> + <p> + If there are no links in the group, or the group’s links + are stored “compactly” (as object header messages), this + value will be the <a href="#UndefinedAddress">undefined + address</a>. + </p> + </td> + </tr> + + <tr> + <td><p>Address of v2 B-tree for Name Index</p></td> + <td><p>This is the address of the version 2 B-tree to index names of links.</p> + <p>If there are no links in the group, or the group’s links + are stored “compactly” (as object header messages), this + value will be the <a href="#UndefinedAddress">undefined + address</a>. + </p> + </td> + </tr> + + <tr> + <td><p>Address of v2 B-tree for Creation Order Index</p></td> + <td><p>This is the address of the version 2 B-tree to index creation order of links.</p> + <p>If there are no links in the group, or the group’s links + are stored “compactly” (as object header messages), this + value will be the <a href="#UndefinedAddress">undefined + address</a>. + </p> + <p>This field exists if bit 1 of <em>flags</em> is set.</p> + </td> + </tr> + + </table> + </div> + + +<br /> +<h4><a name="DatatypeMessage">IV.A.2.d. The Datatype Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Datatype</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0003 + </td></tr> + <tr><td colspan="2"><b>Length:</b> Variable</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for dataset or committed + datatype (formerly named datatype) objects; may not be repeated. + </td></tr> + <tr><td><b>Description:</b></td> + <td><p>The datatype message defines the datatype for each element + of a dataset or a common datatype for sharing between multiple + datasets. A datatype can describe an atomic type like a fixed- + or floating-point type or more complex types like a C struct + (compound datatype), array (array datatype) or C++ vector + (variable-length datatype).</p> + <p>Datatype messages that are part of a dataset object do not + describe how elements are related to one another; the dataspace + message is used for that purpose. Datatype messages that are part of + a committed datatype (formerly named datatype) message describe + a common datatype that can be shared by multiple datasets in the + file.</p> + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Datatype Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Class and Version</td> + <td>Class Bit Field, Bits 0-7</td> + <td>Class Bit Field, Bits 8-15</td> + <td>Class Bit Field, Bits 16-23</td> + </tr> + + <tr> + <td colspan="4">Size</td> + </tr> + + <tr> + <td colspan="4"><br /><br />Properties<br /><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Class and Version</p></td> + <td> + <p>The version of the datatype message and the datatype’s class + information are packed together in this field. The version + number is packed in the top 4 bits of the field and the class + is contained in the bottom 4 bits. + </p> + <p>The version number information is used for changes in the + format of the datatype message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Used by early versions of the library to encode + compound datatypes with explicit array fields. + See the compound datatype description below for + further details. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Used when an array datatype needs to be encoded. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Used when a VAX byte-ordered type needs to be + encoded. Packs various other datatype classes more + efficiently also. + </td> + </tr> + </table></p> + + <p>The class of the datatype determines the format for the class + bit field and properties portion of the datatype message, which + are described below. The + following classes are currently defined: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Fixed-Point</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Floating-Point</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Time</td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>String</td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>Bit field</td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td>Opaque</td> + </tr> + + <tr> + <td align="center"><code>6</code></td> + <td>Compound</td> + </tr> + + <tr> + <td align="center"><code>7</code></td> + <td>Reference</td> + </tr> + + <tr> + <td align="center"><code>8</code></td> + <td>Enumerated</td> + </tr> + + <tr> + <td align="center"><code>9</code></td> + <td>Variable-Length</td> + </tr> + + <tr> + <td align="center"><code>10</code></td> + <td>Array</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Class Bit Fields</p></td> + <td> + <p>The information in these bit fields is specific to each datatype + class and is described below. All bits not defined for a + datatype class are set to zero. + </p> + </td> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>The size of a datatype element in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Properties</p></td> + <td> + <p>This variable-sized sequence of bytes encodes information + specific to each datatype class and is described for each class + below. If there is no property information specified for a + datatype class, the size of this field is zero bytes. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <p>Class specific information for Fixed-Point Numbers (Class 0):</p> + + <div align="center"> + <table class="desc"> + <caption> + Fixed-point Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0</p></td> + <td><p><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</p></td> + </tr> + + <tr> + <td><p>1, 2</p></td> + <td><p><b>Padding type.</b> Bit 1 is the lo_pad bit and bit 2 + is the hi_pad bit. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</p></td> + </tr> + + <tr> + <td><p>3</p></td> + <td><p><b>Signed.</b> If this bit is set then the fixed-point + number is in 2’s complement form.</p></td> + </tr> + + <tr> + <td><p>4-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Fixed-Point Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Offset</td> + <td colspan="2">Bit Precision</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Offset</p></td> + <td> + <p>The bit offset of the first significant bit of the fixed-point + value within the datatype. The bit offset specifies the number + of bits “to the right of” the value (which are set to the + lo_pad bit value). + </p> + </td> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the fixed-point value + within the datatype. This value, combined with the datatype + element’s size and the Bit Offset field specifies the number + of bits “to the left of” the value (which are set to the + hi_pad bit value). + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <p>Class specific information for Floating-Point Numbers (Class 1):</p> + + <div align="center"> + <table class="desc"> + <caption> + Floating-Point Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0, 6</p></td> + <td><p><b>Byte Order.</b> These two non-contiguous bits specify the + “endianness” of the bytes in the datatype element. + <table class="list"> + <tr> + <th width="10%" align="center">Bit 6</th> + <th width="10%" align="center">Bit 0</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td align="center"><code>0</code></td> + <td>Byte order is little-endian + </td> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td align="center"><code>1</code></td> + <td>Byte order is big-endian + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td align="center"><code>0</code></td> + <td>Reserved + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td align="center"><code>1</code></td> + <td>Byte order is VAX-endian + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>1, 2, 3</p></td> + <td><p><b>Padding type.</b> Bit 1 is the low bits pad type, bit 2 + is the high bits pad type, and bit 3 is the internal bits + pad type. If a datum has unused bits at either end or between + the sign bit, exponent, or mantissa, then the value of bit + 1, 2, or 3 is copied to those locations.</p></td> + </tr> + + <tr> + <td><p>4-5</p></td> + <td><p><b>Mantissa Normalization.</b> This 2-bit bit field specifies + how the most significant bit of the mantissa is managed. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>No normalization + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The most significant bit of the mantissa is always set + (except for 0.0). + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>The most significant bit of the mantissa is not stored, + but is implied to be set. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>7</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + + <tr> + <td><p>8-15</p></td> + <td><p><b>Sign Location.</b> This is the bit position of the sign + bit. Bits are numbered with the least significant bit zero.</p></td> + </tr> + + <tr> + <td><p>16-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Floating-Point Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Offset</td> + <td colspan="2">Bit Precision</td> + </tr> + + <tr> + <td>Exponent Location</td> + <td>Exponent Size</td> + <td>Mantissa Location</td> + <td>Mantissa Size</td> + </tr> + + <tr> + <td colspan="4">Exponent Bias</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Offset</p></td> + <td> + <p>The bit offset of the first significant bit of the floating-point + value within the datatype. The bit offset specifies the number + of bits “to the right of” the value. + </p> + </td> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the floating-point value + within the datatype. + </p> + </td> + </tr> + + <tr> + <td><p>Exponent Location</p></td> + <td> + <p>The bit position of the exponent field. Bits are numbered with + the least significant bit number zero. + </p> + </td> + </tr> + + <tr> + <td><p>Exponent Size</p></td> + <td> + <p>The size of the exponent field in bits. + </p> + </td> + </tr> + + <tr> + <td><p>Mantissa Location</p></td> + <td> + <p>The bit position of the mantissa field. Bits are numbered with + the least significant bit number zero. + </p> + </td> + </tr> + + <tr> + <td><p>Mantissa Size</p></td> + <td> + <p>The size of the mantissa field in bits. + </p> + </td> + </tr> + + <tr> + <td><p>Exponent Bias</p></td> + <td> + <p>The bias of the exponent field. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <p>Class specific information for Time (Class 2):</p> + + + <div align="center"> + <table class="desc"> + <caption> + Time Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0</p></td> + <td><p><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</p></td> + </tr> + + <tr> + <td><p>1-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Time Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Precision</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the time value. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <p>Class specific information for Strings (Class 3):</p> + + + <div align="center"> + <table class="desc"> + <caption> + String Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Padding type.</b> This four-bit value determines the + type of padding to use for the string. The values are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Null Terminate: A zero byte marks the end of the + string and is guaranteed to be present after + converting a long string to a short string. When + converting a short string to a long string the value is + padded with additional null characters as necessary. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Null Pad: Null characters are added to the end of + the value during conversions from short values to long + values but conversion in the opposite direction simply + truncates the value. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Space Pad: Space characters are added to the end of + the value during conversions from short values to long + values but conversion in the opposite direction simply + truncates the value. This is the Fortran + representation of the string. + </td> + </tr> + + <tr> + <td align="center"><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>4-7</p></td> + <td><p><b>Character Set.</b> The character set used to + encode the string. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>8-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <p>There are no properties defined for the string class. + </p> + + + <p>Class specific information for bit fields (Class 4):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bitfield Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0</p></td> + <td><p><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</p></td> + </tr> + + <tr> + <td><p>1, 2</p></td> + <td><p><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2 + is the hi_pad type. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</p></td> + </tr> + + <tr> + <td><p>3-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Bit Field Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Offset</td> + <td colspan="2">Bit Precision</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Offset</p></td> + <td> + <p>The bit offset of the first significant bit of the bit field + within the datatype. The bit offset specifies the number + of bits “to the right of” the value. + </p> + </td> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the bit field + within the datatype. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <p>Class specific information for Opaque (Class 5):</p> + + <div align="center"> + <table class="desc"> + <caption> + Opaque Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-7</p></td> + <td><p>Length of ASCII tag in bytes.</p></td> + </tr> + + <tr> + <td><p>8-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Opaque Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />ASCII Tag<br /> + <br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>ASCII Tag</p></td> + <td> + <p>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <p>Class specific information for Compound (Class 6):</p> + + <div align="center"> + <table class="desc"> + <caption> + Compound Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-15</p></td> + <td><p><b>Number of Members.</b> This field contains the number + of members defined for the compound datatype. The member + definitions are listed in the Properties field of the data + type message.</p></td> + </tr> + + <tr> + <td><p>16-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + + <p>The Properties field of a compound datatype is a list of the + member definitions of the compound datatype. The member + definitions appear one after another with no intervening bytes. + The member types are described with a (recursively) encoded datatype + message.</p> + + <p>Note that the property descriptions are different for different + versions of the datatype version. Additionally note that the version + 0 datatype encoding is deprecated and has been replaced with later + encodings in versions of the HDF5 Library from the 1.4 release + onward.</p> + + + <div align="center"> + <table class="format"> + <caption> + Compound Properties Description for Datatype Version 1 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Byte Offset of Member</td> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Dimension Permutation</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Dimension #1 Size (required)</td> + </tr> + + <tr> + <td colspan="4">Dimension #2 Size (required)</td> + </tr> + + <tr> + <td colspan="4">Dimension #3 Size (required)</td> + </tr> + + <tr> + <td colspan="4">Dimension #4 Size (required)</td> + </tr> + + <tr> + <td colspan="4"><br />Member Type Message<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td> + <p>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Byte Offset of Member</p></td> + <td> + <p>This is the byte offset of the member within the datatype. + </p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>If set to zero, this field indicates a scalar member. If set + to a value greater than zero, this field indicates that the + member is an array of values. For array members, the size of + the array is indicated by the ‘Size of Dimension n’ field in + this message. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension Permutation</p></td> + <td> + <p>This field was intended to allow an array field to have + its dimensions permuted, but this was never implemented. + This field should always be set to zero. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This field is the size of a dimension of the array field as + stored in the file. The first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Member Type Message</p></td> + <td> + <p>This field is a datatype message describing the datatype of + the member. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Compound Properties Description for Datatype Version 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Byte Offset of Member</td> + </tr> + + <tr> + <td colspan="4"><br />Member Type Message<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td> + <p>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Byte Offset of Member</p></td> + <td> + <p>This is the byte offset of the member within the datatype. + </p> + </td> + </tr> + + <tr> + <td><p>Member Type Message</p></td> + <td> + <p>This field is a datatype message describing the datatype of + the member. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Compound Properties Description for Datatype Version 3 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Byte Offset of Member <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Member Type Message<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>This NUL-terminated string provides a description for the + opaque type. It is <em>not</em> NUL-padded to a multiple of 8 + bytes.</p></td> + </tr> + + <tr> + <td><p>Byte Offset of Member</p></td> + <td><p>This is the byte offset of the member within the datatype. + The field size is the minimum number of bytes necessary, + based on the size of the datatype element. For example, a + datatype element size of less than 256 bytes uses a 1 byte + length, a datatype element size of 256-65535 bytes uses a + 2 byte length, and so on.</p></td> + </tr> + + <tr> + <td><p>Member Type Message</p></td> + <td><p>This field is a datatype message describing the datatype of + the member.</p></td> + </tr> + + </table> + </div> + + + <br /> + <p>Class specific information for Reference (Class 7):</p> + + <div align="center"> + <table class="desc"> + <caption> + Reference Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Type.</b> This four-bit value contains the type of reference + described. The values defined are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Object Reference: A reference to another object in this + HDF5 file. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Dataset Region Reference: A reference to a region within + a dataset in this HDF5 file. + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>4-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <p>There are no properties defined for the reference class. + </p> + + + <br /> + <p>Class specific information for Enumeration (Class 8):</p> + + <div align="center"> + <table class="desc"> + <caption> + Enumeration Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-15</p></td> + <td><p><b>Number of Members.</b> The number of name/value + pairs defined for the enumeration type.</p></td> + </tr> + + <tr> + <td><p>16-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Enumeration Property Description for Datatype Versions 1 & 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Names<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Values<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each enumeration type is based on some parent type, usually an + integer. The information for that parent type is described + recursively by this field. + </p> + </td> + </tr> + + <tr> + <td><p>Names</p></td> + <td> + <p>The name for each name/value pair. Each name is stored as a null + terminated ASCII string in a multiple of eight bytes. The names + are in no particular order. + </p> + </td> + </tr> + + <tr> + <td><p>Values</p></td> + <td> + <p>The list of values in the same order as the names. The values + are packed (no inter-value padding) and the size of each value + is determined by the parent type. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Enumeration Property Description for Datatype Version 3 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Names<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Values<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each enumeration type is based on some parent type, usually an + integer. The information for that parent type is described + recursively by this field. + </p> + </td> + </tr> + + <tr> + <td><p>Names</p></td> + <td> + <p>The name for each name/value pair. Each name is stored as a null + terminated ASCII string, <em>not</em> padded to a multiple of + eight bytes. The names are in no particular order. + </p> + </td> + </tr> + + <tr> + <td><p>Values</p></td> + <td> + <p>The list of values in the same order as the names. The values + are packed (no inter-value padding) and the size of each value + is determined by the parent type. + </p> + </td> + </tr> + + </table> + </div> + + + + <br /> + <p>Class specific information for Variable-Length (Class 9):</p> + + <div align="center"> + <table class="desc"> + <caption> + Variable-Length Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Type.</b> This four-bit value contains the type of + variable-length datatype described. The values defined are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Sequence: A variable-length sequence of any datatype. + Variable-length sequences do not have padding or + character set information. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>String: A variable-length sequence of characters. + Variable-length strings have padding and character set + information. + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>4-7</p></td> + <td><p><b>Padding type.</b> (variable-length string only) + This four-bit value determines the type of padding + used for variable-length strings. The values are the same + as for the string padding type, as follows: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Null terminate: A zero byte marks the end of a string + and is guaranteed to be present after converting a long + string to a short string. When converting a short string + to a long string, the value is padded with additional null + characters as necessary. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Null pad: Null characters are added to the end of the + value during conversion from a short string to a longer + string. Conversion from a long string to a shorter string + simply truncates the value. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Space pad: Space characters are added to the end of the + value during conversion from a short string to a longer + string. Conversion from a long string to a shorter string + simply truncates the value. This is the Fortran + representation of the string. + </td> + </tr> + + <tr> + <td align="center"><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + <p>This value is set to zero for variable-length sequences.</p> + + </td> + </tr> + + <tr> + <td><p>8-11</p></td> + <td><p><b>Character Set.</b> (variable-length string only) + This four-bit value specifies the character set + to be used for encoding the string: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + <p>This value is set to zero for variable-length sequences.</p> + + </td> + </tr> + + <tr> + <td><p>12-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Variable-Length Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="10%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each variable-length type is based on some parent type. The + information for that parent type is described recursively by + this field. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <p>Class specific information for Array (Class 10):</p> + + <p>There are no bit fields defined for the array class. + </p> + + <p>Note that the dimension information defined in the property for this + datatype class is independent of dataspace information for a dataset. + The dimension information here describes the dimensionality of the + information within a data element (or a component of an element, if the + array datatype is nested within another datatype) and the dataspace for a + dataset describes the size and locations of the elements in a dataset. + </p> + + + <div align="center"> + <table class="format"> + <caption> + Array Property Description for Datatype Version 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Dimension #1 Size</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4">Permutation Index #1</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Permutation Index #n</td> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the array has. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the size of the dimension of the array + as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Permutation Index #n</p></td> + <td> + <p>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. Currently, dimension + permutations are not supported, and these indices should + be set to the index position minus one. In other words, + the first dimension should be set to 0, the second dimension + should be set to 1, and so on. + </p> + </td> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each array type is based on some parent type. The + information for that parent type is described recursively by + this field. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Array Property Description for Datatype Version 3 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Dimension #1 Size</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the array has. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the size of the dimension of the array + as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each array type is based on some parent type. The + information for that parent type is described recursively by + this field. + </p> + </td> + </tr> + + </table> + </div> + + + +<br /> +<h4><a name="OldFillValueMessage">IV.A.2.e. The Data Storage - +Fill Value (Old) Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Fill Value + (old)</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0004</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>The fill value message stores a single data value which + is returned to the application when an uninitialized data element + is read from a dataset. The fill value is interpreted with the + same datatype as the dataset. If no fill value message is present + then a fill value of all zero bytes is assumed.</p> + <p>This fill value message is deprecated in favor of the + “new” fill value message (Message Type 0x0005) and + is only written to the file for forward compatibility with + versions of the HDF5 Library before the 1.6.0 version. + Additionally, it only appears for datasets with a user-defined + fill value (as opposed to the library default fill value or an + explicitly set “undefined” fill value).</p> + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Fill Value Message (Old) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Size</td> + </tr> + + <tr> + <td colspan="4"><br />Fill Value <em>(optional, variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>This is the size of the Fill Value field in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Fill Value</p></td> + <td> + <p>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. + </p> + </td> + </tr> + </table> + </div> + + +<br /> +<h4><a name="FillValueMessage">IV.A.2.f. The Data Storage - +Fill Value Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Fill + Value</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0005</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for dataset objects; + may not be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The fill value message stores a single data value which is + returned to the application when an uninitialized data element + is read from a dataset. The fill value is interpreted with the + same datatype as the dataset.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Fill Value Message - Versions 1 & 2 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Space Allocation Time</td> + <td>Fill Value Write Time</td> + <td>Fill Value Defined</td> + </tr> + + <tr> + <td colspan="4">Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Fill Value <em>(optional, variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the + format of the fill value message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Initial version of this message. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>In this version, the Size and Fill Value fields are + only present if the Fill Value Defined field is set + to 1. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>This version packs the other fields in the message + more efficiently than version 2. + </td> + </tr> + </table></p> + </p> + </td> + </tr> + + <tr> + <td><p>Space Allocation Time</p></td> + <td> + <p>When the storage space for the dataset’s raw data will be + allocated. The allowed values are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Not used. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Early allocation. Storage space for the entire dataset + should be allocated in the file when the dataset is + created. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Late allocation. Storage space for the entire dataset + should not be allocated until the dataset is written + to. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Incremental allocation. Storage space for the + dataset should not be allocated until the portion + of the dataset is written to. This is currently + used in conjunction with chunked data storage for + datasets. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Fill Value Write Time</p></td> + <td> + <p>At the time that storage space for the dataset’s raw data is + allocated, this value indicates whether the fill value should + be written to the raw data storage elements. The allowed values + are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>On allocation. The fill value is always written to + the raw data storage when the storage space is allocated. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Never. The fill value should never be written to + the raw data storage. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Fill value written if set by user. The fill value + will be written to the raw data storage when the storage + space is allocated only if the user explicitly set + the fill value. If the fill value is the library + default or is undefined, it will not be written to + the raw data storage. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Fill Value Defined</p></td> + <td> + <p>This value indicates if a fill value is defined for this + dataset. If this value is 0, the fill value is undefined. + If this value is 1, a fill value is defined for this dataset. + For version 2 or later of the fill value message, this value + controls the presence of the Size and Fill Value fields. + </p> + </td> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>This is the size of the Fill Value field in bytes. This field + is not present if the Version field is greater than 1, + and the Fill Value Defined field is set to 0. + </p> + </td> + </tr> + + <tr> + <td><p>Fill Value</p></td> + <td> + <p>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. This field is + not present if the Version field is greater than 1, + and the Fill Value Defined field is set to 0. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Fill Value Message - Version 3 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Fill Value <em>(optional, variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the + format of the fill value message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Initial version of this message. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>In this version, the Size and Fill Value fields are + only present if the Fill Value Defined field is set + to 1. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>This version packs the other fields in the message + more efficiently than version 2. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>When the storage space for the dataset’s raw data will be + allocated. The allowed values are: + <table class="list"> + <tr> + <th width="20%" align="center">Bits</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0-1</code></td> + <td>Space Allocation Time, with the same + values as versions 1 and 2 of the message. + </td> + </tr> + <tr> + <td align="center"><code>2-3</code></td> + <td>Fill Value Write Time, with the same + values as versions 1 and 2 of the message. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>Fill Value Undefined, indicating that the fill + value has been marked as “undefined” for this dataset. + Bits 4 and 5 cannot both be set. + </td> + </tr> + <tr> + <td align="center"><code>5</code></td> + <td>Fill Value Defined, with the same values as + versions 1 and 2 of the message. + Bits 4 and 5 cannot both be set. + </td> + </tr> + <tr> + <td align="center"><code>6-7</code></td> + <td>Reserved (zero). + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>This is the size of the Fill Value field in bytes. This field + is not present if the Version field is greater than 1, + and the Fill Value Defined flag is set to 0. + </p> + </td> + </tr> + + <tr> + <td><p>Fill Value</p></td> + <td> + <p>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. This field is + not present if the Version field is greater than 1, + and the Fill Value Defined flag is set to 0. + </p> + </td> + </tr> + </table> + </div> + + +<br /> +<h4><a name="LinkMessage">IV.A.2.g. The Link Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Link</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0006</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies </td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be + repeated. </td></tr> + <tr><td><b>Description:</b></td> + <td><p>This message encodes the information for a link in a + group’s object header, when the group is storing its links + “compactly”, or in the group’s fractal heap, + when the group is storing its links “densely”.</p> + <p>A group is storing its links compactly when the fractal heap + address in the <em><a href="#LinkInfoMessage">Link Info + Message</a></em> is set to the “undefined address” + value.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Link Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td>Link type <em>(optional)</em></td> + <td bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Creation Order <em>(8 bytes, optional)</em><br /><br /></td> + </tr> + <tr> + <td>Link Name Character Set <em>(optional)</em></td> + <td>Length of Link Name (variable size)</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Link Name (variable size)</td> + </tr> + <tr> + <td colspan="4"><br />Link Information (variable size)<br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes version 1.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This field contains information about the link and controls + the presence of other fields below. + <table class="list"> + <tr> + <th width="20%" align="center">Bits</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0-1</code></td> + <td>Determines the size of the <em>Length of Link Name</em> + field. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 1 byte. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 2 bytes. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 4 bytes. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 8 bytes. + </td> + </tr> + </table> + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Creation Order Field Present: if set, the <em>Creation + Order</em> field is present. If not set, creation order + information is not stored for links in this group. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Link Type Field Present: if set, the link is not + a hard link and the <em>Link Type</em> field is present. + If not set, the link is a hard link. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>Link Name Character Set Field Present: if set, the + link name is not represented with the ASCII character + set and the <em>Link Name Character Set</em> field is + present. If not set, the link name is represented with + the ASCII character set. + </td> + </tr> + <tr> + <td align="center"><code>5-7</code></td> + <td>Reserved (zero). + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Link type</p></td> + <td><p>This is the link class type and can be one of the following + values: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>A hard link (should never be stored in the file) + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>A soft link. + </td> + </tr> + <tr> + <td align="center"><code>2-63</code></td> + <td>Reserved for future HDF5 internal use. + </td> + </tr> + <tr> + <td align="center"><code>64</code></td> + <td>An external link. + </td> + </tr> + <tr> + <td align="center"><code>65-255</code></td> + <td>Reserved, but available for user-defined link types. + </td> + </tr> + </table></p> + + <p>This field is present if bit 3 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td><p>This 64-bit value is an index of the link’s creation time within + the group. Values start at 0 when the group is created an increment + by one for each link added to the group. Removing a link from a + group does not change existing links’ creation order field. + </p> + <p>This field is present if bit 2 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Link Name Character Set</p></td> + <td><p>This is the character set for encoding the link’s name: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding (this should never be stored + in the file) + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + </table></p> + + <p>This field is present if bit 4 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Length of link name</p></td> + <td><p>This is the length of the link’s name. The size of this field + depends on bits 0 and 1 of <em>Flags</em>.</p> + </td> + </tr> + + <tr> + <td><p>Link name</p></td> + <td><p>This is the name of the link, non-NULL terminated.</p> + </td> + </tr> + + <tr> + <td><p>Link information</p></td> + <td><p>The format of this field depends on the <em>link type</em>.</p> + <p>For <b>hard</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%"><i>Size of Offsets</i> bytes:</td> + <td width="80%">The address of the object header for the object that the + link points to. + </td> + </tr> + </table> + </p> + + <p> + For <b>soft</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-2:</td> + <td width="80%">Length of soft link value.</td> + </tr> + <tr> + <td><em>Length of soft link value</em> bytes:</td> + <td>A non-NULL-terminated string storing the value of the + soft link. + </td> + </tr> + </table> + </p> + + <p> + For <b>external</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-2:</td> + <td width="80%">Length of external link value.</td> + </tr> + <tr> + <td><em>Length of external link value</em> bytes:</td> + <td>The first byte contains the version number in the + upper 4 bits and flags in the lower 4 bits for the external + link. Both version and flags are defined to be zero in + this document. The remaining bytes consist of two + NULL-terminated strings, with no padding between them. + The first string is the name of the HDF5 file containing + the object linked to and the second string is the full path + to the object linked to, within the HDF5 file’s + group hierarchy. + </td> + </tr> + </table> + </p> + + <p> + For <b>user-defined</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-2:</td> + <td width="80%">Length of user-defined data.</td> + </tr> + <tr> + <td><em>Length of user-defined link value</em> bytes:</td> + <td>The data supplied for the user-defined link type.</td> + </tr> + </table> + </p> + + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="ExternalFileListMessage">IV.A.2.h. The Data Storage - +External Data Files Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> External + Data Files</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0007</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The external data storage message indicates that the data + for an object is stored outside the HDF5 file. The filename of + the object is stored as a Universal Resource Location (URL) of + the actual filename containing the data. An external file list + record also contains the byte offset of the start of the data + within the file and the amount of space reserved in the file + for that data.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + External File List Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="2">Allocated Slots</td> + <td colspan="2">Used Slots</td> + </tr> + + <tr> + <td colspan="4"><br />Heap Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Slot Definitions...<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the format of + External Data Storage Message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The current version used by the library.</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Allocated Slots</p></td> + <td> + <p>The total number of slots allocated in the message. Its value must be at least as + large as the value contained in the Used Slots field. (The current library simply + uses the number of Used Slots for this message)</p> + </td> + </tr> + + <tr> + <td><p>Used Slots</p></td> + <td> + <p>The number of initial slots which contains valid information.</p> + </td> + </tr> + + <tr> + <td><p>Heap Address</p></td> + <td> + <p>This is the address of a local heap which contains the names for the external + files (The local heap information can be found in Disk Format Level 1D in this + document). The name at offset zero in the heap is always the empty string.</p> + </td> + </tr> + + <tr> + <td><p>Slot Definitions</p></td> + <td> + <p>The slot definitions are stored in order according to the array addresses they + represent.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + External File List Slot + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name Offset in Local Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Offset in External Data File<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data Size in External File<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name Offset in Local Heap</p></td> + <td> + <p>The byte offset within the local name heap for the name + of the file. File names are stored as a URL which has a + protocol name, a host name, a port number, and a file + name: + <code><em>protocol</em>:<em>port</em>//<em>host</em>/<em>file</em></code>. + If the protocol is omitted then “file:” is assumed. If + the port number is omitted then a default port for that + protocol is used. If both the protocol and the port + number are omitted then the colon can also be omitted. If + the double slash and host name are omitted then + “localhost” is assumed. The file name is the only + mandatory part, and if the leading slash is missing then + it is relative to the application’s current working + directory (the use of relative names is not + recommended). + </p> + </td> + </tr> + + <tr> + <td><p>Offset in External Data File</p></td> + <td> + <p>This is the byte offset to the start of the data in the + specified file. For files that contain data for a single + dataset this will usually be zero.</p> + </td> + </tr> + + <tr> + <td><p>Data Size in External File</p></td> + <td> + <p>This is the total number of bytes reserved in the + specified file for raw data storage. For a file that + contains exactly one complete dataset which is not + extendable, the size will usually be the exact size of the + dataset. However, by making the size larger one allows + HDF5 to extend the dataset. The size can be set to a value + larger than the entire file since HDF5 will read zeroes + past the end of the file without failing.</p> + </td> + </tr> + </table> + </div> + + +<br /> +<h4><a name="LayoutMessage">IV.A.2.i. The Data Storage - Layout +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Data Storage - + Layout</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0008</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for datasets; may not + be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>Data layout describes how the elements of a multi-dimensional + array are stored in the HDF5 file. Three types of data layout + are supported: + <ol> + <li>Contiguous: The array is stored in one contiguous area of + the file. This layout requires that the size of the array be + constant: data manipulations such as chunking, compression, + checksums, or encryption are not permitted. The message stores + the total storage size of the array. The offset of an element + from the beginning of the storage area is computed as in a C + array.</li> + <li>Chunked: The array domain is regularly decomposed into + chunks, and each chunk is allocated and stored separately. This + layout supports arbitrary element traversals, compression, + encryption, and checksums. (these features are described + in other messages). The message stores the size of a chunk + instead of the size of the entire array; the storage size of + the entire array can be calculated by traversing the B-tree + that stores the chunk addresses.</li> + <li>Compact: The array is stored in one contiguous block, as + part of this object header message.</li> + </ol></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Data Layout Message (Versions 1 and 2) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Layout Class</td> + <td>Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4">Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Data Address<sup>O</sup> <em>(optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Dimension 0 Size</td> + </tr> + + <tr> + <td colspan="4">Dimension 1 Size</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4">Dataset Element Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Compact Data Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Compact Data... <em>(variable size, optional)</em><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the format of the data + layout message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by version 1.4 and before of the library to encode layout information. + Data space is always allocated when the data set is created.</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Used by version 1.6.x of the library to encode layout information. + Data space is allocated only when it is necessary.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td><p>An array has a fixed dimensionality. This field + specifies the number of dimension size fields later in the + message. The value stored for chunked storage is 1 greater than + the number of dimensions in the dataset’s dataspace. + For example, 2 is stored for a 1 dimensional dataset. + </p> + </td> + </tr> + + <tr> + <td><p>Layout Class</p></td> + <td><p>The layout class specifies the type of storage for the data + and how the other fields of the layout message are to be + interpreted. + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Compact Storage + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Contiguous Storage + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Chunked Storage + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Data Address</p></td> + <td><p>For contiguous storage, this is the address of the raw + data in the file. For chunked storage this is the address + of the v1 B-tree that is used to look up the addresses of the + chunks. This field is not present for compact storage. + If the version for this message is greater than 1, the address + may have the “undefined address” value, to indicate that + storage has not yet been allocated for this array.</p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td><p>For contiguous and compact storage the dimensions define + the entire size of the array while for chunked storage they define + the size of a single chunk. In all cases, they are in units of + array elements (not bytes). The first dimension stored in the list + of dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dataset Element Size</p></td> + <td><p>The size of a dataset element, in bytes. This field is only + present for chunked storage. + </p> + </td> + </tr> + + <tr> + <td><p>Compact Data Size</p></td> + <td><p>This field is only present for compact data storage. + It contains the size of the raw data for the dataset array, in + bytes.</p> + </td> + </tr> + + <tr> + <td><p>Compact Data</p></td> + <td><p>This field is only present for compact data storage. + It contains the raw data for the dataset array.</p> + </td> + </tr> + </table> + </div> + + <br /> + <p>Version 3 of this message re-structured the format into specific + properties that are required for each layout class.</p> + + + <div align="center"> + <table class="format"> + <caption> + <b>Data Layout Message (Version 3)</b> + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Layout Class</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Properties <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the format of layout message + and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Used by the version 1.6.3 and later of the library to store properties + for each layout class.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Layout Class</p></td> + <td><p>The layout class specifies the type of storage for the data + and how the other fields of the layout message are to be + interpreted. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Compact Storage + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Contiguous Storage + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Chunked Storage + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Properties</p></td> + <td><p>This variable-sized field encodes information specific to each + layout class and is described below. If there is no property + information specified for a layout class, the size of this field + is zero bytes.</p></td> + </tr> + </table> + </div> + + <br /> + <p>Class-specific information for compact layout (Class 0): (Note: The dimensionality information + is in the Dataspace message)</p> + + + <div align="center"> + <table class="format"> + <caption> + Compact Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="2">Size</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Raw Data... <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size</p></td> + <td><p>This field contains the size of the raw data for the dataset + array, in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Raw Data</p></td> + <td><p>This field contains the raw data for the dataset array.</p></td> + </tr> + </table> + </div> + + + <br /> + <p>Class-specific information for contiguous layout (Class 1): (Note: The dimensionality information + is in the Dataspace message)</p> + + + <div align="center"> + <table class="format"> + <caption> + Contiguous Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This is the address of the raw data in the file. + The address may have the “undefined address” value, to indicate + that storage has not yet been allocated for this array.</p></td> + </tr> + + <tr> + <td><p>Size</p></td> + <td><p>This field contains the size allocated to store the raw data, + in bytes. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <p>Class-specific information for chunked layout (Class 2):</p> + + + <div align="center"> + <table class="format"> + <caption> + Chunked Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Dimension 0 Size</td> + </tr> + + <tr> + <td colspan="4">Dimension 1 Size</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4">Dataset Element Size</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td><p>A chunk has a fixed dimensionality. This field specifies + the number of dimension size fields later in the message.</p></td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This is the address of the v1 B-tree that is used to look up the + addresses of the chunks that actually store portions of the array + data. The address may have the “undefined address” value, to + indicate that storage has not yet been allocated for this array.</p></td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td><p>These values define the dimension size of a single chunk, in + units of array elements (not bytes). The first dimension stored in + the list of dimensions is the slowest changing dimension and the + last dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dataset Element Size</p></td> + <td><p>The size of a dataset element, in bytes. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="BogusMessage">IV.A.2.j. The Bogus Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Bogus</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0009</td></tr> + <tr><td colspan="2"><b>Length:</b> 4 bytes</td></tr> + <tr><td colspan="2"><b>Status:</b> For testing only; should never + be stored in a valid file.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message is used for testing the HDF5 Library’s + response to an “unknown” message type and should + never be encountered in a valid HDF5 file.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Bogus Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Bogus Value</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bogus Value</p></td> + <td> + <p>This value should always be: <code>0xdeadbeef</code>.</p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="GroupInfoMessage">IV.A.2.k. The Group Info Message +</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Group Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000A</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>This message stores information for the constants defining + a “new style” group’s behavior. Constant + information will be stored in this message and variable + information will be stored in the + <a href="#LinkInfoMessage">Link Info</a> message.</p> + <p>Note: the “estimated entry” information below is + used when determining the size of the object header for the + group when it is created.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Group Info Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Link Phase Change: Maximum Compact Value <em>(optional)</em></td> + </tr> + <tr> + <td colspan="2">Link Phase Change: Minimum Dense Value <em>(optional)</em></td> + <td colspan="2">Estimated Number of Entries <em>(optional)</em></td> + </tr> + <tr> + <td colspan="2">Estimated Link Name Length of Entries <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is the group information flag with the following definition: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, link phase change values are stored. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the estimated entry information is non-default + and is stored. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Link Phase Change: Maximum Compact Value</p></td> + <td><p>The is the maximum number of links to store “compactly” (in + the group’s object header).</p> + <p>This field is present if bit 0 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Link Phase Change: Minimum Dense Value</p></td> + <td><p>This is the minimum number of links to store “densely” (in + the group’s fractal heap). The fractal heap’s address is + located in the <a href="#LinkInfoMessage">Link Info</a> + message.</p> + <p>This field is present if bit 0 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Estimated Number of Entries</p></td> + <td><p>This is the estimated number of entries in groups.</p> + <p>If this field is not present, the default value of <code>4</code> + will be used for the estimated number of group entries.</p> + <p>This field is present if bit 1 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Estimated Link Name Length of Entries</p></td> + <td><p>This is the estimated length of entry name.</p> + <p>If this field is not present, the default value of <code>8</code> + will be used for the estimated link name length of group entries.</p> + <p>This field is present if bit 1 of <em>Flags</em> is set.</p> + </td> + </tr> + + </table> + </div> + </p> + +<br /> +<h4><a name="FilterMessage">IV.A.2.l. The Data Storage - Filter +Pipeline Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> + Data Storage - Filter Pipeline</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000B</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>This message describes the filter pipeline which should + be applied to the data stream by providing filter identification + numbers, flags, a name, and client data.</p> + <p>This message may be present in the object headers of both + dataset and group objects. For datasets, it specifies the + filters to apply to raw data. For groups, it specifies the + filters to apply to the group’s fractal heap. Currently, + only datasets using chunked data storage use the filter + pipeline on their raw data.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Filter Pipeline Message - Version 1 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Number of Filters</td> + <td colspan="2">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Filter Description List <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This table + describes version 1.</p></td> + </tr> + + <tr> + <td><p>Number of Filters</p></td> + <td><p>The total number of filters described in this + message. The maximum possible number of filters in a + message is 32.</p></td> + </tr> + + <tr> + <td><p>Filter Description List</p></td> + <td><p>A description of each filter. A filter description + appears in the next table.</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Filter Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="2">Filter Identification Value</td> + <td colspan="2">Name Length</td> + </tr> + + <tr> + <td colspan="2">Flags</td> + <td colspan="2">Number Client Data Values</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Client Data <em>(variable size, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Padding <em>(variable size, optional)</em></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filter Identification Value</p></td> + <td> + <p> + This value, often referred to as a filter identifier, + is designed to be a unique identifier for the filter. + Values from zero through 32,767 are reserved for filters + supported by The HDF Group in the HDF5 Library and for + filters requested and supported by third parties. + Filters supported by The HDF Group are documented immediately + below. Information on 3rd-party filters can be found at + The HDF Group’s + <a href="http://www.hdfgroup.org/services/contributions.html"> + Contributions</a> page.</p> + + <p> + To request a filter identifier, please contact + The HDF Group’s Help Desk at + <img src="Graphics/help.png" valign="middle" height="14" + alt="The HDF Group Help Desk">. + You will be asked to provide the following information:</p> + <ol> + <li>Contact information for the developer requesting the + new identifier</li> + <li>A short description of the new filter</li> + <li>Links to any relevant information, including licensing + information</li> + </ol> + <p> + Values from 32768 to 65535 are reserved for non-distributed uses + (for example, internal company usage) or for application usage + when testing a feature. The HDF Group does not track or document + the use of the filters with identifiers from this range.</p> + + <p> + The filters currently in library version 1.8.0 are + listed below: + + <table class="list"> + <tr> + <th width="20%" align="center">Identification</th> + <th width="15%" align="left">Name</th> + <th width="65%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>N/A</td> + <td>Reserved</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>deflate</td> + <td>GZIP deflate compression</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>shuffle</td> + <td>Data element shuffling</td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>fletcher32</td> + <td>Fletcher32 checksum</td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>szip</td> + <td>SZIP compression</td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td>nbit</td> + <td>N-bit packing</td> + </tr> + + <tr> + <td align="center"><code>6</code></td> + <td>scaleoffset</td> + <td>Scale and offset encoded values</td> + </tr> + </table> + </p></td> + </tr> + + <tr> + <td><p>Name Length</p></td> + <td><p>Each filter has an optional null-terminated ASCII name + and this field holds the length of the name including the + null termination padded with nulls to be a multiple of + eight. If the filter has no name then a value of zero is + stored in this field.</p></td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>The flags indicate certain properties for a filter. The + bit values defined so far are: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set then the filter is an optional filter. + During output, if an optional filter fails it will be + silently skipped in the pipeline.</td> + </tr> + + <tr> + <td align="center"><code>1-15</code></td> + <td>Reserved (zero)</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Number of Client Data Values</p></td> + <td><p>Each filter can store integer values to control + how the filter operates. The number of entries in the + <em>Client Data</em> array is stored in this field.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>If the <em>Name Length</em> field is non-zero then it will + contain the size of this field, padded to a multiple of eight. This + field contains a null-terminated, ASCII character + string to serve as a comment/name for the filter.</p></td> + </tr> + + <tr> + <td><p>Client Data</p></td> + <td><p>This is an array of four-byte integers which will be + passed to the filter function. The <em>Client Data Number</em> of + Values determines the number of elements in the array.</p></td> + </tr> + + <tr> + <td><p>Padding</p></td> + <td><p>Four bytes of zeroes are added to the message at this + point if the Client Data Number of Values field contains + an odd number.</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Filter Pipeline Message - Version 2 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Number of Filters</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Filter Description List <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This table + describes version 2.</p></td> + </tr> + + <tr> + <td><p>Number of Filters</p></td> + <td><p>The total number of filters described in this + message. The maximum possible number of filters in a + message is 32.</p></td> + </tr> + + <tr> + <td><p>Filter Description List</p></td> + <td><p>A description of each filter. A filter description + appears in the next table.</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Filter Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="2">Filter Identification Value</td> + <td colspan="2">Name Length <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="2">Flags</td> + <td colspan="2">Number Client Data Values</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Client Data <em>(variable size, optional)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filter Identification Value</p></td> + <td> + <p> + This value, often referred to as a filter identifier, + is designed to be a unique identifier for the filter. + Values from zero through 32,767 are reserved for filters + supported by The HDF Group in the HDF5 Library and for + filters requested and supported by third parties. + Filters supported by The HDF Group are documented immediately + below. Information on 3rd-party filters can be found at + The HDF Group’s + <a href="http://www.hdfgroup.org/services/contributions.html"> + Contributions</a> page.</p> + + <p> + To request a filter identifier, please contact + The HDF Group’s Help Desk at + <img src="Graphics/help.png" valign="middle" height="14" + alt="The HDF Group Help Desk">. + You will be asked to provide the following information:</p> + <ol> + <li>Contact information for the developer requesting the + new identifier</li> + <li>A short description of the new filter</li> + <li>Links to any relevant information, including licensing + information</li> + </ol> + <p> + Values from 32768 to 65535 are reserved for non-distributed uses + (for example, internal company usage) or for application usage + when testing a feature. The HDF Group does not track or document + the use of the filters with identifiers from this range.</p> + + <p> + The filters currently in library version 1.8.0 are + listed below: + + <table class="list"> + <tr> + <th width="20%" align="center">Identification</th> + <th width="15%" align="left">Name</th> + <th width="65%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>N/A</td> + <td>Reserved</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>deflate</td> + <td>GZIP deflate compression</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>shuffle</td> + <td>Data element shuffling</td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>fletcher32</td> + <td>Fletcher32 checksum</td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>szip</td> + <td>SZIP compression</td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td>nbit</td> + <td>N-bit packing</td> + </tr> + + <tr> + <td align="center"><code>6</code></td> + <td>scaleoffset</td> + <td>Scale and offset encoded values</td> + </tr> + </table> + </p></td> + </tr> + + <tr> + <td><p>Name Length</p></td> + <td><p>Each filter has an optional null-terminated ASCII name + and this field holds the length of the name including the + null termination padded with nulls to be a multiple of + eight. If the filter has no name then a value of zero is + stored in this field.</p> + <p>Filters with IDs less than 256 (in other words, filters + that are defined in this format documentation) do not store + the <em>Name Length</em> or <em>Name</em> fields. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>The flags indicate certain properties for a filter. The + bit values defined so far are: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set then the filter is an optional filter. + During output, if an optional filter fails it will be + silently skipped in the pipeline.</td> + </tr> + + <tr> + <td align="center"><code>1-15</code></td> + <td>Reserved (zero)</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Number of Client Data Values</p></td> + <td><p>Each filter can store integer values to control + how the filter operates. The number of entries in the + <em>Client Data</em> array is stored in this field.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>If the <em>Name Length</em> field is non-zero then it will + contain the size of this field, <em>not</em> padded to a multiple + of eight. This field contains a <em>non-</em>null-terminated, + ASCII character string to serve as a comment/name for the filter. + </p> + <p>Filters that are defined in this format documentation + such as deflate and shuffle do not store the <em>Name + Length</em> or <em>Name</em> fields. + </p> + </td> + </tr> + + <tr> + <td><p>Client Data</p></td> + <td><p>This is an array of four-byte integers which will be + passed to the filter function. The Client Data Number of + Values</em> determines the number of elements in the array.</p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="AttributeMessage">IV.A.2.m. The Attribute Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Attribute</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000C</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>The <em>Attribute</em> message is used to store objects + in the HDF5 file which are used as attributes, or + “metadata” about the current object. An attribute + is a small dataset; it has a name, a datatype, a dataspace, and + raw data. Since attributes are stored in the object header, they + should be relatively small (in other words, less than 64KB). + They can be associated with any type of object which has an + object header (groups, datasets, or committed (named) + datatypes).</p> + <p>In 1.8.x versions of the library, attributes can be larger + than 64KB. See the + <a href="UG/HDF5_Users_Guide-Responsive%20HTML5/index.html#t=HDF5_Users_Guide%2FAttributes%2FHDF5_Attributes.htm%3Frhtocid%3Dtoc8.2_1%23TOC_8_5_Special_Issuesbc-13"> + “Special Issues”</a> section of the Attributes chapter + in the <cite>HDF5 User’s Guide</cite> for more information.</p> + <p>Note: Attributes on an object must have unique names: + the HDF5 Library currently enforces this by causing the + creation of an attribute with a duplicate name to fail. + Attributes on different objects may have the same name, + however.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Attribute Message (Version 1) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Reserved (zero)</td> + <td colspan="2">Name Size</td> + </tr> + + <tr> + <td colspan="2">Datatype Size</td> + <td colspan="2">Dataspace Size</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Datatype <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dataspace <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number information is used for changes in the format of the + attribute message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by the library before version 1.6 to encode attribute message. + This version does not support shared datatypes.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Name Size</p></td> + <td><p>The length of the attribute name in bytes including the + null terminator. Note that the <em>Name</em> field below may + contain additional padding not represented by this + field.</p></td> + </tr> + + <tr> + <td><p>Datatype Size</p></td> + <td><p>The length of the datatype description in the <em>Datatype</em> + field below. Note that the <em>Datatype</em> field may contain + additional padding not represented by this field.</p></td> + </tr> + + <tr> + <td><p>Dataspace Size</p></td> + <td><p>The length of the dataspace description in the <em>Dataspace</em> + field below. Note that the <em>Dataspace</em> field may contain + additional padding not represented by this field.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>The null-terminated attribute name. This field is + padded with additional null characters to make it a + multiple of eight bytes.</p></td> + </tr> + + <tr> + <td><p>Datatype</p></td> + <td><p>The datatype description follows the same format as + described for the datatype object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</p></td> + </tr> + + <tr> + <td><p>Dataspace</p></td> + <td><p>The dataspace description follows the same format as + described for the dataspace object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</p></td> + </tr> + + <tr> + <td><p>Data</p></td> + <td><p>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. This + field is <em>not</em> padded with additional bytes.</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Attribute Message (Version 2) + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Name Size</td> + </tr> + + <tr> + <td colspan="2">Datatype Size</td> + <td colspan="2">Dataspace Size</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Datatype <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dataspace <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number information is used for changes in the + format of the attribute message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Used by the library of version 1.6.x and after to encode + attribute messages. + This version supports shared datatypes. The fields of + name, datatype, and dataspace are not padded with + additional bytes of zero. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This bit field contains extra information about + interpreting the attribute message: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, datatype is shared.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>If set, dataspace is shared.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Name Size</p></td> + <td><p>The length of the attribute name in bytes including the + null terminator.</p></td> + </tr> + + <tr> + <td><p>Datatype Size</p></td> + <td><p>The length of the datatype description in the <em>Datatype</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Dataspace Size</p></td> + <td><p>The length of the dataspace description in the <em>Dataspace</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>The null-terminated attribute name. This field is <em>not</em> + padded with additional bytes.</p></td> + </tr> + + <tr> + <td><p>Datatype</p></td> + <td><p>The datatype description follows the same format as + described for the datatype object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s datatype is + shared, this field will contain a “shared message” encoding + instead of the datatype encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Dataspace</p></td> + <td><p>The dataspace description follows the same format as + described for the dataspace object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s dataspace is + shared, this field will contain a “shared message” encoding + instead of the dataspace encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes.</p> + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td><p>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. + </p> + <p>This field is <em>not</em> padded with additional zero bytes. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Attribute Message (Version 3) + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Name Size</td> + </tr> + + <tr> + <td colspan="2">Datatype Size</td> + <td colspan="2">Dataspace Size</td> + </tr> + + <tr> + <td>Name Character Set Encoding</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Datatype <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dataspace <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number information is used for changes in the + format of the attribute message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Used by the library of version 1.8.x and after to + encode attribute messages. + This version supports attributes with non-ASCII names. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This bit field contains extra information about + interpreting the attribute message: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, datatype is shared.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>If set, dataspace is shared.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Name Size</p></td> + <td><p>The length of the attribute name in bytes including the + null terminator.</p></td> + </tr> + + <tr> + <td><p>Datatype Size</p></td> + <td><p>The length of the datatype description in the <em>Datatype</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Dataspace Size</p></td> + <td><p>The length of the dataspace description in the <em>Dataspace</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Name Character Set Encoding</p></td> + <td><p>The character set encoding for the attribute’s name: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>The null-terminated attribute name. This field is <em>not</em> + padded with additional bytes.</p></td> + </tr> + + <tr> + <td><p>Datatype</p></td> + <td><p>The datatype description follows the same format as + described for the datatype object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s datatype is + shared, this field will contain a “shared message” encoding + instead of the datatype encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Dataspace</p></td> + <td><p>The dataspace description follows the same format as + described for the dataspace object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s dataspace is + shared, this field will contain a “shared message” encoding + instead of the dataspace encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes.</p> + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td><p>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. + </p> + <p>This field is <em>not</em> padded with additional zero bytes. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="CommentMessage">IV.A.2.n. The Object Comment +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object + Comment</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000D</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The object comment is designed to be a short description of + an object. An object comment is a sequence of non-zero + (<code>\0</code>) ASCII characters with no other formatting + included by the library.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Name Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Comment <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>A null terminated ASCII character string.</p></td> + </tr> + </table> + </div> + +<br /> +<h4><a name="OldModificationTimeMessage">IV.A.2.o. The Object +Modification Time (Old) Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object + Modification Time (Old)</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000E</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>The object modification date and time is a timestamp + which indicates (using ISO-8601 date and time format) the last + modification of an object. The time is updated when any object + header message changes according to the system clock where the + change was posted. All fields of this message should be + interpreted as coordinated universal time (UTC).</p> + <p>This modification time message is deprecated in favor of + the “new” <a href="#ModificationTimeMessage">Object + Modification Time</a> message and is no longer written to the + file in versions of the HDF5 Library after the 1.6.0 + version.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Modification Time Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Year</td> + </tr> + + <tr> + <td colspan="2">Month</td> + <td colspan="2">Day of Month</td> + </tr> + + <tr> + <td colspan="2">Hour</td> + <td colspan="2">Minute</td> + </tr> + + <tr> + <td colspan="2">Second</td> + <td colspan="2">Reserved</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Year</p></td> + <td><p>The four-digit year as an ASCII string. For example, + <code>1998</code>. + </p></td> + </tr> + + <tr> + <td><p>Month</p></td> + <td><p>The month number as a two digit ASCII string where + January is <code>01</code> and December is <code>12</code>.</p></td> + </tr> + + <tr> + <td><p>Day of Month</p></td> + <td><p>The day number within the month as a two digit ASCII + string. The first day of the month is <code>01</code>.</p></td> + </tr> + + <tr> + <td><p>Hour</p></td> + <td><p>The hour of the day as a two digit ASCII string where + midnight is <code>00</code> and 11:00pm is <code>23</code>.</p></td> + </tr> + + <tr> + <td><p>Minute</p></td> + <td><p>The minute of the hour as a two digit ASCII string where + the first minute of the hour is <code>00</code> and + the last is <code>59</code>.</p></td> + </tr> + + <tr> + <td><p>Second</p></td> + <td><p>The second of the minute as a two digit ASCII string + where the first second of the minute is <code>00</code> + and the last is <code>59</code>.</p></td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td><p>This field is reserved and should always be zero.</p></td> + </tr> + </table> + </div> + +<br /> +<h4><a name="SOHMTableMessage">IV.A.2.p. The Shared Message Table +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Shared Message + Table</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000F</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message is used to locate the table of shared object + header message (SOHM) indexes. Each index consists of information + to find the shared messages from either the heap or object header. + This message is <em>only</em> found in the superblock + extension.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Shared Message Table Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Shared Object Header Message Table Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td>Number of Indices</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes version 0.</p></td> + </tr> + + <tr> + <td><p>Shared Object Header Message Table Address</p></td> + <td><p>This field is the address of the master table for shared + object header message indexes.</p> + </td> + </tr> + + <tr> + <td><p>Number of Indices</p></td> + <td><p>This field is the number of indices in the master table. + </p></td> + </tr> + + </table> + </div> + +<br /> +<h4><a name="ContinuationMessage">IV.A.2.q. The Object Header +Continuation Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object Header + Continuation</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0010</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The object header continuation is the location in the file + of a block containing more header messages for the current data + object. This can be used when header blocks become too large or + are likely to change over time.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Object Header Continuation Message + </caption> + + <tr> + <th width=25%>byte</th> + <th width=25%>byte</th> + <th width=25%>byte</th> + <th width=25%>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Offset<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Length<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Offset</p></td> + <td><p>This value is the address in the file where the + header continuation block is located.</p></td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This value is the length in bytes of the header continuation + block in the file.</p></td> + </tr> + </table> + </div> + <br /> + + <p>The format of the header continuation block that this message points + to depends on the version of the object header that the message is + contained within. + </p> + + <p> + Continuation blocks for version 1 object headers have no special + formatting information; they are merely a list of object header + message info sequences (type, size, flags, reserved bytes and data + for each message sequence). See the description + of <a href="#V1ObjectHeaderPrefix">Version 1 Data Object Header Prefix.</a> + </p> + + <p>Continuation blocks for version 2 object headers <em>do</em> have + special formatting information as described here + (see also the description of + <a href="#V2ObjectHeaderPrefix">Version 2 Data Object Header Prefix.</a>): + </p> + <div align="center"> + <table class="format"> + <caption> + Version 2 Object Header Continuation Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Header Message Type #1</td> + <td colspan="2">Size of Header Message Data #1</td> + <td>Header Message #1 Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #1 Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td>Header Message Type #n</td> + <td colspan="2">Size of Header Message Data #n</td> + <td>Header Message #n Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #n Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #n<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Gap <em>(optional, variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>OCHK</code>” + is used to indicate the + beginning of an object header continuation block. This gives file + consistency checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Type</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Size of Header Message #n Data</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Header Message #n Flags</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Header Message #n Creation Order</p></td> + <td> + <p>This field stores the order that a message of a given type + was created in.</p> + <p>This field is present if bit 2 of <em>flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Data</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Gap</p></td> + <td> + <p>A gap in an object header chunk is inferred by the end of the + messages for the chunk before the beginning of the chunk’s + checksum. Gaps are always smaller than the size of an + object header message prefix (message type + message size + + message flags).</p> + <p>Gaps are formed when a message (typically an attribute message) + in an earlier chunk is deleted and a message from a later + chunk that does not quite fit into the free space is moved + into the earlier chunk.</p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the object header chunk. + </p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="SymbolTableMessage">IV.A.2.r. The Symbol Table +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Symbol Table + Message</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0011</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for + “old style” groups; may not be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>Each “old style” group has a v1 B-tree and a + local heap for storing symbol table entries, which are located + with this message.</td></tr> + <tr><td colspan="2"><b>Format of data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + <b>Symbol Table Message</b> + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />v1 B-tree Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Local Heap Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>v1 B-tree Address</p></td> + <td><p>This value is the address of the v1 B-tree containing the + symbol table entries for the group.</p></td> + </tr> + + <tr> + <td><p>Local Heap Address</p></td> + <td><p>This value is the address of the local heap containing + the link names for the symbol table entries for the group.</p></td> + </tr> + </table> + </div> + +<br /> +<h4><a name="ModificationTimeMessage">IV.A.2.s. The Object +Modification Time Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object + Modification Time</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0012</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The object modification time is a timestamp which indicates + the time of the last modification of an object. The time is + updated when any object header message changes according to + the system clock where the change was posted.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Modification Time Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Seconds After UNIX Epoch</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number is used for changes in the format of Object Modification Time + and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by Version 1.6.1 and after of the library to encode time. In + this version, the time is the seconds after Epoch.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Seconds After UNIX Epoch</p></td> + <td><p>A 32-bit unsigned integer value that stores the number of + seconds since 0 hours, 0 minutes, 0 seconds, January 1, 1970, + Coordinated Universal Time.</p></td> + </tr> + </table> + </div> + +<br /> +<h4><a name="BtreeKValuesMessage">IV.A.2.t. The B-tree +‘K’ Values Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> B-tree + ‘K’ Values</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0013</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message retrieves non-default ‘K’ values + for internal and leaf nodes of a group or indexed storage v1 + B-trees. This message is <em>only</em> found in the superblock + extension.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + B-tree ‘K’ Values Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="2">Indexed Storage Internal Node K</td> + <td bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="2">Group Internal Node K</td> + <td colspan="2">Group Leaf Node K</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Indexed Storage Internal Node K</p></td> + <td><p>This is the node ‘K’ value for each internal node of an + indexed storage v1 B-tree. See the description of this field + in version 0 and 1 of the superblock as well the section on + v1 B-trees. + </p> + </td> + </tr> + + <tr> + <td><p>Group Internal Node K</p></td> + <td><p>This is the node ‘K’ value for each internal node of a group + v1 B-tree. See the description of this field in version 0 and + 1 of the superblock as well as the section on v1 B-trees. + </p> + </td> + </tr> + + <tr> + <td><p>Group Leaf Node K</p></td> + <td><p>This is the node ‘K’ value for each leaf node of a group v1 + B-tree. See the description of this field in version 0 and 1 + of the superblock as well as the section on v1 B-trees. + </p> + </td> + </tr> + + </table> + </div> + +<br /> +<h4><a name="DrvInfoMessage">IV.A.2.u. The Driver Info +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Driver + Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0014</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + + <tr><td> + <b>Description:</b></td> + <td>This message contains information needed by the file driver + to reopen a file. This message is <em>only</em> found in the + superblock extension: see the <a href="#SuperblockExt"> + “Disk Format: Level 0C - Superblock Extension”</a> + section for more information. For more information on the fields + in the driver info message, see the <a href="#DriverInfo"> + “Disk Format : Level 0B - File Driver Info”</a> + section; those who use the multi and family file drivers will + find this section particularly helpful.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Driver Info Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Driver Identification</td> + </tr> + + <tr> + <td colspan="2">Driver Information Size</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Driver Information <em>(variable size)</em><br /><br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Driver Identification</p></td> + <td><p>This is an eight-byte ASCII string without null termination which + identifies the driver. + </p> + </td> + </tr> + + <tr> + <td><p>Driver Information Size</p></td> + <td><p>The size in bytes of the <em>Driver Information</em> field of this + message.</p> + </td> + </tr> + + <tr> + <td><p>Driver Information</p></td> + <td><p>Driver information is stored in a format defined by the file driver.</p> + </td> + </tr> + </table> + </div> + +<br /> +<h4><a name="AinfoMessage">IV.A.2.v. The Attribute Info +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Attribute + Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0015</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message stores information about the attributes on an + object, such as the maximum creation index for the attributes + created and the location of the attribute storage when the + attributes are stored “densely”.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Attribute Info Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Maximum Creation Index <em>(optional)</em></td> + </tr> + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Attribute Name v2 B-tree Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Attribute Creation Order v2 B-tree Address<sup>O</sup> <em>(optional)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is the attribute index information flag with the + following definition: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, creation order for attributes is tracked. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, creation order for attributes is indexed. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Maximum Creation Index</p></td> + <td><p>The is the maximum creation order index value for the + attributes on the object.</p> + <p>This field is present if bit 0 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap Address</p></td> + <td><p>This is the address of the fractal heap to store dense + attributes.</p> + </td> + </tr> + + <tr> + <td><p>Attribute Name v2 B-tree Address</p></td> + <td><p>This is the address of the version 2 B-tree to index the + names of densely stored attributes.</p> + </td> + </tr> + + <tr> + <td><p>Attribute Creation Order v2 B-tree Address</p></td> + <td><p>This is the address of the version 2 B-tree to index the + creation order of densely stored attributes.</p> + <p>This field is present if bit 1 of <em>Flags</em> is set.</p> + </td> + </tr> + + </table> + </div> + +<br /> +<h4><a name="RefCountMessage">IV.A.2.w. The Object Reference +Count Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object Reference + Count</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0016</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message stores the number of hard links (in groups or + objects) pointing to an object: in other words, its + <em>reference count</em>.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Object Reference Count + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Reference count</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td><p>The unsigned 32-bit integer is the reference count for the + object. This message is only present in “version 2” + (or later) object headers, and if not present those object + header versions, the reference count for the object is assumed + to be 1.</p> + </td> + </tr> + + </table> + </div> + +<br /> +<h4><a name="FsinfoMessage">IV.A.2.x. The File Space Info +Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> File Space + Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0018</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td> + <b>Description:</b></td> + <td>This message stores the file space management strategy (see + description below) that the library uses in handling file space + request for the file. It also contains the free-space section + threshold used by the library’s free-space managers for + the file. If the strategy is 1, this message also contains the + addresses of the file’s free-space managers which track + free space for each type of file space allocation. There are + six basic types of file space allocation: superblock, B-tree, + raw data, global heap, local heap, and object header. See the + description of <a href="#FreeSpaceManager">Free-space + Manager</a> as well the description of allocation types in + <a href="#AppendixB">Appendix B</a>.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + File Space Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Strategy</td> + <td colspan="2">Threshold<sup>L</sup></td> + </tr> + <tr> + <td colspan="4">Super-block Free-space Manager Address<sup>O</sup></td> + </tr> + <tr> + <td colspan="4">B-tree Free-space Manager Address<sup>O</sup></td> + </tr> + <tr> + <td colspan="4">Raw Data Free-space Manager Address<sup>O</sup></td> + </tr> + <tr> + <td colspan="4">Global Heap Free-space Manager Address<sup>O</sup></td> + </tr> + <tr> + <td colspan="4">Local Heap Free-space Manager Address<sup>O</sup></td> + </tr> + <tr> + <td colspan="4">Object Header Free-space Manager Address<sup>O</sup></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are of the size + specified in “Size of Offsets” field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are of the size + specified in “Size of Lengths” field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>This is the version number of this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Strategy</p></td> + <td><p>This is the file space management strategy for the file. + There are four types of strategies: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>With this strategy, the HDF5 Library’s free-space managers track the + free space that results from the manipulation of HDF5 objects + in the HDF5 file. The free space information is saved when the + file is closed, and reloaded when the file is reopened. + <br /> + When space is needed for file metadata or raw data, + the HDF5 Library first requests space from the library’s free-space + managers. If the request is not satisfied, the library requests space + from the aggregators. If the request is still not satisfied, + the library requests space from the virtual file driver. + That is, the library will use all of the mechanisms for allocating + space. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>This is the HDF5 Library’s default file space management strategy. + With this strategy, the library’s free-space managers track the free space + that results from the manipulation of HDF5 objects in the HDF5 file. + The free space information is NOT saved when the file is closed and + the free space that exists upon file closing becomes unaccounted + space in the file. + <br /> + As with strategy #1, the library will try all of the mechanisms + for allocating space. When space is needed for file metadata or + raw data, the library first requests space from the free-space + managers. If the request is not satisfied, the library requests + space from the aggregators. If the request is still not satisfied, + the library requests space from the virtual file driver. + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>With this strategy, the HDF5 Library does not track free space that results + from the manipulation of HDF5 objects in the HDF5 file and + the free space becomes unaccounted space in the file. + <br /> + When space is needed for file metadata or raw data, + the library first requests space from the aggregators. + If the request is not satisfied, the library requests space from + the virtual file driver. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>With this strategy, the HDF5 Library does not track free space that results + from the manipulation of HDF5 objects in the HDF5 file and + the free space becomes unaccounted space in the file. + <br /> + When space is needed for file metadata or raw data, + the library requests space from the virtual file driver. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Threshold</p></td> + <td><p>This is the free-space section threshold. + The library’s free-space managers will track only + free-space sections with size greater than or equal to + <em>threshold</em>. The default is to track free-space + sections of all sizes.</p> + </td> + </tr> + <tr> + <td><p>Superblock Free-space Manager Address</p></td> + <td><p>This is the address of the free-space manager for + H5FD_MEM_SUPER allocation type. + </p> + </td> + </tr> + + <tr> + <td><p>B-tree Free-space Manager Address</p></td> + <td><p>This is the address of the free-space manager for + H5FD_MEM_BTREE allocation type. + </p> + </td> + </tr> + + <tr> + <td><p>Raw Data Free-space Manager Address</p></td> + <td><p>This is the address of the free-space manager for + H5FD_MEM_DRAW allocation type. + </p> + </td> + </tr> + + <tr> + <td><p>Global Heap Free-space Manager Address</p></td> + <td><p>This is the address of the free-space manager for + H5FD_MEM_GHEAP allocation type. + </p> + </td> + </tr> + + <tr> + <td><p>Local Heap Free-space Manager Address</p></td> + <td><p>This is the address of the free-space manager for + H5FD_MEM_LHEAP allocation type. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Free-space Manager Address</p></td> + <td><p>This is the address of the free-space manager for + H5FD_MEM_OHDR allocation type. + </p> + </td> + </tr> + </table> + </div> + <br /> + + +<br /> +<h3><a name="DataStorage"> +IV.B. Disk Format: Level 2B - Data Object Data Storage</a></h3> + +<p>The data for an object is stored separately from its header + information in the file and may not actually be located in the HDF5 file + itself if the header indicates that the data is stored externally. The + information for each record in the object is stored according to the + dimensionality of the object (indicated in the dataspace header message). + Multi-dimensional array data is stored in C order; in other words, the + “last” dimension changes fastest.</p> + +<p>Data whose elements are composed of atomic datatypes are stored in IEEE + format, unless they are specifically defined as being stored in a different + machine format with the architecture-type information from the datatype + header message. This means that each architecture will need to [potentially] + byte-swap data values into the internal representation for that particular + machine.</p> + +<p> Data with a variable-length datatype is stored in the global heap + of the HDF5 file. Global heap identifiers are stored in the + data object storage.</p> + +<p>Data whose elements are composed of reference datatypes are stored in + several different ways depending on the particular reference type involved. + Object pointers are just stored as the offset of the object header being + pointed to with the size of the pointer being the same number of bytes as + offsets in the file.</p> + +<p>Dataset region references are stored as a heap-ID which points to +the following information within the file-heap: an offset of the object +pointed to, number-type information (same format as header message), +dimensionality information (same format as header message), sub-set start +and end information (in other words, a coordinate location for each), +and field start and end names (in other words, a [pointer to the] string +indicating the first field included and a [pointer to the] string name +for the last field). </p> + +<p>Data of a compound datatype is stored as a contiguous stream of the items + in the structure, with each item formatted according to its datatype.</p> + + + +<br /> +<br /> +<hr /> +<h2><a name="AppendixA"> +V. Appendix A: Definitions</a></h2> + +<p>Definitions of various terms used in this document are included in +this section.</p> + + <div align="center"> + <table class="glossary"> + <tr> + <th width="20%">Term</th> + <th>Definition</th> + </tr> + + <tr> + <td>Undefined Address</td> + <td>The <a name="UndefinedAddress">undefined + address</a> for a file is a file address with all bits + set: in other words, <code>0xffff...ff</code>.</td> + </tr> + + <tr> + <td>Unlimited Size</td> + <td>The <a name="UnlimitedDim">unlimited size</a> + for a size is a value with all bits set: in other words, + <code>0xffff...ff</code>.</td> + </tr> + + </table> + </div> + + + +<br /> +<br /> +<hr /> +<h2><a name="AppendixB"> +VI. Appendix B: File Memory Allocation Types</a></h2> + +<p>There are six basic types of file memory allocation as follows: +</p> + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Basic Allocation Type</th> + <th>Description</th> + </tr> + + <tr> + <td>H5FD_MEM_SUPER</td> + <td>File memory allocated for <em>Superblock.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_BTREE</td> + <td>File memory allocated for <em>B-tree.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_DRAW</td> + <td>File memory allocated for raw data.</td> + </tr> + + <tr> + <td>H5FD_MEM_GHEAP</td> + <td>File memory allocated for <em>Global Heap.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_LHEAP</td> + <td>File memory allocated for <em>Local Heap.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_OHDR</td> + <td>File memory allocated for <em>Object Header.</em></td> + </tr> + </table> + </div> + +<p>There are other file memory allocation types that are mapped to the +above six basic allocation types because they are similar in nature. +The mapping is listed in the following table: +</p> + + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Basic Allocation Type</th> + <th>Mapping of Allocation Types to Basic Allocation Types</th> + </tr> + + <tr> + <td>H5FD_MEM_SUPER</td> + <td><em>none</em></td> + </tr> + + <tr> + <td>H5FD_MEM_BTREE</td> + <td>H5FD_MEM_SOHM_INDEX</td> + </tr> + + <tr> + <td>H5FD_MEM_DRAW</td> + <td>H5FD_MEM_FHEAP_HUGE_OBJ</td> + </tr> + + <tr> + <td>H5FD_MEM_GHEAP</td> + <td><em>none</em></td> + </tr> + + <tr> + <td>H5FD_MEM_LHEAP</td> + <td>H5FD_MEM_FHEAP_DBLOCK, H5FD_MEM_FSPACE_SINFO</td> + </tr> + + <tr> + <td>H5FD_MEM_OHDR</td> + <td>H5FD_MEM_FHEAP_HDR, H5FD_MEM_FHEAP_IBLOCK, H5FD_MEM_FSPACE_HDR, H5FD_MEM_SOHM_TABLE</td> + </tr> + </table> + </div> + +<p>Allocation types that are mapped to basic allocation types are described below: +</p> + + <div align="center"> + <table class="desc"> + <tr> + <th width="30%">Allocation Type</th> + <th>Description</th> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_HDR</td> + <td>File memory allocated for <em>Fractal Heap Header.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_DBLOCK</td> + <td>File memory allocated for <em>Fractal Heap Direct Blocks.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_IBLOCK</td> + <td>File memory allocated for <em>Fractal Heap Indirect Blocks.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_HUGE_OBJ</td> + <td>File memory allocated for huge objects in the fractal heap.</td> + </tr> + + <tr> + <td>H5FD_MEM_FSPACE_HDR</td> + <td>File memory allocated for <em>Free-space Manager Header.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FSPACE_SINFO</td> + <td>File memory allocated for <em>Free-space Section List</em> of the free-space manager.</td> + </tr> + <tr> + <td>H5FD_MEM_SOHM_TABLE</td> + <td>File memory allocated for <em>Shared Object Header Message Table.</em></td> + </tr> + <tr> + <td>H5FD_MEM_SOHM_INDEX</td> + <td>File memory allocated for <em>Shared Message Record List.</em></td> + </tr> + </table> + </div> +</body> +</html> diff --git a/doxygen/examples/H5.format.html b/doxygen/examples/H5.format.html new file mode 100644 index 0000000..e16805f --- /dev/null +++ b/doxygen/examples/H5.format.html @@ -0,0 +1,20400 @@ +<html> + <head> + <title> + HDF5 File Format Specification Version 3.0 + </title> + + <style> + h1 { display: block; + margin-top: 24px; + margin-bottom: 24px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + font-size: 300%; + } + + h2 { display: block; + margin-top: 60px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + border-style: solid; + border-top-style: medium; + border-top-color: #A9A9A9; + border-bottom: none; + border-left: none; + border-right: none; + font-size: 250%; + } + + h3 { display: block; + margin-top: 40px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + font-size: 200%; + } + + h4 { display: block; + margin-top: 32px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + font-size: 150%; + } + + p { display: block; + margin-top: 8px; + margin-bottom: 8px; + margin-left: 0px; + margin-right: 0px; + text-indent: 0px; + font-size: 100%; + } + <!-- + p.item { margin-left: 2em; + text-indent: -2em + } --> + <!-- p.item2 { margin-left: 2em; text-indent: 2em} --> + + table.format { border:solid; + border-collapse:collapse; + caption-side:top; + text-align:center; + width:80%; + } + table.format th { border:ridge; + padding:4px; + width:25%; + } + table.format td { border:ridge; + padding:4px; + } + table.format caption { font-weight:bold; + font-size:larger; + } + + table.note {border:none; + text-align:right; + width:80%; + } + + table.desc { border:solid; + border-collapse:collapse; + caption-size:top; + text-align:left; + width:80%; + } + table.desc tr { vertical-align:top; + } + table.desc th { border-style:ridge; + font-size:larger; + padding:4px; + <!-- text-decoration:underline; --> + } + table.desc td { border-style:ridge; + <!-- padding: 4px; --> + vertical-align:text-top; + } + table.desc caption { font-weight:bold; + font-size:larger; + } + + table.list { border:none; + width:100% + } + table.list tr { vertical-align:text-top; + } + table.list th { border:none; + text-decoration:underline; + vertical-align:text-top; + } + table.list td { border:none; + vertical-align:text-top; + } + + table.msgdesc { border:none; + text-align:left; + width: 80% + } + table.msgdesc tr { vertical-align:text-top; + border-spacing:0; + padding:0; } + table.msgdesc th { border:none; + text-decoration:underline; + vertical-align:text-top; } + table.msgdesc td { border:none; + vertical-align:text-top; + } + + table.list80 { border:none; + width:80% + } + table.list80 tr { vertical-align:text-top; + } + table.list80 th { border:none; + text-decoration:underline; + vertical-align:text-top; + } + table.list80 td { border:none; + vertical-align:text-top; + } + + table.glossary { border:none; + text-align:left; + width: 80% + } + table.glossary tr { vertical-align:text-top; + border-spacing:0; + padding:0; } + table.glossary th { border:none; + text-align:left; + text-decoration:underline; + vertical-align:text-top; } + table.glossary td { border:none; + text-align:left; + vertical-align:text-top; + } + + div { page-break-inside:avoid; + page-break-after:auto + } + + </style> + + <!-- #BeginLibraryItem "/ed_libs/styles_Format.lbi" --> + <!-- + * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * + * Copyright by The HDF Group. * + * Copyright by the Board of Trustees of the University of Illinois. * + * All rights reserved. * + * * + * This file is part of HDF5. The full HDF5 copyright notice, including * + * terms governing use, modification, and redistribution, is contained in * + * the files COPYING and Copyright.html. COPYING can be found at the root * + * of the source code distribution tree; Copyright.html can be found at the * + * root level of an installed copy of the electronic HDF5 document set and * + * is linked from the top-level documents page. It can also be found at * + * http://www.hdfgroup.org/HDF5/doc/Copyright.html. If you do not have * + * access to either file, you may request a copy from help@hdfgroup.org. * + * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * + --> + <!-- #EndLibraryItem --><!-- #BeginLibraryItem "/ed_libs/NavBar_ADevG.lbi" --> + </head> + <body> + <!-- #EndLibraryItem --> + + <center> + <table border="0" width="90%"> + <tr> + <td valign="top"> + <ol type="I"> + <li><a href="#Intro">Introduction</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#ThisDocument">This Document</a></li> + <li><a href="#ChangesForHdf5_1_12">Changes for HDF5 1.12</a></li> + <li><a href="#ChangesForHdf5_1_10">Changes for HDF5 1.10</a></li> + </ol> + </font> + + <li><a href="#FileMetaData">Disk Format: Level 0 - File Metadata</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#Superblock">Disk Format: Level 0A - Format Signature + and Superblock</a></li> + <li><a href="#DriverInfo">Disk Format: Level 0B - File Driver + Info</a></li> + <li><a href="#SuperblockExt">Disk Format: Level 0C - Superblock + Extension</a></li> + </ol> + </font> + <li><a href="#FileInfra">Disk Format: Level 1 - File Infrastructure</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#Btrees">Disk Format: Level 1A - B-trees and B-tree + Nodes</a> + <ol type="1"> + <li><a href="#V1Btrees">Disk Format: Level 1A1 - Version 1 + B-trees</a></li> + <li><a href="#V2Btrees">Disk Format: Level 1A2 - Version 2 + B-trees</a></li> + </ol> + </li> + <li><a href="#SymbolTable">Disk Format: Level 1B - Group Symbol + Table Nodes</a></li> + <li><a href="#SymbolTableEntry">Disk Format: Level 1C - Symbol + Table Entry</a></li> + <li><a href="#LocalHeap">Disk Format: Level 1D - Local Heaps</a></li> + <li><a href="#GlobalHeap">Disk Format: Level 1E - Global Heap</a></li> + <li><a href="#GlobalHeapVDS">Disk Format: Level 1F - Global Heap + Block for Virtual Datasets</a></li> + <li><a href="#FractalHeap">Disk Format: Level 1G - Fractal Heap</a></li> + <li><a href="#FreeSpaceManager">Disk Format: Level 1H - Free-space + Manager</a></li> + <li><a href="#SOHMTable">Disk Format: Level 1I - Shared Object + Header Message Table</a></li> + </ol> + </font> + <li><a href="#DataObject">Disk Format: Level 2 - Data Objects</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#ObjectHeader">Disk Format: Level 2A - Data Object Headers</a></li> + <ol type="1"> + <li><a href="#ObjectHeaderPrefix">Disk Format: Level 2A1 - + Data Object Header Prefix</a> + <ol type="a"> + <li><a href="#V1ObjectHeaderPrefix">Version 1 Data + Object Header Prefix</a></li> + <li><a href="#V2ObjectHeaderPrefix">Version 2 Data + Object Header Prefix</a></li> + </ol> + </li> + <li><a href="#ObjectHeaderMessages">Disk Format: Level 2A2 - + Data Object Header Messages</a></li> + <ol type="a"> + <li><a href="#NILMessage">The NIL Message</a></li> <!-- 0x0000 --> + <li><a href="#DataspaceMessage">The Dataspace Message</a></li> <!-- 0x0001 --> + <li><a href="#LinkInfoMessage">The Link Info Message</a></li> <!-- 0x0002 --> + <li><a href="#DatatypeMessage">The Datatype Message</a></li> <!-- 0x0003 --> + <li><a href="#OldFillValueMessage">The Data Storage - + Fill Value (Old) Message</a></li> <!-- 0x0004 --> + </ol> + </ol> + </ol> + </font> + </ol> + </td> + + <td> </td> + + <td valign="top"> + <ol type="I" start="4"> + <li><a href="#DataObject">Disk Format: Level 2 - Data + Objects</a><font size="-1"><i> (Continued)</i></li> + <ol type="A"> + <li><a href="#ObjectHeader">Disk Format: Level 2A - Data Object + Headers</a><i> (Continued)</i> + <ol type="1" start="2"> + <li><a href="#ObjectHeaderMessages">Disk Format: Level 2A2 - + Data Object Header Messages</a><i> (Continued)</i></li> + <ol type="a" start="6"> + <li><a href="#FillValueMessage">The Data Storage - + Fill Value Message</a></li> <!-- 0x0005 --> + <li><a href="#LinkMessage">The Link Message</a></li> <!-- 0x0006 --> + <li><a href="#ExternalFileListMessage">The Data Storage - + External Data Files Message</a></li> <!-- 0x0007 --> + <li><a href="#LayoutMessage">The Data Layout Message</a></li> <!-- 0x0008 --> + <li><a href="#BogusMessage">The Bogus Message</a></li> <!-- 0x0009 --> + <li><a href="#GroupInfoMessage">The Group Info + Message</a></li> <!-- 0x000a --> + <li><a href="#FilterMessage">The Data Storage - + Filter Pipeline Message</a></li> <!-- 0x000b --> + <li><a href="#AttributeMessage">The Attribute + Message</a></li> <!-- 0x000c --> + <li><a href="#CommentMessage">The Object Comment + Message</a></li> <!-- 0x000d --> + <li><a href="#OldModificationTimeMessage">The Object + Modification Time (Old) Message</a></li> <!-- 0x000e --> + <li><a href="#SOHMTableMessage">The Shared Message + Table Message</a></li> <!-- 0x000f --> + <li><a href="#ContinuationMessage">The Object Header + Continuation Message</a></li> <!-- 0x0010 --> + <li><a href="#SymbolTableMessage">The Symbol + Table Message</a></li> <!-- 0x0011 --> + <li><a href="#ModificationTimeMessage">The Object + Modification Time Message</a></li> <!-- 0x0012 --> + <li><a href="#BtreeKValuesMessage">The B-tree + ‘K’ Values Message</a></li> <!-- 0x0013 --> + <li><a href="#DrvInfoMessage">The Driver Info + Message</a></li> <!-- 0x0014 --> + <li><a href="#AinfoMessage">The Attribute Info + Message</a></li> <!-- 0x0015 --> + <li><a href="#RefCountMessage">The Object Reference + Count Message</a></li> <!-- 0x0016 --> + <li><a href="#FsinfoMessage">The File Space Info + Message</a></li> <!-- 0x0017 --> + </ol> + </ol> + </li> + <li><a href="#DataStorage">Disk Format: Level 2B - Data Object Data Storage</a></li> + </ol> + </font> + <li><a href="#AppendixA">Appendix A: Definitions</a></li> + <li><a href="#AppendixB">Appendix B: File Space Allocation + Types</a></li> + <li><a href="#AppendixC"> + Appendix C: Types of Indexes for Dataset Chunks</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#SingleChunk">The Single Chunk Index</a></li> + <li><a href="#Implicit">The Implicit Index</a></li> + <li><a href="#FixedArray">The Fixed Array Index</a></li> + <li><a href="#ExtensibleArray">The Extensible Array Index</a></li> + <li><a href="#AppendV2Btrees">The Version 2 B-trees Index</a></li> + </ol> + </font> + <li><a href="#AppendixD"> + Appendix D: Encoding for Dataspace and Reference</a></li> + <font size="-1"> + <ol type="A"> + <li><a href="#DataspaceEncode">Dataspace Encoding</a></li> + <li><a href="#ReferenceEncodeRV">Reference Encoding (Revised)</a></li> + <li><a href="#ReferenceEncodeDP">Reference Encoding (Backward Compatibility)</a></li> + </ol> + </font> + </ol> + </td></tr> + </table> + </center> + + + <a name="Intro"><h2>I. Introduction</h2></a> + + <table align="right" width="100"> + <tr><td> </td><td align="center"> + <hr /> + <img src="FF-IH_FileGroup.gif" alt="HDF5 Groups" hspace="15" vspace="15"> + </td><td> </td></tr> + <tr><td> </td><td align="center"> + <strong>Figure 1:</strong> Relationships among the HDF5 root group, other groups, and objects + <hr /> + </td><td> </td></tr> + + <tr><td> </td><td align="center"> + <img src="FF-IH_FileObject.gif" alt="HDF5 Objects" hspace="15" vspace="15"> + </td><td> </td></tr> + <tr><td> </td><td align="center"> + <strong>Figure 2:</strong> HDF5 objects -- datasets, datatypes, or dataspaces + <hr /> + </td><td> </td></tr> + </table> + + + <p>The format of an HDF5 file on disk encompasses several + key ideas of the HDF4 and AIO file formats as well as + addressing some shortcomings therein. The new format is + more self-describing than the HDF4 format and is more + uniformly applied to data objects in the file.</p> + + <p>An HDF5 file appears to the user as a directed graph. + The nodes of this graph are the higher-level HDF5 objects + that are exposed by the HDF5 APIs:</p> + + <ul> + <li>Groups</li> + <li>Datasets</li> + <li>Committed (formerly Named) datatypes</li> + </ul> + + <p>At the lowest level, as information is actually written to the disk, + an HDF5 file is made up of the following objects:</p> + <ul> + <li>A superblock</li> + <li>B-tree nodes</li> + <li>Heap blocks</li> + <li>Object headers</li> + <li>Object data</li> + <li>Free space</li> + </ul> + + <p>The HDF5 Library uses these low-level objects to represent the + higher-level objects that are then presented to the user or + to applications through the APIs. For instance, a group is an + object header that contains a message that points to a local + heap (for storing the links to objects in the group) and to a + B-tree (which indexes the links). A dataset is an object header + that contains messages that describe the datatype, dataspace, + layout, filters, external files, fill value, and other elements + with the layout message pointing to either a raw data chunk or + to a B-tree that points to raw data chunks.</p> + + + <a name="ThisDocument"><h3>I.A. This Document</h3></a> + + <p>This document describes the lower-level data objects; + the higher-level objects and their properties are described + in the <a href="UG/HDF5_Users_Guide-Responsive HTML5/index.html"><cite>HDF5 User’s Guide</cite></a>.</p> + + <p>Three levels of information comprise the file format. + Level 0 contains basic information for identifying and + defining information about the file. Level 1 information contains + the information about the pieces of a file shared by many objects + in the file (such as B-trees and heaps). Level 2 is the rest + of the file and contains all of the data objects with each object + partitioned into header information, also known as + <em>metadata</em>, and data.</p> + + <p>The various components of the lower-level data objects are + described in pairs of tables. The first table shows the format + layout, and the second table describes the fields. The titles + of format layout tables begin with “Layout”. The + titles of the tables where the fields are described begin with + “Fields”. For example, the table that describes the + format of the <a href="#V2Btrees">version 2 B-tree header</a> has + a title of “Layout: Version 2 B-tree Header”, and the + fields in the version 2 B-tree header are described in the table + titled “Fields: Version 2 B-tree Header”. + + <p>The sizes of various fields in the following layout tables are + determined by looking at the number of columns the field spans + in the table. There are exceptions: </p> + <ul> + <li> The size may be overridden by specifying a size in + parentheses</li> + <li> The size of addresses is determined by the + <em><a href="#SizeOfOffsetsV0">Size of Offsets</a></em> field + in the superblock and is indicated in this document with a + superscripted ‘O’</li> + <li> The size of length fields is determined by the + <em><a href="#SizeOfLengthsV0">Size of Lengths</a></em> field in + the superblock and is indicated in this document with a + superscripted ‘L’</li> + </ul> + + <p>Values for all fields in this document should be treated as unsigned + integers, unless otherwise noted in the description of a field. + Additionally, all metadata fields are stored in little-endian byte + order. + </p> + + <p>All checksums used in the format are computed with the + <a href="http://www.burtleburtle.net/bob/hash/doobs.html">Jenkins’ + lookup3</a> algorithm. + </p> + + <p>Whenever a bit flag or field is mentioned for an entry, bits are + numbered from the lowest bit position in the entry. + </p> + + <p>Various format tables in this document have cells with + “This space inserted only to align table nicely”. These + entries in the table are just to make the table presentation nicer + and do not represent any values or padding in the file. + </p> + + <a name="ChangesForHdf5_1_12"> + <h3>I.B. Changes for HDF5 1.12</h3></a> + <p>The following sections have been + changed or added for the 1.12 release:</p> + <ul> + <li>Under <a href="#DatatypeMessage">“The Datatype Message”</a>, + in the Description for “Fields:Datatype Message”, + version 4 was added and Reference class (7) of the datatype was updated to describe version 4.</li> + <li><a href="#AppendixD"> + “Appendix D: Encoding for Dataspace and Reference”</a> + was added. </li> + </ul> + + + <a name="ChangesForHdf5_1_10"> + <h3>I.C. Changes for HDF5 1.10</h3></a> + + <p>The following sections have been + changed or added for the 1.10 release:</p> + <ul> + <li>In the <a href="#Superblock"> + “Disk Format: Level 0A - Format Signature and + Superblock”</a> section, version 3 of the superblock was + added. </li> + <li>In the <a href="#SuperblockExt"> + “Disk Format: Level 0C - Superblock Extension”</a> + section, a link to the Data Storage message was added. </li> + <li>In the <a href="#V2Btrees"> + “Disk Format: Level 1A2 - Version 2 B-trees”</a> + section, additional B-tree types were added. Tables that + describe the <a href="#V2BtreesType10">type 10</a> and + <a href="#V2BtreesType11">11</a> record layouts were added at + the end of the section.</li> + <li>The <a href="#GlobalHeapVDS">“Disk Format: Level 1F - + Global Heap Block for Virtual Datasets”</a> was added. + </li> + <li><a href="#LayoutMessage"> + “The Data Layout Message”</a> section was changed. + The name was changed, and <a href="#DataLayoutV4">version 4</a> + of the data layout message was added for the virtual type.</li> + <li>The <a href="#FsinfoMessage"> + “The File Space Info Message”</a> header message + type was added.</li> + <li><a href="#AppendixC"> + “Appendix C: Types of Indexes for Dataset Chunks”</a> + was added. Five indexing types were added.</li> + </ul> + + + + <h2><a name="FileMetaData"> + II. Disk Format: Level 0 - File Metadata</a></h2> + + + + <h3><a name="Superblock"> + II.A. Disk Format: Level 0A - Format Signature and Superblock</a></h3> + + <p>The superblock may begin at certain predefined offsets within + the HDF5 file, allowing a block of unspecified content for + users to place additional information at the beginning (and + end) of the HDF5 file without limiting the HDF5 Library’s + ability to manage the objects within the file itself. This + feature was designed to accommodate wrapping an HDF5 file in + another file format or adding descriptive information to an HDF5 + file without requiring the modification of the actual file’s + information. The superblock is located by searching for the + HDF5 format signature at byte offset 0, byte offset 512, and at + successive locations in the file, each a multiple of two of + the previous location; in other words, at these byte offsets: + 0, 512, 1024, 2048, and so on.</p> + + <p>The superblock is composed of the format signature, followed by a + superblock version number and information that is specific to each + version of the superblock. + + <p>Currently, there are four versions of the superblock format: + <ul> + <li>Version 0 is the default format.</li> + <li>Version 1 is the same as version 0 but with the + “<em>Indexed Storage Internal Node K</em>” field + for storing non-default B-tree ‘K’ value.</li> + <li>Version 2 has some fields eliminated and compressed from + superblock format versions 0 and 1. It has added checksum support + and superblock extension to store additional superblock + metadata.</li> + <li>Version 3 is the same as version 2 except that the field + “<em>File Consistency Flags</em>” is used for file + locking. This format version will enable support for the latest + version.</li> + </ul> + + <p>Versions 0 and 1 of the superblock are described below:</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Superblock (Versions 0 and 1) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Format Signature + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td>Version # of Superblock</td> + <td>Version # of File’s Free Space Storage</td> + <td>Version # of Root Group Symbol Table Entry</td> + <td>Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td>Version Number of Shared Header Message Format</td> + <td>Size of Offsets</td> + <td>Size of Lengths</td> + <td>Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="2">Group Leaf Node K</td> + <td colspan="2">Group Internal Node K</td> + </tr> + + <tr> + <td colspan="4">File Consistency Flags</td> + </tr> + + <tr> + <td colspan="2" style="border:dotted;">Indexed Storage Internal Node K<sup>1</sup></td> + <td colspan="2" style="border:dotted;">Reserved + <em>(zero)</em><sup>1</sup></td> + </tr> + + <tr> + <td colspan="4"><br />Base Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of File Free space Info<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of File Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Driver Information Block Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Root Group Symbol Table Entry</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with a ‘1’ in the above table are + new in version 1 of the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Superblock (Versions 0 and 1) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Format Signature</p></td> + <td><p>This field contains a constant value and can be used to + quickly identify a file as being an HDF5 file. The + constant value is designed to allow easy identification of + an HDF5 file and to allow certain types of data corruption + to be detected. The file signature of an HDF5 file always + contains the following values:</p> + <center> + <table border align="center" cellpadding="4"> + <tr align="center"> + <td align="right">Decimal:</td> + <td width="8%">137</td> + <td width="8%">72</td> + <td width="8%">68</td> + <td width="8%">70</td> + <td width="8%">13</td> + <td width="8%">10</td> + <td width="8%">26</td> + <td width="8%">10</td> + </tr> + + <tr align="center"> + <td align="right">Hexadecimal:</td> + <td>89</td> + <td>48</td> + <td>44</td> + <td>46</td> + <td>0d</td> + <td>0a</td> + <td>1a</td> + <td>0a</td> + </tr> + + <tr align="center"> + <td align="right">ASCII C Notation:</td> + <td>\211</td> + <td>H</td> + <td>D</td> + <td>F</td> + <td>\r</td> + <td>\n</td> + <td>\032</td> + <td>\n</td> + </tr> + </table> + </center> + <p>This signature both identifies the file as an HDF5 file + and provides for immediate detection of common + file-transfer problems. The first two bytes distinguish + HDF5 files on systems that expect the first two bytes to + identify the file type uniquely. The first byte is + chosen as a non-ASCII value to reduce the probability + that a text file may be misrecognized as an HDF5 file; + also, it catches bad file transfers that clear bit + 7. Bytes two through four name the format. The CR-LF + sequence catches bad file transfers that alter newline + sequences. The control-Z character stops file display + under MS-DOS. The final line feed checks for the inverse + of the CR-LF translation problem. (This is a direct + descendent of the + <a href="http://www.libpng.org/pub/png/spec/iso/index-object.html#5PNG-file-signature">PNG</a> file + signature.)</p> + <p><em>This field is present in version 0+ of the superblock.</em> + </p></td> + </tr> + + <tr> + <td><p>Version Number of the Superblock</p></td> + <td><p>This value is used to determine the format of the + information in the superblock. When the format of the + information in the superblock is changed, the version number + is incremented to the next integer and can be used to + determine how the information in the superblock is + formatted.</p> + + <p>Values of 0, 1 and 2 are defined for this field (the + format of version 2 is described below, not here). + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Version Number of the File’s Free Space + Information</p></td> + <td> + <p>This value is used to determine the format of the + file’s free space information. + </p> + <p>The only value currently valid in this field is ‘0’, which + indicates that the file’s free space is as described + <a href="#FreeSpaceManager">below</a>. + </p> + + <p><em>This field is present in versions 0 and 1 of the + superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Version Number of the Root Group Symbol Table + Entry</p></td> + <td><p>This value is used to determine the format of the + information in the Root Group Symbol Table Entry. When the + format of the information in that field is changed, the + version number is incremented to the next integer and can be + used to determine how the information in the field + is formatted.</p> + <p>The only value currently valid in this field is ‘0’, + which indicates that the root group symbol table entry is + formatted as described <a href="#SymbolTableEntry">below</a>.</p> + <p><em>This field is present in version 0 and 1 of the + superblock.</em></p> + </td> + </tr> + + <tr> + <td><p>Version Number of the Shared Header Message Format</p></td> + <td><p>This value is used to determine the format of the + information in a shared object header message. Since the format + of the shared header messages differs from the other private + header messages, a version number is used to identify changes + in the format. + </p> + <p>The only value currently valid in this field is ‘0’, which + indicates that shared header messages are formatted as + described <a href="#ObjectHeaderMessages">below</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p><a name="SizeOfOffsetsV0">Size of Offsets</a></p></td> + <td><p>This value contains the number of bytes used to store + addresses in the file. The values for the addresses of + objects in the file are offsets relative to a base address, + usually the address of the superblock signature. This + allows a wrapper to be added after the file is created + without invalidating the internal offset locations. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p><a name="SizeOfLengthsV0">Size of Lengths</a></p></td> + <td><p>This value contains the number of bytes used to store + the size of an object. + </p> + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Group Leaf Node K</p></td> + <td> + <p>Each leaf node of a group B-tree will have at + least this many entries but not more than twice this + many. If a group has a single leaf node then it + may have fewer entries. + </p> + <p>This value must be greater than zero. + </p> + <p>See the <a href="#Btrees">description</a> of B-trees below. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Group Internal Node K</p></td> + <td> + <p>Each internal node of a group B-tree will have at + least this many entries but not more than twice this + many. If the group has only one internal + node then it might have fewer entries. + </p> + <p>This value must be greater than zero. + </p> + <p>See the <a href="#Btrees">description</a> of B-trees below. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>File Consistency Flags</p></td> + <td> + <p>This field is unused and should be ignored. + </p> + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Indexed Storage Internal Node K</p></td> + <td> + <p>Each internal node of an indexed storage B-tree will have at + least this many entries but not more than twice this + many. If the index storage B-tree has only one internal + node then it might have fewer entries. + </p> + <p>This value must be greater than zero. + </p> + <p>See the <a href="#Btrees">description</a> of B-trees below. + </p> + + <p><em>This field is present in version 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Base Address</p></td> + <td> + <p>This is the absolute file address of the first byte of + the HDF5 data within the file. The library currently + constrains this value to be the absolute file address + of the superblock itself when creating new files; + future versions of the library may provide greater + flexibility. When opening an existing file and this address does + not match the offset of the superblock, the library assumes + that the entire contents of the HDF5 file have been adjusted in + the file and adjusts the base address and end of file address to + reflect their new positions in the file. Unless otherwise noted, + all other file addresses are relative to this base + address. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Address of Global Free-space Index</p></td> + <td> + <p>The file’s free space is not persistent for version 0 and 1 of + the superblock. + Currently this field always contains the + <a href="#UndefinedAddress">undefined address</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>End of File Address</p></td> + <td> + <p>This is the absolute file address of the first byte past + the end of all HDF5 data. It is used to determine whether a + file has been accidently truncated and as an address where + file data allocation can occur if space from the free list is + not used. + </p> + + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Driver Information Block Address</p></td> + <td> + <p>This is the relative file address of the file driver + information block which contains driver-specific + information needed to reopen the file. If there is no + driver information block then this entry should be the + <a href="#UndefinedAddress">undefined address</a>. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + + <tr> + <td><p>Root Group Symbol Table Entry</p></td> + <td> + <p>This is the <a href="#SymbolTableEntry">symbol table entry</a> + of the root group, which serves as the entry point into + the group graph for the file. + </p> + + <p><em>This field is present in version 0 and 1 of the superblock.</em> + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <br /> + <p>Versions 2 and 3 of the superblock are described below:</p> + + <div align="center"> + <table class="format"> + <caption> + Layout: Superblock (Versions 2 and 3) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Format Signature + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td>Version # of Superblock</td> + <td>Size of Offsets</td> + <td>Size of Lengths</td> + <td>File Consistency Flags</td> + </tr> + + <tr> + <td colspan="4"><br />Base Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Superblock Extension Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of File Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Root Group Object Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Superblock Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Superblock (Versions 2 and 3) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Format Signature</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p></td> + </tr> + + <tr> + <td><p>Version Number of the Superblock</p></td> + <td> + <p>This field has a value of 2 and has the same meaning as for + versions 0 and 1. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Offsets</p></td> + <td> + <p>This field is the same as described for + <a href="#SizeOfOffsetsV0">versions 0 and 1</a> of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Lengths</p></td> + <td> + <p>This field is the same as described for + <a href="#SizeOfLengthsV0">versions 0 and 1</a> of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>File Consistency Flags</p></td> + + <td> + <p>For superblock version + 2: This field is unused and should be ignored.</p> + <p>For superblock version + 3: This value contains flags to ensure file consistency for + file locking. Currently, the following bit flags are defined: + <ul> + <li>Bit 0 if set indicates that the file has been opened for + write access.</li> + <li>Bit 1 is reserved for future use.</li> + <li>Bit 2 if set indicates that the file has been opened for + single-writer/multiple-reader (SWMR) write access.</li> + <li>Bits 3-7 are reserved for future use.</li> + </ul> + <p> + Bit 0 should be set as the first action when a file has been + opened for write access. Bit 2 should be set when a file + has been opened for SWMR write access. These two bits should + be cleared only as the final action when closing a file. + </p> + <p><em>This field is present in version 0+ of the superblock.</em> + </p> + <p><em>The size of this + field has been reduced from 4 bytes in superblock format + versions 0 and 1 to 1 byte.</em> + </p> + </td> + + </tr> + + <tr> + <td><p>Base Address</p></td> + <td> + <p>This field is the same as described for versions 0 and + 1 of the superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Superblock Extension Address</p></td> + <td> + <p>The field is the address of the object header for the + <a href="#SuperblockExt">superblock extension</a>. + If there is no extension then this entry should be the + <a href="#UndefinedAddress">undefined address</a>. + </p> + </td> + </tr> + + <tr> + <td><p>End of File Address</p></td> + <td> + <p>This field is the same as described for versions 0 and 1 of the + superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Root Group Object Header Address</p></td> + <td> + <p>This is the address of + the <a href="#DataObject">root group object header</a>, + which serves as the entry point into the group graph for the file. + </p> + </td> + </tr> + + <tr> + <td><p>Superblock Checksum</p></td> + <td> + <p>The checksum for the superblock. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + + <h3><a name="DriverInfo"> + II.B. Disk Format: Level 0B - File Driver Info</a></h3> + + <p>The <b>driver information block</b> is an optional region of the + file which contains information needed by the file driver + to reopen a file. The format is described below:</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Driver Information Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved</td> + </tr> + + <tr> + <td colspan="4">Driver Information Size</td> + </tr> + + <tr> + <td colspan="4"><br />Driver Identification + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Driver Information + <em>(variable size)</em><br /><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Driver Information Block + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number of the Driver Information Block. + This document describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Driver Information Size</p></td> + <td> + <p>The size in bytes of the <em>Driver Information</em> field. + </p> + </td> + </tr> + + <tr> + <td><p>Driver Identification</p></td> + <td> + <p>This is an eight-byte ASCII string without null + termination which identifies the driver and/or version number + of the Driver Information Block. The predefined driver encoded + in this field by the HDF5 Library is identified by the + letters <code>NCSA</code> followed by the first four characters of + the driver name. If the Driver Information block is not + the original version then the last letter(s) of the + identification will be replaced by a version number in + ASCII, starting with 0. + </p> + <p> + Identification for user-defined drivers is also eight-byte long. + It can be arbitrary but should be unique to avoid + the four character prefix “NCSA”. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Driver Information</p></td> + <td>Driver information is stored in a format defined by the + file driver (see description below).</td> + </tr> + </table> + </div> + + <br /> + <p>The two drivers encoded in the <em>Driver Identification</em> + field are as follows:</p> + <ul> + <li> + Multi driver: + <p> + The identifier for this driver is “NCSAmulti”. + This driver provides a mechanism for segregating raw data and different types of metadata + into multiple files. + These files are viewed by the library as a single virtual HDF5 file with a single file address. + A maximum of 6 files will be created for the following data: + superblock, B-tree, raw data, global heap, local heap, and object header. + More than one type of data can be written to the same file. + </p></li> + <li> + Family driver + <p> + The identifier for this driver is “NCSAfami” and is encoded in this field for library version 1.8 and after. + This driver is designed for systems that do not support files larger than 2 gigabytes + by splitting the HDF5 file address space across several smaller files. + It does nothing to segregate metadata and raw data; + they are mixed in the address space just as they would be in a single contiguous file. + </p></li> + </ul> + <p>The format of the <em>Driver Information</em> field for the + above two drivers are described below:</p> + + <div align="center"> + <table class="format"> + <caption> + Layout: Multi Driver Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Member Mapping</td> + </tr> + + <tr> + <td>Member Mapping</td> + <td>Member Mapping</td> + <td>Reserved</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Member File 1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of Address for Member File 1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Member File 2<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of Address for Member File 2<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />... ...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Member File N<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />End of Address for Member File N<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Name of Member File 1 + <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Name of Member File 2 + <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />... ...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Name of Member File N + <em>(variable size)</em><br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Multi Driver Information + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Member Mapping</p></td> + <td><p>These fields are integer values from 1 to 6 + indicating how the data can be mapped to or merged with another type of + data. + <table class="list"> + <tr> + <th width="20%" align="center">Member Mapping</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">1</td> + <td>The superblock data.</td> + </tr> + <tr> + <td align="center">2</td> + <td>The B-tree data.</td> + </tr> + <tr> + <td align="center">3</td> + <td>The raw data.</td> + </tr> + <tr> + <td align="center">4</td> + <td>The global heap data.</td> + </tr> + <tr> + <td align="center">5</td> + <td>The local heap data.</td> + </tr> + <tr> + <td align="center">6</td> + <td>The object header data.</td> + </tr> + </table></p> + <p>For example, if the third field has the value 3 and all the rest have the + value 1, it means there are two files: one for raw data, and one for superblock, + B-tree, global heap, local heap, and object header.</p> + </td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td><p>These fields are reserved and should always be zero.</p></td> + </tr> + + <tr> + <td><p>Address of Member File N</p></td> + <td><p>This field Specifies the virtual address at which the member file starts.</p> + <p>N is the number of member files.</p> + </td> + </tr> + + <tr> + <td><p>End of Address for Member File N</p></td> + <td><p>This field is the end of the allocated address for the member file. + </p></td> + </tr> + + <tr> + <td><p>Name of Member File N</p></td> + <td><p>This field is the null-terminated name of the member file and + its length should be multiples of 8 bytes. + Additional bytes will be padded with <em>NULL</em>s. The default naming + convention is <em>%s-X.h5</em>, where <em>X</em> is one of the letters + <em>s</em> (for superblock), <em>b</em> (for B-tree), <em>r</em> (for raw data), + <em>g</em> (for global heap), <em>l</em> (for local heap), and <em>o</em> (for + object header). The name of the whole HDF5 file will substitute the <em>%s</em> + in the string. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Family Driver Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="8"><br />Size of Member File<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Family Driver Information + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size of Member File</p></td> + <td><p>This field is the size of the member file in the family of files.</p></td> + </tr> + </table> + </div> + + <h3><a name="SuperblockExt"> + II.C. Disk Format: Level 0C - Superblock Extension</a></h3> + + <p>The <em>superblock extension</em> is used to store superblock metadata + which is either optional, or added after the version of the superblock + was defined. Superblock extensions may only exist when version 2 + or later of the superblock is used. A superblock extension is an object + header which may hold the following messages:</p> + <ul> + <li> + <a href="#SOHMTableMessage">Shared Message Table message</a> containing + information to locate the master table of shared object header message + indices.</li> + <li> + <a href="#BtreeKValuesMessage">B-tree ‘K’ Values message</a> containing + non-default B-tree ‘K’ values.</li> + <li> + <a href="#DrvInfoMessage">Driver Info message</a> containing information + needed by the file driver in order to reopen a file. + See also the + <a href="#DriverInfo">“Disk Format: Level 0B - File Driver + Info”</a> section above.</li> + <li> + <a href="#FsinfoMessage">File Space Info message</a> containing + information about file space handling in the file.</li> + </ul> + + + + <h2><a name="FileInfra"> + III. Disk Format: Level 1 - File Infrastructure</a></h2> + + <h3><a name="Btrees"> + III.A. Disk Format: Level 1A - B-trees and B-tree Nodes</a></h3> + + <p>B-trees allow flexible storage for objects which tend to grow + in ways that cause the object to be stored discontiguously. B-trees + are described in various algorithms books including “Introduction to + Algorithms” by Thomas H. Cormen, Charles E. Leiserson, and Ronald + L. Rivest. B-trees are used in several places in the HDF5 file format, + when an index is needed for another data structure.</p> + + <p>The version 1 B-tree structure described below is the original + index structure. The version 1 B-trees are being phased out in + favor of the version 2 B-trees described below. Note that both + types of structures may be found in the same file depending on + the application settings when creating the file.</p> + + <h4><a name="V1Btrees"> + III.A.1. Disk Format: Level 1A1 - Version 1 B-trees</a></h4> + + <p>Version 1 B-trees in HDF5 files are an implementation of the + B-link tree. The sibling nodes at a particular level in + the tree are stored in a doubly-linked list. See the + “Efficient Locking for Concurrent Operations on B-trees” + paper by Phillip Lehman and S. Bing Yao as published in the + <cite>ACM Transactions on Database Systems</cite>, Vol. 6, No. 4, + December 1981.</p> + + <p>The B-trees implemented by the file format contain one more + key than the number of children. In other words, each child + pointer out of a B-tree node has a left key and a right key. + The pointers out of internal nodes point to sub-trees while + the pointers out of leaf nodes point to symbol nodes and + raw data chunks. + Aside from that difference, internal nodes and leaf nodes + are identical.</p> + + <div align="center"> + <table class="format"> + <caption> + Layout: B-tree Nodes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Node Type</td> + <td>Node Level</td> + <td colspan="2">Entries Used</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Left Sibling<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Right Sibling<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Key 1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Child 1<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Key 2 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Child 2<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Key 2<em>K</em> <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Child 2<em>K</em><sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Key 2<em>K</em>+1 + <em>(variable size)</em></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: B-tree Nodes + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>TREE</code>” + is used to indicate the beginning of a B-tree node. This + gives file consistency checking utilities a better chance + of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Node Type</p></td> + <td> + <p>Each B-tree points to a particular type of data. + This field indicates the type of data as well as + implying the maximum degree <em>K</em> of the tree and + the size of each Key field. + + + <table class="list"> + <tr> + <th width="20%" align="center">Node Type</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>This tree points to group nodes.</td> + </tr> + <tr> + <td align="center">1</td> + <td>This tree points to raw data chunk nodes.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Node Level</p></td> + <td> + <p>The node level indicates the level at which this node + appears in the tree (leaf nodes are at level zero). Not + only does the level indicate whether child pointers + point to sub-trees or to data, but it can also be used + to help file consistency checking utilities reconstruct + damaged trees. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Entries Used</p></td> + <td> + <p>This determines the number of children to which this + node points. All nodes of a particular type of tree + have the same maximum degree, but most nodes will point + to less than that number of children. The valid child + pointers and keys appear at the beginning of the node + and the unused pointers and keys appear at the end of + the node. The unused pointers and keys have undefined + values. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Address of Left Sibling</p></td> + <td> + <p>This is the relative file address of the left sibling of + the current node. If the current + node is the left-most node at this level then this field + is the <a href="#UndefinedAddress">undefined address</a>. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Address of Right Sibling</p></td> + <td> + <p>This is the relative file address of the right sibling of + the current node. If the current + node is the right-most node at this level then this + field is the <a href="#UndefinedAddress">undefined address</a>. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Keys and Child Pointers</p></td> + <td> + <p>Each tree has 2<em>K</em>+1 keys with 2<em>K</em> + child pointers interleaved between the keys. The number + of keys and child pointers actually containing valid + values is determined by the node’s <em>Entries + Used</em> field. If that field is <em>N</em>, then the + B-tree contains <em>N</em> child pointers and + <em>N</em>+1 keys. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Key</p></td> + <td> + <p>The format and size of the key values is determined by + the type of data to which this tree points. The keys are + ordered and are boundaries for the contents of the child + pointer; that is, the key values represented by child + <em>N</em> fall between Key <em>N</em> and Key + <em>N</em>+1. Whether the interval is open or closed on + each end is determined by the type of data to which the + tree points. + </p> + + <p> + The format of the key depends on the node type. + For nodes of node type 0 (group nodes), the key is formatted as + follows: + + <table class="list"> + <tr> + <td width="20%">A single field of + <i><a href="#SizeOfLengthsV0">Size of Lengths</a></i> + bytes:</td> + <td width="80%">Indicates the byte offset into the local heap + for the first object name in the subtree which + that key describes. + </td> + </tr> + </table> + </p> + + + <p> + For nodes of node type 1 (chunked raw data nodes), the key is + formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-4:</td> + <td width="80%">Size of chunk in bytes.</td> + </tr> + <tr> + <td>Bytes 4-8:</td> + <td>Filter mask, a 32-bit bit field indicating which + filters have been skipped for this chunk. Each filter + has an index number in the pipeline (starting at 0, with + the first filter to apply) and if that filter is skipped, + the bit corresponding to its index is set.</td> + </tr> + <tr> + <td>(<em>D + 1</em>) 64-bit fields:</td> + <td>The offset of the + chunk within the dataset where <i>D</i> is the number + of dimensions of the dataset, and the last value is the + offset within the dataset’s datatype and should + always be zero. For example, if + a chunk in a 3-dimensional dataset begins at the + position <code>[5,5,5]</code>, there will be three + such 64-bit values, each with the value of + <code>5</code>, followed by a <code>0</code> value.</td> + </tr> + </table> + </p> + + </td> + </tr> + + <tr valign="top"> + <td><p>Child Pointer</p></td> + <td> + <p>The tree node contains file addresses of subtrees or + data depending on the node level. Nodes at Level 0 point + to data addresses, either raw data chunks or group nodes. + Nodes at non-zero levels point to other nodes of the + same B-tree. + </p> + <p>For raw data chunk nodes, the child pointer is the address + of a single raw data chunk. For group nodes, the child pointer + points to a <a href="#SymbolTable">symbol table</a>, which contains + information for multiple symbol table entries. + </p> + </td> + </tr> + </table> + </div> + + <p> + Conceptually, each B-tree node looks like this:</p> + <center> + <table> + <tr valign="top" align="center"> + <td>key[0]</td><td> </td> + <td>child[0]</td><td> </td> + <td>key[1]</td><td> </td> + <td>child[1]</td><td> </td> + <td>key[2]</td><td> </td> + <td>...</td><td> </td> + <td>...</td><td> </td> + <td>key[<i>N</i>-1]</td><td> </td> + <td>child[<i>N</i>-1]</td><td> </td> + <td>key[<i>N</i>]</td> + </tr> + </table> + </center> + <br /> + + where child[<i>i</i>] is a pointer to a sub-tree (at a level + above Level 0) or to data (at Level 0). + Each key[<i>i</i>] describes an <i>item</i> stored by the B-tree + (a chunk or an object of a group node). The range of values + represented by child[<i>i</i>] is indicated by key[<i>i</i>] + and key[<i>i</i>+1]. + + + <p>The following question must next be answered: + “Is the value described by key[<i>i</i>] contained in + child[<i>i</i>-1] or in child[<i>i</i>]?” + The answer depends on the type of tree. + In trees for groups (node type 0), the object described by + key[<i>i</i>] is the greatest object contained in + child[<i>i</i>-1] while in chunk trees (node type 1) the + chunk described by key[<i>i</i>] is the least chunk in + child[<i>i</i>].</p> + + <p>That means that key[0] for group trees is sometimes unused; + it points to offset zero in the heap, which is always the + empty string and compares as “less-than” any valid + object name.</p> + + <p>And key[<i>N</i>] for chunk trees is sometimes unused; + it contains a chunk offset which compares as “greater-than” + any other chunk offset and has a chunk byte size of zero + to indicate that it is not actually allocated.</p> + + <h4><a name="V2Btrees"> + III.A.2. Disk Format: Level 1A2 - Version 2 B-trees</a></h4> + + <p>Version 2 (v2) B-trees are “traditional” B-trees + with one major difference. Instead of just using a simple pointer + (or address in the file) to a child of an internal node, the pointer + to the child node contains two additional pieces of information: + the number of records in the child node itself, and the total number + of records in the child node and all its descendants. Storing this + additional information allows fast array-like indexing to locate + the n<sup>th</sup> record in the B-tree.</p> + + <p>The entry into a version 2 B-tree is a header which contains global + information about the structure of the B-tree. The <em>root node + address</em> + field in the header points to the B-tree root node, which is either an + internal or leaf node, depending on the value in the header’s + <em>depth</em> field. An internal node consists of records plus + pointers to further leaf or internal nodes in the tree. A leaf node + consists of solely of records. The format of the records depends on + the B-tree type (stored in the header).</p> + + <div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Node Size</td> + </tr> + <tr> + <td colspan="2">Record Size</td> + <td colspan="2">Depth</td> + </tr> + <tr> + <td>Split Percent</td> + <td>Merge Percent</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Root Node Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="2">Number of Records in Root Node</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Total Number of Records in B-tree<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree Header + </caption> + + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>BTHD</code>” + is used to indicate the header of a version 2 (v2) B-tree + node. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this B-tree header. This document + describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field indicates the type of B-tree: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>This B-tree is used for testing only. This + value should <em>not</em> be used for storing + records in actual HDF5 files. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>This B-tree is used for indexing indirectly accessed, + non-filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">2</td> + <td>This B-tree is used for indexing indirectly accessed, + filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">3</td> + <td>This B-tree is used for indexing directly accessed, + non-filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">4</td> + <td>This B-tree is used for indexing directly accessed, + filtered ‘huge’ fractal heap objects. + </td> + </tr> + <tr> + <td align="center">5</td> + <td>This B-tree is used for indexing the ‘name’ field for + links in indexed groups. + </td> + </tr> + <tr> + <td align="center">6</td> + <td>This B-tree is used for indexing the ‘creation order’ + field for links in indexed groups. + </td> + </tr> + <tr> + <td align="center">7</td> + <td>This B-tree is used for indexing shared object header + messages. + </td> + </tr> + <tr> + <td align="center">8</td> + <td>This B-tree is used for indexing the ‘name’ field for + indexed attributes. + </td> + </tr> + <tr> + <td align="center">9</td> + <td>This B-tree is used for indexing the ‘creation order’ + field for indexed attributes. + </td> + </tr> + + <tr> + <td align="center">10</td> + <td>This B-tree is used for indexing chunks of + datasets with no filters and with more than one + dimension of unlimited extent. + </td> + </tr> + + <tr> + <td align="center">11</td> + <td>This B-tree is used for indexing chunks of + datasets with filters and more than one dimension + of unlimited extent. + </td> + </tr> + </table></p> + <p>The format of records for each type is described below.</p> + </td> + </tr> + + <tr valign="top"> + <td><p>Node Size</p></td> + <td> + <p>This is the size in bytes of all B-tree nodes. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Record Size</p></td> + <td> + <p>This field is the size in bytes of the B-tree record. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Depth</p></td> + <td> + <p>This is the depth of the B-tree. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Split Percent</p></td> + <td> + <p>The percent full that a node needs to increase above before it + is split. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Merge Percent</p></td> + <td> + <p>The percent full that a node needs to be decrease below before it + is split. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Root Node Address</p></td> + <td> + <p>This is the address of the root B-tree node. A B-tree with + no records will have the <a href="#UndefinedAddress">undefined + address</a> in this field. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Number of Records in Root Node</p></td> + <td> + <p>This is the number of records in the root node. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Total Number of Records in B-tree</p></td> + <td> + <p>This is the total number of records in the entire B-tree. + </p> + </td> + </tr> + + <tr valign="top"> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the B-tree header. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree Internal Node + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2">Records 0, 1, 2...N-1 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Child Node Pointer 0<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Number of Records N<sub>0</sub> for Child + Node 0 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Total Number of Records for Child Node 0 + <em>(optional, variable size)</em></td> + </tr> + <tr> + <td colspan="4"><br />Child Node Pointer 1<sup>O</sup><br /><br /></td> + </tr> + <td colspan="4"><br />Number of Records N<sub>1</sub> for + Child Node 1 <em>(variable size)</em></td> +</tr> +<tr> + <td colspan="4"><br />Total Number of Records for Child Node 1 + <em>(optional, variable size)</em></td> +</tr> +<tr> + <td colspan="4">...</td> +</tr> +<tr> + <td colspan="4"><br />Child Node Pointer N<sup>O</sup><br /><br /></td> +</tr> +<tr> + <td colspan="4"><br />Number of Records N<sub>n</sub> for + Child Node N <em>(variable size)</em></td> +</tr> +<tr> + <td colspan="4"><br />Total Number of Records for Child Node N + <em>(optional, variable size)</em></td> +</tr> +<tr> + <td colspan="4">Checksum</td> +</tr> +</table> + +<table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> +</table> +</div> + + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree Internal Node + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>BTIN</code>” is + used to indicate the internal node of a B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this B-tree internal node. + This document describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field is the type of the B-tree node. It should always + be the same as the B-tree type in the header. + </p> + </td> + </tr> + + <tr> + <td><p>Records</p></td> + <td> + <p>The size of this field is determined by the number of records + for this node and the record size (from the header). The format + of records depends on the type of B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Child Node Pointer</p></td> + <td> + <p>This field is the address of the child node pointed to by the + internal node. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Records in Child Node</p></td> + <td> + <p>This is the number of records in the child node pointed to by + the corresponding <em>Node Pointer</em>. + </p> + <p>The number of bytes used to store this field is determined by + the maximum possible number of records able to be stored in the + child node. + </p> + <p> + The maximum number of records in a child node is computed + in the following way: + + <ul> + <li>Subtract the fixed size overhead for + the child node (for example, its signature, version, + checksum, and so on and <em>one</em> pointer triplet + of information for the child node (because there is one + more pointer triplet than records in each internal node)) + from the size of nodes for the B-tree. </li> + <li>Divide that result by the size of a record plus the + pointer triplet of information stored to reach each + child node from this node.</li> + </ul> + + </p> + <p> + Note that leaf nodes do not encode any + child pointer triplets, so the maximum number of records in a + leaf node is just the node size minus the leaf node overhead, + divided by the record size. + </p> + <p> + Also note that the first level of internal nodes above the + leaf nodes do not encode the <em>Total Number of Records in Child + Node</em> value in the child pointer triplets (since it is the + same as the <em>Number of Records in Child Node</em>), so the + maximum number of records in these nodes is computed with the + equation above, but using (<em>Child Pointer</em>, <em>Number of + Records in Child Node</em>) pairs instead of triplets. + </p> + <p> + The number of + bytes used to encode this field is the least number of bytes + required to encode the maximum number of records in a child + node value for the child nodes below this level + in the B-tree. + </p> + <p> + For example, if the maximum number of child records is + 123, one byte will be used to encode these values in this + node; if the maximum number of child records is + 20000, two bytes will be used to encode these values in this + node; and so on. The maximum number of bytes used to + encode these values is 8 (in other words, an unsigned + 64-bit integer). + </p> + </td> + </tr> + + <tr> + <td><p>Total Number of Records in Child Node</p></td> + <td> + <p>This is the total number of records for the node pointed to by + the corresponding <em>Node Pointer</em> and all its children. + This field exists only in nodes whose depth in the B-tree node + is greater than 1 (in other words, the “twig” + internal nodes, just above leaf nodes, do not store this + field in their child node pointers). + </p> + <p>The number of bytes used to store this field is determined by + the maximum possible number of records able to be stored in the + child node and its descendants. + </p> + <p> + The maximum possible number of records able to be stored in a + child node and its descendants is computed iteratively, in the + following way: The maximum number of records in a leaf node + is computed, then that value is used to compute the maximum + possible number of records in the first level of internal nodes + above the leaf nodes. Multiplying these two values together + determines the maximum possible number of records in child node + pointers for the level of nodes two levels above leaf nodes. + This process is continued up to any level in the B-tree. + </p> + <p> + The number of bytes used to encode this value is computed in + the same way as for the <em>Number of Records in Child Node</em> + field. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for this node. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree Leaf Node + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2">Record 0, 1, 2...N-1 <em>(variable size)</em></td> + </tr> + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree Leaf Node + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>BTLF</code>“ + is used to indicate the leaf node of a version 2 (v2) B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this B-tree leaf node. + This document describes version 0. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field is the type of the B-tree node. It should always + be the same as the B-tree type in the header. + </p> + </td> + </tr> + + <tr> + <td><p>Records</p></td> + <td> + <p>The size of this field is determined by the number of records + for this node and the record size (from the header). The format + of records depends on the type of B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for this node. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<p>The record layout for each stored (in other words, non-testing) + B-tree type is as follows:</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 1 Record Layout - Indirectly + Accessed, Non-filtered, ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object ID<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 1 Record Layout - Indirectly + Accessed, Non-filtered, ‘Huge’ Fractal Heap Objects + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Huge Object Address</p></td> + <td> + <p>The address of the huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object Length</p></td> + <td> + <p>The length of the huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object ID</p></td> + <td> + <p>The heap ID for the huge object. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 2 Record Layout - Indirectly + Accessed, Filtered, ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Filtered Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask</td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Memory Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object ID<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 2 Record Layout - Indirectly + Accessed, Filtered, ‘Huge’ Fractal Heap Objects + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filtered Huge Object Address</p></td> + <td> + <p>The address of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Length</p></td> + <td> + <p>The length of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td> + <p>A 32-bit bit field indicating which filters have been skipped for + this chunk. Each filter has an index number in the pipeline + (starting at 0, with the first filter to apply) and if that + filter is skipped, the bit corresponding to its index is set. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Memory Size</p></td> + <td> + <p>The size of the de-filtered huge object in memory. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object ID</p></td> + <td> + <p>The heap ID for the huge object. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 3 Record Layout - Directly + Accessed, Non-filtered, ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 3 Record Layout - Directly + Accessed, Non-filtered, ‘Huge’ Fractal Heap Objects + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Huge Object Address</p></td> + <td> + <p>The address of the huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Huge Object Length</p></td> + <td> + <p>The length of the huge object in the file. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 4 Record Layout - Directly + Accessed, Filtered, ‘Huge’ Fractal Heap Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Filtered Huge Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Length<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask</td> + </tr> + <tr> + <td colspan="4"><br />Filtered Huge Object Memory Size<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 4 Record Layout - Directly + Accessed, Filtered, ‘Huge’ Fractal Heap Objects + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filtered Huge Object Address</p></td> + <td> + <p>The address of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Length</p></td> + <td> + <p>The length of the filtered huge object in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td> + <p>A 32-bit bit field indicating which filters have been skipped for + this chunk. Each filter has an index number in the pipeline + (starting at 0, with the first filter to apply) and if that + filter is skipped, the bit corresponding to its index is set. + </p> + </td> + </tr> + + <tr> + <td><p>Filtered Huge Object Memory Size</p></td> + <td> + <p>The size of the de-filtered huge object in memory. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 5 Record Layout - Link Name + for Indexed Group + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Hash of Name</td> + </tr> + <tr> + <td colspan="4">ID <em>(bytes 1-4)</em></td> + </tr> + + <tr> + <td colspan="3">ID <em>(bytes 5-7)</em></td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 5 Record Layout - Link Name + for Indexed Group + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the name for the link. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the link’s name. + </p> + </td> + </tr> + + <tr> + <td><p>ID</p></td> + <td> + <p>This is a 7-byte sequence of bytes and is the heap ID for the + link record in the group’s fractal heap.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 6 Record Layout - Creation + Order for Indexed Group + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Creation Order + <em>(8 bytes)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">ID <em>(bytes 1-4)</em></td> + </tr> + <tr> + <td colspan="3">ID <em>(bytes 5-7)</em></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 6 Record Layout - Creation + Order for Indexed Group + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td> + <p>This field is the creation order value for the link. + </p> + </td> + </tr> + + <tr> + <td><p>ID</p></td> + <td> + <p>This is a 7-byte sequence of bytes and is the heap ID for the + link record in the group’s fractal heap.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 7 Record Layout - Shared + Object Header Messages (Sub-type 0 - Message in Heap) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Hash</td> + </tr> + <tr> + <td colspan="4">Reference Count</td> + </tr> + <tr> + <td colspan="4"><br />Heap ID <em>(8 bytes)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 7 Record Layout - Shared + Object Header Messages (Sub-type 0 - Message in Heap) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This field Indicates the location where the message is stored: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>Shared message is stored in shared message index heap. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>Shared message is stored in object header. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the shared message. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the shared message.</p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td> + <p>The number of objects which reference this message.</p> + </td> + </tr> + + <tr> + <td><p>Heap ID</p></td> + <td> + <p>This is an 8-byte sequence of bytes and is the heap ID for the + shared message in the shared message index’s fractal heap.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 7 Record Layout - Shared + Object Header Messages (Sub-type 1 - Message in Object Header) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Hash</td> + </tr> + <tr> + <td>Reserved (zero)</td> + <td>Message Type</td> + <td colspan="2">Object Header Index</td> + </tr> + <tr> + <td colspan="4"><br />Object Header Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 7 Record Layout - Shared + Object Header Messages (Sub-type 1 - Message in Object Header) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This field Indicates the location where the message is stored: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>Shared message is stored in shared message index heap. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>Shared message is stored in object header. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the shared message. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the shared message.</p> + </td> + </tr> + + <tr> + <td><p>Message Type</p></td> + <td> + <p>The object header message type of the shared message.</p> + </td> + </tr> + + <tr> + <td><p>Object Header Index</p></td> + <td> + <p>This field indicates that the shared message is the n<sup>th</sup> message + of its type in the specified object header.</p> + </td> + </tr> + + <tr> + <td><p>Object Header Address</p></td> + <td> + <p>The address of the object header containing the shared message.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 8 Record Layout - Attribute + Name for Indexed Attributes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Heap ID <em>(8 bytes)</em><br /><br /></td> + </tr> + <tr> + <td colspan>Message Flags</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Creation Order</td> + </tr> + <tr> + <td colspan="4">Hash of Name</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 8 Record Layout - Attribute + Name for Indexed Attributes + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Heap ID</p></td> + <td> + <p>This is an 8-byte sequence of bytes and is the heap ID for the + attribute in the object’s attribute fractal heap.</p> + </td> + </tr> + + <tr> + <td><p>Message Flags</p></td> + <td><p>The object header message flags for the attribute message.</p> + </td> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td> + <p>This field is the creation order value for the attribute. + </p> + </td> + </tr> + + <tr> + <td><p>Hash</p></td> + <td> + <p>This field is hash value of the name for the attribute. The hash + value is the Jenkins’ lookup3 checksum algorithm applied to + the attribute’s name. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree, Type 9 Record Layout - Creation + Order for Indexed Attributes + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Heap ID <em>(8 bytes)</em><br /><br /></td> + </tr> + <tr> + <td colspan>Message Flags</td> + <td colspan="3" bgcolor="#DDDDDD"> + <em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Creation Order</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 9 Record Layout - Creation + Order for Indexed Attributes + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Heap ID</p></td> + <td> + <p>This is an 8-byte sequence of bytes and is the heap ID for the + attribute in the object’s attribute fractal heap.</p> + </td> + </tr> + + <tr> + <td><p>Message Flags</p></td> + <td> + <p>The object header message flags for the attribute message.</p> + </td> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td> + <p>This field is the creation order value for the attribute. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<a name="V2BtType10"></a> + <div align="center"> + <table class="format"> + <caption> + <a name="V2BtreesType10"></a> + Layout: Version 2 B-tree, Type 10 Record Layout - + Non-filtered Dataset Chunks + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dimension 0 Scaled Offset + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dimension 1 Scaled Offset + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dimension #n Scaled Offset + <em>(8 bytes)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 10 Record Layout - + Non-filtered Dataset Chunks +</caption> +<tr> + <th width="30%">Field Name</th> + <th>Description</th> +</tr> + +<tr> + <td><p>Address</p></td> + <td> + <p>This field is the address of the dataset chunk in the file.</p> + </td> +</tr> + +<tr> + <td><p>Dimension #n Scaled Offset</p></td> + <td> + <p>This field is the scaled offset of the chunk within the + dataset. <em>n</em> is the number of dimensions for the + dataset. The first scaled offset stored in the list is for + the slowest changing dimension, and the last scaled offset + stored is for the fastest changing dimension. Scaled offset + is calculated by dividing the chunk dimension sizes into + the chunk offsets.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + <a name="V2BtreesType11"></a> + Layout: Version 2 B-tree, Type 11 Record Layout - Filtered + Dataset Chunks + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Chunk Size + <em>(variable size; at most 8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Filter Mask</td> + </tr> + + <tr> + <td colspan="4"><br />Dimension 0 Scaled Offset + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dimension 1 Scaled Offset + <em>(8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dimension #n Scaled Offset + <em>(8 bytes)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree, Type 11 Record Layout - Filtered + Dataset Chunks +</caption> +<tr> + <th width="30%">Field Name</th> + <th>Description</th> +</tr> + +<tr> + <td><p>Address</p></td> + <td> + <p>This field is the address of the dataset chunk in the file.</p> + </td> +</tr> + +<tr> + <td><p>Chunk Size</p></td> + <td> + <p>This field is the size of the dataset chunk in bytes.</p> + </td> +</tr> + +<tr> + <td><p>Filter Mask</p></td> + <td> + <p>This field is the filter mask which indicates the filter + to skip for the dataset chunk. Each filter has an index + number in the pipeline and if that filter is skipped, + the bit corresponding to its index is set.</p> + </td> +</tr> + +<tr> + <td><p>Dimension #n Scaled Offset</p></td> + <td> + <p>This field is the scaled offset of the chunk within + the dataset. <em>n</em> is the number of dimensions for + the dataset. The first scaled offset stored in the list + is for the slowest changing dimension, and the last scaled + offset stored is for the fastest changing dimension.</p> + </td> +</tr> + +</table> +</div> + +<h3><a name="SymbolTable"> + III.B. Disk Format: Level 1B - Group Symbol Table Nodes</a></h3> + +<p>A group is an object internal to the file that allows + arbitrary nesting of objects within the file (including other + groups). A group maps a set of link names in the group to a set + of relative file addresses of objects in the file. Certain metadata + for an object to which the group points can be cached in the + group’s symbol table entry in addition to being in the + object’s header.</p> + +<p>An HDF5 object name space can be stored hierarchically by + partitioning the name into components and storing each + component as a link in a group. The link for a + non-ultimate component points to the group containing + the next component. The link for the last + component points to the object being named.</p> + +<p>One implementation of a group is a collection of symbol table + nodes indexed by a B-tree. Each symbol table node contains entries + for one or more links. If an attempt is made to add a link to an + already full symbol table node containing 2<em>K</em> entries, then + the node is split and one node contains <em>K</em> symbols and the + other contains <em>K</em>+1 symbols.</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Symbol Table Node (A Leaf of a B-tree) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version Number</td> + <td>Reserved <em>(zero)</em></td> + <td colspan="2">Number of Symbols</td> + </tr> + + <tr> + <td colspan="4"><br /><br />Group Entries<br /><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Symbol Table Node (A Leaf of a B-tree) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>SNOD</code>” is + used to indicate the + beginning of a symbol table node. This gives file + consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version Number</p></td> + <td> + <p>The version number for the symbol table node. This + document describes version 1. (There is no version ‘0’ + of the symbol table node) + </p> + </td> + </tr> + + <tr> + <td><p>Number of Entries</p></td> + <td> + <p>Although all symbol table nodes have the same length, + most contain fewer than the maximum possible number of + link entries. This field indicates how many entries + contain valid data. The valid entries are packed at the + beginning of the symbol table node while the remaining + entries contain undefined values. + </p> + </td> + </tr> + + <tr> + <td><p>Symbol Table Entries</p></td> + <td> + <p>Each link has an entry in the symbol table node. + The format of the entry is described below. + There are 2<em>K</em> entries in each group node, where + <em>K</em> is the “Group Leaf Node K” value from the + <a href="#Superblock">superblock</a>. + </p> + </td> + </tr> + </table> +</div> + +<h3><a name="SymbolTableEntry"> + III.C. Disk Format: Level 1C - Symbol Table Entry </a></h3> + +<p>Each symbol table entry in a symbol table node is designed + to allow for very fast browsing of stored objects. + Toward that design goal, the symbol table entries + include space for caching certain constant metadata from the + object header.</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Symbol Table Entry + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Link Name Offset<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Object Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Cache Type</td> + </tr> + + <tr> + <td colspan="4">Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Scratch-pad Space + <em>(16 bytes)</em><br /><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Symbol Table Entry + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Link Name Offset</p></td> + <td> + <p>This is the byte offset into the group’s local + heap for the name of the link. The name is null + terminated. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Address</p></td> + <td> + <p>Every object has an object header which serves as a + permanent location for the object’s metadata. In addition + to appearing in the object header, some of the object’s metadata + can be cached in the scratch-pad space. + </p> + </td> + </tr> + + <tr> + <td><p>Cache Type</p></td> + <td> + <p>The cache type is determined from the object header. + It also determines the format for the scratch-pad space: + + <table class="list"> + <tr> + <th width="20%" align="center">Type</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center">0</td> + <td>No data is cached by the group entry. This + is guaranteed to be the case when an object header + has a link count greater than one. + </td> + </tr> + <tr> + <td align="center">1</td> + <td>Group object header metadata is cached in the + scratch-pad space. This implies that the symbol table + entry refers to another group. + </td> + </tr> + <tr> + <td align="center">2</td> + <td>The entry is a symbolic link. The first four bytes + of the scratch-pad space are the offset into the local + heap for the link value. The object header address + will be undefined. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td> + <p>These four bytes are present so that the scratch-pad + space is aligned on an eight-byte boundary. They are + always set to zero. + </p> + </td> + </tr> + + <tr> + <td><p>Scratch-pad Space</p></td> + <td> + <p>This space is used for different purposes, depending + on the value of the Cache Type field. Any metadata + about an object represented in the scratch-pad + space is duplicated in the object header for that + object. + </p> + <p> + Furthermore, no data is cached in the group + entry scratch-pad space if the object header for + the object has a link count greater than one. + </p> + </td> + </tr> + </table> +</div> + +<h4>Format of the Scratch-pad Space</h4> + +<p>The symbol table entry scratch-pad space is formatted + according to the value in the Cache Type field.</p> + +<p>If the Cache Type field contains the value zero + <code>(0)</code> then no information is + stored in the scratch-pad space.</p> + +<p>If the Cache Type field contains the value one + <code>(1)</code>, then the scratch-pad space + contains cached metadata for another object header + in the following format:</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Object Header Scratch-pad Format + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address of B-tree<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Name Heap<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Object Header Scratch-pad Format + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address of B-tree</p></td> + <td> + <p>This is the file address for the root of the + group’s B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Name Heap</p></td> + <td> + <p>This is the file address for the group’s local + heap, in which are stored the group’s symbol names. + </p> + </td> + </tr> + </table> +</div> + + +<br /> +<br /> +<br /> +<p>If the Cache Type field contains the value two + <code>(2)</code>, then the scratch-pad space + contains cached metadata for a symbolic link + in the following format:</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Symbolic Link Scratch-pad Format + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Offset to Link Value</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Symbolic Link Scratch-pad Format + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Offset to Link Value</p></td> + <td> + <p>The value of a symbolic link (that is, the name of the + thing to which it points) is stored in the local heap. + This field is the 4-byte offset into the local heap for + the start of the link value, which is null terminated. + </p> + </td> + </tr> + </table> +</div> + +<h3><a name="LocalHeap"> + III.D. Disk Format: Level 1D - Local Heaps</a></h3> + +<p>A local heap is a collection of small pieces of data that are particular + to a single object in the HDF5 file. Objects can be + inserted and removed from the heap at any time. + The address of a heap does not change once the heap is created. + For example, a group stores addresses of objects in symbol table nodes + with the names of links stored in the group’s local heap. +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Local Heap + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Data Segment Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Offset to Head of Free-list<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Data Segment<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Local Heap + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>HEAP</code>” + is used to indicate the + beginning of a heap. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>Each local heap has its own version number so that new + heaps can be added to old files. This document + describes version zero (0) of the local heap. + </p> + </td> + </tr> + + <tr> + <td><p>Data Segment Size</p></td> + <td> + <p>The total amount of disk memory allocated for the heap + data. This may be larger than the amount of space + required by the objects stored in the heap. The extra + unused space in the heap holds a linked list of free blocks. + </p> + </td> + </tr> + + <tr> + <td><p>Offset to Head of Free-list</p></td> + <td> + <p>This is the offset within the heap data segment of the + first free block (or the + <a href="#UndefinedAddress">undefined address</a> if there is no + free block). The free block contains + <a href="#SizeOfLengthsV0">Size of Lengths</a> bytes that + are the offset of the next free block (or the + value ‘1’ if this is the + last free block) followed by Size of Lengths bytes that store + the size of this free block. The size of the free block includes + the space used to store the offset of the next free block and + the size of the current block, making the minimum size of a free + block 2 * Size of Lengths. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Data Segment</p></td> + <td> + <p>The data segment originally starts immediately after + the heap header, but if the data segment must grow as a + result of adding more objects, then the data segment may + be relocated, in its entirety, to another part of the + file. + </p> + </td> + </tr> + </table> +</div> + +<p>Objects within a local heap should be aligned on an 8-byte boundary.</p> + +<h3><a name="GlobalHeap"> + III.E. Disk Format: Level 1E - Global Heap</a></h3> + +<p>Each HDF5 file has a global heap which stores various types of + information which is typically shared between datasets. The + global heap was designed to satisfy these goals:</p> + +<ol type="A"> + <li>Repeated access to a heap object must be efficient without + resulting in repeated file I/O requests. Since global heap + objects will typically be shared among several datasets, it is + probable that the object will be accessed repeatedly.</li> + <li>Collections of related global heap objects should result in + fewer and larger I/O requests. For instance, a dataset of + object references will have a global heap object for each + reference. Reading the entire set of object references + should result in a few large I/O requests instead of one small + I/O request for each reference.</li> + <li>It should be possible to remove objects from the global heap + and the resulting file hole should be eligible to be reclaimed + for other uses.</li> +</ol> + + +<p>The implementation of the heap makes use of the memory management + already available at the file level and combines that with a new + object called a <em>collection</em> to achieve goal B. The global heap + is the set of all collections. Each global heap object belongs to + exactly one collection, and each collection contains one or more global + heap objects. For the purposes of disk I/O and caching, a collection is + treated as an atomic object, addressing goal A. +</p> + +<p>When a global heap object is deleted from a collection (which + occurs when its reference count falls to zero), objects located + after the deleted object in the collection are packed down toward + the beginning of the collection, and the collection’s + global heap object 0 is created (if possible), or its size is + increased to account for the recently freed space. There are + no gaps between objects in each collection, with the possible + exception of the final space in the collection, if it is not + large enough to hold the header for the collection’s + global heap object 0. These features address goal C. +</p> + +<p>The HDF5 Library creates global heap collections as needed, so there may + be multiple collections throughout the file. The set of all of them is + abstractly called the “global heap”, although they do not actually link + to each other, and there is no global place in the file where you can + discover all of the collections. The collections are found simply by + finding a reference to one through another object in the file. For + example, data of variable-length datatype elements is stored in the + global heap and is accessed via a global heap ID. The format for + global heap IDs is described at the end of this section. +</p> + +<p>For more information on global heaps for virtual datasets, see + <a href="#GlobalHeapVDS">“Disk Format: Level 1F - Global Heap + Block for Virtual Datasets.”</a></p> +<br /> + +<div align="center"> + <table class="format"> + <caption> + Layout: A Global Heap Collection + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Collection Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object 1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object 2<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />...<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object <em>N</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Global Heap Object 0 (free space)<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: A Global Heap Collection + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>GCOL</code>” + is used to indicate the + beginning of a collection. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>Each collection has its own version number so that new + collections can be added to old files. This document + describes version one (1) of the collections (there is no + version zero (0)). + </p> + </td> + </tr> + + <tr> + <td><p>Collection Size</p></td> + <td> + <p>This is the size in bytes of the entire collection + including this field. The default (and minimum) + collection size is 4096 bytes which is a typical file + system block size. This allows for 127 16-byte heap + objects plus their overhead (the collection header of 16 bytes + and the 16 bytes of information about each heap object). + </p> + </td> + </tr> + + <tr> + <td><p>Global Heap Object 1 through <em>N</em></p></td> + <td> + <p>The objects are stored in any order with no + intervening unused space. + </p> + </td> + </tr> + + <tr> + <td><p>Global Heap Object 0</p></td> + <td> + <p>Global Heap Object 0 (zero), when present, represents the free + space in the collection. Free space always appears at the end of + the collection. If the free space is too small to store the header + for Object 0 (described below) then the header is implied and is not + written. + <p> + The field <em>Object Size</em> for Object 0 indicates the + amount of possible free space in the collection including the 16-byte + header size of Object 0. + </p> + </td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Global Heap Object + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="2">Heap Object Index</td> + <td colspan="2">Reference Count</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Object Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Object Data<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Global Heap Object + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Heap Object Index</p></td> + <td> + <p>Each object has a unique identification number within a + collection. The identification numbers are chosen so that + new objects have the smallest value possible with the + exception that the identifier <code>0</code> always refers to the + object which represents all free space within the + collection. + </p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td> + <p>All heap objects have a reference count field. An + object which is referenced from some other part of the + file will have a positive reference count. The reference + count for Object 0 is always zero. + </p> + </td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td> + <p>Zero padding to align next field on an 8-byte boundary. + </p> + </td> + </tr> + + <tr> + <td><p>Object Size</p></td> + <td> + <p>This is the size of the object data stored for the object. + The actual storage space allocated for the object data is rounded + up to a multiple of eight. + </p> + </td> + </tr> + + <tr> + <td><p>Object Data</p></td> + <td> + <p>The object data is treated as a one-dimensional array + of bytes to be interpreted by the caller. + </p> + </td> + </tr> + </table> + +</div> + +<br /> +<br /> +<br /> +<p> + <a name="GlobalHeapID"></a> + The format for the ID used to locate an object in the global heap is + described here:</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Global Heap ID + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Collection Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Object Index</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Global Heap ID + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Collection Address</p></td> + <td> + <p>This field is the address of the global heap collection + where the data object is stored. + </p> + </td> + </tr> + + <tr> + <td><p>ID</p></td> + <td> + <p>This field is the index of the data object within the + global heap collection. + </p> + </td> + </tr> + + </table> +</div> + + + +<h3><a name="GlobalHeapVDS"> III.F. Disk Format: Level 1F - Global + Heap Block for Virtual Datasets</a></h3> + +<p>The layout for the global heap block used with virtual datasets is + described below. For more information on global heaps, see + <a href="#GlobalHeap"></a>“Disk Format: Level 1E - Global Heap.”</p> + +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Global Heap Block for Virtual Dataset + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Num Entries<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Source Filename #1 <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Source Dataset #1 <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Source Selection #1 <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Virtual Selection #1 <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td colspan="4"><br />Source Filename #n <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Source Dataset #n <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Source Selection #n <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Virtual Selection #n <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Global Heap Block for Virtual Dataset + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for the block; the value is 0.</p> + </td> + </tr> + + <tr> + <td><p>Num Entries</p></td> + <td><p>The number of entries in the block.</p> + </td> + </tr> + + <tr> + <td><p>Source Filename #n</p></td> + <td> + <p>The source file name where the source dataset is located. + </p> + </td> + </tr> + + <tr> + <td><p>Source Dataset #n</p></td> + <td><p>The source dataset name that is mapped to the + virtual dataset.</p></td> + </tr> + + <tr> + <td><p>Source Selection #n</p></td> + <td> + <p>The <a href="#DataspaceSEL">dataspace selection</a> in the + source dataset that is mapped to the virtual selection. + </p> + </td> + </tr> + + <tr> + <td><p>Virtual Selection #n</p></td> + <td> + <p>This is the <a href="#DataspaceSEL">dataspace selection</a> in the virtual dataset that is + mapped to the source selection. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the block.</p> + </td> + </tr> + + </table> +</div> +<br> + +<h3><a name="FractalHeap"> + III.G. Disk Format: Level 1G - Fractal Heap</a></h3> + +<p> + Each fractal heap consists of a header and zero or more direct and + indirect blocks (described below). The header contains general + information as well as + initialization parameters for the doubling table. The <em>Address + of Root Block</em> field in the header points to the first direct or + indirect block in the heap. +</p> + +<p> + Fractal heaps are based on a data structure called a <em>doubling + table</em>. A doubling table provides a mechanism for quickly + extending an array-like data structure that minimizes the number of + empty blocks in the heap, while retaining very fast lookup of any + element within the array. More information on fractal heaps and + doubling tables can be found in the RFC + “<a href="Supplements/FractalHeap/PrivateHeap.pdf">Private + Heaps in HDF5</a>.” +</p> + +<p> + The fractal heap implements the doubling table structure with + indirect and direct blocks. + Indirect blocks in the heap do not actually contain data for + objects in the heap, their “size” is abstract - + they represent the indexing structure for locating the + direct blocks in the doubling table. + Direct blocks + contain the actual data for objects stored in the heap. +</p> + +<p> + All indirect blocks have a constant number of block entries in each + row, called the <em>width</em> of the doubling table + (see <em>Table Width</em> field in the header). + + The number + of rows for each indirect block in the heap is determined by the + size of the block that the indirect block represents in the + doubling table (calculation of this is shown below) and is + constant, except for the “root” + indirect block, which expands and shrinks its number of rows as + needed. +</p> + +<p> + Blocks in the first <em>two</em> rows of an indirect block + are <em>Starting Block Size</em> number of bytes in size. + For example, if the row <em>width</em> of the doubling table is 4, + then the first eight block entries in the + indirect block are <em>Starting Block Size</em> number of bytes in size. + The blocks in each subsequent row are twice the size of + the blocks in the previous row. In other words, blocks in + the third row are twice the <em>Starting Block Size</em>, + blocks in the fourth row are four times the + <em>Starting Block Size</em>, and so on. Entries for + blocks up to the <em>Maximum Direct Block Size</em> point to + direct blocks, and entries for blocks greater than that size + point to further indirect blocks (which have their own + entries for direct and indirect blocks). + <em>Starting Block Size</em> and + <em>Maximum Direct Block Size</em> are fields + stored in the header. +</p> + +<p> + The number of rows of blocks, <em>nrows</em>, in an + indirect block is calculated by the following expression: + <br /> <br /> + <em>nrows</em> = (log<sub>2</sub>(<em>block_size</em>) - + log<sub>2</sub>(<em><Starting Block Size></em>)) + 1 +</p> +where <em>block_size</em> is the size of the block that the indirect block +represents in the doubling table. +For example, to represent a block with <em>block_size</em> equals to 1024, +and <em>Starting Block Size</em> equals to 256, +three rows are needed. +<p> + The maximum number of rows of direct blocks, <em>max_dblock_rows</em>, + in any indirect block of a fractal heap is given by the + following expression: + <br /> <br /> + <em>max_dblock_rows</em> = + (log<sub>2</sub>(<em><Maximum Direct Block Size></em>) - + log<sub>2</sub>(<em><Starting Block Size></em>)) + 2 +</p> +<p> + Using the computed values for <em>nrows</em> and + <em>max_dblock_rows</em>, along with the <em>width</em> of the + doubling table, the number of direct and indirect block entries + (<em>K</em> and <em>N</em> in the indirect block description, below) + in an indirect block can be computed: + <br /> <br /> + <em>K</em> = MIN(<em>nrows</em>, <em>max_dblock_rows</em>) * + <em><Table Width></em> + + <br /> <br /> + If <em>nrows</em> is less than or equal to <em>max_dblock_rows</em>, + <em>N</em> is 0. Otherwise, <em>N</em> is simply computed: + <br /> <br /> + <em>N</em> = <em>K</em> - (<em>max_dblock_rows</em> * + <em><Table Width></em>) +</p> + +<p> + The size of indirect blocks on disk is determined by the number + of rows in the indirect block (computed above). The size of direct + blocks on disk is exactly the size of the block in the doubling + table. +</p> +<br> + +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="2">Heap ID Length</td> + <td colspan="2">I/O Filters’ Encoded Length</td> + </tr> + + <tr> + <td>Flags</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Maximum Size of Managed Objects</td> + </tr> + + <tr> + <td colspan="4"><br />Next Huge Object ID<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />v2 B-tree Address of Huge Objects<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Amount of Free Space in Managed Blocks<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Managed Block Free Space Manager<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Amount of Managed Space in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Amount of Allocated Managed Space in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Offset of Direct Block Allocation Iterator in Managed Space<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Managed Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Huge Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Huge Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Tiny Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Tiny Objects in Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Table Width</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Starting Block Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Maximum Direct Block Size<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Maximum Heap Size</td> + <td colspan="2">Starting # of Rows in Root Indirect Block</td> + </tr> + + <tr> + <td colspan="4"><br />Address of Root Block<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Current # of Rows in Root Indirect Block</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Filtered Root Direct Block <em>(optional)</em><sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">I/O Filter Mask<em> (optional)</em></td> + </tr> + + <tr> + <td colspan="4">I/O Filter Information<em> (optional, variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap Header + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FRHP</code>” + is used to indicate the + beginning of a fractal heap header. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Heap ID Length</p></td> + <td> + <p>This is the length in bytes of heap object IDs for this heap.</p> + </td> + </tr> + + <tr> + <td><p>I/O Filters’ Encoded Length</p></td> + <td> + <p>This is the size in bytes of the encoded <em>I/O Filter Information</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is the heap status flag and is a bit field + indicating additional information about the fractal heap. + <table class="list"> + <tr> + <th width="20%" align="center">Bit(s)</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the ID value to use for huge object has wrapped + around. If the value for the <em>Next Huge Object ID</em> + has wrapped around, each new huge object inserted into the + heap will require a search for an ID value. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the direct blocks in the heap are checksummed. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Maximum Size of Managed Objects</p></td> + <td> + <p>This is the maximum size of managed objects allowed in the heap. + Objects greater than this this are ‘huge’ objects and will be + stored in the file directly, rather than in a direct block for + the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Next Huge Object ID</p></td> + <td> + <p>This is the next ID value to use for a huge object in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>v2 B-tree Address of Huge Objects</p></td> + <td> + <p>This is the address of the <a href="#V2Btrees">v2 B-tree</a> + used to track huge objects in the heap. The type of records + stored in the <em>v2 B-tree</em> will + be determined by whether the address and length of a huge object + can fit into a heap ID (if yes, it is a “directly” accessed + huge object) and whether there is a filter used on objects + in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Amount of Free Space in Managed Blocks</p></td> + <td> + <p>This is the total amount of free space in managed direct blocks + (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Address of Managed Block Free Space Manager</p></td> + <td> + <p>This is the address of the + <em><a href="#FreeSpaceManager">Free-space Manager</a></em> for + managed blocks. + </p> + </td> + </tr> + + <tr> + <td><p>Amount of Managed Space in Heap</p></td> + <td> + <p>This is the total amount of managed space in the heap (in bytes), + essentially the upper bound of the heap’s linear address space. + </p> + </td> + </tr> + + <tr> + <td><p>Amount of Allocated Managed Space in Heap</p></td> + <td> + <p>This is the total amount of managed space (in bytes) actually + allocated in + the heap. This can be less than the <em>Amount of Managed Space + in Heap</em> field, if some direct blocks in the heap’s linear + address space are not allocated. + </p> + </td> + </tr> + + <tr> + <td><p>Offset of Direct Block Allocation Iterator in Managed Space</p></td> + <td> + <p>This is the linear heap offset where the next direct + block should be allocated at (in bytes). This may be less than + the <em>Amount of Managed Space in Heap</em> value because the + heap’s address space is increased by a “row” of direct blocks + at a time, rather than by single direct block increments. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Managed Objects in Heap</p></td> + <td> + <p>This is the number of managed objects in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Huge Objects in Heap</p></td> + <td> + <p>This is the total size of huge objects in the heap (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Number of Huge Objects in Heap</p></td> + <td> + <p>This is the number of huge objects in the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Tiny Objects in Heap</p></td> + <td> + <p>This is the total size of tiny objects that are packed in heap + IDs (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Number of Tiny Objects in Heap</p></td> + <td> + <p>This is the number of tiny objects that are packed in heap IDs. + </p> + </td> + </tr> + + <tr> + <td><p>Table Width</p></td> + <td> + <p>This is the number of columns in the doubling table for managed + blocks. This value must be a power of two. + </p> + </td> + </tr> + + <tr> + <td><p>Starting Block Size</p></td> + <td> + <p>This is the starting block size to use in the doubling table for + managed blocks (in bytes). This value must be a power of two. + </p> + </td> + </tr> + + <tr> + <td><p>Maximum Direct Block Size</p></td> + <td> + <p>This is the maximum size allowed for a managed direct block. + Objects inserted into the heap that are larger than this value + (less the number of bytes of direct block prefix/suffix) + are stored as ‘huge’ objects. This value must be a power of + two. + </p> + </td> + </tr> + + <tr> + <td><p>Maximum Heap Size</p></td> + <td> + <p>This is the maximum size of the heap’s linear address space for + managed objects (in bytes). The value stored is the log2 of + the actual value, that is: the number of bits of the address space. + ‘Huge’ and ‘tiny’ objects are not counted in this value, since + they do not store objects in the linear address space of the + heap. + </p> + </td> + </tr> + + <tr> + <td><p>Starting # of Rows in Root Indirect Block</p></td> + <td> + <p>This is the starting number of rows for the root indirect block. + A value of 0 indicates that the root indirect block will have + the maximum number of rows needed to address the heap’s <em>Maximum + Heap Size</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Root Block</p></td> + <td> + <p>This is the address of the root block for the heap. It can + be the <a href="#UndefinedAddress">undefined address</a> if + there is no data in the heap. It either points to a direct + block (if the <em>Current # of Rows in the Root Indirect + Block</em> value is 0), or an indirect block. + </p> + </td> + </tr> + + <tr> + <td><p>Current # of Rows in Root Indirect Block</p></td> + <td> + <p>This is the current number of rows in the root indirect block. + A value of 0 indicates that <em>Address of Root Block</em> + points to direct block instead of indirect block. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Filtered Root Direct Block</p></td> + <td> + <p>This is the size of the root direct block, if filters are + applied to heap objects (in bytes). This field is only + stored in the header if the <em>I/O Filters’ Encoded Length</em> + is greater than 0. + </p> + </td> + </tr> + + <tr> + <td><p>I/O Filter Mask</p></td> + <td> + <p>This is the filter mask for the root direct block, if filters + are applied to heap objects. This mask has the same format as + that used for the filter mask in chunked raw data records in a + <a href="#V1Btrees">v1 B-tree</a>. + This field is only + stored in the header if the <em>I/O Filters’ Encoded Length</em> + is greater than 0. + </p> + </td> + </tr> + + <tr> + <td><p>I/O Filter Information</p></td> + <td> + <p>This is the I/O filter information encoding direct blocks and + huge objects, if filters are applied to heap objects. This + field is encoded as a <a href="#FilterMessage">Filter Pipeline</a> + message. + The size of this field is determined by <em>I/O Filters’ + Encoded Length</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the header.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap Direct Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Heap Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Block Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Object Data <em>(variable size)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap Direct Block + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FHDB</code>” + is used to indicate the + beginning of a fractal heap direct block. This gives file consistency + checking utilities a better chance of reconstructing a + damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Heap Header Address</p></td> + <td> + <p>This is the address for the fractal heap header that this + block belongs to. This field is principally used for file + integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Block Offset</p></td> + <td> + <p>This is the offset of the block within the fractal heap’s + address space (in bytes). The number of bytes used to encode + this field is the <em>Maximum Heap Size</em> (in the heap’s + header) divided by 8 and rounded up to the next highest integer, + for values that are not a multiple of 8. This value is + principally used for file integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the direct block.</p> + <p>This field is only present if bit 1 of <em>Flags</em> in the + heap’s header is set.</p> + </td> + </tr> + + <tr> + <td><p>Object Data</p></td> + <td> + <p>This section of the direct block stores the actual data for + objects in the heap. The size of this section is determined by + the direct block’s size minus the size of the other fields + stored in the direct block (for example, the <em>Signature</em>, + <em>Version</em>, and others including the <em>Checksum</em> if it is + present). + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap Indirect Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Heap Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Block Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Child Direct Block #0 Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Size of Filtered Direct Block #0 <em>(optional)</em> <sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask for Direct Block #0 <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Child Direct Block #1 Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Size of Filtered Direct Block #1 <em>(optional)</em><sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask for Direct Block #1 <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4"><br />Child Direct Block #K-1 Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Size of Filtered Direct Block #K-1 <em>(optional)</em><sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">Filter Mask for Direct Block #K-1 <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Child Indirect Block #0 Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Child Indirect Block #1 Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4"><br />Child Indirect Block #N-1 Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap Indirect Block + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FHIB</code>” is used to + indicate the beginning of a fractal heap indirect block. This + gives file consistency checking utilities a better chance of + reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Heap Header Address</p></td> + <td> + <p>This is the address for the fractal heap header that this + block belongs to. This field is principally used for file + integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Block Offset</p></td> + <td> + <p>This is the offset of the block within the fractal heap’s + address space (in bytes). The number of bytes used to encode + this field is the <em>Maximum Heap Size</em> (in the heap’s + header) divided by 8 and rounded up to the next highest integer, + for values that are not a multiple of 8. This value is + principally used for file integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Child Direct Block #K Address</p></td> + <td> + <p>This field is the address of the child direct block. + The size of the [uncompressed] direct block can be computed by + its offset in the heap’s linear address space. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Filtered Direct Block #K</p></td> + <td> + <p>This is the size of the child direct block after passing through + the I/O filters defined for this heap (in bytes). If no I/O + filters are present for this heap, this field is not present. + </p> + </td> + </tr> + <tr> + <td><p>Filter Mask for Direct Block #K</p></td> + <td> + <p>This is the I/O filter mask for the filtered direct block. + This mask has the same format as that used for the filter mask + in chunked raw data records in a <a href="#V1Btrees">v1 B-tree</a>. + If no I/O filters are present for this heap, this field is not + present. + </p> + </td> + </tr> + + <tr> + <td><p>Child Indirect Block #N Address</p></td> + <td> + <p>This field is the address of the child indirect block. + The size of the indirect block can be computed by + its offset in the heap’s linear address space. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the indirect block.</p> + </td> + </tr> + + </table> + +</div> + +<br /> +<p>An object in the fractal heap is identified by means of a fractal heap ID, + which encodes information to locate the object in the heap. + Currently, the fractal heap stores an object in one of three ways, + depending on the object’s size:</p> + +<div align="center"> + <table class="list80"> + <tr> + <th width="20%">Type</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center">Tiny</td> + <td> + <p>When an object is small enough to be encoded in the + heap ID, the object’s data is embedded in the fractal + heap ID itself. There are two sub-types for this type of + object: normal and extended. The sub-type for tiny heap + IDs depends on whether the heap ID is large enough to + store objects greater than 16 bytes or not. If the + heap ID length is 18 bytes or smaller, the + ‘normal’ tiny heap ID form is used. If the + heap ID length is greater than 18 bytes in length, the + “extended” form is used. See the format + description below for both sub-types. + </p> + </td> + </tr> + + <tr> + <td align="center">Huge</td> + <td> + <p>When the size of an object is larger than <em>Maximum Size of + Managed Objects</em> in the <em>Fractal Heap Header</em>, the + object’s data is stored on its own in the file and the object + is tracked/indexed via a version 2 B-tree. All huge objects + for a particular fractal heap use the same v2 B-tree. All huge + objects for a particular fractal heap use the same format for + their huge object IDs. + </p> + + <p>Depending on whether the IDs for a heap are large enough to hold + the object’s retrieval information and whether I/O pipeline filters + are applied to the heap’s objects, 4 sub-types are derived for + huge object IDs for this heap:</p> + + <div align="center"> + <table class="list"> + <tr> + <th align="left" width="35%">Sub-type</th> + <th align="left">Description</th> + </tr> + + <tr> + <td align="left">Directly accessed, non-filtered</td> + <td> + <p>The object’s address and length are embedded in the + fractal heap ID itself and the object is directly accessed + from them. This allows the object to be accessed without + resorting to the B-tree. + </p> + </td> + </tr> + + <tr> + <td align="left">Directly accessed, filtered</td> + <td> + <p>The filtered object’s address, length, filter mask and + de-filtered size are embedded in the fractal heap ID itself + and the object is accessed directly with them. This allows + the object to be accessed without resorting to the B-tree. + </p> + </td> + </tr> + + <tr> + <td align="left">Indirectly accessed, non-filtered</td> + <td> + <p>The object is located by using a B-tree key embedded in + the fractal heap ID to retrieve the address and length from + the version 2 B-tree for huge objects. Then, the address + and length are used to access the object. + </p> + </td> + </tr> + + <tr> + <td align="left">Indirectly accessed, filtered</td> + <td> + <p>The object is located by using a B-tree key embedded in + the fractal heap ID to retrieve the filtered object’s + address, length, filter mask and de-filtered size from the + version 2 B-tree for huge objects. Then, this information + is used to access the object. + </p> + </td> + </tr> + </table> + </div> + + </td> + </tr> + + <tr> + <td align="center">Managed</td> + <td> + <p>When the size of an object does not meet the above two + conditions, the object is stored and managed via the direct and + indirect blocks based on the doubling table. + </p> + </td> + </tr> + </table> +</div> + + +<br /> +<p>The specific format for each type of heap ID is described below: +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap ID for Tiny Objects (Sub-type 1 - + ‘Normal’) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version, Type, and Length</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em></td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap ID for Tiny Objects (Sub-type 1 - + ‘Normal’) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version, Type, and Length</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Tiny objects have a value of <code>2</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>The length of the tiny object. The value stored + is one less than the actual length (since zero-length + objects are not allowed to be stored in the heap). + For example, an object of actual length 1 has an + encoded length of 0, an object of actual length 2 + has an encoded length of 1, and so on. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td> + <p>This is the data for the object. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap ID for Tiny Objects (Sub-type 2 - + ‘Extended’) + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version, Type, and Length</td> + <td>Extended Length</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Data <em>(variable size)</em></td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap ID for Tiny Objects (Sub-type 2 - + ‘Extended’) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version, Type, and Length</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Tiny objects have a value of <code>2</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>These 4 bits, together with the next byte, form an + unsigned 12-bit integer for holding the length of the + object. These 4-bits are bits 8-11 of the 12-bit integer. + See description for the <em>Extended Length</em> field below. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Extended Length</p></td> + <td> + <p>This byte, together with the 4 bits in the previous byte, + forms an unsigned 12-bit integer for holding the length of + the tiny object. These 8 bits are bits 0-7 of the 12-bit + integer formed. The value stored is one less than the actual + length (since zero-length objects are not allowed to be + stored in the heap). For example, an object of actual length + 1 has an encoded length of 0, an object of actual length + 2 has an encoded length of 1, and so on. + </p> + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td> + <p>This is the data for the object. + </p> + </td> + </tr> + + </table> +</div> + + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap ID for Huge Objects (Sub-types 1 and 2): + Indirectly Accessed, Non-filtered/Filtered + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version and Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />v2 B-tree Key<sup>L</sup><em> (variable size)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap ID for Huge Objects (Sub-types 1 and 2): + Indirectly Accessed, Non-filtered/Filtered + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version and Type</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Huge objects have a value of <code>1</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>v2 B-tree Key</p></td> + <td><p>This field is the B-tree key for retrieving the information + from the version 2 B-tree for huge objects needed to access the + object. See the description of <a href="#V2Btrees">v2 B-tree</a> + records sub-types 1 and 2 for a description of the fields. New key + values are derived from <em>Next Huge Object ID</em> in the + <em>Fractal Heap Header</em>.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap ID for Huge Objects (Sub-type 3): + Directly Accessed, Non-filtered + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version and Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address <sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Length <sup>L</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap ID for Huge Objects (Sub-type 3): + Directly Accessed, Non-filtered + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version and Type</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Huge objects have a value of <code>1</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This field is the address of the object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This field is the length of the object in the file.</p> + </td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap ID for Huge Objects (Sub-type 4): + Directly Accessed, Filtered + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version and Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address <sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Length <sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Filter Mask</td> + </tr> + + <tr> + <td colspan="4"><br />De-filtered Size <sup>L</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap ID for Huge Objects (Sub-type 4): + Directly Accessed, Filtered + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version and Type</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Huge objects have a value of <code>1</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This field is the address of the filtered object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This field is the length of the filtered object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td><p>This field is the I/O pipeline filter mask for the + filtered object in the file.</p> + </td> + </tr> + + <tr> + <td><p>Filtered Size</p></td> + <td><p>This field is the size of the de-filtered object in the file.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap ID for Managed Objects + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version and Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Length <em>(variable size)</em></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap ID for Managed Objects + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version and Type</p></td> + <td><p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>6-7</code></td> + <td>The current version of ID format. This document + describes version 0. + </td> + </tr> + <tr> + <td align="center"><code>4-5</code></td> + <td>The ID type. Managed objects have a value of <code>0</code>. + </td> + </tr> + <tr> + <td align="center"><code>0-3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Offset</p></td> + <td><p>This field is the offset of the object in the heap. + This field’s size is the minimum number of bytes + necessary to encode the <em>Maximum Heap Size</em> value + (from the <em>Fractal Heap Header</em>). For example, if the + value of the <em>Maximum Heap Size</em> is less than 256 bytes, + this field is 1 byte in length, a <em>Maximum Heap Size</em> + of 256-65535 bytes uses a 2 byte length, and so on.</p></td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This field is the length of the object in the heap. It + is determined by taking the minimum value of <em>Maximum + Direct Block Size</em> and <em>Maximum Size of Managed + Objects</em> in the <em>Fractal Heap Header</em>. Again, + the minimum number of bytes needed to encode that value is + used for the size of this field.</p></td> + </tr> + </table> +</div> + +<h3><a name="FreeSpaceManager"> + III.H. Disk Format: Level 1H - Free-space Manager</a></h3> + +<p> + Free-space managers are used to describe space within a heap or + the entire HDF5 file that is not currently used for that heap or + file. +</p> + +<p> + The <em>free-space manager header</em> contains metadata information + about the space being tracked, along with the address of the list + of <em>free space sections</em> which actually describes the free + space. The header records information about free-space sections being + tracked, creation parameters for handling free-space sections of a + client, and section information used to locate the collection of + free-space sections. +</p> + +<p> + The <em>free-space section list</em> stores a collection of + free-space sections that is specific to each <em>client</em> of the + free-space manager. + + For example, the fractal heap is a client of the free space manager + and uses it to track unused space within the heap. There are 4 + types of section records for the fractal heap, each of which has + its own format, listed below. +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Free-space Manager Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Total Space Tracked<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Total Number of Sections<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Serialized Sections<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Number of Un-Serialized Sections<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="2">Number of Section Classes</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="2">Shrink Percent</td> + <td colspan="2">Expand Percent</td> + </tr> + + <tr> + <td colspan="2">Size of Address Space</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Maximum Section Size <sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of Serialized Section List<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Serialized Section List Used<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Allocated Size of Serialized Section List<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Free-space Manager Header + </caption> + <tr> + <th width="35%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FSHD</code>” + is used to indicate the beginning of the Free-space Manager + Header. This gives file consistency checking utilities a + better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This is the version number for the Free-space Manager Header + and this document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>This is the client ID for identifying the user of this + free-space manager: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Fractal heap + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>File + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Total Space Tracked</p></td> + <td> + <p>This is the total amount of free space being tracked, in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Total Number of Sections</p></td> + <td> + <p>This is the total number of free-space sections being tracked. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Serialized Sections</p></td> + <td> + <p>This is the number of serialized free-space sections being + tracked. + </p> + </td> + </tr> + <tr> + <td><p>Number of Un-Serialized Sections</p></td> + <td> + <p>This is the number of un-serialized free-space sections being + managed. Un-serialized sections are created by the free-space + client when the list of sections is read in. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Section Classes</p></td> + <td> + <p>This is the number of section classes handled by this free space + manager for the free-space client. + </p> + </td> + </tr> + + <tr> + <td><p>Shrink Percent</p></td> + <td> + <p>This is the percent of current size to shrink the allocated + serialized free-space section list. + </p> + </td> + </tr> + + <tr> + <td><p>Expand Percent</p></td> + <td> + <p>This is the percent of current size to expand the allocated + serialized free-space section list. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Address Space</p></td> + <td> + <p>This is the size of the address space that free-space sections + are within. This is stored as the log<sub>2</sub> of the + actual value (in other words, the number of bits required + to store values within that address space). + </p> + </td> + </tr> + + <tr> + <td><p>Maximum Section Size</p></td> + <td> + <p>This is the maximum size of a section to be tracked. + </p> + </td> + </tr> + + <tr> + <td><p>Address of Serialized Section List</p></td> + <td> + <p>This is the address where the serialized free-space section + list is stored. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Serialized Section List Used</p></td> + <td> + <p>This is the size of the serialized free-space section + list used (in bytes). This value must be less than + or equal to the <em>allocated size of serialized section + list</em>, below. + </p> + </td> + </tr> + + <tr> + <td><p>Allocated Size of Serialized Section List</p></td> + <td> + <p>This is the size of serialized free-space section list + actually allocated (in bytes). + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the free-space manager header.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<p>The free-space sections being managed are stored in a + <em>free-space section list</em>, described below. The sections + in the free-space section list are stored in the following way: + a count of the number of sections describing a particular size of + free space and the size of the free-space described (in bytes), + followed by a list of section description records; then another + section count and size, followed by the list of section + descriptions for that size; and so on.</p> + + +<div align="center"> + <table class="format"> + <caption> + Layout: Free-space Section List + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Free-space Manager Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Number of Section Records in Set #0 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Size of Free-space Section Described in Record Set #0 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #0 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #0 Section Record #0 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #0 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #K-1 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #0 Section Record #K-1 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #0 Section Record #K-1 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Number of Section Records in Set #1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Size of Free-space Section Described in Record Set #1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #0 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #1 Section Record #0 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #0 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #K-1 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #1 Section Record #K-1 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #1 Section Record #K-1 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><strong>...</strong></td> + </tr> + + <tr> + <td colspan="4"><strong>...</strong></td> + </tr> + + <tr> + <td colspan="4">Number of Section Records in Set #N-1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Size of Free-space Section Described in Record Set #N-1 <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #0 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #N-1 Section Record #0 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #0 Data <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #K-1 Offset<em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="1">Record Set #N-1 Section Record #K-1 Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Record Set #N-1 Section Record #K-1 Data <em>(variable size)</td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Free-space Section List + </caption> + <tr> + <th width="35%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FSSE</code>” + is used to indicate the beginning of the Free-space Section + Information. This gives file consistency checking utilities + a better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This is the version number for the Free-space Section List + and this document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Free-space Manager Header Address</p></td> + <td> + <p>This is the address of the <em>Free-space Manager Header</em>. + This field is principally used for file + integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Section Records for Set #N</p></td> + <td> + <p>This is the number of free-space section records for set #N. + The length of this field is the minimum number of bytes needed + to store the <em>number of serialized sections</em> (from the + <em>free-space manager header</em>). + </p> + + <p> + The number of sets of free-space section records is + determined by the <em>size of serialized section list</em> in + the <em>free-space manager header</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Section Size for Record Set #N</p></td> + <td> + <p>This is the size (in bytes) of the free-space section described + for <em>all</em> the section records in set #N. + </p> + + <p> + The length of this field is the minimum number of bytes needed + to store the <em>maximum section size</em> (from the + <em>free-space manager header</em>). + </p> + </td> + </tr> + + <tr> + <td><p>Record Set #N Section #K Offset</p></td> + <td> + <p>This is the offset (in bytes) of the free-space section within + the client for the free-space manager. + </p> + + <p> + The length of this field is the minimum number of bytes needed + to store the <em>size of address space</em> (from the + <em>free-space manager header</em>). + </p> + </td> + </tr> + + <tr> + <td><p>Record Set #N Section #K Type</p></td> + <td> + <p>This is the type of the section record, used to decode the + <em>record set #N section #K data</em> information. The defined + record type for <em>file</em> client is: + + <table class="list"> + <tr> + <th width="20%" align="center">Type</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>File’s section (a range of actual bytes in file) + </td> + </tr> + <tr> + <td align="center"><code>1+</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + <p>The defined record types for a <em>fractal heap</em> client are: + + <table class="list"> + <tr> + <th width="20%" align="center">Type</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Fractal heap “single” section + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Fractal heap “first row” section + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Fractal heap “normal row” section + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Fractal heap “indirect” section + </td> + </tr> + + <tr> + <td align="center"><code>4+</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Record Set #N Section #K Data</p></td> + <td> + <p>This is the section-type specific information for each record + in the record set, described below. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the <em>Free-space Section List</em>. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<p> + The section-type specific data for each free-space section record is + described below: +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: File’s Section Data Record + </caption> + + <tr> + <td colspan="4"><em>No additional record data stored</em></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap “Single” Section Data Record + </caption> + + <tr> + <td colspan="4"><em>No additional record data stored</em></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap “First Row” Section Data + Record + </caption> + + <tr> + <td colspan="4"><em>Same format as “indirect” + section data</em></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap “Normal Row” Section Data + Record + </caption> + + <tr> + <td colspan="4"><em>No additional record data stored</em></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fractal Heap “Indirect” Section + Data Record + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Fractal Heap Indirect Block Offset <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="2">Block Start Row</td> + <td colspan="2">Block Start Column</td> + </tr> + + <tr> + <td colspan="2">Number of Blocks</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fractal Heap “Indirect” Section + Data Record + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Fractal Heap Block Offset</p></td> + <td> + <p>The offset of the indirect block in the fractal heap’s address + space containing the empty blocks. + </p> + <p> + The number of bytes used to encode this field is the minimum + number of bytes needed to encode values for the <em>Maximum + Heap Size</em> (in the fractal heap’s header). + </p> + </td> + </tr> + + <tr> + <td><p>Block Start Row</p></td> + <td> + <p>This is the row that the empty blocks start in. + </p> + </td> + </tr> + + <tr> + <td><p>Block Start Column</p></td> + <td> + <p>This is the column that the empty blocks start in. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Blocks</p></td> + <td> + <p>This is the number of empty blocks covered by the section. + </p> + </td> + </tr> + </table> +</div> + +<h3><a name="SOHMTable"> + III.I. Disk Format: Level 1I - Shared Object Header Message Table</a></h3> + +<p> + The <em>shared object header message table</em> is used to locate + object + header messages that are shared between two or more object headers + in the file. Shared object header messages are stored and indexed + in the file in one of two ways: indexed sequentially in a + <em>shared header message list</em> or indexed with a v2 B-tree. + The shared messages themselves are either stored in a fractal + heap (when two or more objects share the message), or remain in an + object’s header (when only one object uses the message currently, + but the message can be shared in the future). +</p> + +<p> + The <em>shared object header message table</em> + contains a list of shared message index headers. Each index header + records information about the version of the index format, the index + storage type, flags for the message types indexed, the number of + messages in the index, the address where the index resides, + and the fractal heap address if shared messages are stored there. +</p> + +<p> + Each index can be either a list or a v2 B-tree and may transition + between those two forms as the number of messages in the index + varies. Each shared message record contains information used to + locate the shared message from either a fractal heap or an object + header. The types of messages that can be shared are: <em>Dataspace, + Datatype, Fill Value, Filter Pipeline and Attribute</em>. +</p> + +<p> + The <em>shared object header message table</em> is pointed to + from a <a href="#SOHMTableMessage">shared message table</a> message + in the superblock extension for a file. This message stores the + version of the table format, along with the number of index headers + in the table. +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Object Header Message Table + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version for index #0</td> + <td>Index Type for index #0</td> + <td colspan="2">Message Type Flags for index #0</td> + </tr> + + <tr> + <td colspan="4">Minimum Message Size for index #0</td> + </tr> + + <tr> + <td colspan="2">List Cutoff for index #0</td> + <td colspan="2">v2 B-tree Cutoff for index #0</td> + </tr> + + <tr> + <td colspan="2">Number of Messages for index #0</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Index Address<sup>O</sup> for index #0<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup> for index #0<br /><br /></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td>Version for index #N-1</td> + <td>Index Type for index #N-1</td> + <td colspan="2">Message Type Flags for index #N-1</td> + </tr> + + <tr> + <td colspan="4">Minimum Message Size for index #N-1</td> + </tr> + + <tr> + <td colspan="2">List Cutoff for index #N-1</td> + <td colspan="2">v2 B-tree Cutoff for index #N-1</td> + </tr> + + <tr> + <td colspan="2">Number of Messages for index #N-1</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Index Address<sup>O</sup> for index #N-1<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup> for index #N-1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Object Header Message Table + </caption> + <tr> + <th width="35%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>SMTB</code>” + is used to indicate the beginning of the Shared Object + Header Message table. This gives file consistency checking + utilities a better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version for index #N</p></td> + <td> + <p>This is the version number for the list of shared object header message + indexes and this document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Index Type for index #N</p></td> + <td> + <p>The type of index can be an unsorted list or a v2 B-tree. + </p> + </td> + </tr> + + <tr> + <td><p>Message Type Flags for index #N</p></td> + <td> + <p>This field indicates the type of messages tracked in the index, + as follows: + <table class="list"> + <tr> + <th width="20%" align="center">Bits</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the index tracks <em>Dataspace Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the message tracks <em>Datatype Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>If set, the message tracks <em>Fill Value Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>If set, the message tracks <em>Filter Pipeline Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>If set, the message tracks <em>Attribute Messages</em>. + </td> + </tr> + <tr> + <td align="center"><code>5-15</code></td> + <td>Reserved (zero). + </td> + </tr> + </table></p> + + + <p> + An index can track more than one type of message, but each type + of message can only by in one index. + </p> + </td> + </tr> + + <tr> + <td><p>Minimum Message Size for index #N</p></td> + <td> + <p>This is the message size sharing threshold for the index. + If the encoded size of the message is less than this value, the + message is not shared. + </p> + </td> + </tr> + + <tr> + <td><p>List Cutoff for index #N</p></td> + <td> + <p>This is the cutoff value for the indexing of messages to + switch from a list to a v2 B-tree. If the number of messages + is greater than this value, the index should be a v2 B-tree. + </p> + </td> + </tr> + <tr> + <td><p>v2 B-tree Cutoff for index #N</p></td> + <td> + <p>This is the cutoff value for the indexing of messages + to switch from a v2 B-tree back to a list. If the number + of messages is less than this value, the index should be + a list. + </p> + </td> + </tr> + + <tr> + <td><p>Number of Messages for index #N</p></td> + <td> + <p>The number of shared messages being tracked for the index. + </p> + </td> + </tr> + + <tr> + <td><p>Index Address for index #N</p></td> + <td> + <p>This field is the address of the list or v2 B-tree where the + index nodes reside. + </p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap Address for index #N</p></td> + <td> + <p>This field is the address of the fractal heap if shared messages + are stored there. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the table.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<p> + Shared messages are indexed either with a <em>shared message record + list</em>, described below, or using a v2 B-tree (using record type 7). + The number of records in the <em>shared message record list</em> is + determined in the index’s entry in the <em>shared object header message + table</em>. +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Message Record List + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td colspan="4">Shared Message Record #0</td> + </tr> + + <tr> + <td colspan="4">Shared Message Record #1</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Shared Message Record #N-1</td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message Record List + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>SMLI</code>” + is used to indicate the beginning of a list of index nodes. + This gives file consistency checking utilities a better + chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Shared Message Record #N</p></td> + <td> + <p>The record for locating the shared message, either in the + fractal heap for the index, or an object header (see format for + <em>index nodes</em> below). + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the list. + </p> + </td> + </tr> + + </table> +</div> + +<br /> +<p> + The record for each shared message in an index is stored in one + of the following forms: +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Message Record for Messages Stored in a + Fractal Heap + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Hash Value</td> + </tr> + + <tr> + <td colspan="4">Reference Count</td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap ID<br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message Record for Messages Stored in a + Fractal Heap + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This has a value of 0 indicating that the message is stored in + the heap. + </p> + </td> + </tr> + + <tr> + <td><p>Hash Value</p></td> + <td> + <p>This is the hash value for the message. + </p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td> + <p>This is the number of times the message is used in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap ID</p></td> + <td> + <p>This is an 8-byte fractal heap ID for the message as stored in + the fractal heap for the index. + </p> + </td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Message Record for Messages Stored in an + Object Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Message Location</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Hash Value</td> + </tr> + + <tr> + <td>Reserved</td> + <td>Message Type</td> + <td colspan="2">Creation Index</td> + </tr> + + <tr> + <td colspan="4"><br />Object Header Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message Record for Messages Stored in an + Object Header + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Message Location</p></td> + <td> + <p>This has a value of 1 indicating that the message is stored in + an object header. + </p> + </td> + </tr> + + <tr> + <td><p>Hash Value</p></td> + <td> + <p>This is the hash value for the message. + </p> + </td> + </tr> + + <tr> + <td><p>Message Type</p></td> + <td> + <p>This is the message type in the object header. + </p> + </td> + </tr> + + <tr> + <td><p>Creation Index</p></td> + <td> + <p>This is the creation index of the message within the object + header. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Address</p></td> + <td> + <p>This is the address of the object header where the message is + located. + </p> + </td> + </tr> + </table> +</div> + +<h2><a name="DataObject"> + IV. Disk Format: Level 2 - Data Objects </a></h2> + +<p>Data objects contain the “real” user-visible information in the file. + These objects compose the scientific data and other information which + are generally thought of as “data” by the end-user. All the + other information in the file is provided as a framework for + storing and accessing these data objects. +</p> + +<p>A data object is composed of header and data + information. The header information contains the information + needed to interpret the data information for the object as + well as additional “metadata” or pointers to additional + “metadata” used to describe or annotate each object. +</p> + +<h3><a name="ObjectHeader"> + IV.A. Disk Format: Level 2A - Data Object Headers</a></h3> + +<p>The header information of an object is designed to encompass + all of the information about an object, except for the data itself. + This information includes the dataspace, the datatype, information + about how the data is stored on disk (in external files, compressed, + broken up in blocks, and so on), as well as other information used + by the library to speed up access to the data objects or maintain + a file’s integrity. Information stored by user applications + as attributes is also stored in the object’s header. The header + of each object is not necessarily located immediately prior to the + object’s data in the file and in fact may be located in any + position in the file. The order of the messages in an object header + is not significant.</p> + +<p>Object headers are composed of a prefix and a set of messages. The + prefix contains the information needed to interpret the messages and + a small amount of metadata about the object, and the messages contain + the majority of the metadata about the object. +</p> + +<h3><a name="ObjectHeaderPrefix"> + IV.A.1. Disk Format: Level 2A1 - Data Object Header Prefix</a></h3> + + + +<h4><a name="V1ObjectHeaderPrefix"> + IV.A.1.a. Version 1 Data Object Header Prefix</a></h4> + +<p>Header messages are aligned on 8-byte boundaries for version 1 + object headers. +</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Version 1 Object Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Reserved (zero)</td> + <td colspan="2">Total Number of Header Messages</td> + </tr> + + <tr> + <td colspan="4">Object Reference Count</td> + </tr> + + <tr> + <td colspan="4">Object Header Size</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="2">Header Message Type #1</td> + <td colspan="2">Size of Header Message Data #1</td> + </tr> + + <tr> + <td>Header Message #1 Flags</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td colspan="2">Header Message Type #n</td> + <td colspan="2">Size of Header Message Data #n</td> + </tr> + + <tr> + <td>Header Message #n Flags</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #n<br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 1 Object Header + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This value is used to determine the format of the + information in the object header. When the format of the + object header is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted. This + is version one (1) (there was no version zero (0)) of the + object header. + </p> + </td> + </tr> + + <tr> + <td><p>Total Number of Header Messages</p></td> + <td> + <p>This value determines the total number of messages listed in + object headers for this object. This value includes the messages + in continuation messages for this object. + </p> + </td> + </tr> + + <tr> + <td><p>Object Reference Count</p></td> + <td> + <p>This value specifies the number of “hard links” to this object + within the current file. References to the object from external + files, “soft links” in this file and object references in this + file are not tracked. + </p> + </td> + </tr> + + <tr> + <td><p>Object Header Size</p></td> + <td> + <p>This value specifies the number of bytes of header message data + following this length field that contain object header messages + for this object header. This value does not include the size of + object header continuation blocks for this object elsewhere in the + file. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Type</p></td> + <td> + <p>This value specifies the type of information included in the + following header message data. The message types for + header messages are defined in sections below. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Header Message #n Data</p></td> + <td> + <p>This value specifies the number of bytes of header + message data following the header message type and length + information for the current message. The size includes + padding bytes to make the message a multiple of eight + bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Flags</p></td> + <td> + <p>This is a bit field with the following definition: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the message data is constant. This is used + for messages like the datatype message of a dataset. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the message is <em>shared</em> and stored + in another location than the object header. The Header + Message Data field contains a Shared Message + (described in the <a href="#ObjectHeaderMessages">Data Object Header Messages</a> + section below) + and the Size of Header Message Data field + contains the size of that Shared Message. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>If set, the message should not be shared. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>If set, the HDF5 decoder should fail to open this object + if it does not understand the message’s type and the file + is open with permissions allowing write access to the file. + (Normally, unknown messages can just be ignored by HDF5 + decoders) + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>If set, the HDF5 decoder should set bit 5 of this + message’s flags (in other words, this bit field) + if it does not understand the message’s type + and the object is modified in any way. (Normally, + unknown messages can just be ignored by HDF5 + decoders) + </td> + </tr> + <tr> + <td align="center"><code>5</code></td> + <td>If set, this object was modified by software that did not + understand this message. + (Normally, unknown messages should just be ignored by HDF5 + decoders) (Can be used to invalidate an index or a similar + feature) + </td> + </tr> + <tr> + <td align="center"><code>6</code></td> + <td>If set, this message is shareable. + </td> + </tr> + <tr> + <td align="center"><code>7</code></td> + <td>If set, the HDF5 decoder should always fail to open this + object if it does not understand the message’s type (whether + it is open for read-only or read-write access). (Normally, + unknown messages can just be ignored by HDF5 decoders) + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Header Message #n Data</p></td> + <td> + <p>The format and length of this field is determined by the + header message type and size respectively. Some header + message types do not require any data and this information + can be eliminated by setting the length of the message to + zero. The data is padded with enough zeroes to make the + size a multiple of eight. + </p> + </td> + </tr> + </table> +</div> + +<h4><a name="V2ObjectHeaderPrefix"> + IV.A.1.b. Version 2 Data Object Header Prefix</a></h4> + +<p>Note that the “total number of messages” field has been dropped from + the data object header prefix in this version. The number of messages + in the data object header is just determined by the messages encountered + in all the object header blocks.</p> + +<p>Note also that the fields and messages in this version of data object + headers have <em>no</em> alignment or padding bytes inserted - they are + stored packed together.</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 Object Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Access time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Modification Time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Change Time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Birth Time <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="2">Maximum # of compact attributes <em>(optional)</em></td> + <td colspan="2">Minimum # of dense attributes <em>(optional)</em></td> + </tr> + + <tr> + <td>Size of Chunk #0 <em>(variable size)</em></td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td>Header Message Type #1</td> + <td colspan="2">Size of Header Message Data #1</td> + <td>Header Message #1 Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #1 Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td>Header Message Type #n</td> + <td colspan="2">Size of Header Message Data #n</td> + <td>Header Message #n Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #n Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #n<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Gap <em>(optional, variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 Object Header + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>OHDR</code>” + is used to indicate the beginning of an object header. This + gives file consistency checking utilities a better chance + of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This field has a value of 2 indicating version 2 of the object header. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is a bit field indicating additional information + about the object header. + <table class="list"> + <tr> + <th width="20%" align="center">Bit(s)</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0-1</code></td> + <td>This two bit field determines the size of the + <em>Size of Chunk #0</em> field. The values are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>The <em>Size of Chunk #0</em> field is 1 byte. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The <em>Size of Chunk #0</em> field is 2 bytes. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>The <em>Size of Chunk #0</em> field is 4 bytes. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>The <em>Size of Chunk #0</em> field is 8 bytes. + </td> + </tr> + </table> + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>If set, attribute creation order is tracked.</td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>If set, attribute creation order is indexed.</td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>If set, non-default attribute storage phase change + values are stored.</td> + </tr> + <tr> + <td align="center"><code>5</code></td> + <td>If set, access, modification, change and birth times + are stored.</td> + </tr> + <tr> + <td align="center"><code>6-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Access Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after the + UNIX epoch when the object’s raw data was last accessed + (in other words, read or written). + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Modification Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after + the UNIX epoch when the object’s raw data was last + modified (in other words, written). + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Change Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after the + UNIX epoch when the object’s metadata was last changed. + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Birth Time</p></td> + <td> + <p>This 32-bit value represents the number of seconds after the + UNIX epoch when the object was created. + </p> + <p>This field is present if bit 5 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Maximum # of compact attributes</p></td> + <td> + <p>This is the maximum number of attributes to store in the compact + format before switching to the indexed format. + </p> + <p>This field is present if bit 4 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Minimum # of dense attributes</p></td> + <td> + <p>This is the minimum number of attributes to store in the indexed + format before switching to the compact format. + </p> + <p>This field is present if bit 4 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Chunk #0</p></td> + <td> + <p> + This unsigned value specifies the number of bytes of header + message data following this field that contain object header + information. + </p> + <p> + This value does not include the size of object header + continuation blocks for this object elsewhere in the file. + </p> + <p> + The length of this field varies depending on bits 0 and 1 of + the <em>flags</em> field. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Type</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Header Message #n Data</p></td> + <td> + <p>This value specifies the number of bytes of header + message data following the header message type and length + information for the current message. The size of messages + in this version does <em>not</em> include any padding bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Flags</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Creation Order</p></td> + <td> + <p>This field stores the order that a message of a given type + was created in. + </p> + <p>This field is present if bit 2 of <em>flags</em> is set. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Data</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p> + </td> + </tr> + + <tr> + <td><p>Gap</p></td> + <td> + <p>A gap in an object header chunk is inferred by the end of the + messages for the chunk before the beginning of the chunk’s + checksum. Gaps are always smaller than the size of an + object header message prefix (message type + message size + + message flags). + </p> + <p>Gaps are formed when a message (typically an attribute message) + in an earlier chunk is deleted and a message from a later + chunk that does not quite fit into the free space is moved + into the earlier chunk. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the object header chunk. + </p> + </td> + </tr> + </table> +</div> + +<p>The header message types and the message data associated with + them compose the critical “metadata” about each object. Some + header messages are required for each object while others are + optional. Some optional header messages may also be repeated + several times in the header itself, the requirements and number + of times allowed in the header will be noted in each header + message description below. +</p> + + +<h3><a name="ObjectHeaderMessages"> + IV.A.2. Disk Format: Level 2A2 - Data Object Header Messages</a></h3> + +<p>Data object header messages are small pieces of metadata that are + stored in the data object header for each object in an HDF5 file. + Data object header messages provide the metadata required to describe + an object and its contents, as well as optional pieces of metadata + that annotate the meaning or purpose of the object. +</p> + +<p>Data object header messages are either stored directly in the data + object header for the object or are shared between multiple objects + in the file. When a message is shared, a flag in the <em>Message Flags</em> + indicates that the actual <em>Message Data</em> + portion of that message is stored in another location (such as another + data object header, or a heap in the file) and the <em>Message Data</em> + field contains the information needed to locate the actual information + for the message. +</p> + +<p> + The format of shared message data is described here:</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Message (Version 1) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message (Version 1) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number is used when there are changes in the format + of a shared object message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by the library before version 1.6.1. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td><p>The type of shared message location: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Message stored in another object’s header (a <em>committed</em> + message). + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the object header + containing the message to be shared.</p> + </td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + + <caption> + Layout: Shared Message (Version 2) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message (Version 2) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number is used when there are changes in the format + of a shared object message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Used by the library of version 1.6.1 and after. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td><p>The type of shared message location: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Message stored in another object’s header (a <em>committed</em> + message). + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the object header + containing the message to be shared.</p></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Message (Version 3) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Type</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Location <em>(variable size)</em></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message (Version 3) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number indicates changes in the format of shared + object message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Used by the library of version 1.8 and after. In this + version, the <em>Type</em> field can indicate that + the message is stored in the fractal heap. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td><p>The type of shared message location: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Message is not shared and is not shareable. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Message stored in file’s <em>shared object header message</em> + heap (a <em>shared</em> message). + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Message stored in another object’s header (a <em>committed</em> + message). + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Message stored is not shared, but is sharable. + </td> + </tr> + + </table></p> + </td> + </tr> + + <tr> + <td><p>Location</p></td> + <td><p>This field contains either a <a href="#SizeOfOffsetsV0"> + <em>Size of Offsets</em></a>-bytes address of the object header + containing the message to be shared, or an 8-byte fractal heap + ID for the message in the file’s <em>shared object header + message</em> heap. + </p> + </td> + </tr> + </table> +</div> + + +<p>The following is a list of currently defined header messages: +</p> + +<h4><a name="NILMessage">IV.A.2.a. The NIL Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> NIL</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0000</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The NIL message is used to indicate a message which is to be + ignored when reading the header messages for a data object. + [Possibly one which has been deleted for some reason.] + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> Unspecified</td></tr> +</table></center> +<!-- end msgdesc table --> + + +<h4><a name="DataspaceMessage">IV.A.2.b. The Dataspace Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Dataspace</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0001</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies according to the number of + dimensions, as described in the following table.</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for dataset objects; + may not be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The dataspace message describes the number of dimensions (in + other words, “rank”) and size of each dimension that + the data object has. This message is only used for datasets which + have a simple, rectilinear, array-like layout; datasets requiring + a more complex layout are not yet supported. + </td> + </tr> + + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Dataspace Message - Version 1 + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Flags</td> + <td>Reserved</td> + </tr> + + <tr> + <td colspan="4">Reserved</td> + </tr> + + <tr> + <td colspan="4"><br />Dimension #1 Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #1 Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Permutation Index #1<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Permutation Index #n<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Dataspace Message - Version 1 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This value is used to determine the format of the + Dataspace Message. When the format of the + information in the message is changed, the version number + is incremented and can be used to determine how the + information in the object header is formatted. This + document describes version one (1) (there was no version + zero (0)). + </p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the data + object has. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is used to store flags to indicate the + presence of parts of this message. Bit 0 (the least + significant bit) is used to indicate that maximum + dimensions are present. Bit 1 is used to indicate that + permutation indices are present. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the current size of the dimension of the + data as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Maximum Size</p></td> + <td> + <p>This value is the maximum size of the dimension of the + data as stored in the file. This value may be the special + “<a href="#UnlimitedDim">unlimited</a>” size which indicates + that the data may expand along this dimension indefinitely. + If these values are not stored, the maximum size of each + dimension is assumed to be the dimension’s current size. + </p> + </td> + </tr> + + <tr> + <td><p>Permutation Index #n</p></td> + <td> + <p>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. If these values are + not stored, the first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + </table> +</div> + + + +<br /> +<p>Version 2 of the dataspace message dropped the optional + permutation index value support, as it was never implemented in the + HDF5 Library:</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Dataspace Message - Version 2 + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Flags</td> + <td>Type</td> + </tr> + + <tr> + <td colspan="4"><br />Dimension #1 Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #1 Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4"><br />Dimension #n Maximum Size<sup>L</sup> <em>(optional)</em><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Dataspace Message - Version 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This value is used to determine the format of the + Dataspace Message. This field should be ‘2’ for version 2 + format messages. + </p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the data object has. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>This field is used to store flags to indicate the + presence of parts of this message. Bit 0 (the least + significant bit) is used to indicate that maximum + dimensions are present. + </p> + </td> + </tr> + + <tr> + <td><p>Type</p></td> + <td> + <p>This field indicates the type of the dataspace: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>A <em>scalar</em> dataspace; in other words, + a dataspace with a single, dimensionless element. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>A <em>simple</em> dataspace; in other words, + a dataspace with a rank greater than 0 and an + appropriate number of dimensions. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>A <em>null</em> dataspace; in other words, + a dataspace with no elements. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the current size of the dimension of the + data as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Maximum Size</p></td> + <td> + <p>This value is the maximum size of the dimension of the + data as stored in the file. This value may be the special + “<a href="#UnlimitedDim">unlimited</a>” size which indicates + that the data may expand along this dimension indefinitely. + If these values are not stored, the maximum size of each + dimension is assumed to be the dimension’s current size. + </p> + </td> + </tr> + + </table> +</div> + + + +<!-- + <h4><a name="DataSpaceMessage">Header Message Name: Complex Dataspace (Fiber Bundle?)</a></h4> + + <!-- start msgdesc table -- + <center> + <table class="msgdesc"> + <p><b>Header Message Name: ???????</b></td></tr> +<b>Header Message Type: </b>0x0002<br /> +<b>Length:</b> Varies</td></tr> + +<b>Status:</b> One of the <em>Simple Dataspace</em> or +<em>Complex Dataspace</em> messages is required (but not both) and may +not be repeated.<br /> <b>Description:</b> The +<em>Dataspace</em> message describes space that the dataset is +mapped onto in a more comprehensive way than the <em>Simple + Dimensionality</em> message is capable of handling. The +dataspace of a dataset encompasses the type of coordinate system +used to locate the dataset’s elements as well as the structure and +regularity of the coordinate system. The dataspace also +describes the number of dimensions which the dataset inhabits as +well as a possible higher dimensional space in which the dataset +is located within. + +<br /> +<p><b>Format of Data:</b></p> + +<center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Message Layout</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4">Mesh Type</td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimensionality</td> + </tr> + </table> +</center> + +<br /> +<dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Mesh Type: (unsigned 32-bit integer) + <dd>This value indicates whether the grid is + polar/spherical/cartesion, + structured/unstructured and regular/irregular. <br /> + The mesh type value is broken up as follows: <br /> + + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Mesh-type Layout</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="1">Mesh Embedding</td> + <td colspan="1">Coordinate System</td> + <td colspan="1">Structure</td> + <td colspan="1">Regularity</td> + </tr> + </table> + </center> + The following are the definitions of mesh-type bytes: + <dl> + <dt>Mesh Embedding + <dd>This value indicates whether the dataset dataspace + is located within + another dataspace or not: + <dl> <dl> + <dt><STANDALONE> + <dd>The dataset mesh is self-contained and is not + embedded in another mesh. + <dt><EMBEDDED> + <dd>The dataset’s dataspace is located within + another dataspace, as + described in information below. + </dl> </dl> + <dt>Coordinate System + <dd>This value defines the type of coordinate system + used for the mesh: + <dl> <dl> + <dt><POLAR> + <dd>The last two dimensions are in polar + coordinates, higher dimensions are + cartesian. + <dt><SPHERICAL> + <dd>The last three dimensions are in spherical + coordinates, higher dimensions + are cartesian. + <dt><CARTESIAN> + <dd>All dimensions are in cartesian coordinates. + </dl> </dl> + <dt>Structure + <dd>This value defines the locations of the grid-points + on the axes: + <dl> <dl> + <dt><STRUCTURED> + <dd>All grid-points are on integral, sequential + locations, starting from 0. + <dt><UNSTRUCTURED> + <dd>Grid-points locations in each dimension are + explicitly defined and + may be of any numeric datatype. + </dl> </dl> + <dt>Regularity + <dd>This value defines the locations of the dataset + points on the grid: + <dl> <dl> + <dt><REGULAR> + <dd>All dataset elements are located at the + grid-points defined. + <dt><IRREGULAR> + <dd>Each dataset element has a particular + grid-location defined. + </dl> </dl> + </dl> + <p>The following grid combinations are currently allowed:</p> + <dl> <dl> + <dt><POLAR-STRUCTURED-REGULAR> + <dt><SPHERICAL-STRUCTURED-REGULAR> + <dt><CARTESIAN-STRUCTURED-REGULAR> + <dt><POLAR-UNSTRUCTURED-REGULAR> + <dt><SPHERICAL-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-REGULAR> + <dt><CARTESIAN-UNSTRUCTURED-IRREGULAR> + </dl> </dl> + All of the above grid types can be embedded within another + dataspace. + <br /> <br /> + <dt>Logical Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions that the dataset occupies. + + <br /> + <center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Embedded Dimensionality Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4">Embedded Dimensionality</td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Dimension Size #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Dimension Size #n</td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Origin Location #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Embedded Origin Location #n</td> + </tr> + </table> + </center> + + <dt>Embedded Dimensionality: (unsigned 32-bit integer) + <dd>This value is the number of dimensions of the space the + dataset is located within: in other words, a planar dataset + located within a 3-D space, a 3-D dataset + which is a subset of another 3-D space, and so on. + <dt>Embedded Dimension Size: (unsigned 32-bit integer) + <dd>These values are the sizes of the dimensions of the + embedded dataspace + that the dataset is located within. + <dt>Embedded Origin Location: (unsigned 32-bit integer) + <dd>These values comprise the location of the dataset’s + origin within the embedded dataspace. + </dl> +</dl> +[Comment: need some way to handle different orientations of the +dataset dataspace +within the embedded dataspace]<br /> + +<br /> +<center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Structured/Regular Grid Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4">Logical Dimension Size #1</td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimension Maximum #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimension Size #n</td> + </tr> + <tr align="center"> + <td colspan="4">Logical Dimension Maximum #n</td> + </tr> + </table> +</center> + +<br /> +<dl> + <dt>The elements of the dimensionality message are described below: + <dd> + <dl> + <dt>Logical Dimension Size #n: (unsigned 32-bit integer) + <dd>This value is the current size of the dimension of the + data as stored in + the file. The first dimension stored in the list of + dimensions is the slowest + changing dimension and the last dimension stored is the + fastest changing + dimension. + <dt>Logical Dimension Maximum #n: (unsigned 32-bit integer) + <dd>This value is the maximum size of the dimension of the + data as stored in + the file. This value may be the special value + <UNLIMITED> which + indicates that the data may expand along this dimension + indefinitely. + </dl> +</dl> +<br /> +<center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Structured/Irregular Grid Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4"># of Grid Points in Dimension #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4"># of Grid Points in Dimension #n</td> + </tr> + <tr align="center"> + <td colspan="4">Datatype of Grid Point Locations</td> + </tr> + <tr align="center"> + <td colspan="4">Location of Grid Points in Dimension #1</td> + </tr> + <tr align="center"> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr align="center"> + <td colspan="4">Location of Grid Points in Dimension #n</td> + </tr> + </table> +</center> + +<br /> +<center> + <table border cellpadding="4" width="80%"> + <caption align="bottom"> + <b>HDF5 Dataspace Unstructured Grid Information</b> + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr align="center"> + <td colspan="4"># of Grid Points</td> + </tr> + <tr align="center"> + <td colspan="4">Datatype of Grid Point Locations</td> + </tr> + <tr align="center"> + <td colspan="4">Grid Point Locations<br />.<br />.<br /></td> + </tr> + </table> +</center> +--> + +<h4><a name="LinkInfoMessage">IV.A.2.c. The Link Info Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Link Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x002 </td></tr> + <tr><td colspan="2"><b>Length:</b> Varies </td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated. </td></tr> + <tr><td><b>Description:</b></td> + <td>The link info message tracks variable information about the + current state of the links for a “new style” + group’s behavior. Variable information will be stored in + this message and constant information will be stored in the + <a href="#GroupInfoMessage">Group Info</a> message. + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Link Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Maximum Creation Index <em>(8 bytes, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of v2 B-tree for Name Index<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address of v2 B-tree for Creation Order Index<sup>O</sup> <em>(optional)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Link Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This field determines various optional aspects of the link + info message: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, creation order for the links is tracked. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, creation order for the links is indexed. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Maximum Creation Index</p></td> + <td><p>This 64-bit value is the maximum creation order index value + stored for a link in this group.</p> + <p>This field is present if bit 0 of <em>flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap Address</p></td> + <td> + <p> + This is the address of the fractal heap to store dense links. + Each link stored in the fractal heap is stored as a + <a href="#LinkMessage">Link Message</a>. + </p> + <p> + If there are no links in the group, or the group’s links + are stored “compactly” (as object header messages), this + value will be the <a href="#UndefinedAddress">undefined + address</a>. + </p> + </td> + </tr> + + <tr> + <td><p>Address of v2 B-tree for Name Index</p></td> + <td><p>This is the address of the version 2 B-tree to index names of links.</p> + <p>If there are no links in the group, or the group’s links + are stored “compactly” (as object header messages), this + value will be the <a href="#UndefinedAddress">undefined + address</a>. + </p> + </td> + </tr> + + <tr> + <td><p>Address of v2 B-tree for Creation Order Index</p></td> + <td><p>This is the address of the version 2 B-tree to index creation order of links.</p> + <p>If there are no links in the group, or the group’s links + are stored “compactly” (as object header messages), this + value will be the <a href="#UndefinedAddress">undefined + address</a>. + </p> + <p>This field exists if bit 1 of <em>flags</em> is set.</p> + </td> + </tr> + + </table> +</div> + + +<h4><a name="DatatypeMessage">IV.A.2.d. The Datatype Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Datatype</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0003 + </td></tr> + <tr><td colspan="2"><b>Length:</b> Variable</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for dataset or committed + datatype (formerly named datatype) objects; may not be repeated. + </td></tr> + <tr><td><b>Description:</b></td> + <td><p>The datatype message defines the datatype for each element + of a dataset or a common datatype for sharing between multiple + datasets. A datatype can describe an atomic type like a fixed- + or floating-point type or more complex types like a C struct + (compound datatype), array (array datatype), or C++ vector + (variable-length datatype).</p> + <p>Datatype messages that are part of a dataset object do not + describe how elements are related to one another; the dataspace + message is used for that purpose. Datatype messages that are part of + a committed datatype (formerly named datatype) message describe + a common datatype that can be shared by multiple datasets in the + file.</p> + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Datatype Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Class and Version</td> + <td>Class Bit Field, Bits 0-7</td> + <td>Class Bit Field, Bits 8-15</td> + <td>Class Bit Field, Bits 16-23</td> + </tr> + + <tr> + <td colspan="4">Size</td> + </tr> + + <tr> + <td colspan="4"><br /><br />Properties<br /><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Datatype Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Class and Version</p></td> + <td> + <p>The version of the datatype message and the datatype’s class + information are packed together in this field. The version + number is packed in the top 4 bits of the field and the class + is contained in the bottom 4 bits. + </p> + <p>The version number information is used for changes in the + format of the datatype message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Used by early versions of the library to encode + compound datatypes with explicit array fields. + See the compound datatype description below for + further details. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Used when an array datatype needs to be encoded. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Used when a VAX byte-ordered type needs to be + encoded. Packs various other datatype classes more + efficiently also. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>Used to encode the revised reference datatype. + </td> + </tr> + </table></p> + + <p>The class of the datatype determines the format for the class + bit field and properties portion of the datatype message, which + are described below. The + following classes are currently defined: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td><a href="#ClassFixedPoint">Fixed-Point</a></td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td><a href="#ClassFloatingPoint">Floating-Point</a></td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td> <a href="#ClassTime">Time</a></td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td><a href="#ClassString">String</a></td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td><a href="#ClassBitField">Bit field</a></td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td><a href="#ClassOpaque">Opaque</a></td> + </tr> + + <tr> + <td align="center"><code>6</code></td> + <td><a href="#ClassCompound">Compound</a></td> + </tr> + + <tr> + <td align="center"><code>7</code></td> + <td><a href="#ClassReference">Reference</a></td> + </tr> + + <tr> + <td align="center"><code>8</code></td> + <td><a href="#ClassEnum">Enumerated</a></td> + </tr> + + <tr> + <td align="center"><code>9</code></td> + <td><a href="#ClassVarLen">Variable-Length</a></td> + </tr> + + <tr> + <td align="center"><code>10</code></td> + <td><a href="#ClassArray">Array</a></td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Class Bit Fields</p></td> + <td> + <p>The information in these bit fields is specific to each datatype + class and is described below. All bits not defined for a + datatype class are set to zero. + </p> + </td> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>The size of a datatype element in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Properties</p></td> + <td> + <p>This variable-sized sequence of bytes encodes information + specific to each datatype class and is described for each class + below. If there is no property information specified for a + datatype class, the size of this field is zero bytes. + </p> + </td> + </tr> + + </table> +</div> + + +<br /> +<br /> +<a name="ClassFixedPoint"></a> + <p>Class specific information for the Fixed-point Numbers class + (Class 0):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Fixed-point Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0</p></td> + <td><p><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</p></td> + </tr> + + <tr> + <td><p>1, 2</p></td> + <td><p><b>Padding type.</b> Bit 1 is the lo_pad bit and bit 2 + is the hi_pad bit. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</p></td> + </tr> + + <tr> + <td><p>3</p></td> + <td><p><b>Signed.</b> If this bit is set then the fixed-point + number is in 2’s complement form.</p></td> + </tr> + + <tr> + <td><p>4-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Fixed-point Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Offset</td> + <td colspan="2">Bit Precision</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Fixed-point Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Offset</p></td> + <td> + <p>The bit offset of the first significant bit of the fixed-point + value within the datatype. The bit offset specifies the number + of bits “to the right of” the value (which are set to the + lo_pad bit value). + </p> + </td> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the fixed-point value + within the datatype. This value, combined with the datatype + element’s size and the Bit Offset field specifies the number + of bits “to the left of” the value (which are set to the + hi_pad bit value). + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <a name="ClassFloatingPoint"></a> + <p>Class specific information for the Floating-point Numbers class + (Class 1):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Floating-point Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0, 6</p></td> + <td><p><b>Byte Order.</b> These two non-contiguous bits specify the + “endianness” of the bytes in the datatype element. + <table class="list"> + <tr> + <th width="10%" align="center">Bit 6</th> + <th width="10%" align="center">Bit 0</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td align="center"><code>0</code></td> + <td>Byte order is little-endian + </td> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td align="center"><code>1</code></td> + <td>Byte order is big-endian + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td align="center"><code>0</code></td> + <td>Reserved + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td align="center"><code>1</code></td> + <td>Byte order is VAX-endian + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>1, 2, 3</p></td> + <td><p><b>Padding type.</b> Bit 1 is the low bits pad type, bit 2 + is the high bits pad type, and bit 3 is the internal bits + pad type. If a datum has unused bits at either end or between + the sign bit, exponent, or mantissa, then the value of bit + 1, 2, or 3 is copied to those locations.</p></td> + </tr> + + <tr> + <td><p>4-5</p></td> + <td><p><b>Mantissa Normalization.</b> This 2-bit bit field specifies + how the most significant bit of the mantissa is managed. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>No normalization + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The most significant bit of the mantissa is always set + (except for 0.0). + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>The most significant bit of the mantissa is not stored, + but is implied to be set. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Reserved. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>7</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + + <tr> + <td><p>8-15</p></td> + <td><p><b>Sign Location.</b> This is the bit position of the sign + bit. Bits are numbered with the least significant bit zero.</p></td> + </tr> + + <tr> + <td><p>16-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Floating-point Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Offset</td> + <td colspan="2">Bit Precision</td> + </tr> + + <tr> + <td>Exponent Location</td> + <td>Exponent Size</td> + <td>Mantissa Location</td> + <td>Mantissa Size</td> + </tr> + + <tr> + <td colspan="4">Exponent Bias</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Floating-point Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Offset</p></td> + <td> + <p>The bit offset of the first significant bit of the floating-point + value within the datatype. The bit offset specifies the number + of bits “to the right of” the value. + </p> + </td> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the floating-point value + within the datatype. + </p> + </td> + </tr> + + <tr> + <td><p>Exponent Location</p></td> + <td> + <p>The bit position of the exponent field. Bits are numbered with + the least significant bit number zero. + </p> + </td> + </tr> + + <tr> + <td><p>Exponent Size</p></td> + <td> + <p>The size of the exponent field in bits. + </p> + </td> + </tr> + + <tr> + <td><p>Mantissa Location</p></td> + <td> + <p>The bit position of the mantissa field. Bits are numbered with + the least significant bit number zero. + </p> + </td> + </tr> + + <tr> + <td><p>Mantissa Size</p></td> + <td> + <p>The size of the mantissa field in bits. + </p> + </td> + </tr> + + <tr> + <td><p>Exponent Bias</p></td> + <td> + <p>The bias of the exponent field. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <a name="ClassTime"></a> + <p>Class specific information for the Time class (Class 2):</p> + + + <div align="center"> + <table class="desc"> + <caption> + Bits: Time Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0</p></td> + <td><p><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</p></td> + </tr> + + <tr> + <td><p>1-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Time Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Precision</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Time Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the time value. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <a name="ClassString"></a> + <p>Class specific information for the Strings class (Class 3):</p> + + + <div align="center"> + <table class="desc"> + <caption> + Bits: String Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Padding type.</b> This four-bit value determines the + type of padding to use for the string. The values are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Null Terminate: A zero byte marks the end of the + string and is guaranteed to be present after + converting a long string to a short string. When + converting a short string to a long string the value is + padded with additional null characters as necessary. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Null Pad: Null characters are added to the end of + the value during conversions from short values to long + values but conversion in the opposite direction simply + truncates the value. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Space Pad: Space characters are added to the end of + the value during conversions from short values to long + values but conversion in the opposite direction simply + truncates the value. This is the Fortran + representation of the string. + </td> + </tr> + + <tr> + <td align="center"><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>4-7</p></td> + <td><p><b>Character Set.</b> The character set used to + encode the string. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>8-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <p>There are no properties defined for the string class. + </p> + + <br /> + <br /> + <a name="ClassBitField"></a> + <p>Class specific information for the Bit Fields class (Class 4):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Bitfield Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0</p></td> + <td><p><b>Byte Order.</b> If zero, byte order is little-endian; + otherwise, byte order is big endian.</p></td> + </tr> + + <tr> + <td><p>1, 2</p></td> + <td><p><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2 + is the hi_pad type. If a datum has unused bits at either + end, then the lo_pad or hi_pad bit is copied to those + locations.</p></td> + </tr> + + <tr> + <td><p>3-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Bit Field Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="2">Bit Offset</td> + <td colspan="2">Bit Precision</td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Bit Field Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bit Offset</p></td> + <td> + <p>The bit offset of the first significant bit of the bit field + within the datatype. The bit offset specifies the number + of bits “to the right of” the value. + </p> + </td> + </tr> + + <tr> + <td><p>Bit Precision</p></td> + <td> + <p>The number of bits of precision of the bit field + within the datatype. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <br /> + <a name="ClassOpaque"></a> + <p>Class specific information for the Opaque class (Class 5):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Opaque Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-7</p></td> + <td><p>Length of ASCII tag in bytes.</p></td> + </tr> + + <tr> + <td><p>8-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Opaque Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />ASCII Tag<br /> + <br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Opaque Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>ASCII Tag</p></td> + <td> + <p>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <br /> + <a name="ClassCompound"></a> + <p>Class specific information for the Compound class (Class 6):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Compound Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-15</p></td> + <td><p><b>Number of Members.</b> This field contains the number + of members defined for the compound datatype. The member + definitions are listed in the Properties field of the data + type message.</p></td> + </tr> + + <tr> + <td><p>16-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + + <p>The Properties field of a compound datatype is a list of the + member definitions of the compound datatype. The member + definitions appear one after another with no intervening bytes. + The member types are described with a (recursively) encoded datatype + message.</p> + + <p>Note that the property descriptions are different for different + versions of the datatype version. Additionally note that the version + 0 datatype encoding is deprecated and has been replaced with later + encodings in versions of the HDF5 Library from the 1.4 release + onward.</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Compound Properties Description for Datatype Version 1 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Byte Offset of Member</td> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Dimension Permutation</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Dimension #1 Size (required)</td> + </tr> + + <tr> + <td colspan="4">Dimension #2 Size (required)</td> + </tr> + + <tr> + <td colspan="4">Dimension #3 Size (required)</td> + </tr> + + <tr> + <td colspan="4">Dimension #4 Size (required)</td> + </tr> + + <tr> + <td colspan="4"><br />Member Type Message<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Compound Properties Description for Datatype Version 1 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td> + <p>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Byte Offset of Member</p></td> + <td> + <p>This is the byte offset of the member within the datatype. + </p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>If set to zero, this field indicates a scalar member. If set + to a value greater than zero, this field indicates that the + member is an array of values. For array members, the size of + the array is indicated by the ‘Size of Dimension n’ field in + this message. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension Permutation</p></td> + <td> + <p>This field was intended to allow an array field to have + its dimensions permuted, but this was never implemented. + This field should always be set to zero. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This field is the size of a dimension of the array field as + stored in the file. The first dimension stored in the list of + dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Member Type Message</p></td> + <td> + <p>This field is a datatype message describing the datatype of + the member. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Compound Properties Description for Datatype Version 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Byte Offset of Member</td> + </tr> + + <tr> + <td colspan="4"><br />Member Type Message<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Compound Properties Description for Datatype Version 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td> + <p>This NUL-terminated string provides a description for the + opaque type. It is NUL-padded to a multiple of 8 bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Byte Offset of Member</p></td> + <td> + <p>This is the byte offset of the member within the datatype. + </p> + </td> + </tr> + + <tr> + <td><p>Member Type Message</p></td> + <td> + <p>This field is a datatype message describing the datatype of + the member. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Compound Properties Description for Datatype Version 3 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Byte Offset of Member <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Member Type Message<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Compound Properties Description for Datatype Version 3 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>This NUL-terminated string provides a description for the + opaque type. It is <em>not</em> NUL-padded to a multiple of 8 + bytes.</p></td> + </tr> + + <tr> + <td><p>Byte Offset of Member</p></td> + <td><p>This is the byte offset of the member within the datatype. + The field size is the minimum number of bytes necessary, + based on the size of the datatype element. For example, a + datatype element size of less than 256 bytes uses a 1 byte + length, a datatype element size of 256-65535 bytes uses a + 2 byte length, and so on.</p></td> + </tr> + + <tr> + <td><p>Member Type Message</p></td> + <td><p>This field is a datatype message describing the datatype of + the member.</p></td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <a name="ClassReference"></a> + <p>Class specific information for the Reference class (Class 7):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Reference Bit Field Description for Datatype Version < 4 + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Type.</b> This four-bit value contains the reference types which are supported for + backward compatibility. The values defined are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Object Reference (H5R_OBJECT1): A reference to another object in this + HDF5 file. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Dataset Region Reference (H5R_DATASET_REGION1): A reference to a region within + a dataset in this HDF5 file. + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>4-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Bits: Reference Bit Field Description for Datatype Version 4 + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Type.</b> This four-bit value contains the revised reference types. + The values defined are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Object Reference (H5R_OBJECT2): A reference to another object + in this file or an external file. + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Dataset Region Reference (H5R_DATASET_REGION2): A reference to a region within + a dataset in this file or an external file. + </td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>Attribute Reference (H5R_ATTR): A reference to an attribute attached to an + object in this file or an external file. + </td> + </tr> + + <tr> + <td align="center"><code>5-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>4-7</p></td> + <td><p><b>Version.</b> This four-bit value contains the version for encoding + the revised reference types. The values defined are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Unused + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>The version for encoding the revised reference types: Object Reference (2), + Dataset Region Reference (3) and Attribute Reference (4). + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + + </table></p> + + </td> + </tr> + + <tr> + <td><p>8-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <p>There are no properties defined for the reference class. + </p> + + + <br /> + <br /> + <a name="ClassEnum"></a> + <p>Class specific information for the Enumeration class (Class 8):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Enumeration Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-15</p></td> + <td><p><b>Number of Members.</b> The number of name/value + pairs defined for the enumeration type.</p></td> + </tr> + + <tr> + <td><p>16-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Enumeration Property Description for Datatype Versions + 1 and 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Names<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Values<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Enumeration Property Description for Datatype Versions + 1 and 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each enumeration type is based on some parent type, usually an + integer. The information for that parent type is described + recursively by this field. + </p> + </td> + </tr> + + <tr> + <td><p>Names</p></td> + <td> + <p>The name for each name/value pair. Each name is stored as a null + terminated ASCII string in a multiple of eight bytes. The names + are in no particular order. + </p> + </td> + </tr> + + <tr> + <td><p>Values</p></td> + <td> + <p>The list of values in the same order as the names. The values + are packed (no inter-value padding) and the size of each value + is determined by the parent type. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Enumeration Property Description for Datatype Version 3 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Names<br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Values<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Enumeration Property Description for Datatype Version 3 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each enumeration type is based on some parent type, usually an + integer. The information for that parent type is described + recursively by this field. + </p> + </td> + </tr> + + <tr> + <td><p>Names</p></td> + <td> + <p>The name for each name/value pair. Each name is stored as a null + terminated ASCII string, <em>not</em> padded to a multiple of + eight bytes. The names are in no particular order. + </p> + </td> + </tr> + + <tr> + <td><p>Values</p></td> + <td> + <p>The list of values in the same order as the names. The values + are packed (no inter-value padding) and the size of each value + is determined by the parent type. + </p> + </td> + </tr> + + </table> + </div> + + + + <br /> + <a name="ClassVarLen"></a> + <p>Class specific information for the Variable-length class (Class 9):</p> + + <div align="center"> + <table class="desc"> + <caption> + Bits: Variable-length Bit Field Description + </caption> + + <tr> + <th width="10%">Bits</th> + <th>Meaning</th> + </tr> + + <tr> + <td><p>0-3</p></td> + <td><p><b>Type.</b> This four-bit value contains the type of + variable-length datatype described. The values defined are: + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Sequence: A variable-length sequence of any datatype. + Variable-length sequences do not have padding or + character set information. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>String: A variable-length sequence of characters. + Variable-length strings have padding and character set + information. + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>4-7</p></td> + <td><p><b>Padding type.</b> (variable-length string only) + This four-bit value determines the type of padding + used for variable-length strings. The values are the same + as for the string padding type, as follows: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Null terminate: A zero byte marks the end of a string + and is guaranteed to be present after converting a long + string to a short string. When converting a short string + to a long string, the value is padded with additional null + characters as necessary. + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Null pad: Null characters are added to the end of the + value during conversion from a short string to a longer + string. Conversion from a long string to a shorter string + simply truncates the value. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Space pad: Space characters are added to the end of the + value during conversion from a short string to a longer + string. Conversion from a long string to a shorter string + simply truncates the value. This is the Fortran + representation of the string. + </td> + </tr> + + <tr> + <td align="center"><code>3-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + <p>This value is set to zero for variable-length sequences.</p> + + </td> + </tr> + + <tr> + <td><p>8-11</p></td> + <td><p><b>Character Set.</b> (variable-length string only) + This four-bit value specifies the character set + to be used for encoding the string: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>2-15</code></td> + <td>Reserved + </td> + </tr> + </table></p> + + <p>This value is set to zero for variable-length sequences.</p> + + </td> + </tr> + + <tr> + <td><p>12-23</p></td> + <td><p>Reserved (zero).</p></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Variable-length Property Description + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Variable-length Property Description + </caption> + <tr> + <th width="10%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each variable-length type is based on some parent type. The + information for that parent type is described recursively by + this field. + </p> + </td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <a name="ClassArray"></a> + <p>Class specific information for the Array class (Class 10):</p> + + <p>There are no bit fields defined for the array class. + </p> + + <p>Note that the dimension information defined in the property for this + datatype class is independent of dataspace information for a dataset. + The dimension information here describes the dimensionality of the + information within a data element (or a component of an element, if the + array datatype is nested within another datatype) and the dataspace for a + dataset describes the size and locations of the elements in a dataset. + </p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Array Property Description for Datatype Version 2 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Dimension #1 Size</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4">Permutation Index #1</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Permutation Index #n</td> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Array Property Description for Datatype Version 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the array has. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the size of the dimension of the array + as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Permutation Index #n</p></td> + <td> + <p>This value is the index permutation used to map + each dimension from the canonical representation to an + alternate axis for each dimension. Currently, dimension + permutations are not supported, and these indices should + be set to the index position minus one. In other words, + the first dimension should be set to 0, the second dimension + should be set to 1, and so on. + </p> + </td> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each array type is based on some parent type. The + information for that parent type is described recursively by + this field. + </p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Array Property Description for Datatype Version 3 + </caption> + + <tr> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + <th width="25%">Byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Dimension #1 Size</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4"><br />Base Type<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Array Property Description for Datatype Version 3 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td> + <p>This value is the number of dimensions that the array has. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td> + <p>This value is the size of the dimension of the array + as stored in the file. The first dimension stored in + the list of dimensions is the slowest changing dimension + and the last dimension stored is the fastest changing + dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Base Type</p></td> + <td> + <p>Each array type is based on some parent type. The + information for that parent type is described recursively by + this field. + </p> + </td> + </tr> + + </table> + </div> + + + + <h4><a name="OldFillValueMessage">IV.A.2.e. The Data Storage - + Fill Value (Old) Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Fill Value + (old)</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0004</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>The fill value message stores a single data value which + is returned to the application when an uninitialized data element + is read from a dataset. The fill value is interpreted with the + same datatype as the dataset. If no fill value message is present + then a fill value of all zero bytes is assumed.</p> + <p>This fill value message is deprecated in favor of the + “new” fill value message (Message Type 0x0005) and + is only written to the file for forward compatibility with + versions of the HDF5 Library before the 1.6.0 version. + Additionally, it only appears for datasets with a user-defined + fill value (as opposed to the library default fill value or an + explicitly set “undefined” fill value).</p> + </td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Layout: Fill Value Message (Old) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Size</td> + </tr> + + <tr> + <td colspan="4"><br />Fill Value <em>(optional, variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Fill Value Message (Old) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>This is the size of the Fill Value field in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Fill Value</p></td> + <td> + <p>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. + </p> + </td> + </tr> + </table> + </div> + + + <h4><a name="FillValueMessage">IV.A.2.f. The Data Storage - + Fill Value Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Fill + Value</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0005</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for dataset objects; + may not be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The fill value message stores a single data value which is + returned to the application when an uninitialized data element + is read from a dataset. The fill value is interpreted with the + same datatype as the dataset.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Layout: Fill Value Message - Versions 1 and 2 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Space Allocation Time</td> + <td>Fill Value Write Time</td> + <td>Fill Value Defined</td> + </tr> + + <tr> + <td colspan="4">Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Fill Value <em>(optional, variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Fill Value Message - Versions 1 and 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the + format of the fill value message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Initial version of this message. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>In this version, the Size and Fill Value fields are + only present if the Fill Value Defined field is set + to 1. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>This version packs the other fields in the message + more efficiently than version 2. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Space Allocation Time</p></td> + <td> + <p>When the storage space for the dataset’s raw data will be + allocated. The allowed values are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Not used. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Early allocation. Storage space for the entire dataset + should be allocated in the file when the dataset is + created. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Late allocation. Storage space for the entire dataset + should not be allocated until the dataset is written + to. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Incremental allocation. Storage space for the + dataset should not be allocated until the portion + of the dataset is written to. This is currently + used in conjunction with chunked data storage for + datasets. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Fill Value Write Time</p></td> + <td> + <p>At the time that storage space for the dataset’s raw data is + allocated, this value indicates whether the fill value should + be written to the raw data storage elements. The allowed values + are: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>On allocation. The fill value is always written to + the raw data storage when the storage space is allocated. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Never. The fill value should never be written to + the raw data storage. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Fill value written if set by user. The fill value + will be written to the raw data storage when the storage + space is allocated only if the user explicitly set + the fill value. If the fill value is the library + default or is undefined, it will not be written to + the raw data storage. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Fill Value Defined</p></td> + <td> + <p>This value indicates if a fill value is defined for this + dataset. If this value is 0, the fill value is undefined. + If this value is 1, a fill value is defined for this dataset. + For version 2 or later of the fill value message, this value + controls the presence of the Size and Fill Value fields. + </p> + </td> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>This is the size of the Fill Value field in bytes. This field + is not present if the Version field is greater than 1, + and the Fill Value Defined field is set to 0. + </p> + </td> + </tr> + + <tr> + <td><p>Fill Value</p></td> + <td> + <p>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. This field is + not present if the Version field is greater than 1, + and the Fill Value Defined field is set to 0. + </p> + </td> + </tr> + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Fill Value Message - Version 3 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Fill Value <em>(optional, variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Fill Value Message - Version 3 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the + format of the fill value message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Initial version of this message. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>In this version, the Size and Fill Value fields are + only present if the Fill Value Defined field is set + to 1. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>This version packs the other fields in the message + more efficiently than version 2. + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td> + <p>When the storage space for the dataset’s raw data will be + allocated. The allowed values are: + <table class="list"> + <tr> + <th width="20%" align="center">Bits</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0-1</code></td> + <td>Space Allocation Time, with the same + values as versions 1 and 2 of the message. + </td> + </tr> + <tr> + <td align="center"><code>2-3</code></td> + <td>Fill Value Write Time, with the same + values as versions 1 and 2 of the message. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>Fill Value Undefined, indicating that the fill + value has been marked as “undefined” for this dataset. + Bits 4 and 5 cannot both be set. + </td> + </tr> + <tr> + <td align="center"><code>5</code></td> + <td>Fill Value Defined, with the same values as + versions 1 and 2 of the message. + Bits 4 and 5 cannot both be set. + </td> + </tr> + <tr> + <td align="center"><code>6-7</code></td> + <td>Reserved (zero). + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Size</p></td> + <td> + <p>This is the size of the Fill Value field in bytes. This field + is not present if the Version field is greater than 1, + and the Fill Value Defined flag is set to 0. + </p> + </td> + </tr> + + <tr> + <td><p>Fill Value</p></td> + <td> + <p>The fill value. The bytes of the fill value are interpreted + using the same datatype as for the dataset. This field is + not present if the Version field is greater than 1, + and the Fill Value Defined flag is set to 0. + </p> + </td> + </tr> + </table> + </div> + + + <h4><a name="LinkMessage">IV.A.2.g. The Link Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Link</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0006</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies </td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be + repeated. </td></tr> + <tr><td><b>Description:</b></td> + <td><p>This message encodes the information for a link in a + group’s object header, when the group is storing its links + “compactly”, or in the group’s fractal heap, + when the group is storing its links “densely”.</p> + <p>A group is storing its links compactly when the fractal heap + address in the <em><a href="#LinkInfoMessage">Link Info + Message</a></em> is set to the “undefined address” + value.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Layout: Link Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td>Link type <em>(optional)</em></td> + <td bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Creation Order <em>(8 bytes, optional)</em><br /><br /></td> + </tr> + <tr> + <td>Link Name Character Set <em>(optional)</em></td> + <td>Length of Link Name (variable size)</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Link Name (variable size)</td> + </tr> + <tr> + <td colspan="4"><br />Link Information (variable size)<br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Link Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes version 1.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This field contains information about the link and controls + the presence of other fields below. + <table class="list"> + <tr> + <th width="20%" align="center">Bits</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0-1</code></td> + <td>Determines the size of the <em>Length of Link Name</em> + field. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 1 byte. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 2 bytes. + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 4 bytes. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>The size of the <em>Length of Link Name</em> + field is 8 bytes. + </td> + </tr> + </table> + </td> + </tr> + <tr> + <td align="center"><code>2</code></td> + <td>Creation Order Field Present: if set, the <em>Creation + Order</em> field is present. If not set, creation order + information is not stored for links in this group. + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Link Type Field Present: if set, the link is not + a hard link and the <em>Link Type</em> field is present. + If not set, the link is a hard link. + </td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>Link Name Character Set Field Present: if set, the + link name is not represented with the ASCII character + set and the <em>Link Name Character Set</em> field is + present. If not set, the link name is represented with + the ASCII character set. + </td> + </tr> + <tr> + <td align="center"><code>5-7</code></td> + <td>Reserved (zero). + </td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Link type</p></td> + <td><p>This is the link class type and can be one of the following + values: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>A hard link (should never be stored in the file) + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>A soft link. + </td> + </tr> + <tr> + <td align="center"><code>2-63</code></td> + <td>Reserved for future HDF5 internal use. + </td> + </tr> + <tr> + <td align="center"><code>64</code></td> + <td>An external link. + </td> + </tr> + <tr> + <td align="center"><code>65-255</code></td> + <td>Reserved, but available for user-defined link types. + </td> + </tr> + </table></p> + + <p>This field is present if bit 3 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Creation Order</p></td> + <td><p>This 64-bit value is an index of the link’s creation time within + the group. Values start at 0 when the group is created an increment + by one for each link added to the group. Removing a link from a + group does not change existing links’ creation order field. + </p> + <p>This field is present if bit 2 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Link Name Character Set</p></td> + <td><p>This is the character set for encoding the link’s name: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding (this should never be stored + in the file) + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + </table></p> + + <p>This field is present if bit 4 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Length of link name</p></td> + <td><p>This is the length of the link’s name. The size of this field + depends on bits 0 and 1 of <em>Flags</em>.</p> + </td> + </tr> + + <tr> + <td><p>Link name</p></td> + <td><p>This is the name of the link, non-NULL terminated.</p> + </td> + </tr> + + <tr> + <td><p>Link information</p></td> + <td><p>The format of this field depends on the <em>link type</em>.</p> + <p>For <b>hard</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%"><i><a href="#SizeOfOffsetsV0"> + Size of Offsets</a></i> bytes:</td> + <td width="80%">The address of the object header for the object that the + link points to. + </td> + </tr> + </table> + </p> + + <p> + For <b>soft</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-2:</td> + <td width="80%">Length of soft link value.</td> + </tr> + <tr> + <td><em>Length of soft link value</em> bytes:</td> + <td>A non-NULL-terminated string storing the value of the + soft link. + </td> + </tr> + </table> + </p> + + <p> + For <b>external</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-2:</td> + <td width="80%">Length of external link value.</td> + </tr> + <tr> + <td><em>Length of external link value</em> bytes:</td> + <td>The first byte contains the version number in the + upper 4 bits and flags in the lower 4 bits for the external + link. Both version and flags are defined to be zero in + this document. The remaining bytes consist of two + NULL-terminated strings, with no padding between them. + The first string is the name of the HDF5 file containing + the object linked to and the second string is the full path + to the object linked to, within the HDF5 file’s + group hierarchy. + </td> + </tr> + </table> + </p> + + <p> + For <b>user-defined</b> links, the field is formatted as follows: + + <table class="list"> + <tr> + <td width="20%">Bytes 1-2:</td> + <td width="80%">Length of user-defined data.</td> + </tr> + <tr> + <td><em>Length of user-defined link value</em> bytes:</td> + <td>The data supplied for the user-defined link type.</td> + </tr> + </table> + </p> + + </td> + </tr> + </table> + </div> + + <h4><a name="ExternalFileListMessage">IV.A.2.h. The Data Storage - + External Data Files Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> External + Data Files</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0007</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The external data storage message indicates that the data + for an object is stored outside the HDF5 file. The filename of + the object is stored as a Universal Resource Location (URL) of + the actual filename containing the data. An external file list + record also contains the byte offset of the start of the data + within the file and the amount of space reserved in the file + for that data.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Layout: External File List Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="2">Allocated Slots</td> + <td colspan="2">Used Slots</td> + </tr> + + <tr> + <td colspan="4"><br />Heap Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Slot Definitions...<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: External File List Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the format of + External Data Storage Message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>The current version used by the library.</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Allocated Slots</p></td> + <td> + <p>The total number of slots allocated in the message. Its value must be at least as + large as the value contained in the Used Slots field. (The current library simply + uses the number of Used Slots for this message)</p> + </td> + </tr> + + <tr> + <td><p>Used Slots</p></td> + <td> + <p>The number of initial slots which contains valid information.</p> + </td> + </tr> + + <tr> + <td><p>Heap Address</p></td> + <td> + <p>This is the address of a local heap which contains the names for the external + files (The local heap information can be found in Disk Format Level 1D in this + document). The name at offset zero in the heap is always the empty string.</p> + </td> + </tr> + + <tr> + <td><p>Slot Definitions</p></td> + <td> + <p>The slot definitions are stored in order according to the array addresses they + represent.</p> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: External File List Slot + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Name Offset in Local Heap<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Offset in External Data File<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data Size in External File<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: External File List Slot + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name Offset in Local Heap</p></td> + <td> + <p>The byte offset within the local name heap for the name + of the file. File names are stored as a URL which has a + protocol name, a host name, a port number, and a file + name: + <code><em>protocol</em>:<em>port</em>//<em>host</em>/<em>file</em></code>. + If the protocol is omitted then “file:” is assumed. If + the port number is omitted then a default port for that + protocol is used. If both the protocol and the port + number are omitted then the colon can also be omitted. If + the double slash and host name are omitted then + “localhost” is assumed. The file name is the only + mandatory part, and if the leading slash is missing then + it is relative to the application’s current working + directory (the use of relative names is not + recommended). + </p> + </td> + </tr> + + <tr> + <td><p>Offset in External Data File</p></td> + <td> + <p>This is the byte offset to the start of the data in the + specified file. For files that contain data for a single + dataset this will usually be zero.</p> + </td> + </tr> + + <tr> + <td><p>Data Size in External File</p></td> + <td> + <p>This is the total number of bytes reserved in the + specified file for raw data storage. For a file that + contains exactly one complete dataset which is not + extendable, the size will usually be the exact size of the + dataset. However, by making the size larger one allows + HDF5 to extend the dataset. The size can be set to a value + larger than the entire file since HDF5 will read zeroes + past the end of the file without failing.</p> + </td> + </tr> + </table> + </div> + + + <h4><a name="LayoutMessage">IV.A.2.i. The Data Layout Message</a></h4> + + <!-- start msgdesc table --> + <center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Data Layout</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0008</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for datasets; may not + be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The Data Layout message + describes how the elements of a multi-dimensional array are stored + in the HDF5 file. Four types of data layout are supported: + <ol> + <li>Contiguous: The array is stored in one contiguous area of + the file. This layout requires that the size of the array be + constant: data manipulations such as chunking, compression, + checksums, or encryption are not permitted. The message stores + the total storage size of the array. The offset of an element + from the beginning of the storage area is computed as in a C + array.</li> + <li>Chunked: The array domain is regularly decomposed into + chunks, and each chunk is allocated and stored separately. This + layout supports arbitrary element traversals, compression, + encryption, and checksums (these features are described + in other messages). The message stores the size of a chunk + instead of the size of the entire array; the storage size of + the entire array can be calculated by traversing the chunk index + that stores the chunk addresses.</li> + <li>Compact: The array is stored in one contiguous block as + part of this object header message.</li> + <li>Virtual: This is only supported for version 4 of the Data + Layout message. The message stores information that is used to + locate the global heap collection containing the Virtual Dataset + (VDS) mapping information. The mapping associates the VDS to + the source dataset elements that are stored across a collection + of HDF5 files.</li> + </ol></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> + </table></center> + <!-- end msgdesc table --> + + <div align="center"> + <table class="format"> + <caption> + Layout: Data Layout Message (Versions 1 and 2) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Dimensionality</td> + <td>Layout Class</td> + <td>Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4">Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Data Address<sup>O</sup> <em>(optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Dimension 1 Size</td> + </tr> + + <tr> + <td colspan="4">Dimension 2 Size</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4">Dataset Element Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4">Compact Data Size <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Compact Data... <em>(variable size, optional)</em><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Data Layout Message (Versions 1 and 2) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the format of the data + layout message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by version 1.4 and before of the library to encode layout information. + Data space is always allocated when the data set is created.</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Used by version 1.6.[0,1,2] of the library to encode layout information. + Data space is allocated only when it is necessary.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td><p>An array has a fixed dimensionality. This field + specifies the number of dimension size fields later in the + message. The value stored for chunked storage is 1 greater than + the number of dimensions in the dataset’s dataspace. + For example, 2 is stored for a 1 dimensional dataset. + </p> + </td> + </tr> + + <tr> + <td><p>Layout Class</p></td> + <td><p>The layout class specifies the type of storage for the data + and how the other fields of the layout message are to be + interpreted. + + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Compact Storage + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Contiguous Storage + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Chunked Storage + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Data Address</p></td> + <td><p>For contiguous storage, this is the address of the raw + data in the file. For chunked storage this is the address + of the <a href="#V1Btrees">v1 B-tree</a> that is used to look up the addresses of the + chunks. This field is not present for compact storage. + If the version for this message is greater than 1, the address + may have the “undefined address” value, to indicate that + storage has not yet been allocated for this array.</p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td><p>For contiguous and compact storage the dimensions define + the entire size of the array while for chunked storage they define + the size of a single chunk. In all cases, they are in units of + array elements (not bytes). The first dimension stored in the list + of dimensions is the slowest changing dimension and the last + dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dataset Element Size</p></td> + <td><p>The size of a dataset element, in bytes. This field is only + present for chunked storage. + </p> + </td> + </tr> + + <tr> + <td><p>Compact Data Size</p></td> + <td><p>This field is only present for compact data storage. + It contains the size of the raw data for the dataset array, in + bytes.</p> + </td> + </tr> + + <tr> + <td><p>Compact Data</p></td> + <td><p>This field is only present for compact data storage. + It contains the raw data for the dataset array.</p> + </td> + </tr> + </table> + </div> + + <br /> + <p>Version 3 of this message re-structured the format into specific + properties that are required for each layout class.</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Data Layout Message (Version 3) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Layout Class</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Properties <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Data Layout Message (Version 3) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The version number information is used for changes in the format of layout message + and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Used by the version 1.6.3 and later of the library to store properties + for each layout class.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Layout Class</p></td> + <td><p>The layout class specifies the type of storage for the data + and how the other fields of the layout message are to be + interpreted. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Compact Storage + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Contiguous Storage + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Chunked Storage + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Properties</p></td> + <td><p>This variable-sized field encodes information specific to each + layout class and is described below. If there is no property + information specified for a layout class, the size of this field + is zero bytes.</p></td> + </tr> + </table> + </div> + + <br /> + <a name="CompactStorage"></a> + <p>Class-specific information for compact storage (layout class 0): (Note: The dimensionality information + is in the Dataspace message)</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Compact Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="2">Size</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Raw Data... <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Compact Storage Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size</p></td> + <td><p>This field contains the size of the raw data for the dataset + array, in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Raw Data</p></td> + <td><p>This field contains the raw data for the dataset array.</p></td> + </tr> + </table> + </div> + + + <br /> + <a name="ContiguousStorage"></a> + <p>Class-specific information for contiguous storage (layout class 1): + (Note: The dimensionality information is in the Dataspace message)</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Contiguous Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Size<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Contiguous Storage Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This is the address of the raw data in the file. + The address may have the “undefined address” value, to indicate + that storage has not yet been allocated for this array.</p></td> + </tr> + + <tr> + <td><p>Size</p></td> + <td><p>This field contains the size allocated to store the raw data, + in bytes. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + <p>Class-specific information for chunked storage (layout class 2):</p> + + + <div align="center"> + <table class="format"> + <caption> + Layout: Chunked Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Dimensionality</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Dimension 0 Size</td> + </tr> + + <tr> + <td colspan="4">Dimension 1 Size</td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Dimension #n Size</td> + </tr> + + <tr> + <td colspan="4">Dataset Element Size</td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Chunked Storage Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td><p>A chunk has a fixed dimensionality. This field specifies + the number of dimension size fields later in the message.</p></td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This is the address of the <a href="#V1Btrees">v1 B-tree</a> + that is used to look up the + addresses of the chunks that actually store portions of the array + data. The address may have the “undefined address” value, to + indicate that storage has not yet been allocated for this array.</p></td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td><p>These values define the dimension size of a single chunk, in + units of array elements (not bytes). The first dimension stored in + the list of dimensions is the slowest changing dimension and the + last dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Dataset Element Size</p></td> + <td><p>The size of a dataset element, in bytes. + </p> + </td> + </tr> + </table> + </div> + + + <br /> + + <p><a name="DataLayoutV4"> + Version 4</a> of this message is similar to version 3 but has + additional information for the virtual layout class as well as + indexing information for the chunked layout class.</p> + + <div align="center"> + <table class="format"> + <caption> + Layout: Data Layout Message (Version 4) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Layout Class</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Properties <em>(variable size)</em><br /><br /></td> + </tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Data Layout Message (Version 4) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>The value for this field is 4 and is used by version 1.10.0 + and later of the library to store properties for each layout + class and indexing information for the chunked layout. + </p> + </td> + </tr> + + <tr> + <td><p>Layout Class</p></td> + <td><p>The layout class specifies the type of storage for the data + and how the other fields of the layout message are to be + interpreted. + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Compact Storage + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Contiguous Storage + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Chunked Storage + </td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>Virtual Storage + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Properties</p></td> + <td><p>This variable-sized field encodes information specific to a + layout class as follows: + <table class="list"> + <tr> + <th align="left" width="20%">Layout Class</th> + <th align="left" width="80%">Description</th> + </tr> + + <tr> + <td align="left">Compact Storage</td> + <td>See <a href="#CompactStorage">Compact Storage + Property Description</i></a> for the version 3 +Data Layout message. +</td> +</tr> + +<tr> + <td align="left">Contiguous Storage</td> + <td>See <a href="#ContiguousStorage">Contiguous Storage + Property Description</i></a> for the version 3 +Data Layout message. +</td> +</tr> + +<tr> + <td align="left">Chunked Storage</td> + <td>See <a href="#ChunkedStorage">Chunked Storage + Property Description</i></a> below. +</td> +</tr> + +<tr> + <td align="left">Virtual Storage</td> + <td>See <a href="#VirtualStorage">Virtual Storage + Property Description</i></a> below. +</td> +</tr> +</table> + +</p></td> +</tr> +</table> +</div> + +<br /> +<a name="ChunkedStorage"></a> +<p>Class-specific information for chunked storage (layout + class 2):</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Chunked Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Flags</td> + <td>Dimensionality</td> + <td>Dimension Size Encoded Length</td> + <td colspan="1" bgcolor="#DDDDDD"><em>This space inserted to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Dimension 0 Size <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Dimension 1 Size <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4">...</td> + </tr> + + <tr> + <td colspan="4">Dimension #n Size <em>(variable size)</em></td> + </tr> + + <tr> + <td>Chunk Indexing Type</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Indexing Type Information <em>(variable size)</em></td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Chunked Storage Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is the chunked layout feature flag:</p> + + <table class="list"> + <tr> + <th width="55%" align="left">Value</th> + <th width="45%" align="left">Description</th> + </tr> + + <tr> + <td align="left"><code>DONT_FILTER_PARTIAL_BOUND_CHUNKS (bit 0)</code></td> + <td>Do not apply filter to a partial edge chunk. + + </td> + </tr> + + <tr> + <td align="left"><code>SINGLE_INDEX_WITH_FILTER (bit 1)</code></td> + <td>A filtered chunk for <i>Single Chunk</i> indexing. + </td> + </tr> + + </table> + + </td> + + </tr> + + <tr> + <td><p>Dimensionality</p></td> + <td><p>A chunk has fixed dimension. This field specifies + the number of <em>Dimension Size</em> fields later in the message.</p></td> + </tr> + + <tr> + <td><p>Dimension Size Encoded Length</p></td> + <td> + <p>This is the size in bytes used to encode <em>Dimension Size</em>. + </p> + </td> + </tr> + + <tr> + <td><p>Dimension #n Size</p></td> + <td><p>These values define the dimension size of a single chunk, in + units of array elements (not bytes). The first dimension stored in + the list of dimensions is the slowest changing dimension and the + last dimension stored is the fastest changing dimension. + </p> + </td> + </tr> + + <tr> + <td><p>Chunk Indexing Type</p></td> + <td><p>There are five indexing types used to look up addresses + of the chunks. For more information on each type, see + <a href="#AppendixC">“Appendix C: Types of Indexes for + Dataset Chunks.”</a> + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td><a href="#SingleChunk"><i>Single Chunk</i></a> indexing type. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td><a href="#Implicit"><i>Implicit</i></a> indexing type. + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td><a href="#FixedArray"><i>Fixed Array</i></a> indexing type. + </td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td><a href="#ExtensibleArray"><i>Extensible Array</i></a> indexing type. + </td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td><a href="#V2Btrees"><i>Version 2 B-tree</i></a> indexing type. + </td> + </tr> + + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Indexing Type Information</p></td> + <td><p>This variable-sized field encodes information specific to + an indexing type. More information on what is encoded with + each type can be found below this table. + <ul> + <li>See <a href="#IndexInfoSingle"><i>Single Chunk</i></a> below.</li> + <li>See <a href="#IndexInfoImplicit"><i>Implicit</i></a> below.</li> + <li>See <a href="#IndexInfoFixed"><i>Fixed Array</i></a> below.</li> + <li>See <a href="#IndexInfoExtensible"><i>Extensible Array</i></a> below.</li> + <li>See <a href="#IndexInfoV2Btrees"><i>Version 2 B-tree</i></a> below.</li> + </ul> + </p> + </td> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This is the address specific to an indexing type. + The address may be undefined if the chunk or index storage is not allocated yet. + <table class="list"> + <tr> + <th width="40%" align="left">Value</th> + <th width="60%" align="left">Description</th> + </tr> + + <tr> + <td align="left"><i>Single Chunk index</i></td> + <td align="left">Address of the single chunk.</td> + </td> + </tr> + + <tr> + <td align="left"><i>Implicit index</i></td> + <td align="left">Address of the array of dataset chunks.</td> +</td> +</tr> + +<tr> + <td align="left"><i>Fixed Array index</i></td> + <td align="left">Address of the index.</td> +</tr> + +<tr> + <td align="left"><i>Extensible Array index</i></td> + <td align="left">Address of the index.</td> +</td> +</tr> + +<tr> + <td align="left"><i>Version 2 B-tree index</i></td> + <td align="left">Address of the index.</td> +</td> +</tr> + +</table> + +</p> +</td> +</tr> + +</table> +</div> + +<br /> + +<ol> + <li> + <a name="IndexInfoSingle"></a> + Index-specific information for <i>Single Chunk</i>: + </li> + + <p>The following information exists only when the chunk is filtered. + In other words, when <code>DONT_FILTER_PARTIAL_BOUND_CHUNKS</code> + (bit 0) is enabled in the field <em>flags</em>.</p> + + <div align="center"> + <table class="format"> + <caption> + Layout: Single Chunk Indexing Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Size of filtered chunk<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Filters for chunk</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="55%"> </td> + <td width="45%"> <!-- width is slightly different: these + tables are part of an ordered list; see <ol> tags. --> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Single Chunk Indexing Information + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Size of filtered chunk</p></td> + <td><p>This field is the size of a filtered chunk.</p></td> + </tr> + + <tr> + <td><p>Filters for chunk</p></td> + <td><p>This field contains filters for the chunk.</p></td> + </tr> + </table> + </div> +</p> + +<br /> + +<li> + <a name="IndexInfoImplicit"></a> + Index-specific information for <i>Implicit</i>: +</li> + +<div align="center"> + <table class="format"> + <caption> + Layout: Implicit Indexing Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4" bgcolor="#DDDDDD"> + <em>No specific indexing information</em></td> + </tr> + + </table> +</div> + +<br /> +<li> + <a name="IndexInfoFixed"></a> + Index-specific information for <i>Fixed Array</i>: +</li> + +<div align="center"> + <table class="format"> + <caption> + Layout: Fixed Array Indexing Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="1">Page Bits</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fixed Array Indexing Information + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Page Bits</p></td> + <td><p>This field contains the number of bits needed to store the + maximum number of elements in a data block page.</p></td> + </tr> + + </table> +</div> +</p> + +<br /> +<li> + <a name="IndexInfoExtensible"></a> + Index-specific information for <i>Extensible Array</i>: +</li> + +<div align="center"> + <table class="format"> + <caption> + Layout: Extensible Array Indexing Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Max Bits</td> + <td>Index Elements</td> + <td>Min Pointers</td> + <td>Min Elements</td> + </tr> + + <td colspan="2">Page Bits</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> +</tr> + +</table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Extensible Array Indexing Information + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Max Bits</p></td> + <td><p>This field contains the number of bits needed to store the maximum number of elements + in the array. + </p> + </td> + </tr> + + <tr> + <td><p>Index Elements</p></td> + <td><p>This field contains the number of elements to store in the + index block. + </p> + </td> + </tr> + + <tr> + <td><p>Min Pointers</p></td> + <td><p>This field contains the minimum number of data block pointers + for a superblock. + </p> + </td> + </tr> + + <tr> + <td><p>Min Elements</p></td> + <td><p>This field contains the minimum number of elements per data block. + </p> + </td> + </tr> + + <tr> + <td><p>Page Bits</p></td> + <td><p>This field contains the number of bits needed to store the + maximum number of elements in a data block page. + </p> + </td> + </tr> + + </table> +</div> +</p> +<br /> + +<li> + <a name="IndexInfoV2Btrees"></a> + Index-specific information for <i>Version 2 B-tree</i>: +</li> + +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 B-tree Indexing Information + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Node Size</td> + </tr> + + <tr> + <td>Split Percent</td> + <td>Merge Percent</td> + <td colspan="2" bgcolor="#DDDDDD"> + <em>This space inserted only to align table nicely</em></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 B-tree Indexing Information + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Node Size</p></td> + <td><p>This field is the size in bytes of a B-tree node. + </p> + </td> + </tr> + + <tr> + <td><p>Split Percent</p></td> + <td><p>This field is the percentage full of a B-tree node at which to split the node.</p></td> + </tr> + + <tr> + <td><p>Merge Percent</p></td> + <td><p>This field is the percentage full of a B-tree node at which to merge the node.</p></td> + </tr> + </table> +</div> +</ol> + + + +<br /> +<a name="VirtualStorage"></a> +<p> + Class-specific information for virtual storage (layout class 3):</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Virtual Storage Property Description + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Index</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Virtual Storage Property Description + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>This is the address of the global heap collection where + the VDS mapping entries are stored. + See <a href="#GlobalHeapVDS">“Disk Format: Level 1F - + Global Heap Block for Virtual Datasets.”</a> + </p></td> + </tr> + + <tr> + <td><p>Index</p></td> + <td><p>This is the index of the data object within the global heap collection. + </p> + </td> + </tr> + </table> +</div> + +<h4><a name="BogusMessage">IV.A.2.j. The Bogus Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Bogus</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0009</td></tr> + <tr><td colspan="2"><b>Length:</b> 4 bytes</td></tr> + <tr><td colspan="2"><b>Status:</b> For testing only; should never + be stored in a valid file.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message is used for testing the HDF5 Library’s + response to an “unknown” message type and should + never be encountered in a valid HDF5 file.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Bogus Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Bogus Value</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Bogus Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Bogus Value</p></td> + <td> + <p>This value should always be: <code>0xdeadbeef</code>.</p> + </td> + </tr> + </table> +</div> + +<h4><a name="GroupInfoMessage">IV.A.2.k. The Group Info Message +</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Group Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000A</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>This message stores information for the constants defining + a “new style” group’s behavior. Constant + information will be stored in this message and variable + information will be stored in the + <a href="#LinkInfoMessage">Link Info</a> message.</p> + <p>Note: the “estimated entry” information below is + used when determining the size of the object header for the + group when it is created.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Group Info Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Link Phase Change: Maximum Compact Value <em>(optional)</em></td> + </tr> + <tr> + <td colspan="2">Link Phase Change: Minimum Dense Value <em>(optional)</em></td> + <td colspan="2">Estimated Number of Entries <em>(optional)</em></td> + </tr> + <tr> + <td colspan="2">Estimated Link Name Length of Entries <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Group Info Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is the group information flag with the following definition: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, link phase change values are stored. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, the estimated entry information is non-default + and is stored. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Link Phase Change: Maximum Compact Value</p></td> + <td><p>The is the maximum number of links to store “compactly” (in + the group’s object header).</p> + <p>This field is present if bit 0 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Link Phase Change: Minimum Dense Value</p></td> + <td><p>This is the minimum number of links to store “densely” (in + the group’s fractal heap). The fractal heap’s address is + located in the <a href="#LinkInfoMessage">Link Info</a> + message.</p> + <p>This field is present if bit 0 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Estimated Number of Entries</p></td> + <td><p>This is the estimated number of entries in groups.</p> + <p>If this field is not present, the default value of <code>4</code> + will be used for the estimated number of group entries.</p> + <p>This field is present if bit 1 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Estimated Link Name Length of Entries</p></td> + <td><p>This is the estimated length of entry name.</p> + <p>If this field is not present, the default value of <code>8</code> + will be used for the estimated link name length of group entries.</p> + <p>This field is present if bit 1 of <em>Flags</em> is set.</p> + </td> + </tr> + + </table> +</div> +<!-- </p> --> + +<h4><a name="FilterMessage">IV.A.2.l. The Data Storage - Filter + Pipeline Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> + Data Storage - Filter Pipeline</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000B</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>This message describes the filter pipeline which should + be applied to the data stream by providing filter identification + numbers, flags, a name, and client data.</p> + <p>This message may be present in the object headers of both + dataset and group objects. For datasets, it specifies the + filters to apply to raw data. For groups, it specifies the + filters to apply to the group’s fractal heap. Currently, + only datasets using chunked data storage use the filter + pipeline on their raw data.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Filter Pipeline Message - Version 1 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Number of Filters</td> + <td colspan="2">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4">Reserved (zero)</td> + </tr> + + <tr> + <td colspan="4"><br />Filter Description List <em>(variable size)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Filter Pipeline Message - Version 1 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This table + describes version 1.</p></td> + </tr> + + <tr> + <td><p>Number of Filters</p></td> + <td><p>The total number of filters described in this + message. The maximum possible number of filters in a + message is 32.</p></td> + </tr> + + <tr> + <td><p>Filter Description List</p></td> + <td><p>A description of each filter. A filter description + appears in the next table.</p></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Filter Description - Version 1 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="2">Filter Identification Value</td> + <td colspan="2">Name Length</td> + </tr> + + <tr> + <td colspan="2">Flags</td> + <td colspan="2">Number Client Data Values</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Client Data <em>(variable size, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Padding <em>(variable size, optional)</em></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Filter Description - Version 1 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filter Identification Value</p></td> + <td> + <p> + This value, often referred to as a filter identifier, + is designed to be a unique identifier for the filter. + Values from zero through 32,767 are reserved for filters + supported by The HDF Group in the HDF5 Library and for + filters requested and supported by third parties. + Filters supported by The HDF Group are documented immediately + below. Information on 3rd-party filters can be found at + The HDF Group’s + <a href="http://www.hdfgroup.org/services/contributions.html"> + Contributions</a> page.</p> + + <p> + To request a filter identifier, please contact + The HDF Group’s Help Desk at + <img src="Graphics/help.png" valign="middle" height="14" + alt="The HDF Group Help Desk">. + You will be asked to provide the following information:</p> + <ol> + <li>Contact information for the developer requesting the + new identifier</li> + <li>A short description of the new filter</li> + <li>Links to any relevant information, including licensing + information</li> + </ol> + <p> + Values from 32768 to 65535 are reserved for non-distributed uses + (for example, internal company usage) or for application usage + when testing a feature. The HDF Group does not track or document + the use of the filters with identifiers from this range.</p> + + <p> + The filters currently in library version 1.8.0 are + listed below: + + <table class="list"> + <tr> + <th width="20%" align="center">Identification</th> + <th width="15%" align="left">Name</th> + <th width="65%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>N/A</td> + <td>Reserved</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>deflate</td> + <td>GZIP deflate compression</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>shuffle</td> + <td>Data element shuffling</td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>fletcher32</td> + <td>Fletcher32 checksum</td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>szip</td> + <td>SZIP compression</td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td>nbit</td> + <td>N-bit packing</td> + </tr> + + <tr> + <td align="center"><code>6</code></td> + <td>scaleoffset</td> + <td>Scale and offset encoded values</td> + </tr> + </table> + </p></td> + </tr> + + <tr> + <td><p>Name Length</p></td> + <td><p>Each filter has an optional null-terminated ASCII name + and this field holds the length of the name including the + null termination padded with nulls to be a multiple of + eight. If the filter has no name then a value of zero is + stored in this field.</p></td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>The flags indicate certain properties for a filter. The + bit values defined so far are: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set then the filter is an optional filter. + During output, if an optional filter fails it will be + silently skipped in the pipeline.</td> + </tr> + + <tr> + <td align="center"><code>1-15</code></td> + <td>Reserved (zero)</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Number of Client Data Values</p></td> + <td><p>Each filter can store integer values to control + how the filter operates. The number of entries in the + <em>Client Data</em> array is stored in this field.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>If the <em>Name Length</em> field is non-zero then it will + contain the size of this field, padded to a multiple of eight. This + field contains a null-terminated, ASCII character string to serve + as a comment/name for the filter.</p></td> + </tr> + + <tr> + <td><p>Client Data</p></td> + <td><p>This is an array of four-byte integers which will be + passed to the filter function. The <em>Client Data Number</em> of + Values determines the number of elements in the array.</p></td> + </tr> + + <tr> + <td><p>Padding</p></td> + <td><p>Four bytes of zeroes are added to the message at this + point if the Client Data Number of Values field contains + an odd number.</p></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Filter Pipeline Message - Version 2 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Number of Filters</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Filter Description List <em>(variable size)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Filter Pipeline Message - Version 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This table + describes version 2.</p></td> + </tr> + + <tr> + <td><p>Number of Filters</p></td> + <td><p>The total number of filters described in this + message. The maximum possible number of filters in a + message is 32.</p></td> + </tr> + + <tr> + <td><p>Filter Description List</p></td> + <td><p>A description of each filter. A filter description + appears in the next table.</p></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Filter Description - Version 2 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="2">Filter Identification Value</td> + <td colspan="2">Name Length <em>(optional)</em></td> + </tr> + + <tr> + <td colspan="2">Flags</td> + <td colspan="2">Number Client Data Values</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size, optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Client Data <em>(variable size, optional)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Filter Description - Version 2 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Filter Identification Value</p></td> + <td> + <p> + This value, often referred to as a filter identifier, + is designed to be a unique identifier for the filter. + Values from zero through 32,767 are reserved for filters + supported by The HDF Group in the HDF5 Library and for + filters requested and supported by third parties. + Filters supported by The HDF Group are documented immediately + below. Information on 3rd-party filters can be found at + The HDF Group’s + <a href="http://www.hdfgroup.org/services/contributions.html"> + Contributions</a> page.</p> + + <p> + To request a filter identifier, please contact + The HDF Group’s Help Desk at + <img src="Graphics/help.png" valign="middle" height="14" + alt="The HDF Group Help Desk">. + You will be asked to provide the following information:</p> + <ol> + <li>Contact information for the developer requesting the + new identifier</li> + <li>A short description of the new filter</li> + <li>Links to any relevant information, including licensing + information</li> + </ol> + <p> + Values from 32768 to 65535 are reserved for non-distributed uses + (for example, internal company usage) or for application usage + when testing a feature. The HDF Group does not track or document + the use of the filters with identifiers from this range.</p> + + <p> + The filters currently in library version 1.8.0 are + listed below: + + <table class="list"> + <tr> + <th width="20%" align="center">Identification</th> + <th width="15%" align="left">Name</th> + <th width="65%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>N/A</td> + <td>Reserved</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>deflate</td> + <td>GZIP deflate compression</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>shuffle</td> + <td>Data element shuffling</td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>fletcher32</td> + <td>Fletcher32 checksum</td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>szip</td> + <td>SZIP compression</td> + </tr> + + <tr> + <td align="center"><code>5</code></td> + <td>nbit</td> + <td>N-bit packing</td> + </tr> + + <tr> + <td align="center"><code>6</code></td> + <td>scaleoffset</td> + <td>Scale and offset encoded values</td> + </tr> + </table> + </p></td> + </tr> + + <tr> + <td><p>Name Length</p></td> + <td><p>Each filter has an optional null-terminated ASCII name + and this field holds the length of the name including the + null termination padded with nulls to be a multiple of + eight. If the filter has no name then a value of zero is + stored in this field.</p> + <p>Filters with IDs less than 256 (in other words, filters + that are defined in this format documentation) do not store + the <em>Name Length</em> or <em>Name</em> fields. + </p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>The flags indicate certain properties for a filter. The + bit values defined so far are: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set then the filter is an optional filter. + During output, if an optional filter fails it will be + silently skipped in the pipeline.</td> + </tr> + + <tr> + <td align="center"><code>1-15</code></td> + <td>Reserved (zero)</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Number of Client Data Values</p></td> + <td><p>Each filter can store integer values to control + how the filter operates. The number of entries in the + <em>Client Data</em> array is stored in this field.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>If the <em>Name Length</em> field is non-zero, then it will + contain the size of this field, <em>not</em> padded to a multiple + of eight. This field contains a <em>non-</em>null-terminated, + ASCII character string to serve as a comment/name for the filter. + </p> + <p>Filters that are defined in this format documentation + such as deflate and shuffle do not store the <em>Name + Length</em> or <em>Name</em> fields. + </p> + </td> + </tr> + + <tr> + <td><p>Client Data</p></td> + <td><p>This is an array of four-byte integers which will be + passed to the filter function. The Client Data Number of + Values</em> determines the number of elements in the array.</p> +</td> +</tr> +</table> +</div> + +<h4><a name="AttributeMessage">IV.A.2.m. The Attribute Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Attribute</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000C</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>The <em>Attribute</em> message is used to store objects + in the HDF5 file which are used as attributes, or + “metadata” about the current object. An attribute + is a small dataset; it has a name, a datatype, a dataspace, and + raw data. Since attributes are stored in the object header, they + should be relatively small (in other words, less than 64KB). + They can be associated with any type of object which has an + object header (groups, datasets, or committed (named) + datatypes).</p> + <p>In 1.8.x versions of the library, attributes can be larger + than 64KB. See the + <a href="UG/HDF5_Users_Guide-Responsive%20HTML5/index.html#t=HDF5_Users_Guide%2FAttributes%2FHDF5_Attributes.htm%3Frhtocid%3Dtoc8.2_1%23TOC_8_5_Special_Issuesbc-13"> + “Special Issues”</a> section of the Attributes chapter + in the <cite>HDF5 User’s Guide</cite> for more information.</p> + <p>Note: Attributes on an object must have unique names: + the HDF5 Library currently enforces this by causing the + creation of an attribute with a duplicate name to fail. + Attributes on different objects may have the same name, + however.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Attribute Message (Version 1) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Reserved (zero)</td> + <td colspan="2">Name Size</td> + </tr> + + <tr> + <td colspan="2">Datatype Size</td> + <td colspan="2">Dataspace Size</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Datatype <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dataspace <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Attribute Message (Version 1) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number information is used for changes in the format of the + attribute message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by the library before version 1.6 to encode attribute message. + This version does not support shared datatypes.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Name Size</p></td> + <td><p>The length of the attribute name in bytes including the + null terminator. Note that the <em>Name</em> field below may + contain additional padding not represented by this + field.</p></td> + </tr> + + <tr> + <td><p>Datatype Size</p></td> + <td><p>The length of the datatype description in the <em>Datatype</em> + field below. Note that the <em>Datatype</em> field may contain + additional padding not represented by this field.</p></td> + </tr> + + <tr> + <td><p>Dataspace Size</p></td> + <td><p>The length of the dataspace description in the <em>Dataspace</em> + field below. Note that the <em>Dataspace</em> field may contain + additional padding not represented by this field.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>The null-terminated attribute name. This field is + padded with additional null characters to make it a + multiple of eight bytes.</p></td> + </tr> + + <tr> + <td><p>Datatype</p></td> + <td><p>The datatype description follows the same format as + described for the datatype object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</p></td> + </tr> + + <tr> + <td><p>Dataspace</p></td> + <td><p>The dataspace description follows the same format as + described for the dataspace object header message. This + field is padded with additional zero bytes to make it a + multiple of eight bytes.</p></td> + </tr> + + <tr> + <td><p>Data</p></td> + <td><p>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. This + field is <em>not</em> padded with additional bytes.</p></td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Attribute Message (Version 2) + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Name Size</td> + </tr> + + <tr> + <td colspan="2">Datatype Size</td> + <td colspan="2">Dataspace Size</td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Datatype <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dataspace <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Attribute Message (Version 2) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number information is used for changes in the + format of the attribute message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Used by the library of version 1.6.x and after to encode + attribute messages. + This version supports shared datatypes. The fields of + name, datatype, and dataspace are not padded with + additional bytes of zero. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This bit field contains extra information about + interpreting the attribute message: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, datatype is shared.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>If set, dataspace is shared.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Name Size</p></td> + <td><p>The length of the attribute name in bytes including the + null terminator.</p></td> + </tr> + + <tr> + <td><p>Datatype Size</p></td> + <td><p>The length of the datatype description in the <em>Datatype</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Dataspace Size</p></td> + <td><p>The length of the dataspace description in the <em>Dataspace</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>The null-terminated attribute name. This field is <em>not</em> + padded with additional bytes.</p></td> + </tr> + + <tr> + <td><p>Datatype</p></td> + <td><p>The datatype description follows the same format as + described for the datatype object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s datatype is + shared, this field will contain a “shared message” encoding + instead of the datatype encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Dataspace</p></td> + <td><p>The dataspace description follows the same format as + described for the dataspace object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s dataspace is + shared, this field will contain a “shared message” encoding + instead of the dataspace encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes.</p> + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td><p>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. + </p> + <p>This field is <em>not</em> padded with additional zero bytes. + </p> + </td> + </tr> + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Attribute Message (Version 3) + </caption> + + <tr align="center"> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Name Size</td> + </tr> + + <tr> + <td colspan="2">Datatype Size</td> + <td colspan="2">Dataspace Size</td> + </tr> + + <tr> + <td>Name Character Set Encoding</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Name <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Datatype <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Dataspace <em>(variable size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data <em>(variable size)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Attribute Message (Version 3) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number information is used for changes in the + format of the attribute message and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Used by the library of version 1.8.x and after to + encode attribute messages. + This version supports attributes with non-ASCII names. + </td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This bit field contains extra information about + interpreting the attribute message: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, datatype is shared.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>If set, dataspace is shared.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Name Size</p></td> + <td><p>The length of the attribute name in bytes including the + null terminator.</p></td> + </tr> + + <tr> + <td><p>Datatype Size</p></td> + <td><p>The length of the datatype description in the <em>Datatype</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Dataspace Size</p></td> + <td><p>The length of the dataspace description in the <em>Dataspace</em> + field below.</p></td> + </tr> + + <tr> + <td><p>Name Character Set Encoding</p></td> + <td><p>The character set encoding for the attribute’s name: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>ASCII character set encoding + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>UTF-8 character set encoding + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>The null-terminated attribute name. This field is <em>not</em> + padded with additional bytes.</p></td> + </tr> + + <tr> + <td><p>Datatype</p></td> + <td><p>The datatype description follows the same format as + described for the datatype object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s datatype is + shared, this field will contain a “shared message” encoding + instead of the datatype encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Dataspace</p></td> + <td><p>The dataspace description follows the same format as + described for the dataspace object header message. + </p> + <p>If the + <em>Flag</em> field indicates this attribute’s dataspace is + shared, this field will contain a “shared message” encoding + instead of the dataspace encoding. + </p> + <p>This field is <em>not</em> padded with additional bytes.</p> + </td> + </tr> + + <tr> + <td><p>Data</p></td> + <td><p>The raw data for the attribute. The size is determined + from the datatype and dataspace descriptions. + </p> + <p>This field is <em>not</em> padded with additional zero bytes. + </p> + </td> + </tr> + </table> +</div> + +<h4><a name="CommentMessage">IV.A.2.n. The Object Comment + Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object + Comment</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000D</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The object comment is designed to be a short description of + an object. An object comment is a sequence of non-zero + (<code>\0</code>) ASCII characters with no other formatting + included by the library.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Object Comment Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Comment <em>(variable size)</em><br /><br /></td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Object Comment Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Name</p></td> + <td><p>A null terminated ASCII character string.</p></td> + </tr> + </table> +</div> + +<h4><a name="OldModificationTimeMessage">IV.A.2.o. The Object + Modification Time (Old) Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object + Modification Time (Old)</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000E</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td><p>The object modification date and time is a timestamp + which indicates (using ISO-8601 date and time format) the last + modification of an object. The time is updated when any object + header message changes according to the system clock where the + change was posted. All fields of this message should be + interpreted as coordinated universal time (UTC).</p> + <p>This modification time message is deprecated in favor of + the “new” <a href="#ModificationTimeMessage">Object + Modification Time</a> message and is no longer written to the + file in versions of the HDF5 Library after the 1.6.0 + version.</p></td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Modification Time Message (Old) + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Year</td> + </tr> + + <tr> + <td colspan="2">Month</td> + <td colspan="2">Day of Month</td> + </tr> + + <tr> + <td colspan="2">Hour</td> + <td colspan="2">Minute</td> + </tr> + + <tr> + <td colspan="2">Second</td> + <td colspan="2">Reserved</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Modification Time Message (Old) + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Year</p></td> + <td><p>The four-digit year as an ASCII string. For example, + <code>1998</code>. + </p></td> + </tr> + + <tr> + <td><p>Month</p></td> + <td><p>The month number as a two digit ASCII string where + January is <code>01</code> and December is <code>12</code>.</p></td> + </tr> + + <tr> + <td><p>Day of Month</p></td> + <td><p>The day number within the month as a two digit ASCII + string. The first day of the month is <code>01</code>.</p></td> + </tr> + + <tr> + <td><p>Hour</p></td> + <td><p>The hour of the day as a two digit ASCII string where + midnight is <code>00</code> and 11:00pm is <code>23</code>.</p></td> + </tr> + + <tr> + <td><p>Minute</p></td> + <td><p>The minute of the hour as a two digit ASCII string where + the first minute of the hour is <code>00</code> and + the last is <code>59</code>.</p></td> + </tr> + + <tr> + <td><p>Second</p></td> + <td><p>The second of the minute as a two digit ASCII string + where the first second of the minute is <code>00</code> + and the last is <code>59</code>.</p></td> + </tr> + + <tr> + <td><p>Reserved</p></td> + <td><p>This field is reserved and should always be zero.</p></td> + </tr> + </table> +</div> + +<h4><a name="SOHMTableMessage">IV.A.2.p. The Shared Message Table + Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Shared Message + Table</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x000F</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message is used to locate the table of shared object + header message (SOHM) indexes. Each index consists of information + to find the shared messages from either the heap or object header. + This message is <em>only</em> found in the superblock + extension.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Shared Message Table Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Shared Object Header Message Table Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td>Number of Indices</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + </table> + + <table class="note"> + <tr> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Shared Message Table Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes version 0.</p></td> + </tr> + + <tr> + <td><p>Shared Object Header Message Table Address</p></td> + <td><p>This field is the address of the master table for shared + object header message indexes.</p> + </td> + </tr> + + <tr> + <td><p>Number of Indices</p></td> + <td><p>This field is the number of indices in the master table. + </p></td> + </tr> + + </table> +</div> + +<h4><a name="ContinuationMessage">IV.A.2.q. The Object Header + Continuation Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object Header + Continuation</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0010</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The object header continuation is the location in the file + of a block containing more header messages for the current data + object. This can be used when header blocks become too large or + are likely to change over time.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Object Header Continuation Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Offset<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Length<sup>L</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Object Header Continuation Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Offset</p></td> + <td><p>This value is the address in the file where the + header continuation block is located.</p></td> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>This value is the length in bytes of the header continuation + block in the file.</p></td> + </tr> + </table> +</div> +<br /> + +<p>The format of the header continuation block that this message points + to depends on the version of the object header that the message is + contained within. +</p> + +<p> + Continuation blocks for version 1 object headers have no special + formatting information; they are merely a list of object header + message info sequences (type, size, flags, reserved bytes and data + for each message sequence). See the description + of <a href="#V1ObjectHeaderPrefix">Version 1 Data Object Header Prefix.</a> +</p> + +<p>Continuation blocks for version 2 object headers <em>do</em> have + special formatting information as described here + (see also the description of + <a href="#V2ObjectHeaderPrefix">Version 2 Data Object Header Prefix.</a>): +</p> +<div align="center"> + <table class="format"> + <caption> + Layout: Version 2 Object Header Continuation Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + <tr> + <td>Header Message Type #1</td> + <td colspan="2">Size of Header Message Data #1</td> + <td>Header Message #1 Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #1 Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #1<br /><br /></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td>Header Message Type #n</td> + <td colspan="2">Size of Header Message Data #n</td> + <td>Header Message #n Flags</td> + </tr> + + <tr> + <td colspan="2">Header Message #n Creation Order <em>(optional)</em></td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Message Data #n<br /><br /></td> + </tr> + + <tr> + <td colspan="4">Gap <em>(optional, variable size)</em></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 Object Header Continuation Block + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>OCHK</code>” + is used to indicate the beginning of an object header + continuation block. This gives file consistency checking + utilities a better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Type</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Size of Header Message #n Data</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Header Message #n Flags</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Header Message #n Creation Order</p></td> + <td> + <p>This field stores the order that a message of a given type + was created in.</p> + <p>This field is present if bit 2 of <em>flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Header Message #n Data</p></td> + <td> + <p>Same format as version 1 of the object header, described above. + </p></td> + </tr> + + <tr> + <td><p>Gap</p></td> + <td> + <p>A gap in an object header chunk is inferred by the end of the + messages for the chunk before the beginning of the chunk’s + checksum. Gaps are always smaller than the size of an + object header message prefix (message type + message size + + message flags).</p> + <p>Gaps are formed when a message (typically an attribute message) + in an earlier chunk is deleted and a message from a later + chunk that does not quite fit into the free space is moved + into the earlier chunk.</p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>This is the checksum for the object header chunk. + </p> + </td> + </tr> + </table> +</div> + +<h4><a name="SymbolTableMessage">IV.A.2.r. The Symbol Table + Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Symbol Table + Message</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0011</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Required for + “old style” groups; may not be repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>Each “old style” group has a v1 B-tree and a + local heap for storing symbol table entries, which are located + with this message.</td></tr> + <tr><td colspan="2"><b>Format of data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Symbol Table Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />v1 B-tree Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Local Heap Address<sup>O</sup><br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Symbol Table Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>v1 B-tree Address</p></td> + <td><p>This value is the address of the v1 B-tree containing the + symbol table entries for the group.</p></td> + </tr> + + <tr> + <td><p>Local Heap Address</p></td> + <td><p>This value is the address of the local heap containing + the link names for the symbol table entries for the group.</p></td> + </tr> + </table> +</div> + +<h4><a name="ModificationTimeMessage">IV.A.2.s. The Object + Modification Time Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object + Modification Time</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0012</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>The object modification time is a timestamp which indicates + the time of the last modification of an object. The time is + updated when any object header message changes according to + the system clock where the change was posted.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Modification Time Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3">Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4">Seconds After UNIX Epoch</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Modification Time Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number is used for changes in the format of Object Modification Time + and is described here: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Never used.</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Used by Version 1.6.1 and after of the library to encode time. In + this version, the time is the seconds after Epoch.</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Seconds After UNIX Epoch</p></td> + <td><p>A 32-bit unsigned integer value that stores the number of + seconds since 0 hours, 0 minutes, 0 seconds, January 1, 1970, + Coordinated Universal Time.</p></td> + </tr> + </table> +</div> + +<h4><a name="BtreeKValuesMessage">IV.A.2.t. The B-tree + ‘K’ Values Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> B-tree + ‘K’ Values</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0013</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message retrieves non-default ‘K’ values + for internal and leaf nodes of a group or indexed storage v1 + B-trees. This message is <em>only</em> found in the superblock + extension.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: B-tree ‘K’ Values Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="2">Indexed Storage Internal Node K</td> + <td bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="2">Group Internal Node K</td> + <td colspan="2">Group Leaf Node K</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: B-tree ‘K’ Values Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Indexed Storage Internal Node K</p></td> + <td><p>This is the node ‘K’ value for each internal node of an + indexed storage v1 B-tree. See the description of this field + in version 0 and 1 of the superblock as well the section on + v1 B-trees. + </p> + </td> + </tr> + + <tr> + <td><p>Group Internal Node K</p></td> + <td><p>This is the node ‘K’ value for each internal node of a group + v1 B-tree. See the description of this field in version 0 and + 1 of the superblock as well as the section on v1 B-trees. + </p> + </td> + </tr> + + <tr> + <td><p>Group Leaf Node K</p></td> + <td><p>This is the node ‘K’ value for each leaf node of a group v1 + B-tree. See the description of this field in version 0 and 1 + of the superblock as well as the section on v1 B-trees. + </p> + </td> + </tr> + + </table> +</div> + +<h4><a name="DrvInfoMessage">IV.A.2.u. The Driver Info + Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Driver + Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0014</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + + <tr><td> + <b>Description:</b></td> + <td>This message contains information needed by the file driver + to reopen a file. This message is <em>only</em> found in the + superblock extension: see the <a href="#SuperblockExt"> + “Disk Format: Level 0C - Superblock Extension”</a> + section for more information. For more information on the fields + in the driver info message, see the <a href="#DriverInfo"> + “Disk Format: Level 0B - File Driver Info”</a> + section; those who use the multi and family file drivers will + find this section particularly helpful.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Driver Info Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4"><br />Driver Identification</td> + </tr> + + <tr> + <td colspan="2">Driver Information Size</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Driver Information <em>(variable size)</em><br /><br /><br /></td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Driver Info Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Driver Identification</p></td> + <td><p>This is an eight-byte ASCII string without null termination which + identifies the driver. + </p> + </td> + </tr> + + <tr> + <td><p>Driver Information Size</p></td> + <td><p>The size in bytes of the <em>Driver Information</em> field of this + message.</p> + </td> + </tr> + + <tr> + <td><p>Driver Information</p></td> + <td><p>Driver information is stored in a format defined by the file driver.</p> + </td> + </tr> + </table> +</div> + +<h4><a name="AinfoMessage">IV.A.2.v. The Attribute Info + Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Attribute + Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0015</td></tr> + <tr><td colspan="2"><b>Length:</b> Varies</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message stores information about the attributes on an + object, such as the maximum creation index for the attributes + created and the location of the attribute storage when the + attributes are stored “densely”.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Attribute Info Message + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Flags</td> + <td colspan="2">Maximum Creation Index <em>(optional)</em></td> + </tr> + <tr> + <td colspan="4"><br />Fractal Heap Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Attribute Name v2 B-tree Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Attribute Creation Order v2 B-tree Address<sup>O</sup> <em>(optional)</em><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Attribute Info Message + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is the attribute index information flag with the + following definition: + + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, creation order for attributes is tracked. + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>If set, creation order for attributes is indexed. + </td> + </tr> + <tr> + <td align="center"><code>2-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + <tr> + <td><p>Maximum Creation Index</p></td> + <td><p>The is the maximum creation order index value for the + attributes on the object.</p> + <p>This field is present if bit 0 of <em>Flags</em> is set.</p> + </td> + </tr> + + <tr> + <td><p>Fractal Heap Address</p></td> + <td><p>This is the address of the fractal heap to store dense + attributes. + Each attribute stored in the fractal heap is described by + the <a href="#AttributeMessage">Attribute Message.</a> + </p> + </td> + </tr> + + <tr> + <td><p>Attribute Name v2 B-tree Address</p></td> + <td><p>This is the address of the version 2 B-tree to index the + names of densely stored attributes.</p> + </td> + </tr> + + <tr> + <td><p>Attribute Creation Order v2 B-tree Address</p></td> + <td><p>This is the address of the version 2 B-tree to index the + creation order of densely stored attributes.</p> + <p>This field is present if bit 1 of <em>Flags</em> is set.</p> + </td> + </tr> + + </table> +</div> + +<h4><a name="RefCountMessage">IV.A.2.w. The Object Reference + Count Message</a></h4> + +<!-- start msgdesc table --> +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> Object Reference + Count</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0016</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td><b>Description:</b></td> + <td>This message stores the number of hard links (in groups or + objects) pointing to an object: in other words, its + <em>reference count</em>.</td></tr> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<!-- end msgdesc table --> + +<div align="center"> + <table class="format"> + <caption> + Layout: Object Reference Count + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Reference count</td> + </tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Object Reference Count + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for this message. This document describes + version 0.</p> + </td> + </tr> + + <tr> + <td><p>Reference Count</p></td> + <td><p>The unsigned 32-bit integer is the reference count for the + object. This message is only present in “version 2” + (or later) object headers, and if not present those object + header versions, the reference count for the object is assumed + to be 1.</p> + </td> + </tr> + + </table> +</div> + +<br /> + +<h4><a name="FsinfoMessage">IV.A.2.x. The File Space Info + Message</a></h4> + +<center> + <table class="msgdesc"> + <tr><td colspan="2"><b>Header Message Name:</b> File Space + Info</td></tr> + <tr><td colspan="2"><b>Header Message Type:</b> 0x0017</td></tr> + <tr><td colspan="2"><b>Length:</b> Fixed</td></tr> + <tr><td colspan="2"><b>Status:</b> Optional; may not be + repeated.</td></tr> + <tr><td> + <b>Description:</b></td> + <td>This message stores the file space management information + that the library uses in handling file space + requests for the file. Version 0 of the message is used for release 1.10.0 only. + Version 1 of the message is used for release 1.10.1+. + There is no File Space Info message before release 1.10 as the library does + not track file space across multiple file opens. + <p> + Note that version 0 is deprecated starting release 1.10.1. + That means when the 1.10.1+ library opens an HDF5 file with a version 0 message, + the library will decode and map the message to version 1. + On file close, it will encode the message as a version 1 message. + <p> + The library uses the following three mechanisms to manage file space in an HDF5 file: + <ul> + <li> Free-space managers + <br> They track free-space sections of various sizes in the file that are not currently + allocated. Each free-space manager corresponds to a file space type. + There are two main groups of file space types: metadata and raw data. + Metadata is further divided into five types: superblock, B-tree, global heap, + local heap, and object header. + See the description of <a href="#FreeSpaceManager">Free-space + Manager</a> as well the description of file space allocation types in + <a href="#AppendixB">Appendix B</a> + </li> + <li> Aggregators + <br> The library manages two aggregators, one for metadata and one for raw data. + Aggregator is a contiguous block of free-space in the file. + The size of each aggregator is tunable via public routines + <code>H5Pset_meta_block_size</code> and <code>H5Pset_small_data_block_size</code> respectively. + </li> + <li> Virtual file drivers + <br> The library's virtual file driver interface dispatches requests for additional + space to the allocation routine of the file driver associated with the file. + For example, if the sec2 file driver is being used, its allocation routine will + increase the size of the file to service the requests. + </li> + </ul> + <p> + For release 1.10.0, the library derives the following four file space strategies + based on the mechanisms: + <ul> + <li>H5F_FILE_SPACE_ALL + <ul> + <li>Mechanisms used: free-space managers, aggregators, and virtual file drivers</li> + <li>Does not persist free-space across file opens</li> + <li>This strategy is the library default</li> + </ul> + </li> + <li>H5F_FILE_SPACE_ALL_PERSIST</li> + <ul> + <li>Mechanisms used: free-space managers, aggregators, and virtual file drivers</li> + <li>Persist free-space across file opens</li> + </ul> + <li>H5F_FILE_SPACE_AGGR_VFD</li> + <ul> + <li>Mechanisms used: aggregators and virtual file drivers</li> + <li>Does not persist free-space across file opens</li> + </ul> + <li>H5F_FILE_SPACE_VFD</li> + <ul> + <li>Mechanisms used: virtual file drivers</li> + <li>Does not persist free-space across file opens</li> + </ul> + </ul> + For release 1.10.1+, the free-space manager mechanism is modified to handle paged aggregation + which aggregates small metadata and raw data allocations into constant-sized well-aligned pages + to allow efficient I/O accesses. + With the support of this feature, the library derives the following four file space strategies: + <ul> + <li>H5F_FSPACE_STRATEGY_FSM_AGGR </li> + <ul> + <li>Mechanisms used: free-space managers, aggregators, and virtual file drivers</li> + <li>This strategy is the library default</li> + </ul> + <li>H5F_FSPACE_STRATEGY_PAGE</li> + <ul> + <li>Mechanisms used: free-space managers with embedded paged aggregation and virtual file drivers</li> + </ul> + <li>H5F_FSPACE_STRATEGY_AGGR</li> + <ul> + <li>Mechanisms used: aggregators and virtual file drivers</li> + </ul> + <li>H5F_FSPACE_STRATEGY_NONE</li> + <ul> + <li>Mechanisms used: virtual file drivers</li> + </ul> + </ul> + The default is not persisting free-space across file opens for the above four strategies. + User can use the public routine <code>H5Pset_file_space_strategy</code> to request + persisting free-space. + </td></tr> + <p> + <tr><td colspan="2"><b>Format of Data:</b> See the tables + below.</td></tr> +</table></center> +<p> + <div align="center"> + <table class="format"> + <caption> + Layout: File Space Info - Version 0 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Strategy</td> + <td colspan="2">Threshold<sup>L</sup></td> + </tr> + <tr> + <td colspan="4"><br />Free-space manager address<sup>O</sup> for H5FD_MEM_SUPER<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Free-space manager address<sup>0</sup> for H5FD_MEM_BTREE<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Free-space manager address<sup>0</sup> for H5FD_MEM_DRAW<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Free-space manager address<sup>0</sup> for H5FD_MEM_GHEAP<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Free-space manager address<sup>0</sup> for H5FD_MEM_LHEAP<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Free-space manager address<sup>0</sup> for H5FD_MEM_OHDR<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: File Space Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>This is version 0 of this message.</p> + </td> + </tr> + + <tr> + <td><p>Strategy</p></td> + <td><p>This is the file space strategy used to manage file space. + There are four types: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>H5F_FILE_SPACE_ALL_PERSIST</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>H5F_FILE_SPACE_ALL</td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>H5F_FILE_SPACE_AGGR_VFD</td> + </tr> + <tr> + <td align="center"><code>4</code></td> + <td>H5F_FILE_SPACE_VFD</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Threshold</p></td> + <td><p>This is the smallest free-space section size that the + free-space manager will track. + </td> + </tr> + <tr> + <td><p>Free-space manager addresses</p></td> + <td><p>These are the six free-space manager addresses for the + six file space allocation types: + <ul> + <li>H5FD_MEM_SUPER</li> + <li>H5FD_MEM_BTREE</li> + <li>H5FD_MEM_DRAW</li> + <li>H5FD_MEM_GHEAP</li> + <li>H5FD_MEM_LHEAP</li> + <li>H5FD_MEM_OHDR</li> + </ul> + Note that these six fields exist only if the value for the field + “<em>Strategy</em>” is H5F_FILE_SPACE_ALL_PERSIST. + </p> + </td> + </tr> + + </table> + </div> + <br /> + + <div align="center"> + <table class="format"> + <caption> + Layout: File Space Info - Version 1 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Version</td> + <td>Strategy</td> + <td>Persisting free-space</td> + <td colspan="1" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4">Free-space Section Threshold<sup>L</sup></td> + </tr> + + <tr> + <td colspan="4">File Space Page Size</td> + </tr> + + <tr> + <td colspan="2">Page-end Metadata threshold</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />EOA<sup>0</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup> of small-sized free-space manager for H5FD_MEM_SUPER<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of small-sized free-space manager for H5FD_MEM_BTREE<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of small-sized free-space manager for H5FM_MEM_DRAW<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of small-sized free-space manager for H5FD_MEM_GHEAP<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of small-sized free-space manager for H5FD_MEM_LHEAP<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of small-sized free-space manager for H5FD_MEM_OHDR<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of large-sized free-space manager for H5FD_MEM_SUPER<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of large-sized free-space manager for H5FD_MEM_BTREE<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of large-sized free-space manager for H5FM_MEM_DRAW<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of large-sized free-space manager for H5FD_MEM_GHEAP<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of large-sized free-space manager for H5FD_MEM_LHEAP<br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Address<sup>O</sup> of large-sized free-space manager for H5FD_MEM_OHDR<br /><br /></td> + </tr> + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: File Space Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>This is version 1 of this message.</p> + </td> + </tr> + + <tr> + <td><p>Strategy</p></td> + <td><p>This is the file space strategy used to manage file space. + There are four types: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>H5F_FSPACE_STRATEGY_FSM_AGGR</td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>H5F_FSPACE_STRATEGY_PAGE</td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>H5F_FSPACE_STRATEGY_AGGR</td> + </tr> + <tr> + <td align="center"><code>3</code></td> + <td>H5F_FSPACE_STRATEGY_NONE</td> + </tr> + </table></p> + </td> + </tr> + + <tr> + <td><p>Persisting free-space</p></td> + <td><p>True or false in persisting free-space. + </td> + </tr> + + <tr> + <td><p>Free-space Section Threshold</p></td> + <td><p>This is the smallest free-space section size that the + free-space manager will track. + </td> + </tr> + + <tr> + <td><p>File space page size</p></td> + <td><p>This is the file space page size, which is used when the paged aggregation feature + is enabled. + </td> + </tr> + + <tr> + <td><p>Page-end metadata threshold</p></td> + <td><p>This is the smallest free-space section size at the end of a page that + the free-space manager will track. This is used when the paged aggregation feature + is enabled. + </td> + </tr> + + <tr> + <td><p>EOA</p></td> + <td><p>The EOA before the allocation of free-space manager header and section info for the + self-referential free-space managers when persisting free-space. + <br> + Note that self-referential free-space managers are managers that involve file space + allocation for the managers' free-space header and section info. + </td> + </tr> + + <tr> + <td><p>Addresses of small-sized free-space managers</p></td> + <td><p>These are the addresses of the six small-sized free-space managers for + the six file space allocation types: + </p> + <ul> + <li>H5FD_MEM_SUPER</li> + <li>H5FD_MEM_BTREE</li> + <li>H5FD_MEM_DRAW</li> + <li>H5FD_MEM_GHEAP</li> + <li>H5FD_MEM_LHEAP</li> + <li>H5FD_MEM_OHDR</li> + </ul> + Note that these six fields exist only if the value for the field + “<em>Persisting free-space</em>” is true. +</ul> +</td> +</tr> + +<tr> + <td><p>Addresses of large-sized free-space managers</p></td> + <td><p>These are the addresses of the six large-sized free-space managers for + the six file space allocation types: + </p> + <ul> + <li>H5FD_MEM_SUPER</li> + <li>H5FD_MEM_BTREE</li> + <li>H5FD_MEM_DRAW</li> + <li>H5FD_MEM_GHEAP</li> + <li>H5FD_MEM_LHEAP</li> + <li>H5FD_MEM_OHDR</li> + </ul> + Note that these six fields exist only if the value for the field + “<em>Persisting free-space</em>” is true. +</ul> +</td> +</tr> + +</table> +</div> + +<h3><a name="DataStorage"> + IV.B. Disk Format: Level 2B - Data Object Data Storage</a></h3> + +<p>The data for an object is stored separately from its header + information in the file and may not actually be located in the HDF5 file + itself if the header indicates that the data is stored externally. The + information for each record in the object is stored according to the + dimensionality of the object (indicated in the dataspace header message). + Multi-dimensional array data is stored in C order; in other words, the + “last” dimension changes fastest.</p> + +<p>Data whose elements are composed of atomic datatypes are stored in IEEE + format, unless they are specifically defined as being stored in a different + machine format with the architecture-type information from the datatype + header message. This means that each architecture will need to [potentially] + byte-swap data values into the internal representation for that particular + machine.</p> + +<p> Data with a variable-length datatype is stored in the global heap + of the HDF5 file. Global heap identifiers are stored in the + data object storage.</p> + +<p>Data whose elements are composed of reference datatypes are stored in + several different ways depending on the particular reference type involved. + Object pointers are just stored as the offset of the object header being + pointed to with the size of the pointer being the same number of bytes as + offsets in the file.</p> + +<p>Dataset region references are stored as a heap-ID which points to + the following information within the file-heap: an offset of the object + pointed to, number-type information (same format as header message), + dimensionality information (same format as header message), sub-set start + and end information (in other words, a coordinate location for each), + and field start and end names (in other words, a [pointer to the] string + indicating the first field included and a [pointer to the] string name + for the last field). </p> + +<p>Data of a compound datatype is stored as a contiguous stream of the items + in the structure, with each item formatted according to its datatype. +<p> + Description of datatypes for variable-length, references and compound classes can be found + in <a href="#DatatypeMessage">Datatype Message</a>. +<p> + Information about global heap and heap ID can be found in <a href="#GlobalHeap">Global Heap</a>. +<p> + For reference datatype, + see also the encoding description for <a href="#ReferenceEncodeRV">Reference Encoding (Revised) </a> and + <a href="#ReferenceEncodeDP">Reference Encoding (Backward Compatibility)</a> in Appendix D. +</p> + +<h2><a name="AppendixA"> + V. Appendix A: Definitions</a></h2> + +<p>Definitions of various terms used in this document are included in + this section.</p> + +<div align="center"> + <table class="glossary"> + <tr> + <th width="20%">Term</th> + <th>Definition</th> + </tr> + + <tr> + <td>Undefined Address</td> + <td>The <a name="UndefinedAddress">undefined + address</a> for a file is a file address with all bits + set: in other words, <code>0xffff...ff</code>.</td> + </tr> + + <tr> + <td>Unlimited Size</td> + <td>The <a name="UnlimitedDim">unlimited size</a> + for a size is a value with all bits set: in other words, + <code>0xffff...ff</code>.</td> + </tr> + + </table> +</div> + + +<h2><a name="AppendixB"> + VI. Appendix B: File Space Allocation Types</a></h2> + +<p>There are six basic types of file space allocation as follows: +</p> +<div align="center"> + <table class="desc"> + <tr> + <th width="30%">Basic Allocation Type</th> + <th>Description</th> + </tr> + + <tr> + <td>H5FD_MEM_SUPER</td> + <td>File space allocated for <em>Superblock.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_BTREE</td> + <td>File space allocated for <em>B-tree.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_DRAW</td> + <td>File space allocated for <em>raw data</em>.</td> + </tr> + + <tr> + <td>H5FD_MEM_GHEAP</td> + <td>File space allocated for <em>Global Heap.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_LHEAP</td> + <td>File space allocated for <em>Local Heap.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_OHDR</td> + <td>File space allocated for <em>Object Header.</em></td> + </tr> + </table> +</div> + +<br /> +<p>There are other file space allocation types that are mapped to the + above six basic types because they are similar in nature. + The mapping and the corresponding description are listed in the following two tables: +</p> + +<div align="center"> + <table class="desc"> + <tr> + <th width="30%">Basic Allocation Type</th> + <th>Mapping of Allocation Types to Basic Allocation Types</th> + </tr> + + <tr> + <td>H5FD_MEM_SUPER</td> + <td><em>none</em></td> + </tr> + + <tr> + <td>H5FD_MEM_BTREE</td> + <td>H5FD_MEM_SOHM_INDEX</td> + </tr> + + <tr> + <td>H5FD_MEM_DRAW</td> + <td>H5FD_MEM_FHEAP_HUGE_OBJ</td> + </tr> + + <tr> + <td>H5FD_MEM_GHEAP</td> + <td><em>none</em></td> + </tr> + + <tr> + <td>H5FD_MEM_LHEAP</td> + <td>H5FD_MEM_FHEAP_DBLOCK, H5FD_MEM_FSPACE_SINFO</td> + </tr> + + <tr> + <td>H5FD_MEM_OHDR</td> + <td>H5FD_MEM_FHEAP_HDR, H5FD_MEM_FHEAP_IBLOCK, H5FD_MEM_FSPACE_HDR, H5FD_MEM_SOHM_TABLE</td> + </tr> + </table> +</div> + +<br /> +</p> + +<div align="center"> + <table class="desc"> + <tr> + <th width="30%">Allocation Type</th> + <th>Description</th> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_HDR</td> + <td>File space allocated for <em>Fractal Heap Header.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_DBLOCK</td> + <td>File space allocated for <em>Fractal Heap Direct Blocks.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_IBLOCK</td> + <td>File space allocated for <em>Fractal Heap Indirect Blocks.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FHEAP_HUGE_OBJ</td> + <td>File space allocated for huge objects in the fractal heap.</td> + </tr> + + <tr> + <td>H5FD_MEM_FSPACE_HDR</td> + <td>File space allocated for <em>Free-space Manager Header.</em></td> + </tr> + + <tr> + <td>H5FD_MEM_FSPACE_SINFO</td> + <td>File space allocated for <em>Free-space Section List</em> of the free-space manager.</td> + </tr> + <tr> + <td>H5FD_MEM_SOHM_TABLE</td> + <td>File space allocated for <em>Shared Object Header Message Table.</em></td> + </tr> + <tr> + <td>H5FD_MEM_SOHM_INDEX</td> + <td>File space allocated for <em>Shared Message Record List.</em></td> + </tr> + </table> +</div> + +<h2><a name="AppendixC"> VII. Appendix C: + Types of Indexes for Dataset Chunks</a></h2> + +<p>For an HDF5 file without the latest format enabled, the library + uses the <a href="#V1Btrees">Version 1 B-tree</a> to index dataset + chunks.</p> + +<p>For an HDF5 file with the latest format enabled, the library uses + one of the following five indexing types depending on a chunked + dataset’s dimension specification and the way it is extended. +</p> + +<a name="SingleChunk"> + <h3>VII.A. The Single Chunk Index</h3></a> + +<p>The <i>Single Chunk</i> index can be used when the dataset fulfills + the following condition:</p> + +<ul> + <li>the current, maximum, and chunk dimension sizes are all the same</li> +</ul> + +<p>The dataset has only one chunk, and the address of the single + chunk is stored in the version 4 <i>Data Layout</i> message. + See the <a href="#ChunkedStorage">Chunked Storage Property + Description</i></a> layout and field description tables.</p> + +<a name="Implicit"> + <h3>VII.B. The Implicit Index</h3></a> + +<p>The <i>Implicit</i> index can be used when the dataset fulfills + the following conditions:</p> + +<ul> + <li>fixed maximum dimension sizes</li> + <li>no filter applied to the dataset</li> + <li>the timing for the space allocation of the dataset chunks is + <code>H5P_ALLOC_TIME_EARLY</code></li> +</ul> + +<p>Since the dataset’s dimension sizes are known and storage space + is to be allocated early, an array of dataset chunks are allocated + based on the maximum dimension sizes when the dataset is created. + The base address of the array is stored in the version 4 + <i>Data Layout</i> message. See the + <a href="#ChunkedStorage">Chunked Storage Property + Description</i></a> layout and field description tables. +</p> + +<p>When accessing a dataset chunk with a specified offset, the + address of the chunk in the array is computed as below:</p> + +<dir><p><code>base address + (size of a chunk in bytes * chunk index + associated with the offset)</code></p></dir> + +<p>A chunk index starts at 0 and increases according to the + fastest changing dimension, then the next fastest, and so on. + <a name="ChunkIndex"></a> + The chunk index for a dataset chunk offset is computed as below: + <ol> + <li>Calculate the scaled offset for each dimension in + <code>scaled_offset</code>: + <br /> + <pre> + scaled_offset = chunk_offset/chunk_dims + </pre></li> + <li>Calculate the # of chunks for each dimension in + <code>nchunks</code>: + <br /> + <pre> + nchunks = (curr_dims + chunk_dims - 1)/chunk_dims + </pre></li> + + <li>Calculate the down chunks for each dimension in + <code>down_chunks</code>: + <br /> + <pre> + /* n is the # of dimensions */ + for(i = (int)(n-1), acc = 1; i >= 0; i--) { + down_chunks[i] = acc; + acc *= nchunks[i]; + } + </pre> + </li> + + <li>Calculate the chunk index in <code>chunk_index</code>: + <br /> + <pre> + /* n is the # of dimensions */ + for(u = 0, chunk_index = 0; u < n; u++) + chunk_index += down_chunks[u] * scaled_offset[u]; + </pre> + </li> + </ol> +<p> + For example, for a 2-dimensional dataset with + <code>curr_dims[4,5]</code> and <code>chunk_dims[3,2]</code>, + there will be a total of 6 chunks, with 3 chunks in the fastest + changing dimension and 2 chunks in the slowest changing dimension. + See the figure below. + The chunk index for the chunk offset <code>[3,4]</code> + is computed as below: + <ol> + <code> + <li>scaled_offset[0] = 1, scaled_offset[1] = 2</li> + <li>nchunks[0] = 2, nchunks[1] = 3</li> + <li>down_chunks[0] = 3, down_chunks[1] = 1</li> + <li>chunk_index = 5</li> + </code> + </ol> + + + <table align="center" width="400" border="0"> + <tr valign="center" align="center"> + <td> + <hr size="2"/> + <img height="250" src="FileFormatSpecChunkDiagram.jpg" + alt="Chunk Diagram"></td> + </tr> + <tr valign="top" align="center"> + <td> + <hr size="1" /> + <b>Figure 3. Implicit index chunk diagram </b> + <hr size="2"/></td> + </tr> + </table> + + + + + + <a name="FixedArray"> + <h3>VII.C. The Fixed Array Index</h3></a> + +<p>The <i>Fixed Array</i> index can be used when the dataset fulfills + the following condition:</p> +<ul> + <li>fixed maximum dimension sizes</li> +</ul> + +<p>Since the maximum number of chunks is known, an array of + in-file-on-disk addresses based on the maximum number of chunks is + allocated when data is written to the dataset. To access a dataset + chunk with a specified offset, the + <a href="#ChunkIndex">chunk index</i></a> associated with the offset +is calculated. The index is mapped into the array to locate the +disk address for the chunk.</p> + +<p>The Fixed Array (FA) index structure provides space and speed + improvements in locating chunks over index structures that handle + more dynamic data accesses like a + <a href="#AppendV2Btrees">Version 2 B-tree</a> index. + The entry into the Fixed Array is the Fixed Array header which + contains metadata about the entries stored in the array. The + header contains a pointer to a data block which stores the array + of entries that describe the dataset chunks. For greater efficiency, + the array will be divided into multiple pages if the number of + entries exceeds a threshold value. The space for the data block + and possibly data block pages are allocated as a single contiguous + block of space.</p> + +<p>The content of the data block depends on whether paging is + activated or not. When paging is not used, elements that describe + the chunks are stored in the data block. If paging is turned on, + the data block contains a bitmap indicating which pages are + initialized. Then subsequent data block pages will contain the + entries that describe the chunks.</p> + +<p>An entry describes either a filtered or non-filtered dataset + chunk. The formats for both element types are described below. +</p> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fixed Array Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td>Entry Size</td> + <td>Page Bits</td> + </tr> + + <tr> + <td colspan="4"><br />Max Num + Entries<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data Block + Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fixed Array Header + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FAHD</code>” + is used to indicate the beginning of a Fixed Array header. + This gives file consistency checking utilities a better + chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>The ID for identifying the client of the + Fixed Array: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Non-filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Entry Size</p></td> + <td> + <p>The size in bytes of an entry in the Fixed Array. + </p> + </td> + </tr> + + <tr> + <td><p>Page Bits</p></td> + <td> + <p>The number of bits needed to store the maximum + number of entries in a + <a href="#FADataBlockPage">data block page.</a></p> + </td> + </tr> + + <tr> + <td><p>Max Num Entries</p></td> + <td> + <p>The maximum number of entries in the Fixed + Array.</p> + </td> + </tr> + + <tr> + <td><p>Data Block Address</p></td> + <td> + <p>The address of the data block in the Fixed Array. + </p> + </td> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for the header.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Fixed Array Data Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Page Bitmap <em>(variable size and + optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Elements <em>(variable size and + optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fixed Array Data Block + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>FADB</code>” + is used to indicate the beginning of a Fixed Array data + block. This gives file consistency checking utilities a + better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>The ID for identifying the client of the + Fixed Array: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Non-filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Header Address</p></td> + <td> + <p>The address of the Fixed Array header. Principally used + for file integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Page Bitmap</p></td> + <td><p>A bitmap indicating which data block pages are initialized.</p> + <p>Exists only if the data block is paged.</p></td> + </tr> + + <tr> + <td><p>Elements</p></td> + <td> + <p>Contains the elements stored in the data block + and exists only if the data block is not paged. + There are two element types: + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td><a href="#FaNonFilterChunk">Non-filtered + dataset chunks</i></a> +</td> +</tr> +<tr> + <td align="center"><code>1</code></td> + <td><a href="#FaFilterChunk">Filtered dataset + chunks</i></a> +</td> +</tr> +</table> +</p> +</td> +</tr> + +<tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for the Fixed Array data block.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption><a name="FADataBlockPage"> + Layout: Fixed Array Data Block Page</a> + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Elements <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Fixed Array Data Block Page + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Elements</p></td> + <td> + <p>Contains the elements stored in the data block page. + There are two element types: + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td><a href="#FaNonFilterChunk">Non-filtered dataset chunks</i></a> +</td> +</tr> +<tr> + <td align="center"><code>1</code></td> + <td><a href="#FaFilterChunk">Filtered dataset chunks</i></a> +</td> +</tr> +</table> +</p> +</td> +</tr> + +<tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for a Fixed Array data block page.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> +<a name="FaNonFilterChunk"></a> +<div align="center"> + <table class="format"> + <caption> + Layout: Data Block Element for Non-filtered Dataset Chunk + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Data Block Element for Non-filtered Dataset Chunk + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the dataset chunk in the file. + </p> + </td> + </tr> + + </table> +</div> +<!-- </p> --> + +<br /> +<br /> +<br /> +<a name="FaFilterChunk"></a> +<div align="center"> + <table class="format"> + <caption> + Layout: Data Block Element for Filtered Dataset Chunk + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Chunk Size <em>(variable size; at most + 8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Filter Mask</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Data Block Element for Filtered Dataset Chunk + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the dataset chunk in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Chunk Size</p></td> + <td><p>The size of the dataset chunk in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td><p>Indicates the filter to skip for the dataset chunk. Each + filter has an index number in the pipeline; if that filter is + skipped, the bit corresponding to its index is set. + </p> + </td> + </tr> + + </table> +</div> + +<a name="ExtensibleArray"> + <h3>VII.D. The Extensible Array Index</h3></a> + +<p>The <i>Extensible Array</i> index can be used when the dataset + fulfills the following condition:</p> + +<ul> + <li>only one dimension of unlimited extent</li> +</ul> + +<p>The Extensible Array (EA) is a data structure that is used as a + chunk index in datasets where the dataspace has a single + unlimited dimension. In other words, one dimension is set to + <code>H5S_UNLIMITED</code>, and the other dimensions are any number + of fixed-size dimensions. The idea behind the extensible array is + that a particular data object can be located via a lightweight + indexing structure of fixed depth for a given address space. This + indexing structure requires only a few (2-3) file operations per + element lookup and gives good cache performance. Unlike the B-tree + structure, the extensible array is optimized for appends. Where a + B-tree would always add at the rightmost node under these + circumstances, either creating a deep tree (version 1) or requiring + expensive rebalances to correct (version 2), the extensible array + has already mapped out a pre-balanced internal structure. This + optimized internal structure is instantiated as needed when chunk + records are inserted into the structure.</p> + + + +<!-- + + <p>A description of the rationale that leads to the present + implementation of the extensible array can be found at + <a href="https://svn.hdfgroup.org/hdf5doc/trunk/projects/1_10_alpha/ReviseChunks/skip_lists"> + https://svn.hdfgroup.org/hdf5doc/trunk/projects/1_10_alpha/ReviseChunks/skip_lists</a>. + </p> + +<p>The current implementation differs from the data structure + described in that reference in some ways, but the basic idea is the + same.</p> + +--> + + + +<p>An Extensible Array consists of a header, an index block, + secondary blocks, data blocks, and (optional) data block pages. The + general scheme is that the index block is used to reference a + secondary block, which is, in turn, used to reference the data block + page where the chunk information is stored. The data blocks will + be paged for efficiency when their size passes a threshold value. + These pages are laid out contiguously on the disk after the data + block, are initialized as needed, and are tracked via bitmaps + stored in the secondary block. The number of secondary and data + blocks/pages in a chunk index varies as they are allocated as + needed and the first few are (conceptually) stored in parent + elements as an optimization.</p> + +<div align="center"> + <table class="format"> + <caption> + Layout: Extensible Array Header + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td>Element Size</td> + <td>Max Nelmts Bits</td> + </tr> + + <tr> + <td>Index Blk Elmts</td> + <td>Data Blk Min Elmts</td> + <td>Secondary Blk Min Data Ptrs</td> + <td>Max Data Blk Page Nelmts Bits</td> + </tr> + + <tr> + <td colspan="4"><br />Num Secondary Blks<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Secondary Blk Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Num Data Blks<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Data Blk Size<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Max Index Set<sup>L</sup><br /><br /></td> + </tr> + <tr> + <td colspan="4"><br />Num Elements<sup>L</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Index Block Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘L’ in the above table are + of the size specified in the <a href="#SizeOfLengthsV0">Size + of Lengths</a> field in the superblock.) + </td></tr> + <tr> + <td> </td> + <td> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Extensible Array Header + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>EAHD</code>” + is used to indicate the beginning of an Extensible Array + header. This gives file consistency checking utilities a + better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>The ID for identifying the client of the + Fixed Array: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Non-filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Element Size</p></td> + <td> + <p>The size in bytes of an element in the Extensible Array. + </p> + </td> + </tr> + + <tr> + <td><p>Max Nelmts Bits</p></td> + <td> + <p>The number of bits needed to store the + maximum number of elements in the Extensible Array.</p> + </td> + </tr> + + <tr> + <td><p>Index Blk Elmts</p></td> + <td> + <p>The number of elements to store in the index block. + </p> + </td> + </tr> + + <tr> + <td><p>Data Blk Min Elmts</p></td> + <td> + <p>The minimum number of elements per data block. + </p> + </td> + </tr> + + <tr> + <td><p>Secondary Blk Min Data Ptrs</p></td> + <td> + <p>The minimum number of data block pointers for a + secondary block. + </p> + </td> + </tr> + + <tr> + <td><p>Max Dblk Page Nelmts Bits</p></td> + <td> + <p>The number of bits needed to store the maximum number + of elements in a data block page. + </p> + </td> + </tr> + + <tr> + <td><p>Num Secondary Blks</p></td> + <td> + <p>The number of secondary blocks created. + </p> + </td> + </tr> + + <tr> + <td><p>Secondary Blk Size</p></td> + <td> + <p>The size of the secondary blocks created. + </p> + </td> + </tr> + + <tr> + <td><p>Num Data Blks</p></td> + <td> + <p>The number of data blocks created. + </p> + </td> + </tr> + + <tr> + <td><p>Data Blk Size</p></td> + <td> + <p>The size of the data blocks created. + </p> + </td> + </tr> + + <tr> + <td><p>Max Index Set</p></td> + <td> + <p>The maximum index set. + </p> + </td> + </tr> + + <tr> + <td><p>Num Elmts</p></td> + <td> + <p>The number of elements realized. + </p> + </td> + </tr> + + <tr> + <td><p>Index Block Address</p></td> + <td> + <p>The address of the index block. + </p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for the header.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Extensible Array Index Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Elements <em>(variable size and + optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data Block Addresses <em>(variable + size and optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Secondary Block Addresses <em>(variable + size and optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Extensible Array Index Block + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>EAIB</code>” + is used to indicate the beginning of an Extensible Array + Index Block. This gives file consistency checking utilities + a better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>The client ID for identifying the user of the + Extensible Array: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Non-filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Header Address</p></td> + <td> + <p>The address of the Extensible Array header. Principally + used for file integrity checking.</p> + </td> + </tr> + + <tr> + <td><p>Elements</p></td> + <td> + <p>Contains the elements that are stored directly in + the index block. An optimization to avoid unnecessary + secondary blocks. + <br /> + <br /> + There are two element types: + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td><a href="#EaNonFilterChunk">Non-filtered dataset chunks</i></a> +</td> +</tr> +<tr> + <td align="center"><code>1</code></td> + <td><a href="#EaFilterChunk">Filtered dataset chunks</i></a> +</td> +</tr> +</table> +</p> +</td> +</tr> + +<tr> + <td><p>Data Block Addresses</p></td> + <td> + <p>Contains the addresses of the data blocks + that are stored directly in the Index Block. An + optimization to avoid unnecessary secondary blocks.</p> + </td> +</tr> + +<tr> + <td><p>Secondary Block Addresses</p></td> + <td> + <p>Contains the addresses of the secondary + blocks.</p> + </td> +</tr> + +<tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for the Extensible Array Index Block.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Extensible Array Secondary Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Block Offset <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Page Bitmap <em>(variable size and + optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Data Block Addresses <em>(variable + size and optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Extensible Array Secondary Block + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>EASB</code>” + is used to indicate the beginning of an Extensible Array + Secondary Block. This gives file consistency checking utilities + a better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>The ID for identifying the client of the + Extensible Array: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Non-filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Header Address</p></td> + <td> + <p>The address of the Extensible Array header. Principally + used for file integrity checking.</p> + </td> + </tr> + + <tr> + <td><p>Block Offset</p></td> + <td> + <p>Stores the offset of the block in the array. + </p> + </td> + </tr> + + <tr> + <td><p>Page Bitmap</p></td> + <td> + <p>A bitmap indicating which + data block pages are initialized. + <p> + Exists only if the data block is paged. + </td> + </tr> + + <tr> + <td><p>Data Block Addresses</p></td> + <td> + <p>Contains the addresses of the data blocks + referenced by this secondary block.</p> + </td> + </tr> + + <tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for the Extensible Array + Secondary Block.</p> + </td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Extensible Array Data Block + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4">Signature</td> + </tr> + + <tr> + <td>Version</td> + <td>Client ID</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Header Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Block Offset <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Elements <em>(variable size and + optional)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Extensible Array Data Block + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Signature</p></td> + <td> + <p>The ASCII character string “<code>EADB</code>” + is used to indicate the beginning of an Extensible Array + data block. This gives file consistency checking utilities + a better chance of reconstructing a damaged file. + </p> + </td> + </tr> + + <tr> + <td><p>Version</p></td> + <td> + <p>This document describes version 0.</p> + </td> + </tr> + + <tr> + <td><p>Client ID</p></td> + <td> + <p>The ID for identifying the client of the + Extensible Array: + + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>Non-filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>1</code></td> + <td>Filtered dataset chunks + </td> + </tr> + <tr> + <td align="center"><code>2+</code></td> + <td>Reserved. + </td> + </tr> + </table> + </p> + </td> + </tr> + + <tr> + <td><p>Header Address</p></td> + <td> + <p>The address of the Extensible Array header. Principally + used for file integrity checking. + </p> + </td> + </tr> + + <tr> + <td><p>Block Offset</p></td> + <td> + <p>The offset of the block in the array. + </td> + </tr> + + <tr> + <td><p>Elements</p></td> + <td> + <p>Contains the elements stored in the data block and + exists only if the data block is not paged. + <br /> + <br /> + There are two element types: + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td><a href="#EaNonFilterChunk">Non-filtered dataset chunks</i></a> +</td> +</tr> +<tr> + <td align="center"><code>1</code></td> + <td><a href="#EaFilterChunk">Filtered dataset chunks</i></a> +</td> +</tr> +</table> +</p> +</td> +</tr> + +<tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for the Extensible Array data block.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> +<div align="center"> + <table class="format"> + <caption> + Layout: Extensible Array Data Block Page + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td colspan="4"><br />Elements <em>(variable + size)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Checksum</td> + </tr> + + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Extensible Array Data Block Page + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Elements</p></td> + <td> + <p>Contains the elements stored in the data block + page.</p> + <p> + There are two element types: + <table class="list"> + <tr> + <th width="20%" align="center">ID</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td><a href="#EaNonFilterChunk">Non-filtered dataset chunks</i></a> +</td> +</tr> +<tr> + <td align="center"><code>1</code></td> + <td><a href="#EaFilterChunk">Filtered dataset chunks</i></a> +</td> +</tr> +</table> +</p> +</td> +</tr> + +<tr> + <td><p>Checksum</p></td> + <td> + <p>The checksum for an Extensible Array data block + page.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> +<a name="EaNonFilterChunk"></a> +<div align="center"> + <table class="format"> + <caption> + Layout: Data Block Element for Non-filtered Dataset Chunk + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr><td> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Data Block Element for Non-filtered Dataset Chunk + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the dataset chunk in the file. + </p> + </td> + </tr> + + </table> +</div> +</p> + +<br /> +<br /> +<br /> +<a name="EaFilterChunk"></a> +<div align="center"> + <table class="format"> + <caption> + Layout: Data Block Element for Filtered Dataset Chunk + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Address<sup>O</sup><br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br />Chunk Size<em> (variable size; at + most 8 bytes)</em><br /><br /></td> + </tr> + + <tr> + <td colspan="4">Filter Mask</td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> +</div> + +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Data Block Element for Filtered Dataset Chunk + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Address</p></td> + <td><p>The address of the dataset chunk in the file. + </p> + </td> + </tr> + + <tr> + <td><p>Chunk Size</p></td> + <td><p>The size of the dataset chunk in bytes. + </p> + </td> + </tr> + + <tr> + <td><p>Filter Mask</p></td> + <td><p>Indicates the filter to skip for the dataset chunk. + Each filter has an index number in the pipeline; if that + filter is skipped, the bit corresponding to its index is set. + </p> + </td> + </tr> + + </table> +</div> + +<a name="AppendV2Btrees"> + <h3>VII.E. The Version 2 B-trees Index</h3></a> + +<p>The <i>Version 2 B-trees</i> index can be used when the dataset + fulfills the following condition:</p> + +<ul> + <li>more than one dimension of unlimited extent</li> +</ul> + +<p>Version 2 B-trees can be used to index various objects in the + library. See <a href="#V2Btrees">“Version 2 B-trees”</a> + for more information. The B-tree types <a href="#V2BtType10">10</a> + and <a href="#V2BtreesType11">11</a> record layouts are for + indexing dataset chunks.</p> + +<h2><a name="AppendixD"> VIII. Appendix D: + Encoding for dataspace and reference</a></h2> + +<a name="DataspaceEncode"> + <h3>VIII.A. Dataspace Encoding </h3></a> +<i>H5Sencode</i> is a public routine that encodes a dataspace description into a buffer while +<i>H5Sdecode</i> is the corresponding routine that decodes the description encoded in the buffer. +<p> + See the reference manual description for these two public routines. + + <br /> + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Dataspace Description for H5Sencode/H5Sdecode + </caption> + + <tr> + <th>byte</th> + <th>byte</th> + <th>byte</th> + <th>byte</th> + </tr> + + <tr> + <td>Dataspace ID</td> + <td>Encode Version</td> + <td>Size of Size</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + <tr> + <td colspan="4"><br />Size of Extent + <br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Dataspace Message + <em>(variable size)</em> + <br /><br /></td> + </tr> + + <tr> + <td colspan="4"><br /><br />Dataspace Selection + <em>(variable size)</em> + <br /><br /></td> + </tr> + + </table> + + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Dataspace Description for H5Sencode/H5Sdecode + </caption> + <tr> + <th width="40%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Dataspace ID</p></td> + <td> + <p>The datspace message ID which is 1.</p> + </td> + </tr> + + <tr> + <td><p>Encode Version</p></td> + <td> + <p>H5S_ENCODE_VERSION which is 0. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Size</p></td> + <td> + <p>The number of bytes used to store the size of an object. + </p> + </td> + </tr> + + <tr> + <td><p>Size of Extent</p></td> + <td> + <p>Size of the dataspace message. + </p> + </td> + </tr> + + <tr> + <td><p>Dataspace Message</p></td> + <td> + <p>The dataspace message information. See + <a href="#DataspaceMessage">Dataspace Message.</a></p> +</p> +</td> +</tr> + +<tr> + <td><p>Dataspace Selection</p></td> + <td> + <p>The dataspace selection information. See + <a href="#DataspaceSEL">Dataspace Selection.</a></p> + </td> +</tr> + +</table> +</div> + + +<br /> +<br /> +<br /> +<a name="DataspaceSEL"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Dataspace Selection + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Selection Type</td> + </tr> + <tr> + <td colspan="4"><br />Selection Info (<em>variable + size</em>)<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Dataspace Selection + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Selection Type</p></td> + <td> + <p>There are 4 types of selection: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>H5S_SEL_NONE: Nothing selected + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>H5S_SEL_POINTS: Sequence of points selected + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>H5S_SEL_HYPER: Hyperslab selected + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>H5S_SEL_ALL: Entire extent selected + </td> + </tr> + </table> + </td> + + </tr> + + <tr> + <td><p>Selection Info</p></td> + <td> + <p>There are 4 types of selection info: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td>Selection info for <a href="#SelNONE">H5S_SEL_NONE</a> + </td> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>Selection info for <a href="#SelPOINTS">H5S_SEL_POINTS</a> + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>Selection info for <a href="#SelHYPER">H5S_SEL_HYPER</a> + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>Selection for <a href="#SelALL">H5S_SEL_ALL</a> + </td> + </tr> + </table> + </td> + + </tr> + </table> + </div> + + + <br /> + <br /> + <br /> +<a name="SelNONE"/></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Selection Info for H5S_SEL_NONE + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Version</td> + </tr> + <tr> + <td colspan="4"><br />Reserved <em>(zero, 8 bytes)</em><br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Selection Info for H5S_SEL_NONE + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for the H5S_SEL_NONE Selection Info. + The value is 1.</p></td> + </tr> + </table> + </div> + + + <br /> + <br /> + <br /> + <a name="SelPOINTS"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Selection Info for H5S_SEL_POINTS + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Version</td> + </tr> + <tr> + <td colspan="4"><br /><br />Points Selection Info <em>(variable size)</em> + <br /><br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Selection Info for H5S_SEL_POINTS + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for the H5S_SEL_POINTS Selection Info. + The value is either 1 or 2.</p></td> + </tr> + + <tr> + <td><p>Points Selection Info</p></td> + <td><p>Depending on <em>version</em>: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>See <a href="#SelPOINTSV1">Version 1 Points Selection Info</a> + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>See <a href="#SelPOINTSV2">Version 2 Points Selection Info</a> + </td> + </tr> + + </table> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + <a name="SelPOINTSV1"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 1 Points Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Reserved <em>(zero)</em></td> + </tr> + + <tr> + <td colspan="4">Length</td> + </tr> + <tr> + <td colspan="4">Rank</td> + </tr> + <tr> + <td colspan="4">Num Points</td> + </tr> + <tr> + <td colspan="4">Point #1: coordinate #1</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Point #1: coordinate #u</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Point #n: coordinate #1</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Point #n: coordinate #u</td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 1 Points Selection Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>The size in bytes from <em>Length</em> to the end of the + selection info.</td> + </tr> + + <tr> + <td><p>Rank</p></td> + <td><p>The number of dimensions.</p></td> + </tr> + <tr> + <td><p>Num Points</p></td> + <td><p>The number of points in the selection.</p></td> + </tr> + <tr> + <td><p>Point #n: coordinate #u</p></td> + <td><p>The array of points in the selection. + <p>The points selected are #1 to #n where n is <em>Num Points</em>. + <p>The list of coordinates for each point are #1 to #u where u is + <em>Rank</em>.</p></td> + </tr> + </table> + </div> + + + <br /> + <br /> + <br /> + <a name="SelPOINTSV2"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 2 Points Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="1">Encode Size</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted only to align table nicely</em> + </td> + </tr> + + <tr> + <td colspan="4">Rank</td> + </tr> + <tr> + <td colspan="4">Num Points<p>(2, 4 or 8 bytes)<br /></td> + </tr> + <tr> + <td colspan="4">Point #1: coordinate #1<p>(2, 4 or 8 bytes)<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Point #1: coordinate #u<p>(2, 4 or 8 bytes)<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Point #n: coordinate #1 <p>(2, 4 or 8 bytes)<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Point #n: coordinate #u<p>(2, 4 or 8 bytes)<br /></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 Points Selection Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Encode Size</td> + <td><p>The size for encoding the points selection info which can be 2, 4 or 8 bytes. + </td> + </tr> + + <tr> + <td><p>Rank</p></td> + <td><p>The number of dimensions.</p></td> + </tr> + <tr> + <td><p>Num Points</p></td> + <td><p>The number of points in the selection. + <p>The field <em>Encode Size</em> indicates the size of this field</p></td> + </tr> + <tr> + <td><p>Point #n: coordinate #u</p></td> + <td><p>The array of points in the selection. + <p>The points selected are #1 to #n where n is <em>Num Points</em>. + <p>The list of coordinates for each point are #1 to #u where u is + <em>Rank</em>. + <p>The field <em>Encode Size</em> indicates the size of this field</p></td> + </tr> + </table> + </div> + + + <br /> + <br /> + <br /> + <a name="SelHYPER"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Selection Info for H5S_SEL_HYPER + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Version</td> + </tr> + <tr> + <td colspan="4"><br />Hyperslab Selection Info + (<em>variable size</em>)<br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Selection Info for H5S_SEL_HYPER + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for the H5S_SEL_HYPER selection info. + The value is 1, 2 or 3.</p></td> + </tr> + + <tr> + <td><p>Hyperslab Selection Info</p></td> + <td><p>Depending on <em>version</em>: + <table class="list"> + <tr> + <th width="20%" align="center">Version</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>1</code></td> + <td>See <a href="#SelHYPERV1">Version 1 Hyperslab Selection Info</a>. + </td> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>See <a href="#SelHYPERV2">Version 2 Hyperslab Selection Info</a> + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>See <a href="#SelHYPERV3">Version 3 Hyperslab Selection Info</a> + </td> + </tr> + </table> + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + <a name="SelHYPERV1"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 1 Hyperslab Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Reserved</td> + </tr> + <tr> + <td colspan="4">Length</td> + </tr> + <tr> + <td colspan="4">Rank</td> + </tr> + <tr> + <td colspan="4">Num Blocks</td> + </tr> + <tr> + <td colspan="4">Starting Offset #1 for Block #1</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Starting Offset #n for Block #1</td> + </tr> + + <tr> + <td colspan="4">Ending Offset #1 for Block #1</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Ending Offset #n for Block #1</td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td colspan="4">Starting Offset #1 for Block #u</td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Starting Offset #n for Block #u</td> + </tr> + + <tr> + <td colspan="4">Ending Offset #1 for Block #u</em></td> +</tr> +<tr> + <td colspan="4">.<br />.<br />.<br /></td> +</tr> +<tr> + <td colspan="4">Ending Offset #n for Block #u</td> +</tr> + +</table> +</div> + +<br /> +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Version 1 Hyperslab Selection Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>The size in bytes from the field <em>Rank</em> to the + end of the Selection Info.</td> + </tr> + + <tr> + <td><p>Rank</p></td> + <td><p>The number of dimensions in the dataspace.</p></td> + </tr> + + <tr> + <td><p>Num Blocks</p></td> + <td><p>The number of blocks in the selection.</p></td> + </tr> + + <tr> + <td><p>Starting Offset #n for Block #u</p></td> + <td><p>The offset #n of the starting element in block #u. + <p>#n is from 1 to <em>Rank</em>. + <p>#u is from 1 to <em>Num Blocks</em> moving from the fastest + changing dimension to the slowest changing dimension. + </p></td> + </tr> + + <tr> + <td><p>Ending Offset #n for Block #u</p></td> + <td><p>The offset #n of the ending element in block #u. + <p>#n is from 1 to <em>Rank</em>. + <p>#u is from 1 to <em>Num Blocks</em> moving from the fastest + changing dimension to the slowest changing dimension. + </p></td> + </tr> + + </table> +</div> + +<br /> +<br /> +<br /> +<a name="SelHYPERV2"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 2 Hyperslab Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Flags</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Length</td> + </tr> + <tr> + <td colspan="4">Rank</td> + </tr> + <tr> + <td colspan="4">Start #1 <em>(8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Stride #1 <em>(8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Count #1 <em>(8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Block #1 <em>(8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Start #n <em>(8 bytes)</em><p></td> + </tr> + + <tr> + <td colspan="4">Stride #n <em>(8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Count #n <em>(8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Block #n <em>(8 bytes)</em><p></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 2 Hyperslab Selection Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is a bit field with the following definition. + Currently, this is always set to 0x1. + <p> + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td>If set, it a a regular hyperslab, otherwise, irregular. + </td> + </tr> + + </table> + </td> + + </tr> + + <tr> + <td><p>Length</p></td> + <td><p>The size in bytes from the field <em>Rank</em> to the + end of the Selection Info.</td> + </tr> + + <tr> + <td><p>Rank</p></td> + <td><p>The number of dimensions in the dataspace.</td> + </tr> + + <tr> + <td><p>Start #n</p></td> + <td><p>The offset of the starting element in the block. + <p>#n is from 1 to <em>Rank</em>. + </p></td> + </tr> + + <tr> + <td><p>Stride #n</p></td> + <td><p>The number of elements to move in each dimension. + <p>#n is from 1 to <em>Rank</em>. + </p></td> + </tr> + + <tr> + <td><p>Count #n</p></td> + <td><p>The number of blocks to select in each dimension. + <p>#n is from 1 to <em>Rank</em>. + </p></td> + </tr> + + <tr> + <td><p>Block #n</p></td> + <td><p>The size (in elements) of each block in each dimension. + <p>#n is from 1 to <em>Rank</em>. + </p></td> + </tr> + </table> + </div> + + + + + <br /> + <br /> + <br /> + <a name="SelHYPERV3"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 3 Hyperslab Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Flags</td> + <td>Encode Size</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + <tr> + <td colspan="4">Rank</td> + </tr> + <tr> + <td colspan="4"><br />Regular/Irregular Hyperslab Selection Info + <p><em>(variable size)</em><br /><br/></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 3 Hyperslab Selection Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This is a bit field with the following definition: + <p> + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + <tr> + <td align="center"><code>0</code></td> + <td>If set, it is a regular hyperslab, otherwise, irregular. + </td> + </tr> + + </table> + </td> + </tr> + + <tr> + <td><p>Encode Size</p></td> + <td><p>The size for encoding hyperslab selection info, which can 2, 4 or 8 bytes.</td> + </tr> + + <tr> + <td><p>Rank</p></td> + <td><p>The number of dimensions in the dataspace.</td> + </tr> + + <tr> + <td><p>Regular/Irregular Hyperslab Selection Info</p></td> + <td><p>This is the selection info for version 3 hyperslab which can be regular or irregular. + <p>If bit 0 of the field <em>Flags</em> is set, + See <a href="#SelHYPERV3REG">Version 3 Regular Hyperslab Selection Info</a> + <p>Otherwise, see <a href="#SelHYPERV3IRREG">Version 3 Irregular Hyperslab Selection Info</a> + </td> + + </tr> + + </table> + </div> + + + <br /> + <br /> + <br /> + <a name="SelHYPERV3REG"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 3 Regular Hyperslab Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Start #1 <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Stride #1 <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Count #1 <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Block #1 <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Start #n <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + + <tr> + <td colspan="4">Stride #n <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Count #n <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Block #n <p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 3 Regular Hyperslab Selection Info + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Start #n</p></td> + <td><p>The offset of the starting element in the block. + <p>#n is from 1 to <em>Rank</em>. + <p>The field <em>Encode Size</em> indicates the size of this field. + </p></td> + </tr> + + <tr> + <td><p>Stride #n</p></td> + <td><p>The number of elements to move in each dimension. + <p>#n is from 1 to <em>Rank</em>. + <p>The field <em>Encode Size</em> indicates the size of this field. + </p></td> + </tr> + + <tr> + <td><p>Count #n</p></td> + <td><p>The number of blocks to select in each dimension. + <p>#n is from 1 to <em>Rank</em>. + <p>The field <em>Encode Size</em> indicates the size of this field. + </p></td> + </tr> + + <tr> + <td><p>Block #n</p></td> + <td><p>The size (in elements) of each block in each dimension. + <p>#n is from 1 to <em>Rank</em>. + <p>The field <em>Encode Size</em> indicates the size of this field. + </p></td> + </tr> + </table> + </div> + + <br /> + <br /> + <br /> + <a name="SelHYPERV3IRREG"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Version 3 Irregular Hyperslab Selection Info + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Num Blocks<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">Starting Offset #1 for Block #1<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Starting Offset #n for Block #1<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + + <tr> + <td colspan="4">Ending Offset #1 for Block #1<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Ending Offset #n for Block #1<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + + <tr> + <td colspan="4">Starting Offset #1 for Block #u<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Starting Offset #n for Block #u<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + + <tr> + <td colspan="4">Ending Offset #1 for Block #u<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + <tr> + <td colspan="4">.<br />.<br />.<br /></td> + </tr> + <tr> + <td colspan="4">Ending Offset #n for Block #u<p><em>(2, 4 or 8 bytes)</em><p></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Version 3 Irregular Hyperslab Selection Info + </caption> + + <tr> + <td><p>Num Blocks</p></td> + <td><p>The number of blocks in the selection. + <p>The field <em>Encode Size</em> indicates the size of this field</p></td> + </tr> + + <tr> + <td><p>Starting Offset #n for Block #u</p></td> + <td><p>The offset #n of the starting element in block #u. + <p>#n is from 1 to <em>Rank</em>. + <p>#u is from 1 to <em>Num Blocks</em> moving from the fastest + changing dimension to the slowest changing dimension. + <p>The field <em>Encode Size</em> indicates the size of this field + </p></td> + </tr> + + <tr> + <td><p>Ending Offset #n for Block #u</p></td> + <td><p>The offset #n of the ending element in block #u. + <p>#n is from 1 to <em>Rank</em>. + <p>#u is from 1 to <em>Num Blocks</em> moving from the fastest + changing dimension to the slowest changing dimension. + <p>The field <em>Encode Size</em> indicates the size of this field + </p></td> + </tr> + + </table> + </div> + + + <br /> + <br /> + <br /> + <a name="SelALL"></a> + <div align="center"> + <table class="format"> + <caption> + Layout: Selection Info for H5S_SEL_ALL + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4">Version</td> + </tr> + <tr> + <td colspan="4"><br />Reserved <em>(zero, + 8 bytes)</em><br /><br /></td> + </tr> + + </table> + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Selection Info for H5S_SEL_ALL + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Version</p></td> + <td><p>The version number for the H5S_SEL_ALL Selection Info; + the value is 1.</p></td> + </tr> + </table> + </div> + + <a name="ReferenceEncodeRV"> + <h3>VIII.B. Reference Encoding (Revised)</h3></a> + <p> + <br /> + For the following reference type, + the Reference Header and Reference Block are stored together as the dataset's raw data: + <ul> + <li>Object Reference (H5R_OBJECT2) (without reference to an external file)</li> + </ul> + <p> + For the following reference types, + the Reference Header plus the <a href="#GlobalHeapID">Global Heap ID</a> are stored + as the dataset's raw data in the file. + The global heap ID is used to locate the Reference Block stored in the global heap: + <ul> + <li>Object Reference (H5R_OBJECT2) (with reference to an external file)</li> + <li>Dataset Region Reference (H5R_DATASET_REGION2) (with/without reference to an external file)</li> + <li>Attribute Reference (H5R_ATTR) (with/without reference to an external file)</li> + </ul> + <br /> + <br /> + + <div align="center"> + <table class="format"> + <caption> + Layout: Reference Header + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Reference Type</td> + <td>Flags</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + + </table> + + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Reference Header + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Reference Type</p></td> + <td> + <p>There are 3 types of references: + <table class="list"> + <tr> + <th width="20%" align="center">Value</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>2</code></td> + <td>H5R_OBJECT2: Object Reference + </td> + </tr> + + <tr> + <td align="center"><code>3</code></td> + <td>H5R_DATASET_REGION2: Dataset Region Reference + </td> + </tr> + + <tr> + <td align="center"><code>4</code></td> + <td>H5R_ATTR: Attribute Reference + </td> + </tr> + + </table> + + </td> + </tr> + + <tr> + <td><p>Flags</p></td> + <td><p>This field describes the reference: + <table class="list"> + <tr> + <th width="20%" align="center">Bit</th> + <th width="80%" align="left">Description</th> + </tr> + + <tr> + <td align="center"><code>0</code></td> + <td>If set, the reference is to an external file. + </td> + </tr> + <tr> + <td align="center"><code>1-7</code></td> + <td>Reserved</td> + </tr> + </table></p> + + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + + <div align="center"> + <table class="format"> + <caption> + Layout: Reference Block + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td>Token Size</td> + <td colspan="3" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + <tr> + <td colspan=4><br /><br />Token + <em>(variable size)</em><br /> <br /><br /></td> + </tr> + <tr> + <td colspan=2>Length of External File Name</td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> + </tr> + <tr> + <td colspan=4><br /><br />External File Name + <em>(variable size)</em><br /><br /><br /></td> + </tr> + <tr> + <td colspan=4>Size of Dataspace Selection</td> + </tr> + <tr> + <td colspan=4>Rank of Dataspace Selection</td> + </tr> + <tr> + <td colspan=4><br /><br />Dataspace Selection Information + <em>(variable size)</em><br /><br /> <br /></td> +</td> +</tr> +<tr> + <td colspan=2>Length of Attribute Name </td> + <td colspan="2" bgcolor="#DDDDDD"><em>This space inserted + only to align table nicely</em></td> +</tr> +<tr> + <td colspan=4><br /><br />Attribute Name + <em>(variable size)</em><br /><br /><br /></td> +</tr> + +</table> + +</div> + +<br /> +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Reference Block + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Token size</p></td> + <td><p>This is the size of the token for the object. + </td> + </tr> + + <tr> + <td><p>Token</p></td> + <td> + <p> + This is the token for the object. + </p> + </td> + </tr> + + <tr> + <td><p>Length fo External File Name</p></td> + <td><p>This is the length for the external file name. + <p>This field exists if bit 0 of <em>flags</em> is set.</p> + </p> + </td> + </tr> + + <tr> + <td><p>External File Name</p></td> + <td><p>This is the name of the external file being referenced.</p> +</p> +<p>This field exists if bit 0 of <em>flags</em> is set.</p> +</td> +</tr> + +<tr> + <td><p>Dataspace Selection Information</p></td> + <td><p>See <a href="#DataspaceSEL">Dataspace Selection.</a></p> +</p> +<p>This field exists if the <em>Reference Type</em> is H5R_DATASET_REGION2.</p> +</td> +</tr> + +<tr> + <td><p>Length of Attribute Name</p></td> + <td><p>This is the length of the attribute name. + <p>This field exists if the <em>Reference Type</em> is H5R_ATTRIBUTE.</p> + </td> +</tr> + +<tr> + <td><p>Attribute Name</p></td> + <td><p>This is the name of the attribute being referenced. + <p>This field exists if the <em>Reference Type</em> is H5R_ATTRIBUTE.</p> + </td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> + + +<a name="ReferenceEncodeDP"> + <h3>VIII.C. Reference Encoding (Backward Compatibility)</h3></a> +<p> + <br /> + The two references described below are maintained to preserve compatibility with previous versions of the library. +<p> + For the following reference type, + the reference encoding is stored as the dataset's raw data in the file: + <ul> + <li>Object Reference (H5R_OBJECT1)</li> + </ul> +<p> + For the following reference type, + the <a href="#GlobalHeapID">Global Heap ID</a> is stored as the dataset's raw data in the file. + The global heap ID is used to locate the reference encoding + stored in the global heap: + <ul> + <li>Dataset Region Reference (H5R_DATASET_REGION1)</li> + </ul> + + <br /> + <br /> + <div align="center"> + <table class="format"> + <caption> + Layout: Reference for H5R_OBJECT1 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Object Address<sup>O</sup><br /><br /></td> + </tr> + + </table> + + <table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> + </table> + + </div> + + <br /> + <br /> + <div align="center"> + <table class="desc"> + <caption> + Fields: Reference for H5R_OBJECT1 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Object Address</p></td> + <td> + <p>Address of the object being referenced + </td> + </tr> + + </table> + </div> + + <br /> + <br /> + <br /> + + <div align="center"> + <table class="format"> + <caption> + Layout: Reference for H5R_DATASET_REGION1 + </caption> + + <tr> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + <th width="25%">byte</th> + </tr> + + <tr> + <td colspan="4"><br />Object Address<sup>O</sup><br /><br /></td> + </tr> + <tr> + <td colspan=4><br /><br />Dataspace Selection Information + <em>(variable size)</em><br /><br /> <br /></td> +</td> +</tr> + +</table> + +<table class="note"> + <tr> + <td width="60%"> </td> + <td width="40%"> + (Items marked with an ‘O’ in the above table are + of the size specified in the <a href="#SizeOfOffsetsV0">Size + of Offsets</a> field in the superblock.) + </td></tr> +</table> + +</div> + +<br /> +<br /> +<div align="center"> + <table class="desc"> + <caption> + Fields: Reference for H5R_DATASET_REGION1 + </caption> + <tr> + <th width="30%">Field Name</th> + <th>Description</th> + </tr> + + <tr> + <td><p>Object Address</p></td> + <td><p>This is the address of the object being referenced. + </td> + </tr> + + <tr> + <td><p>Dataspace Selection Information</p></td> + <td><p>This is the dataspace selection for the object being referenced. + See <a href="#DataspaceSEL">Dataspace Selection.</a></p> +</p> +</td> +</tr> + +</table> +</div> + +<br /> +<br /> +<br /> + + +</body> +</html> diff --git a/doxygen/examples/H5A_examples.c b/doxygen/examples/H5A_examples.c new file mode 100644 index 0000000..f332efa --- /dev/null +++ b/doxygen/examples/H5A_examples.c @@ -0,0 +1,145 @@ +/* -*- c-file-style: "stroustrup" -*- */ + +#include "hdf5.h" + +#include <stdio.h> +#include <stdlib.h> + +int +main(void) +{ + int ret_val = EXIT_SUCCESS; + + //! <!-- [create] --> + { + __label__ fail_acpl, fail_attr, fail_file; + hid_t file, acpl, fspace, attr; + + unsigned mode = H5F_ACC_TRUNC; + char file_name[] = "f1.h5"; + // attribute names can be arbitrary Unicode strings + char attr_name[] = "Χαρακτηριστικό"; + + if ((file = H5Fcreate(file_name, mode, H5P_DEFAULT, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + if ((acpl = H5Pcreate(H5P_ATTRIBUTE_CREATE)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_acpl; + } + // use UTF-8 encoding for the attribute name + if (H5Pset_char_encoding(acpl, H5T_CSET_UTF8) < 0) { + ret_val = EXIT_FAILURE; + goto fail_fspace; + } + // create a scalar (singleton) attribute + if ((fspace = H5Screate(H5S_SCALAR)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_fspace; + } + // create an attribute on the root group + if ((attr = H5Acreate2(file, attr_name, H5T_STD_I32LE, fspace, acpl, H5P_DEFAULT)) == + H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_attr; + } + + H5Aclose(attr); +fail_attr: + H5Sclose(fspace); +fail_fspace: + H5Pclose(acpl); +fail_acpl: + H5Fclose(file); +fail_file:; + } + //! <!-- [create] --> + + //! <!-- [read] --> + { + __label__ fail_attr, fail_file; + hid_t file, attr; + + unsigned mode = H5F_ACC_RDONLY; + char file_name[] = "f1.h5"; + char attr_name[] = "Χαρακτηριστικό"; + int value; + + if ((file = H5Fopen(file_name, mode, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + if ((attr = H5Aopen(file, attr_name, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_attr; + } + // read the attribute value + if (H5Aread(attr, H5T_NATIVE_INT, &value) < 0) + ret_val = EXIT_FAILURE; + + // do something w/ the attribute value + + H5Aclose(attr); +fail_attr: + H5Fclose(file); +fail_file:; + } + //! <!-- [read] --> + + //! <!-- [update] --> + { + __label__ fail_attr, fail_file; + hid_t file, attr; + + unsigned mode = H5F_ACC_RDWR; + char file_name[] = "f1.h5"; + char attr_name[] = "Χαρακτηριστικό"; + int value = 1234; + + if ((file = H5Fopen(file_name, mode, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + if ((attr = H5Aopen(file, attr_name, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_attr; + } + // update the attribute value + if (H5Awrite(attr, H5T_NATIVE_INT, &value) < 0) + ret_val = EXIT_FAILURE; + + H5Aclose(attr); +fail_attr: + H5Fclose(file); +fail_file:; + } + //! <!-- [update] --> + + //! <!-- [delete] --> + { + __label__ fail_attr, fail_file; + hid_t file; + + unsigned mode = H5F_ACC_RDWR; + char file_name[] = "f1.h5"; + char attr_name[] = "Χαρακτηριστικό"; + + if ((file = H5Fopen(file_name, mode, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + // delete the attribute + if (H5Adelete(file, attr_name) < 0) { + ret_val = EXIT_FAILURE; + goto fail_attr; + } + +fail_attr: + H5Fclose(file); +fail_file:; + } + //! <!-- [delete] --> + + return ret_val; +} diff --git a/doxygen/examples/H5D_examples.c b/doxygen/examples/H5D_examples.c new file mode 100644 index 0000000..aad057d --- /dev/null +++ b/doxygen/examples/H5D_examples.c @@ -0,0 +1,173 @@ +/* -*- c-file-style: "stroustrup" -*- */ + +#include "hdf5.h" + +#include <stdio.h> +#include <stdlib.h> + +int +main(void) +{ + int ret_val = EXIT_SUCCESS; + + //! <!-- [create] --> + { + __label__ fail_lcpl, fail_dset, fail_file; + hid_t file, lcpl, fspace, dset; + + unsigned mode = H5F_ACC_TRUNC; + char file_name[] = "d1.h5"; + // link names can be arbitrary Unicode strings + char dset_name[] = "σύνολο/δεδομένων"; + + if ((file = H5Fcreate(file_name, mode, H5P_DEFAULT, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + if ((lcpl = H5Pcreate(H5P_LINK_CREATE)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_lcpl; + } + // use UTF-8 encoding for link names + if (H5Pset_char_encoding(lcpl, H5T_CSET_UTF8) < 0) { + ret_val = EXIT_FAILURE; + goto fail_fspace; + } + // create intermediate groups as needed + if (H5Pset_create_intermediate_group(lcpl, 1) < 0) { + ret_val = EXIT_FAILURE; + goto fail_fspace; + } + // create a 1D dataspace + if ((fspace = H5Screate_simple(1, (hsize_t[]){10}, NULL)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_fspace; + } + // create a 32-bit integer dataset + if ((dset = H5Dcreate2(file, dset_name, H5T_STD_I32LE, fspace, lcpl, H5P_DEFAULT, H5P_DEFAULT)) == + H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_dset; + } + + H5Dclose(dset); +fail_dset: + H5Sclose(fspace); +fail_fspace: + H5Pclose(lcpl); +fail_lcpl: + H5Fclose(file); +fail_file:; + } + //! <!-- [create] --> + + //! <!-- [read] --> + { + __label__ fail_dset, fail_file; + hid_t file, dset; + + unsigned mode = H5F_ACC_RDONLY; + char file_name[] = "d1.h5"; + // assume a priori knowledge of dataset name and size + char dset_name[] = "σύνολο/δεδομένων"; + int elts[10]; + + if ((file = H5Fopen(file_name, mode, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + if ((dset = H5Dopen2(file, dset_name, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_dset; + } + // read all dataset elements + if (H5Dread(dset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, elts) < 0) + ret_val = EXIT_FAILURE; + + // do something w/ the dataset elements + + H5Dclose(dset); +fail_dset: + H5Fclose(file); +fail_file:; + } + //! <!-- [read] --> + + //! <!-- [update] --> + { + __label__ fail_update, fail_fspace, fail_dset, fail_file; + hid_t file, dset, fspace; + + unsigned mode = H5F_ACC_RDWR; + char file_name[] = "d1.h5"; + char dset_name[] = "σύνολο/δεδομένων"; + int new_elts[6][2] = {{-1, 1}, {-2, 2}, {-3, 3}, {-4, 4}, {-5, 5}, {-6, 6}}; + + if ((file = H5Fopen(file_name, mode, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + if ((dset = H5Dopen2(file, dset_name, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_dset; + } + // get the dataset's dataspace + if ((fspace = H5Dget_space(dset)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_fspace; + } + // select the first 5 elements in odd positions + if (H5Sselect_hyperslab(fspace, H5S_SELECT_SET, (hsize_t[]){1}, (hsize_t[]){2}, (hsize_t[]){5}, + NULL) < 0) { + ret_val = EXIT_FAILURE; + goto fail_update; + } + + // (implicitly) select and write the first 5 elements of the second column of NEW_ELTS + if (H5Dwrite(dset, H5T_NATIVE_INT, H5S_ALL, fspace, H5P_DEFAULT, new_elts) < 0) + ret_val = EXIT_FAILURE; + +fail_update: + H5Sclose(fspace); +fail_fspace: + H5Dclose(dset); +fail_dset: + H5Fclose(file); +fail_file:; + } + //! <!-- [update] --> + + //! <!-- [delete] --> + { + __label__ fail_delete, fail_file; + hid_t file; + + unsigned mode = H5F_ACC_RDWR; + char file_name[] = "d1.h5"; + char group_name[] = "σύνολο"; + char dset_name[] = "σύνολο/δεδομένων"; + + if ((file = H5Fopen(file_name, mode, H5P_DEFAULT)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + // delete (unlink) the dataset + if (H5Ldelete(file, dset_name, H5P_DEFAULT) < 0) { + ret_val = EXIT_FAILURE; + goto fail_delete; + } + // the previous call deletes (unlinks) only the dataset + if (H5Ldelete(file, group_name, H5P_DEFAULT) < 0) { + ret_val = EXIT_FAILURE; + goto fail_delete; + } + +fail_delete: + H5Fclose(file); +fail_file:; + } + + //! <!-- [delete] --> + + return ret_val; +} diff --git a/doxygen/examples/H5F_examples.c b/doxygen/examples/H5F_examples.c new file mode 100644 index 0000000..a7ce6fb --- /dev/null +++ b/doxygen/examples/H5F_examples.c @@ -0,0 +1,187 @@ +/* -*- c-file-style: "stroustrup" -*- */ + +#include "hdf5.h" + +#include <stdio.h> +#include <stdlib.h> + +int +main(void) +{ + int ret_val = EXIT_SUCCESS; + + //! <!-- [life_cycle] --> + { + __label__ fail_fapl, fail_fcpl, fail_file; + hid_t fcpl, fapl, file; + + if ((fcpl = H5Pcreate(H5P_FILE_CREATE)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_fcpl; + } + else { + // adjust the file creation properties + } + + if ((fapl = H5Pcreate(H5P_FILE_ACCESS)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_fapl; + } + else { + // adjust the file access properties + } + + unsigned mode = H5F_ACC_EXCL; + char name[] = "f1.h5"; + + if ((file = H5Fcreate(name, mode, fcpl, fapl)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + + // do something useful with FILE + + H5Fclose(file); +fail_file: + H5Pclose(fapl); +fail_fapl: + H5Pclose(fcpl); +fail_fcpl:; + } + //! <!-- [life_cycle] --> + + //! <!-- [life_cycle_w_open] --> + { + __label__ fail_fapl, fail_file; + hid_t fapl, file; + + if ((fapl = H5Pcreate(H5P_FILE_ACCESS)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_fapl; + } + else { + // adjust the file access properties + } + + unsigned mode = H5F_ACC_RDWR; + char name[] = "f1.h5"; + + if ((file = H5Fopen(name, mode, fapl)) == H5I_INVALID_HID) { + ret_val = EXIT_FAILURE; + goto fail_file; + } + + // do something useful with FILE + + H5Fclose(file); +fail_file: + H5Pclose(fapl); +fail_fapl:; + } + //! <!-- [life_cycle_w_open] --> + + //! <!-- [minimal] --> + { + unsigned mode = H5F_ACC_TRUNC; + char name[] = "f11.h5"; + + hid_t file = H5Fcreate(name, mode, H5P_DEFAULT, H5P_DEFAULT); + if (file != H5I_INVALID_HID) + H5Fclose(file); + else + ret_val = EXIT_FAILURE; + } + //! <!-- [minimal] --> + + //! <!-- [open] --> + { + unsigned mode = H5F_ACC_RDONLY; + char name[] = "f11.h5"; + + hid_t file = H5Fopen(name, mode, H5P_DEFAULT); + if (file != H5I_INVALID_HID) + H5Fclose(file); + else + ret_val = EXIT_FAILURE; + } + //! <!-- [open] --> + + //! <!-- [flush] --> + { + unsigned mode = H5F_ACC_RDWR; + char name[] = "f11.h5"; + + hid_t file = H5Fopen(name, mode, H5P_DEFAULT); + if (file != H5I_INVALID_HID) { + int step; + for (step = 0; step < 1000; ++step) { + + // do important work & flush every 20 steps + + if (step % 20 == 0) { + if (H5Fflush(file, H5F_SCOPE_LOCAL) < 0) { + perror("H5Fflush failed."); + ret_val = EXIT_FAILURE; + break; + } + } + } + + if (H5Fclose(file) < 0) + perror("H5Fclose failed."); + } + else + ret_val = EXIT_FAILURE; + } + //! <!-- [flush] --> + + //! <!-- [libver_bounds] --> + { + unsigned mode = H5F_ACC_RDWR; + char name[] = "f11.h5"; + + hid_t file = H5Fopen(name, mode, H5P_DEFAULT); + if (file != H5I_INVALID_HID) { + if (H5Fset_libver_bounds(file, H5F_LIBVER_EARLIEST, H5F_LIBVER_V18) >= 0) { + + // object creation will not exceed HDF5 version 1.8.x + } + else + perror("H5Fset_libver_bounds failed."); + + if (H5Fclose(file) < 0) + perror("H5Fclose failed."); + } + else + ret_val = EXIT_FAILURE; + } + //! <!-- [libver_bounds] --> + + //! <!-- [mount] --> + { + hid_t file = H5Fopen("f11.h5", H5F_ACC_RDWR, H5P_DEFAULT); + if (file != H5I_INVALID_HID) { + hid_t group, child; + if ((group = H5Gcreate1(file, "mount_point", H5P_DEFAULT)) != H5I_INVALID_HID) { + if ((child = H5Fopen("f1.h5", H5F_ACC_RDONLY, H5P_DEFAULT)) != H5I_INVALID_HID) { + if (H5Fmount(group, ".", child, H5P_DEFAULT) >= 0) { + + // do something useful w/ the mounted file + } + else { + ret_val = EXIT_FAILURE; + perror("H5Fmount failed."); + } + H5Fclose(child); + } + H5Gclose(group); + } + H5Fclose(file); + } + else + ret_val = EXIT_FAILURE; + } + //! <!-- [mount] --> + + return ret_val; +} diff --git a/doxygen/examples/H5Pget_metadata_read_attempts.1.c b/doxygen/examples/H5Pget_metadata_read_attempts.1.c new file mode 100644 index 0000000..da325c0 --- /dev/null +++ b/doxygen/examples/H5Pget_metadata_read_attempts.1.c @@ -0,0 +1,22 @@ +/* Get a copy of file access property list */ +fapl = H5Pcreate(H5P_FILE_ACCESS); + +/* Retrieve the # of read attempts from the file access property list */ +H5Pget_metadata_read_attempts(fapl, &attempts); + +/* + * The value returned in "attempts" will be 1 (default for non-SWMR access). + */ + +/* Set the # of read attempts to 20 */ +H5Pset_metadata_read_attempts(fapl, 20); + +/* Retrieve the # of read attempts from the file access property list */ +H5Pget_metadata_read_attempts(fapl, &attempts); + +/* + * The value returned in "attempts" will be 20 as set. + */ + +/* Close the property list */ +H5Pclose(fapl); diff --git a/doxygen/examples/H5Pget_metadata_read_attempts.2.c b/doxygen/examples/H5Pget_metadata_read_attempts.2.c new file mode 100644 index 0000000..2cd12db --- /dev/null +++ b/doxygen/examples/H5Pget_metadata_read_attempts.2.c @@ -0,0 +1,44 @@ +/* Open the file with SWMR access and default file access property list */ +fid = H5Fopen(FILE, (H5F_ACC_RDONLY | H5F_ACC_SWMR_READ), H5P_DEFAULT); + +/* Get the file's file access roperty list */ +file_fapl = H5Fget_access_plist(fid); + +/* Retrieve the # of read attempts from the file's file access property list */ +H5Pget_metadata_read_attempts(file_fapl, &attempts); + +/* + * The value returned in "attempts" will be 100 (default for SWMR access). + */ + +/* Close the property list */ +H5Pclose(file_fapl); + +/* Close the file */ +H5Fclose(fid); + +/* Create a copy of file access property list */ +fapl = H5Pcreate(H5P_FILE_ACCESS); + +/* Set the # of read attempts */ +H5Pset_metadata_read_attempts(fapl, 20); + +/* Open the file with SWMR access and the non-default file access property list */ +fid = H5Fopen(FILE, (H5F_ACC_RDONLY | H5F_ACC_SWMR_READ), fapl); + +/* Get the file's file access roperty list */ +file_fapl = H5Fget_access_plist(fid); + +/* Retrieve the # of read attempts from the file's file access property list */ +H5Pget_metadata_read_attempts(file_fapl, &attempts); + +/* + * The value returned in "attempts" will be 20. + */ + +/* Close the property lists */ +H5Pclose(file_fapl); +H5Pclose(fapl); + +/* Close the file */ +H5Fclose(fid); diff --git a/doxygen/examples/H5Pget_metadata_read_attempts.3.c b/doxygen/examples/H5Pget_metadata_read_attempts.3.c new file mode 100644 index 0000000..4b5ea3a --- /dev/null +++ b/doxygen/examples/H5Pget_metadata_read_attempts.3.c @@ -0,0 +1,44 @@ +/* Open the file with non-SWMR access and default file access property list */ +fid = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT); + +/* Get the file's file access roperty list */ +file_fapl = H5Fget_access_plist(fid); + +/* Retrieve the # of read attempts from the file's file access property list */ +H5Pget_metadata_read_attempts(file_fapl, &attempts); + +/* + * The value returned in "attempts" will be 1 (default for non-SWMR access). + */ + +/* Close the property list */ +H5Pclose(file_fapl); + +/* Close the file */ +H5Fclose(fid); + +/* Create a copy of file access property list */ +fapl = H5Pcreate(H5P_FILE_ACCESS); + +/* Set the # of read attempts */ +H5Pset_metadata_read_attempts(fapl, 20); + +/* Open the file with non-SWMR access and the non-default file access property list */ +fid = H5Fopen(FILE, H5F_ACC_RDONLY, fapl); + +/* Get the file's file access roperty list */ +file_fapl = H5Fget_access_plist(fid); + +/* Retrieve the # of read attempts from the file's file access property list */ +H5Pget_metadata_read_attempts(file_fapl, &attempts); + +/* + * The value returned in "attempts" will be 1 (default for non-SWMR access). + */ + +/* Close the property lists */ +H5Pclose(file_fapl); +H5Pclose(fapl); + +/* Close the file */ +H5Fclose(fid); diff --git a/doxygen/examples/H5Pget_object_flush_cb.c b/doxygen/examples/H5Pget_object_flush_cb.c new file mode 100644 index 0000000..d18f3df --- /dev/null +++ b/doxygen/examples/H5Pget_object_flush_cb.c @@ -0,0 +1,41 @@ +hid_t fapl_id; +unsigned counter; +H5F_object_flush_t *ret_cb; +unsigned * ret_counter; + +/* Create a copy of the file access property list */ +fapl_id = H5Pcreate(H5P_FILE_ACCESS); + +/* Set up the object flush property values */ +/* flush_cb: callback function to invoke when an object flushes (see below) */ +/* counter: user data to pass along to the callback function */ +H5Pset_object_flush_cb(fapl_id, flush_cb, &counter); + +/* Open the file */ +file_id = H5Fopen(FILE, H5F_ACC_RDWR, H5P_DEFAULT); + +/* Get the file access property list for the file */ +fapl = H5Fget_access_plist(file_id); + +/* Retrieve the object flush property values for the file */ +H5Pget_object_flush_cb(fapl, &ret_cb, &ret_counter); +/* ret_cb will point to flush_cb() */ +/* ret_counter will point to counter */ + +/* +. +. +. +. +. +. +*/ + +/* The callback function for the object flush property */ +static herr_t +flush_cb(hid_t obj_id, void *_udata) +{ + unsigned *flush_ct = (unsigned *)_udata; + ++(*flush_ct); + return 0; +} diff --git a/doxygen/examples/H5Pset_metadata_read_attempts.c b/doxygen/examples/H5Pset_metadata_read_attempts.c new file mode 100644 index 0000000..7c2f65d --- /dev/null +++ b/doxygen/examples/H5Pset_metadata_read_attempts.c @@ -0,0 +1,59 @@ +//! [SWMR Access] +/* Create a copy of file access property list */ +fapl = H5Pcreate(H5P_FILE_ACCESS); + +/* Set the # of read attempts */ +H5Pset_metadata_read_attempts(fapl, 20); + +/* Open the file with SWMR access and the non-default file access property list */ +fid = H5Fopen(FILE, (H5F_ACC_RDONLY | H5F_ACC_SWMR_READ), fapl); + +/* Get the file's file access roperty list */ +file_fapl = H5Fget_access_plist(fid); + +/* Retrieve the # of read attempts from the file's file access property list */ +H5Pget_metadata_read_attempts(file_fapl, &attempts); + +/* + * The value returned in "attempts" will be 20. + * The library will use 20 as the number of read attempts + * when reading checksummed metadata in the file + */ + +/* Close the property list */ +H5Pclose(fapl); +H5Pclose(file_fapl); + +/* Close the file */ +H5Fclose(fid); +//! [SWMR Access] + +//! [non-SWMR Access] +/* Create a copy of file access property list */ +fapl = H5Pcreate(H5P_FILE_ACCESS); + +/* Set the # of read attempts */ +H5Pset_metadata_read_attempts(fapl, 20); + +/* Open the file with SWMR access and the non-default file access property list */ +fid = H5Fopen(FILE, H5F_ACC_RDONLY, fapl); + +/* Get the file's file access roperty list */ +file_fapl = H5Fget_access_plist(fid); + +/* Retrieve the # of read attempts from the file's file access property list */ +H5Pget_metadata_read_attempts(file_fapl, &attempts); + +/* + * The value returned in "attempts" will be 1 (default for non-SWMR access). + * The library will use 1 as the number of read attempts + * when reading checksummed metadata in the file + */ + +/* Close the property lists */ +H5Pclose(fapl); +H5Pclose(file_fapl); + +/* Close the file */ +H5Fclose(fid); +//! [non-SWMR Access] diff --git a/doxygen/examples/H5Pset_object_flush_cb.c b/doxygen/examples/H5Pset_object_flush_cb.c new file mode 100644 index 0000000..1dfa90d --- /dev/null +++ b/doxygen/examples/H5Pset_object_flush_cb.c @@ -0,0 +1,41 @@ +hid_t file_id, fapl_id; +hid_t dataset_id, dapl_id; +unsigned counter; + +/* Create a copy of the file access property list */ +fapl_id = H5Pcreate(H5P_FILE_ACCESS); + +/* Set up the object flush property values */ +/* flush_cb: callback function to invoke when an object flushes (see below) */ +/* counter: user data to pass along to the callback function */ +H5Pset_object_flush_cb(fapl_id, flush_cb, &counter); + +/* Open the file */ +file_id = H5Fopen(FILE, H5F_ACC_RDWR, H5P_DEFAULT); + +/* Create a group */ +gid = H5Gcreate2(fid, “group”, H5P_DEFAULT, H5P_DEFAULT_H5P_DEFAULT); + +/* Open a dataset */ +dataset_id = H5Dopen2(file_id, DATASET, H5P_DEFAULT); + +/* The flush will invoke flush_cb() with counter */ +H5Dflush(dataset_id); +/* counter will be equal to 1 */ + +/* ... */ + +/* The flush will invoke flush_cb() with counter */ +H5Gflush(gid); +/* counter will be equal to 2 */ + +/* ... */ + +/* The callback function for object flush property */ +static herr_t +flush_cb(hid_t obj_id, void *_udata) +{ + unsigned *flush_ct = (unsigned *)_udata; + ++(*flush_ct); + return 0; +} diff --git a/doxygen/examples/ImageSpec.html b/doxygen/examples/ImageSpec.html new file mode 100644 index 0000000..1b700ff --- /dev/null +++ b/doxygen/examples/ImageSpec.html @@ -0,0 +1,1203 @@ +<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> +<html> +<head> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> + <meta name="GENERATOR" content="Mozilla/4.72 [en] (WinNT; U) [Netscape]"> + <title>Image Specification</title> + +The HDF5 specification defines the standard objects and storage for the +standard HDF5 objects. (For information about the HDF5 library, model and +specification, see the HDF documentation.) This document is an additional +specification do define a standard profile for how to store image data +in HDF5. Image data in HDF5 is stored as HDF5 datasets with standard attributes +to define the properties of the image. +<p>This specification is primarily concerned with two dimensional raster +data similar to HDF4 Raster Images. Specifications for storing other +types of imagery will be covered in other documents. +<p>This specification defines: +<ul> +<li> +Standard storage and attributes for an Image dataset (<a href="#Sect1">Section +1</a>)</li> + +<li> +Standard storage and attributes for Palettes (<a href="#sect2">Section +2</a>)</li> + +<li> +Standard for associating Palettes with Images. (<a href="#Sect3">Section +3</a>)</li> +</ul> + +<h2> +<a NAME="Sect1"></a>1. HDF5 Image Specification</h2> + +<h3> +1.1 Overview</h3> +Image data is stored as an HDF5 dataset with values of HDF5 class Integer +or Float. A common example would be a two dimensional dataset, with +elements of class Integer, e.g., a two dimensional array of unsigned 8 +bit integers. However, this specification does not limit the dimensions +or number type that may be used for an Image. +<p>The dataset for an image is distinguished from other datasets by giving +it an attribute "CLASS=IMAGE". In addition, the Image dataset may +have an optional attribute "PALETTE" that is an array of object references +for zero or more palettes. The Image dataset may have additional attributes +to describe the image data, as defined in <a href="#Sect1.2">Section 1.2</a>. +<p>A Palette is an HDF5 dataset which contains color map information. +A Pallet dataset has an attribute "CLASS=PALETTE" and other attributes +indicating the type and size of the palette, as defined in <a href="#sect2">Section +2.1</a>. A Palette is an independent object, which can be shared +among several Image datasets. +<h3> +<a NAME="Sect1.2"></a>1.2 Image Attributes</h3> +The attributes for the Image are scalars unless otherwise noted. +The length of String valued attributes should be at least the number of +characters. Optionally, String valued attributes may be stored in a String +longer than the minimum, in which case it must be zero terminated or null +padded. "Required" attributes must always be used. "Optional" attributes +must be used when required. +<br> +<h4> +Attributes</h4> + +<dl> +<dt> +Attribute name="<b>CLASS</b>" (Required)</dt> + +<dd> +This attribute is type H5T_C_S1, with size 5.</dd> + +<dd> +For all Images, the value of this attribute is "IMAGE".</dd> + +<dd> +</dd> + +<dd> +This attribute identifies this data set as intended to be interpreted as +an image that conforms to the specifications on this page.</dd> +</dl> + +<dt> +Attribute name="<b>PALETTE</b>"</dt> + +<dl> +<dd> +A Image dataset within an HDF5 file may optionally specify an array of +palettes to be viewed with. The dataset will have an attribute field called +"<b>PALETTE</b>" which contains a one-dimensional array of object reference +pointers (HDF5 datatype H5T_STD_REF_OBJ) which refer to palettes in the +file. The palette datasets must conform to the Palette specification in +<a href="#sect2">section +2 below</a>. The first palette in this array will be the default palette +that the data may be viewed with.</dd> +</dl> + +<dl> +<dt> +</dt> + +<dt> +Attribute name="<b>IMAGE_SUBCLASS</b>"</dt> + +<dd> +If present, the value of this attribute indicates the type of Palette that +should be used with the Image. This attribute is a scalar of type +H5T_C_S1, with size according to the string plus one. The values +are:</dd> + +<dl> +<dt> +"IMAGE_GRAYSCALE" (length 15)</dt> + +<dd> +A grayscale image</dd> + +<dt> +"IMAGE_BITMAP" (length 12)</dt> + +<dd> +A bit map image</dd> + +<dt> +"IMAGE_TRUECOLOR" (length 15)</dt> + +<dd> +A truecolor image</dd> + +<dt> +"IMAGE_INDEXED" (length 13)</dt> + +<dd> +An indexed image</dd> + +<dd> +</dd> +</dl> + +<dt> +Attribute name="<b>INTERLACE_MODE</b>"</dt> + +<dd> +For images with more than one component for each pixel, this optional attribute +specifies the layout of the data. The values are type H5T_C_S1 of length +15. See <a href="#Section1.3">section 1.3</a> for information about the +storage layout for data.</dd> + +<dd> +"INTERLACE_PIXEL" (default): the component value for a pixel are contiguous.</dd> + +<dd> +"INTERLACE_PLANE": each component is stored as a plane.</dd> + +<dt> +</dt> + +<dt> +Attribute name="<b>DISPLAY_ORIGIN</b>"</dt> + +<dd> +This optional attribute indicates the intended orientation of the data +on a two-dimensional raster display. The value indicates which corner +the pixel at (0, 0) should be viewed. The values are type H5T_C_S1 +of length 2. If DISPLAY_ORIGIN is not set, the orientation is undefined.</dd> + +<dd> +"UL": (0,0) is at the upper left.</dd> + +<dd> +"LL": (0,0) is at the lower left.</dd> + +<dd> +"UR": (0,0) is at the upper right.</dd> + +<dd> +"LR": (0,0) is at the lower right.</dd> +</dl> + +<dt> +Attribute name="<b>IMAGE_WHITE_IS_ZERO</b>"</dt> + +<dl> +<dd> +This attribute is of type H5T_NATIVE_UCHAR. 0 = false, 1 = true . +This is used for images with IMAGE_SUBCLASS="IMAGE_GRAYSCALE" or "IMAGE_BITMAP".</dd> +</dl> + +<dl> +<dt> +Attribute name="<b>IMAGE_MINMAXRANGE</b>"</dt> + +<dd> +If present, this attribute is an array of two numbers, of the same HDF5 +datatype as the data. The first element is the minimum value of the +data, and the second is the maximum. This is used for images with +IMAGE_SUBCLASS="IMAGE_GRAYSCALE", "IMAGE_BITMAP" or "IMAGE_INDEXED".</dd> +</dl> + +<dt> +Attribute name="<b>IMAGE_BACKGROUNDINDEX</b>"</dt> + +<dl> +<dd> +If set, this attribute indicates the index value that should be interpreted +as the "background color". This attribute is HDF5 type H5T_NATIVE_UINT.</dd> +</dl> + +<dt> +Attribute name="<b>IMAGE_TRANSPARENCY</b>"</dt> + +<dl> +<dd> +If set, this attribute indicates the index value that should be interpreted +as the "transparent color". This attribute is HDF5 type H5T_NATIVE_UINT. +This attribute may not be used for IMAGE_SUBCLASS="IMAGE_TRUE_COLOR".</dd> +</dl> + +<dt> +Attribute name="<b>IMAGE_ASPECTRATIO</b>"</dt> + +<dl> +<dd> +If set, this attribute indicates the aspect ratio.</dd> +</dl> + +<dt> +Attribute name="<b>IMAGE_COLORMODEL</b>"</dt> + +<dl> +<dd> +If set, this attribute indicates the color model of Palette that should +be used with the Image. This attribute is of type H5T_C_S1, with +size 3, 4, or 5. The value is one of the color models described in +the Palette specification in <a href="#sect2.2">section 2.2 below</a>. +This attribute may be used only for IMAGE_SUBCLASS="IMAGE_TRUECOLOR" or +"IMAGE_INDEXED".</dd> +</dl> + +<dt> +Attribute name="<b>IMAGE_GAMMACORRECTION</b>"</dt> + +<dl> +<dd> +If set, this attribute gives the Gamma correction. The attribute +is type H5T_NATIVE_FLOAT. This attribute may be used only for IMAGE_SUBCLASS="IMAGE_TRUECOLOR" +or "IMAGE_INDEXED".</dd> +</dl> +Attribute name="<b>IMAGE_VERSION</b>" (Required) +<dl> +<dd> +This attribute is of type H5T_C_S1, with size corresponding to the length +of the version string. This attribute identifies the version number +of this specification to which it conforms. The current version number +is "1.2".</dd> + +<br> +<p> +<br> +<br> +<center><table BORDER=2 BGCOLOR="#FFFFFF" > +<caption><b>Table 1. Attributes of an Image Dataset</b></caption> + +<tr> +<td><b>Attribute Name</b></td> + +<td><b>(R = Required</b> +<br><b>O= Optional)</b></td> + +<td><b>Type</b></td> + +<td><b>String Size</b></td> + +<td><b>Value</b></td> +</tr> + +<tr> +<td>CLASS</td> + +<td>R</td> + +<td>String</td> + +<td>5</td> + +<td>"IMAGE"</td> +</tr> + +<tr> +<td>PALETTE</td> + +<td>O</td> + +<td>Array Object References</td> + +<td></td> + +<td><references to Palette datasets><sup>1</sup></td> +</tr> + +<tr> +<td>IMAGE_SUBCLASS</td> + +<td>O<sup>2</sup></td> + +<td>String</td> + +<td>15, +<br>12, +<br>15, +<br>13</td> + +<td> +<dt> +"IMAGE_GRAYSCALE",</dt> + +<dt> +"IMAGE_BITMAP",</dt> + +<dt> +"IMAGE_TRUECOLOR",</dt> + +<dt> +"IMAGE_INDEXED"</dt> +</td> +</tr> + +<tr> +<td>INTERLACE_MODE</td> + +<td>O<sup>3,6</sup></td> + +<td>String</td> + +<td>15</td> + +<td>The layout of components if more than one component per pixel.</td> +</tr> + +<tr> +<td>DISPLAY_ORIGIN</td> + +<td>O</td> + +<td>String</td> + +<td>2</td> + +<td>If set, indicates the intended location of the pixel (0,0).</td> +</tr> + +<tr> +<td>IMAGE_WHITE_IS_ZERO</td> + +<td>O<sup>3,4</sup></td> + +<td>Unsigned Integer</td> + +<td></td> + +<td>0 = false, 1 = true</td> +</tr> + +<tr> +<td>IMAGE_MINMAXRANGE</td> + +<td>O<sup>3,5</sup></td> + +<td>Array [2] <same datatype as data values></td> + +<td></td> + +<td>The (<minimum>, <maximum>) value of the data.</td> +</tr> + +<tr> +<td>IMAGE_BACKGROUNDINDEX</td> + +<td>O<sup>3</sup></td> + +<td>Unsigned Integer</td> + +<td></td> + +<td>The index of the background color.</td> +</tr> + +<tr> +<td>IMAGE_TRANSPARENCY</td> + +<td>O<sup>3,5</sup></td> + +<td>Unsigned Integer</td> + +<td></td> + +<td>The index of the transparent color.</td> +</tr> + +<tr> +<td>IMAGE_ASPECTRATIO</td> + +<td>O<sup>3,4</sup></td> + +<td>Unsigned Integer</td> + +<td></td> + +<td>The aspect ratio.</td> +</tr> + +<tr> +<td>IMAGE_COLORMODEL</td> + +<td>O<sup>3,6</sup></td> + +<td>String</td> + +<td>3, 4, or 5</td> + +<td>The color model, as defined below in the Palette specification for +attribute <b>PAL_COLORMODEL</b>.</td> +</tr> + +<tr> +<td>IMAGE_GAMMACORRECTION</td> + +<td>O<sup>3,6</sup></td> + +<td>Float</td> + +<td></td> + +<td>The gamma correction.</td> +</tr> + +<tr> +<td>IMAGE_VERSION</td> + +<td>R</td> + +<td>String</td> + +<td>3</td> + +<td>"1.2"</td> +</tr> +</table></center> + +<dl><font size=-1>1. The first element of the array is the default +Palette.</font> +<br><font size=-1>2. This attribute is <b>required</b> for images +that use one of the standard color map types listed.</font> +<br><font size=-1>3. This attribute is <b>required</b> if set for the source +image, in the case that the image is translated from another file into +HDF5.</font> +<br><font size=-1>4. This applies to: IMAGE_SUBCLASS="IMAGE_GRAYSCALE" +or "IMAGE_BITMAP".</font> +<br><font size=-1>5. This applies to: IMAGE_SUBCLASS="IMAGE_GRAYSCALE", +"IMAGE_BITMAP", or "IMAGE_INDEXED".</font> +<br><font size=-1>6. This applies to: IMAGE_SUBCLASS="IMAGE_TRUECOLOR", +or "IMAGE_INDEXED".</font></dl> +</dl> +Table 2 summarizes the standard attributes for an Image datasets using +the common sub-classes. R means that the attribute listed on the leftmost +column is Required for the image subclass on the first row, O means that +the attribute is Optional for that subclass and N that the attribute cannot +be applied to that subclass. The two first rows show the only required +attributes +for all subclasses. +<br> +<table BORDER WIDTH="100%" > +<caption><b>Table 2a. Applicability of Attributes to IMAGE sub-classes</b></caption> + +<tr> +<td WIDTH="20%"><b>IMAGE_SUBCLASS</b><sup>1</sup></td> + +<td WIDTH="20%"><b>IMAGE_GRAYSCALE</b></td> + +<td WIDTH="20%"><b>IMAGE_BITMAP</b></td> +</tr> + +<tr> +<td WIDTH="20%">CLASS</td> + +<td WIDTH="20%">R</td> + +<td WIDTH="20%">R</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_VERSION</td> + +<td WIDTH="20%">R</td> + +<td WIDTH="20%">R</td> +</tr> + +<tr> +<td>INTERLACE_MODE</td> + +<td>N</td> + +<td>N</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_WHITE_IS_ZERO</td> + +<td WIDTH="20%">R</td> + +<td WIDTH="20%">R</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_MINMAXRANGE</td> + +<td WIDTH="20%">O</td> + +<td WIDTH="20%">O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_BACKGROUNDINDEX</td> + +<td WIDTH="20%">O</td> + +<td WIDTH="20%">O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_TRANSPARENCY</td> + +<td WIDTH="20%">O</td> + +<td WIDTH="20%">O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_ASPECTRATIO</td> + +<td WIDTH="20%">O</td> + +<td WIDTH="20%">O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_COLORMODEL</td> + +<td WIDTH="20%">N</td> + +<td WIDTH="20%">N</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_GAMMACORRECTION</td> + +<td WIDTH="20%">N</td> + +<td WIDTH="20%">N</td> +</tr> + +<tr> +<td WIDTH="20%">PALETTE</td> + +<td WIDTH="20%">O</td> + +<td WIDTH="20%">O</td> +</tr> + +<tr> +<td>DISPLAY_ORIGIN</td> + +<td>O</td> + +<td>O</td> +</tr> +</table> + +<blockquote> </blockquote> + +<table BORDER WIDTH="100%" > +<caption><b>Table 2b. Applicability of Attributes to IMAGE sub-classes</b></caption> + +<tr> +<td WIDTH="20%"><b>IMAGE_SUBCLASS</b></td> + +<td WIDTH="20%"><b>IMAGE_TRUECOLOR</b></td> + +<td><b>IMAGE_INDEXED</b></td> +</tr> + +<tr> +<td WIDTH="20%">CLASS</td> + +<td WIDTH="20%">R</td> + +<td>R</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_VERSION</td> + +<td WIDTH="20%">R</td> + +<td>R</td> +</tr> + +<tr> +<td>INTERLACE_MODE</td> + +<td>R</td> + +<td>N</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_WHITE_IS_ZERO</td> + +<td WIDTH="20%">N</td> + +<td>N</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_MINMAXRANGE</td> + +<td WIDTH="20%">N</td> + +<td>O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_BACKGROUNDINDEX</td> + +<td WIDTH="20%">N</td> + +<td>O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_TRANSPARENCY</td> + +<td WIDTH="20%">N</td> + +<td>O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_ASPECTRATIO</td> + +<td WIDTH="20%">O</td> + +<td>O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_COLORMODEL</td> + +<td WIDTH="20%">O</td> + +<td>O</td> +</tr> + +<tr> +<td WIDTH="20%">IMAGE_GAMMACORRECTION</td> + +<td WIDTH="20%">O</td> + +<td>O</td> +</tr> + +<tr> +<td WIDTH="20%">PALETTE</td> + +<td WIDTH="20%">O</td> + +<td>O</td> +</tr> + +<tr> +<td>DISPLAY_ORIGIN</td> + +<td>O</td> + +<td>O</td> +</tr> +</table> + +<h3> +<a NAME="Section1.3"></a>1.3 Storage Layout and Properties for Images</h3> +In the case of an image with more than one component per pixel (e.g., Red, +Green, and Blue), the data may be arranged in one of two ways. Following +HDF4 terminology, the data may be interlaced by pixel or by plane, which +should be indicated by the INTERLACE_MODE attribute. In both +cases, the dataset will have a dataspace with three dimensions, height, +width, and components. The interlace modes specify different orders +for the dimensions. +<br> +<table BORDER COLS=2 WIDTH="100%" > +<caption><b>Table 3. Storage of multiple component image data.</b></caption> + +<tr> +<td><b>Interlace Mode</b></td> + +<td><b>Dimensions in the Dataspace</b></td> +</tr> + +<tr> +<td>INTERLACE_PIXEL</td> + +<td>[height][width][pixel components]</td> +</tr> + +<tr> +<td>INTERLACE_PLANE</td> + +<td>[pixel components][height][width]</td> +</tr> +</table> + +<p>For example, consider a 5 (rows) by 10 (column) image, with Red, Green, +and Blue components. Each component is an unsigned byte. In HDF5, +the datatype would be declared as an unsigned 8 bit integer. For +pixel interlace, the dataspace would be a three dimensional array, with +dimensions: [10][5][3]. For plane interleave, the dataspace would +be three dimensions: [3][10][5]. +<p>In the case of images with only one component, the dataspace may be +either a two dimensional array, or a three dimensional array with the third +dimension of size 1. For example, a 5 by 10 image with 8 bit color +indexes would be an HDF5 dataset with type unsigned 8 bit integer. +The dataspace could be either a two dimensional array, with dimensions +[10][5], or three dimensions, with dimensions either [10][5][1] or [1][10][5]. +<p>Image datasets may be stored with any chunking or compression properties +supported by HDF5. +<p><b>A note concerning compatibility with HDF5 GR interface: </b>An Image +dataset is stored as an HDF5 dataset. It is important to note that +the order of the dimensions is the same as for any other HDF5 dataset. +For a two dimensional image that is to be stored as a series of horizontal +scan lines, with the scan lines contiguous (i.e., the fastest changing +dimension is 'width'), the image will have a dataspace with <i>dim[0] = +height</i> and <i>dim[1]</i> = <i>width</i>. This is completely consistent +with all other HDF5 datasets. +<p>Users familiar with HDF4 should be cautioned that <i>this is not the +same as HDF4</i>, and specifically is not consistent with what the HDF4 +GR interface does. +<br> +<h2> +<a NAME="sect2"></a>2. HDF5 Palette Specification</h2> + +<h3> +2.1 Overview</h3> +A palette is the means by which color is applied to an image and is also +referred to as a color lookup table. It is a table in which every row contains +the numerical representation of a particular color. In the example of an +8 bit standard RGB color model palette, this numerical representation of +a color is presented as a triplet specifying the intensity of red, green, +and blue components that make up each color. +<center> +<p><img SRC="Palettes.fm.anc.gif" ></center> + +<p>In this example, the color component numeric type is an 8 bit unsigned +integer. While this is most common and recommended for general use, other +component color numeric datatypes, such as a 16 bit unsigned integer , +may be used. This type is specified as the type attribute of the palette +dataset. (see H5Tget_type(), H5Tset_type()) +<p>The minimum and maximum values of the component color numeric are specified +as attribute of the palette dataset. See below (attribute PAL_MINMAXNUMERIC). +If these attributes do not exist, it is assumed that the range of values +will fill the space of the color numeric type. i.e. with an 8 bit unsigned +integer, the valid range would be 0 to 255 for each color component. +<p>The HDF5 palette specification additionally allows for color models +beyond RGB. YUV, HSV, CMY, CMYK, YCbCr color models are supported, and +may be specified as a color model attribute of the palette dataset. <i>(see +"Palette Attributes" for details)</i>. +<p>In HDF 4 and earlier, palettes were limited to 256 colors. The HDF5 +palette specification allows for palettes of varying length. The length +is specified as the number of rows of the palette dataset. +<br> +<br> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#666666" > +<tr> +<td><font color="#FFFFFF">Important Note: The specification of the Indexed +Palette will change substantially in the next version. The Palette +described here is <i>denigrated</i> and is not supported.</font></td> +</tr> +</table> + +<br> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td><i>Denigrated</i> +<p>In a standard palette, the color entries are indexed directly. HDF5 +supports the notion of a range index table. Such a table defines an ascending +ordered list of ranges that map dataset values to the palette. If a range +index table exists for the palette, the PAL_TYPE attribute will be set +to "RANGEINDEX", and the PAL_RANGEINDEX attribute will contain an object +reference to a range index table array. If not, the PAL_TYPE attribute +either does not exist, or will be set to "STANDARD". +<p>The range index table array consists of a one dimensional array with +the same length as the palette dataset - 1. Ideally, the range index would +be of the same type as the dataset it refers to, however this is not a +requirement. +<p><b>Example 2: A range index array of type floating point</b> +<center> +<p><img SRC="PaletteExample1.gif" ></center> + +<p>The range index array attribute defines the "<i>to</i>" of the range. +Notice that the range index array attribute is one less entry in size than +the palette. The first entry of 0.1259, specifies that all values below +and up to 0.1259 inclusive, will map to the first palette entry. The second +entry signifies that all values greater than 0.1259 up to 0.3278 inclusive, +will map to the second palette entry, etc. All value greater than the last +range index array attribute (100000) map to the last entry in the palette.</td> +</tr> +</table> + +<h3> +<a NAME="sect2.2"></a>2.2. Palette Attributes</h3> +A palette exists in an HDF file as an independent data set with accompanying +attributes. The Palette attributes are scalars except where noted +otherwise. String values should have size the length of the string +value plus one. "Required" attributes must be used. "Optional" +attributes must be used when required. +<p>These attributes are defined as follows: +<dl> +<dt> +Attribute name="<b>CLASS</b>" (Required)</dt> + +<dd> +This attribute is of type H5T_C_S1, with size 7.</dd> + +<dd> +For all palettes, the value of this attribute is "PALETTE". This attribute +identifies this palette data set as a palette that conforms to the specifications +on this page.</dd> + +<dt> +Attribute name="<b>PAL_COLORMODEL</b>" (Required)</dt> + +<dd> +This attribute is of type H5T_C_S1, with size 3, 4, or 5.</dd> + +<dd> +Possible values for this are "RGB", "YUV", "CMY", "CMYK", "YCbCr", "HSV".</dd> + +<dd> +This defines the color model that the entries in the palette data set represent.</dd> + +<dl> +<dt> +"RGB"</dt> + +<dd> +Each color index contains a triplet where the the first value defines the +red component, second defines the green component, and the third the blue +component.</dd> + +<dt> +"CMY"</dt> + +<dd> +Each color index contains a triplet where the the first value defines the +cyan component, second defines the magenta component, and the third the +yellow component.</dd> + +<dt> +"CMYK"</dt> + +<dd> +Each color index contains a quadruplet where the the first value defines +the cyan component, second defines the magenta component, the third the +yellow component, and the forth the black component.</dd> + +<dt> +"YCbCr"</dt> + +<dd> +Class Y encoding model. Each color index contains a triplet where the the +first value defines the luminance, second defines the Cb Chromonance, and +the third the Cr Chromonance.</dd> + +<dt> +"YUV"</dt> + +<dd> +Composite encoding color model. Each color index contains a triplet where +the the first value defines the luminance component, second defines the +chromonance component, and the third the value component.</dd> + +<dt> +"HSV"</dt> + +<dd> +Each color index contains a triplet where the the first value defines the +hue component, second defines the saturation component, and the third the +value component. The hue component defines the hue spectrum with a low +value representing magenta/red progressing to a high value which would +represent blue/magenta, passing through yellow, green, cyan. A low value +for the saturation component means less color saturation than a high value. +A low value for <i>value</i> will be darker than a high value.</dd> + +<dd> +</dd> +</dl> + +<dt> +Attribute name="<b>PAL_TYPE</b>" (Required)</dt> + +<dd> +This attribute is of type H5T_C_S1, with size 9 or 10.</dd> + +<dd> +The current supported values for this attribute are : "STANDARD8" or "RANGEINDEX"</dd> + +<dd> +A PAL_TYPE of "STANDARD8" defines a palette dataset such that the first +entry defines index 0, the second entry defines index 1, etc. up until +the length of the palette - 1. This assumes an image dataset with direct +indexes into the palette.</dd> +</dl> + +<dl> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td><i>Denigrated</i> +<p>If the PAL_TYPE is set to "RANGEINDEX", there will be an additional +attribute with a name of "<b>PAL_RANGEINDEX</b>", (See example 2 +for more details)</td> +</tr> +</table> + +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td> +<dt> +Attribute name="<b>PAL_RANGEINDEX</b>" <i>(Denigrated)</i></dt> + +<dl> +<dd> +The <b>PAL_RANGEINDEX</b> attribute contains an HDF object reference (HDF5 +datatype H5T_STD_REF_OBJ) pointer which specifies a range index array in +the file to be used for color lookups for the palette. (Only for +PAL_TYPE="RANGEINDEX")</dd> +</dl> +</td> +</tr> +</table> + +<dt> +Attribute name="<b>PAL_MINMAXNUMERIC</b>"</dt> + +<dl> +<dt> +If present, this attribute is an array of two numbers, of the same HDF5 +datatype as the palette elements or color numerics.</dt> + +<br>They specify the minimum and maximum values of the color numeric components. +For example, if the palette was an RGB of type Float, the color numeric +range for Red, Green, and Blue could be set to be between 0.0 and 1.0. +The intensity of the color guns would then be scaled accordingly to be +between this minimum and maximum attribute.</dl> +Attribute name="<b>PAL_VERSION</b>" (Required) +<dl>This attribute is of type H5T_C_S1, with size corresponding to the +length of the version string. This attribute identifies the version +number of this specification to which it conforms. The current version +is "1.2".</dl> + +<center><table BORDER=2 BGCOLOR="#FFFFFF" > +<caption><b>Table 4. Attributes of a Palette Dataset</b></caption> + +<tr> +<td><b>Attribute Name</b></td> + +<td><b>(R = Required,</b> +<br><b>O = Optional)</b></td> + +<td><b>Type</b></td> + +<td><b>String Size</b></td> + +<td><b>Value</b></td> +</tr> + +<tr> +<td>CLASS</td> + +<td>R</td> + +<td>String</td> + +<td> +<center>7</center> +</td> + +<td>"PALETTE"</td> +</tr> + +<tr> +<td>PAL_COLORMODEL</td> + +<td>R</td> + +<td>String</td> + +<td> +<center>3, 4, or 5</center> +</td> + +<td>Color Model: "RGB", YUV", "CMY", "CMYK", "YCbCr", or "HSV"</td> +</tr> + +<tr> +<td>PAL_TYPE</td> + +<td>R</td> + +<td>String</td> + +<td> +<center>9</center> + +<p><br> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td>or 10</td> +</tr> +</table> +</td> + +<td>"STANDARD8" +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td>or "RANGEINDEX" <i>(Denigrated)</i></td> +</tr> +</table> +</td> +</tr> + +<tr> +<td> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td><i>Denigrated</i> +<br>RANGE_INDEX</td> +</tr> +</table> +</td> + +<td></td> + +<td> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td>Object Reference </td> +</tr> +</table> +</td> + +<td></td> + +<td> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td><Object Reference to Dataset of range index values></td> +</tr> +</table> +</td> +</tr> + +<tr> +<td>PAL_MINMAXNUMERIC</td> + +<td>O</td> + +<td>Array[2] of <same datatype as palette></td> + +<td></td> + +<td>The first value is the <Minimum value for color values>, the second +value is <Maximum value for color values><sup>2</sup></td> +</tr> + +<tr> +<td>PAL_VERSION</td> + +<td>R</td> + +<td>String</td> + +<td>4</td> + +<td>"1.2"</td> +</tr> +</table></center> + +<dl> +<table BORDER COLS=1 WIDTH="100%" BGCOLOR="#CCCCCC" > +<tr> +<td><font size=-1>1. The RANGE_INDEX attribute is required if the +PAL_TYPE is "RANGEINDEX". Otherwise, the RANGE_INDEX attribute should +be omitted. (Range index is denigrated.)</font></td> +</tr> +</table> +<font size=-1>2. The minimum and maximum are optional. If not +set, the range is assumed to the maximum range of the number type. +If one of these attributes is set, then both should be set. The value +of the minimum must be less than or equal to the value of the maximum.</font></dl> +</dl> +Table 5 summarized the uses of the standard attributes for a palette dataset. +R means that the attribute listed on the leftmost column is Required for +the palette type on the first row, O means that the attribute is Optional +for that type and N that the attribute cannot be applied to that type. +The four first rows show the attributes that are always required +for the two palette types. +<br> +<br> +<table BORDER WIDTH="100%" > +<caption><b>Table 5. Applicability of Attributes</b></caption> + +<tr> +<td WIDTH="33%"><b>PAL_TYPE</b></td> + +<td WIDTH="33%"><b>STANDARD8</b></td> + +<td WIDTH="34%"><b>RANGEINDEX</b></td> +</tr> + +<tr> +<td WIDTH="33%">CLASS</td> + +<td WIDTH="33%">R</td> + +<td WIDTH="34%">R</td> +</tr> + +<tr> +<td WIDTH="33%">PAL_VERSION</td> + +<td WIDTH="33%">R</td> + +<td WIDTH="34%">R</td> +</tr> + +<tr> +<td WIDTH="33%">PAL_COLORMODEL</td> + +<td WIDTH="33%">R</td> + +<td WIDTH="34%">R</td> +</tr> + +<tr> +<td WIDTH="33%">RANGE_INDEX</td> + +<td WIDTH="33%">N</td> + +<td WIDTH="34%">R</td> +</tr> + +<tr> +<td WIDTH="33%">PAL_MINMAXNUMERIC</td> + +<td WIDTH="33%">O</td> + +<td WIDTH="34%">O</td> +</tr> +</table> + +<h3> +2.3. Storage Layout for Palettes</h3> +The values of the Palette are stored as a dataset. The datatype can +be any HDF 5 atomic numeric type. The dataset will have dimensions +(<tt>nentries</tt> by <tt>ncomponents</tt>), where '<tt>nentries</tt>' +is the number of colors (usually 256) and '<tt>ncomponents'</tt> is the +number of values per color (3 for <b>RGB</b>, 4 for <b>CMYK</b>, etc.) +<br> +<h2> +<a NAME="Sect3"></a>3. Consistency and Correlation of Image and Palette +Attributes</h2> +The objects in this specification are an extension to the base HDF5 specification +and library. They are accessible with the standard HDF5 library, +but the semantics of the objects are not enforced by the base library. +For example, it is perfectly possible to add an attribute called <b>IMAGE</b> +to <i>any</i> dataset, or to include an object reference to <i>any</i> +HDF5 dataset in a <b>PALETTE</b> attribute. This would be a valid +HDF5 file, but not conformant to this specification. The rules defined +in this specification must be implemented with appropriate software, and +applications must use conforming software to assure correctness. +<p>The Image and Palette specifications include several redundant standard +attributes, such as the <b>IMAGE_COLORMODEL</b> and the <b>PAL_COLORMODEL</b>. +These attributes are informative not normative, in that it is acceptable +to attach a Palette to an Image dataset even if their attributes do not +match. Software is not required to enforce consistency, and files +may contain mismatched associations of Images and Palettes. In all +cases, it is up to applications to determine what kinds of images and color +models can be supported. +<p>For example, an Image that was created from a file with an "RGB" may +have a "YUV" Palette in its <b>PALETTE</b> attribute array. This +would be a legal HDF5 file and also conforms to this specification, although +it may or may not be correct for a given application.</p> + +</body> +</html> diff --git a/doxygen/examples/PaletteExample1.gif b/doxygen/examples/PaletteExample1.gif Binary files differnew file mode 100644 index 0000000..8694d9d --- /dev/null +++ b/doxygen/examples/PaletteExample1.gif diff --git a/doxygen/examples/Palettes.fm.anc.gif b/doxygen/examples/Palettes.fm.anc.gif Binary files differnew file mode 100644 index 0000000..d344c03 --- /dev/null +++ b/doxygen/examples/Palettes.fm.anc.gif diff --git a/doxygen/examples/TableSpec.html b/doxygen/examples/TableSpec.html new file mode 100644 index 0000000..474176e --- /dev/null +++ b/doxygen/examples/TableSpec.html @@ -0,0 +1,193 @@ +<html> +<head> + <title>HDF5 Table Specification</title> +</head> + +The HDF5 specification defines the standard objects and storage for the +standard HDF5 objects. (For information about the HDF5 library, model and +specification, see the HDF documentation.) This document is an additional +specification do define a standard profile for how to store tables in HDF5. +Table data in HDF5 is stored as HDF5 datasets with standard attributes to define +the properties of the tables. + +<h2> +1. Overview</h2> +A generic table is a sequence of records, each record has a name and a type. +Table data is stored as an HDF5 one dimensional compound dataset. A table +is defined as a collection of records whose values are stored in fixed-length +fields. All records have the same structure and all values in each field have +the same data type. +<p>The dataset for a table is distinguished from other datasets by giving +it an attribute "CLASS=TABLE". +Optional attributes allow the storage of a title for the Table and for +each column, and a fill value for each column. +<h2> +2. Table Attributes</h2> +The attributes for the Table are strings. They are written with the <a href="RM_H5LT.html#H5LTset_attribute_string"><code>H5LTset_attribute_string</code></a> +Lite API function. "Required" attributes must always be used. "Optional" attributes +must be used when required. +<br> +<h4> +Attributes</h4> + +<dl> +<dt> +Attribute name="<b>CLASS</b>" (Required)</dt> + +<dd> +This attribute is type H5T_C_S1, with size 5.</dd> + +<dd> +For all Tables, the value of this attribute is "TABLE".</dd> + +<dd> +This attribute identifies this data set as intended to be interpreted as Table that conforms to the specifications on this page.</dd> +</dl> + +<dl> +Attribute name="<b>VERSION</b>" (Required) + +<dd> +This attribute is of type H5T_C_S1, with size corresponding to the length +of the version string. This attribute identifies the version number +of this specification to which it conforms. The current version number +is "0.2".</dd> + +</dl> + +<dl> +<dt> +Attribute name="<b>TITLE</b>" (Optional)</dt> + +<dd> +The <b>TITLE</b> is an optional String that is to be used as the +informative title of the whole table. +The <b>TITLE</b> is set with the parameter <code> table_title</code> of the function +<a href="RM_H5TB.html#H5TBmake_table"> <code> H5TBmake_table</code></a>. </dd> +</dl> + +<dl> +<dt> +Attribute name="<b>FIELD_(n)_NAME</b>" (Required)</dt> + +<dd> +The <b>FIELD_(n)_NAME</b> is an optional String that is to be used as the +informative title of column <b>n</b> of the table. +For each of the fields the word FIELD_ is concatenated with + the zero based field (n) index together with the name of the field.</dd> + +</dl> +<dl> +<dt> +Attribute name="<b>FIELD_(n)_FILL</b>" (Optional)</dt> + +<dd> +The <b>FIELD_(n)_FILL</b> is an optional String that is the fill value for +column <b>n</b> of the table. +For each of the fields the word FIELD_ is concatenated with + the zero based field (n) index together with the fill value, if present. +This value is written only when a fill value is defined for the table.</dd> + +</dl> + +<dl> + +<br> +<center><table BORDER=2 BGCOLOR="#FFFFFF" > +<caption><b>Table 1. Attributes of an Image Dataset</b></caption> + +<tr> +<td><b>Attribute Name</b></td> + +<td><b>(R = Required</b> +<br><b>O= Optional)</b></td> + +<td><b>Type</b></td> + +<td><b>String Size</b></td> + +<td><b>Value</b></td> +</tr> + +<tr> +<td>CLASS</td> + +<td>R</td> + +<td>String</td> + +<td>5</td> + +<td>"TABLE"</td> +</tr> + +<tr> +<td>VERSION</td> + +<td>R</td> + +<td>String</td> + +<td>3</td> + +<td>"0.2"</td> +</tr> + +<tr> +<td>TITLE</td> + +<td>O</td> + +<td>String</td> + +<td> </td> + +<td> + +<tr> +<td>FIELD_(n)_NAME</td> + +<td>R</td> + +<td>String</td> + +<td> </td> + +<td> + + +<tr> +<td>FIELD_(n)_FILL</td> + +<td>O*</td> + +<td>String</td> + +<td> </td> + +<td> + +</table> +</center> + + </dl> +<p> +<center> + +</center> +<i>* </i>The attribute FIELD_(n)_FILL is written to the table if a fill value is +specified on the creation of the Table. Otherwise, it is not.<p>The following +section of code shows the calls necessary to the creation of a table. + +<p><code>/* Create a new HDF5 file using default properties. */<br> + file_id = H5Fcreate( "my_table.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT );</code> </p> + +<p><code>/* Call the make table function */<br> +</code> <code>H5TBmake_table( "Table Title", file_id, "Table1", NFIELDS, NRECORDS, dst_size, <br> + field_names, dst_offset, field_type, <br> + chunk_size, fill_data, compress, p_data ) </code> </p> + +<p><code> /* Close the file. */<br> + status = H5Fclose( file_id );</code> </p> + +</body> diff --git a/doxygen/examples/ThreadSafeLibrary.html b/doxygen/examples/ThreadSafeLibrary.html new file mode 100644 index 0000000..8daf386 --- /dev/null +++ b/doxygen/examples/ThreadSafeLibrary.html @@ -0,0 +1,787 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" + "http://www.w3.org/TR/REC-html40/loose.dtd"> +<html lang="en-US"> +<head> + <title>Thread Safe Library</title> +</head> + +<h1>1. Library header files and conditional compilation</h1> + +<p> +The following code is placed at the beginning of H5private.h: +</p> + +<blockquote> + <pre> + #ifdef H5_HAVE_THREADSAFE + #include <pthread.h> + #endif + </pre> +</blockquote> + +<p> +<code>H5_HAVE_THREADSAFE</code> is defined when the HDF-5 library is +compiled with the --enable-threadsafe configuration option. In general, +code for the non-threadsafe version of HDF-5 library are placed within +the <code>#else</code> part of the conditional compilation. The exception +to this rule are the changes to the <code>FUNC_ENTER</code> (in +H5private.h), <code>HRETURN</code> and <code>HRETURN_ERROR</code> (in +H5Eprivate.h) macros (see section 3.2). +</p> + + +<h1>2. Global variables/structures</h1> + +<h2>2.1 Global library initialization variable</h2> + +<p> +In the threadsafe implementation, the global library initialization +variable <code>H5_libinit_g</code> is changed to a global structure +consisting of the variable with its associated lock (locks are explained +in section 4.1): +</p> + +<blockquote> + <pre> + hbool_t H5_libinit_g = FALSE; + </pre> +</blockquote> + +<p> +becomes +</p> + +<blockquote> + <pre> + H5_api_t H5_g; + </pre> +</blockquote> + +<p> +where <code>H5_api_t</code> is +</p> + +<blockquote> + <pre> + typedef struct H5_api_struct { + H5_mutex_t init_lock; /* API entrance mutex */ + hbool_t H5_libinit_g; + } H5_api_t; + </pre> +</blockquote> + +<p> +All former references to <code>H5_libinit_g</code> in the library are now +made using the macro <code>H5_INIT_GLOBAL</code>. If the threadsafe +library is to be used, the macro is set to <code>H5_g.H5_libinit_g</code> +instead. +</p> + +<h2>2.2 Global serialization variable</h2> + +<p> +A new global boolean variable <code>H5_allow_concurrent_g</code> is used +to determine if multiple threads are allowed to an API call +simultaneously. This is set to <code>FALSE</code>. +</p> + +<p> +All APIs that are allowed to do so have their own local variable that +shadows the global variable and is set to <code>TRUE</code>. In phase 1, +no such APIs exist. +</p> + +<p> +It is defined in <code>H5.c</code> as follows: +</p> + +<blockquote> + <pre> + hbool_t H5_allow_concurrent_g = FALSE; + </pre> +</blockquote> + +<h2>2.3 Global thread initialization variable</h2> + +<p> +The global variable <code>H5_first_init_g</code> of type +<code>pthread_once_t</code> is used to allow only the first thread in the +application process to call an initialization function using +<code>pthread_once</code>. All subsequent calls to +<code>pthread_once</code> by any thread are disregarded. +</p> + +<p> +The call sets up the mutex in the global structure <code>H5_g</code> (see +section 3.1) via an initialization function +<code>H5_first_thread_init</code>. The first thread initialization +function is described in section 4.2. +</p> + +<p> +<code>H5_first_init_g</code> is defined in <code>H5.c</code> as follows: +</p> + +<blockquote> + <pre> + pthread_once_t H5_first_init_g = PTHREAD_ONCE_INIT; + </pre> +</blockquote> + +<h2>2.4 Global key for per-thread error stacks</h2> + +<p> +A global pthread-managed key <code>H5_errstk_key_g</code> is used to +allow pthreads to maintain a separate error stack (of type +<code>H5E_t</code>) for each thread. This is defined in <code>H5.c</code> +as: +</p> + +<blockquote> + <pre> + pthread_key_t H5_errstk_key_g; + </pre> +</blockquote> + +<p> +Error stack management is described in section 4.3. +</p> + +<h2>2.5 Global structure and key for thread cancellation prevention</h2> + +<p> +We need to preserve the thread cancellation status of each thread +individually by using a key <code>H5_cancel_key_g</code>. The status is +preserved using a structure (of type <code>H5_cancel_t</code>) which +maintains the cancellability state of the thread before it entered the +library and a count (which works very much like the recursive lock +counter) which keeps track of the number of API calls the thread makes +within the library. +</p> + +<p> +The structure is defined in <code>H5private.h</code> as: +</p> + +<blockquote> + <pre> + /* cancelability structure */ + typedef struct H5_cancel_struct { + int previous_state; + unsigned int cancel_count; + } H5_cancel_t; + </pre> +</blockquote> + +<p> +Thread cancellation is described in section 4.4. +</p> + + +<h1>3. Changes to Macro expansions</h1> + +<h2>3.1 Changes to FUNC_ENTER</h2> + +<p> +The <code>FUNC_ENTER</code> macro is now extended to include macro calls +to initialize first threads, disable cancellability and wraps a lock +operation around the checking of the global initialization flag. It +should be noted that the cancellability should be disabled before +acquiring the lock on the library. Doing so otherwise would allow the +possibility that the thread be cancelled just after it has acquired the +lock on the library and in that scenario, if the cleanup routines are not +properly set, the library would be permanently locked out. +</p> + +<p> +The additional macro code and new macro definitions can be found in +Appendix E.1 to E.5. The changes are made in <code>H5private.h</code>. +</p> + +<h2>3.2 Changes to HRETURN and HRETURN_ERROR</h2> + +<p> +The <code>HRETURN</code> and <code>HRETURN_ERROR</code> macros are the +counterparts to the <code>FUNC_ENTER</code> macro described in section +3.1. <code>FUNC_LEAVE</code> makes a macro call to <code>HRETURN</code>, +so it is also covered here. +</p> + +<p> +The basic changes to these two macros involve adding macro calls to call +an unlock operation and re-enable cancellability if necessary. It should +be noted that the cancellability should be re-enabled only after the +thread has released the lock to the library. The consequence of doing +otherwise would be similar to that described in section 3.1. +</p> + +<p> +The additional macro code and new macro definitions can be found in +Appendix E.9 to E.9. The changes are made in <code>H5Eprivate.h</code>. +</p> + +<h1>4. Implementation of threadsafe functionality</h1> + +<h2>4.1 Recursive Locks</h2> + +<p> +A recursive mutex lock m allows a thread t1 to successfully lock m more +than once without blocking t1. Another thread t2 will block if t2 tries +to lock m while t1 holds the lock to m. If t1 makes k lock calls on m, +then it also needs to make k unlock calls on m before it releases the +lock. +</p> + +<p> +Our implementation of recursive locks is built on top of a pthread mutex +lock (which is not recursive). It makes use of a pthread condition +variable to have unsuccessful threads wait on the mutex. Waiting threads +are awaken by a signal from the final unlock call made by the thread +holding the lock. +</p> + +<p> +Recursive locks are defined to be the following type +(<code>H5private.h</code>): +</p> + +<blockquote> + <pre> + typedef struct H5_mutex_struct { + pthread_t owner_thread; /* current lock owner */ + pthread_mutex_t atomic_lock; /* lock for atomicity of new mechanism */ + pthread_cond_t cond_var; /* condition variable */ + unsigned int lock_count; + } H5_mutex_t; + </pre> +</blockquote> + +<p> +Detailed implementation code can be found in Appendix A. The +implementation changes are made in <code>H5TS.c</code>. +</p> + +<h2>4.2 First thread initialization</h2> + +<p> +Because the mutex lock associated with a recursive lock cannot be +statically initialized, a mechanism is required to initialize the +recursive lock associated with <code>H5_g</code> so that it can be used +for the first time. +</p> + +<p> +The pthreads library allows this through the pthread_once call which as +described in section 3.3 allows only the first thread accessing the +library in an application to initialize <code>H5_g</code>. +</p> + +<p> +In addition to initializing <code>H5_g</code>, it also initializes the +key (see section 3.4) for use with per-thread error stacks (see section +4.3). +</p> + +<p> +The first thread initialization mechanism is implemented as the function +call <code>H5_first_thread_init()</code> in <code>H5TS.c</code>. This is +described in appendix B. +</p> + +<h2>4.3 Per-thread error stack management</h2> + +<p> +Pthreads allows individual threads to access dynamic and persistent +per-thread data through the use of keys. Each key is associated with +a table that maps threads to data items. Keys can be initialized by +<code>pthread_key_create()</code> in pthreads (see sections 3.4 and 4.2). +Per-thread data items are accessed using a key through the +<code>pthread_getspecific()</code> and <code>pthread_setspecific()</code> +calls to read and write to the association table respectively. +</p> + +<p> +Per-thread error stacks are accessed through the key +<code>H5_errstk_key_g</code> which is initialized by the first thread +initialization call (see section 4.2). +</p> + +<p> +In the non-threadsafe version of the library, there is a global stack +variable <code>H5E_stack_g[1]</code> which is no longer defined in the +threadsafe version. At the same time, the macro call to gain access to +the error stack <code>H5E_get_my_stack</code> is changed from: +</p> + +<blockquote> + <pre> + #define H5E_get_my_stack() (H5E_stack_g+0) + </pre> +</blockquote> + +<p> +to: +</p> + +<blockquote> + <pre> + #define H5E_get_my_stack() H5E_get_stack() + </pre> +</blockquote> + +<p> +where <code>H5E_get_stack()</code> is a surrogate function that does the +following operations: +</p> + +<ol> + <li>if a thread is attempting to get an error stack for the first + time, the error stack is dynamically allocated for the thread and + associated with <code>H5_errstk_key_g</code> using + <code>pthread_setspecific()</code>. The way we detect if it is the + first time is through <code>pthread_getspecific()</code> which + returns <code>NULL</code> if no previous value is associated with + the thread using the key.</li> + + <li>if <code>pthread_getspecific()</code> returns a non-null value, + then that is the pointer to the error stack associated with the + thread and the stack can be used as usual.</li> +</ol> + +<p> +A final change to the error reporting routines is as follows; the current +implementation reports errors to always be detected at thread 0. In the +threadsafe implementation, this is changed to report the number returned +by a call to <code>pthread_self()</code>. +</p> + +<p> +The change in code (reflected in <code>H5Eprint</code> of file +<code>H5E.c</code>) is as follows: +</p> + +<blockquote> + <pre> + #ifdef H5_HAVE_THREADSAFE + fprintf (stream, "HDF5-DIAG: Error detected in thread %d." + ,pthread_self()); + #else + fprintf (stream, "HDF5-DIAG: Error detected in thread 0."); + #endif + </pre> +</blockquote> + +<p> +Code for <code>H5E_get_stack()</code> can be found in Appendix C. All the +above changes were made in <code>H5E.c</code>. +</p> + +<h2>4.4 Thread Cancellation safety</h2> + +<p> +To prevent thread cancellations from killing a thread while it is in the +library, we maintain per-thread information about the cancellability +status of the thread before it entered the library so that we can restore +that same status when the thread leaves the library. +</p> + +<p> +By <i>enter</i> and <i>leave</i> the library, we mean the points when a +thread makes an API call from a user application and the time that API +call returns. Other API or callback function calls made from within that +API call are considered <i>within</i> the library. +</p> + +<p> +Because other API calls may be made from within the first API call, we +need to maintain a counter to determine which was the first and +correspondingly the last return. +</p> + +<p> +When a thread makes an API call, the macro <code>H5_API_SET_CANCEL</code> +calls the worker function <code>H5_cancel_count_inc()</code> which does +the following: +</p> + +<ol> + <li>if this is the first time the thread has entered the library, + a new cancellability structure needs to be assigned to it.</li> + <li>if the thread is already within the library when the API call is + made, then cancel_count is simply incremented. Otherwise, we set + the cancellability state to <code>PTHREAD_CANCEL_DISABLE</code> + while storing the previous state into the cancellability structure. + <code>cancel_count</code> is also incremented in this case.</li> +</ol> + +<p> +When a thread leaves an API call, the macro +<code>H5_API_UNSET_CANCEL</code> calls the worker function +<code>H5_cancel_count_dec()</code> which does the following: +</p> + +<ol> + <li>if <code>cancel_count</code> is greater than 1, indicating that the + thread is not yet about to leave the library, then + <code>cancel_count</code> is simply decremented.</li> + <li>otherwise, we reset the cancellability state back to its original + state before it entered the library and decrement the count (back + to zero).</li> +</ol> + +<p> +<code>H5_cancel_count_inc</code> and <code>H5_cancel_count_dec</code> are +described in Appendix D and may be found in <code>H5TS.c</code>. +</p> + +<h1>5. Test programs</h1> + +<p> +Except where stated, all tests involve 16 simultaneous threads that make +use of HDF-5 API calls without any explicit synchronization typically +required in a non-threadsafe environment. +</p> + +<h2>5.1 Data set create and write</h2> + +<p> +The test program sets up 16 threads to simultaneously create 16 +different datasets named from <i>zero</i> to <i>fifteen</i> for a single +file and then writing an integer value into that dataset equal to the +dataset's named value. +</p> + +<p> +The main thread would join with all 16 threads and attempt to match the +resulting HDF-5 file with expected results - that each dataset contains +the correct value (0 for <i>zero</i>, 1 for <i>one</i> etc ...) and all +datasets were correctly created. +</p> + +<p> +The test is implemented in the file <code>ttsafe_dcreate.c</code>. +</p> + +<h2>5.2 Test on error stack</h2> + +<p> +The error stack test is one in which 16 threads simultaneously try to +create datasets with the same name. The result, when properly serialized, +should be equivalent to 16 attempts to create the dataset with the same +name. +</p> + +<p> +The error stack implementation runs correctly if it reports 15 instances +of the dataset name conflict error and finally generates a correct HDF-5 +containing that single dataset. Each thread should report its own stack +of errors with a thread number associated with it. +</p> + +<p> +The test is implemented in the file <code>ttsafe_error.c</code>. +</p> + +<h2>5.3 Test on cancellation safety</h2> + +<p> +The main idea in thread cancellation safety is as follows; a child thread +is spawned to create and write to a dataset. Following that, it makes a +<code>H5Diterate</code> call on that dataset which activates a callback +function. +</p> + +<p> +A deliberate barrier is invoked at the callback function which waits for +both the main and child thread to arrive at that point. After that +happens, the main thread proceeds to make a thread cancel call on the +child thread while the latter sleeps for 3 seconds before proceeding to +write a new value to the dataset. +</p> + +<p> +After the iterate call, the child thread logically proceeds to wait +another 3 seconds before writing another newer value to the dataset. +</p> + +<p> +The test is correct if the main thread manages to read the second value +at the end of the test. This means that cancellation did not take place +until the end of the iteration call despite of the 3 second wait within +the iteration callback and the extra dataset write operation. +Furthermore, the cancellation should occur before the child can proceed +to write the last value into the dataset. +</p> + +<h2>5.4 Test on attribute creation</h2> + +<p> +A main thread makes 16 threaded calls to <code>H5Acreate</code> with a +generated name for each attribute. Sixteen attributes should be created +for the single dataset in random (chronological) order and receive values +depending on its generated attribute name (e.g. <i>attrib010</i> would +receive the value 10). +</p> + +<p> +After joining with all child threads, the main thread proceeds to read +each attribute by generated name to see if the value tallies. Failure is +detected if the attribute name does not exist (meaning they were never +created) or if the wrong values were read back. +</p> + +<h1>A. Recursive Lock implementation code</h1> + +<blockquote> + <pre> + void H5_mutex_init(H5_mutex_t *H5_mutex) + { + H5_mutex->owner_thread = NULL; + pthread_mutex_init(&H5_mutex->atomic_lock, NULL); + pthread_cond_init(&H5_mutex->cond_var, NULL); + H5_mutex->lock_count = 0; + } + + void H5_mutex_lock(H5_mutex_t *H5_mutex) + { + pthread_mutex_lock(&H5_mutex->atomic_lock); + + if (pthread_equal(pthread_self(), H5_mutex->owner_thread)) { + /* already owned by self - increment count */ + H5_mutex->lock_count++; + } else { + if (H5_mutex->owner_thread == NULL) { + /* no one else has locked it - set owner and grab lock */ + H5_mutex->owner_thread = pthread_self(); + H5_mutex->lock_count = 1; + } else { + /* if already locked by someone else */ + while (1) { + pthread_cond_wait(&H5_mutex->cond_var, &H5_mutex->atomic_lock); + + if (H5_mutex->owner_thread == NULL) { + H5_mutex->owner_thread = pthread_self(); + H5_mutex->lock_count = 1; + break; + } /* else do nothing and loop back to wait on condition*/ + } + } + } + + pthread_mutex_unlock(&H5_mutex->atomic_lock); + } + + void H5_mutex_unlock(H5_mutex_t *H5_mutex) + { + pthread_mutex_lock(&H5_mutex->atomic_lock); + H5_mutex->lock_count--; + + if (H5_mutex->lock_count == 0) { + H5_mutex->owner_thread = NULL; + pthread_cond_signal(&H5_mutex->cond_var); + } + pthread_mutex_unlock(&H5_mutex->atomic_lock); + } + </pre> +</blockquote> + +<h1>B. First thread initialization</h1> + +<blockquote> + <pre> + void H5_first_thread_init(void) + { + /* initialize global API mutex lock */ + H5_g.H5_libinit_g = FALSE; + H5_g.init_lock.owner_thread = NULL; + pthread_mutex_init(&H5_g.init_lock.atomic_lock, NULL); + pthread_cond_init(&H5_g.init_lock.cond_var, NULL); + H5_g.init_lock.lock_count = 0; + + /* initialize key for thread-specific error stacks */ + pthread_key_create(&H5_errstk_key_g, NULL); + + /* initialize key for thread cancellability mechanism */ + pthread_key_create(&H5_cancel_key_g, NULL); + } + </pre> +</blockquote> + + +<h1>C. Per-thread error stack acquisition</h1> + +<blockquote> + <pre> + H5E_t *H5E_get_stack(void) + { + H5E_t *estack; + + if (estack = pthread_getspecific(H5_errstk_key_g)) { + return estack; + } else { + /* no associated value with current thread - create one */ + estack = (H5E_t *)malloc(sizeof(H5E_t)); + pthread_setspecific(H5_errstk_key_g, (void *)estack); + return estack; + } + } + </pre> +</blockquote> + +<h1>D. Thread cancellation mechanisms</h1> + +<blockquote> + <pre> + void H5_cancel_count_inc(void) + { + H5_cancel_t *cancel_counter; + + if (cancel_counter = pthread_getspecific(H5_cancel_key_g)) { + /* do nothing here */ + } else { + /* + * first time thread calls library - create new counter and + * associate with key + */ + cancel_counter = (H5_cancel_t *)malloc(sizeof(H5_cancel_t)); + cancel_counter->cancel_count = 0; + pthread_setspecific(H5_cancel_key_g, (void *)cancel_counter); + } + + if (cancel_counter->cancel_count == 0) { + /* thread entering library */ + pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, + &(cancel_counter->previous_state)); + } + + cancel_counter->cancel_count++; + } + + void H5_cancel_count_dec(void) + { + H5_cancel_t *cancel_counter = pthread_getspecific(H5_cancel_key_g); + + if (cancel_counter->cancel_count == 1) + pthread_setcancelstate(cancel_counter->previous_state, NULL); + + cancel_counter->cancel_count--; + } + </pre> +</blockquote> + +<h1>E. Macro expansion codes</h1> + +<h2>E.1 <code>FUNC_ENTER</code></h2> + +<blockquote> + <pre> + /* Initialize the library */ \ + H5_FIRST_THREAD_INIT \ + H5_API_UNSET_CANCEL \ + H5_API_LOCK_BEGIN \ + if (!(H5_INIT_GLOBAL)) { \ + H5_INIT_GLOBAL = TRUE; \ + if (H5_init_library() < 0) { \ + HRETURN_ERROR (H5E_FUNC, H5E_CANTINIT, err, \ + "library initialization failed"); \ + } \ + } \ + H5_API_LOCK_END \ + : + : + : + </pre> +</blockquote> + +<h2>E.2 <code>H5_FIRST_THREAD_INIT</code></h2> + +<blockquote> + <pre> + /* Macro for first thread initialization */ + #define H5_FIRST_THREAD_INIT \ + pthread_once(&H5_first_init_g, H5_first_thread_init); + </pre> +</blockquote> + + +<h2>E.3 <code>H5_API_UNSET_CANCEL</code></h2> + +<blockquote> + <pre> + #define H5_API_UNSET_CANCEL \ + if (H5_IS_API(FUNC)) { \ + H5_cancel_count_inc(); \ + } + </pre> +</blockquote> + + +<h2>E.4 <code>H5_API_LOCK_BEGIN</code></h2> + +<blockquote> + <pre> + #define H5_API_LOCK_BEGIN \ + if (H5_IS_API(FUNC)) { \ + H5_mutex_lock(&H5_g.init_lock); + </pre> +</blockquote> + + +<h2>E.5 <code>H5_API_LOCK_END</code></h2> + +<blockquote> + <pre> + #define H5_API_LOCK_END } + </pre> +</blockquote> + + +<h2>E.6 <code>HRETURN</code> and <code>HRETURN_ERROR</code></h2> + +<blockquote> + <pre> + : + : + H5_API_UNLOCK_BEGIN \ + H5_API_UNLOCK_END \ + H5_API_SET_CANCEL \ + return ret_val; \ + } + </pre> +</blockquote> + +<h2>E.7 <code>H5_API_UNLOCK_BEGIN</code></h2> + +<blockquote> + <pre> + #define H5_API_UNLOCK_BEGIN \ + if (H5_IS_API(FUNC)) { \ + H5_mutex_unlock(&H5_g.init_lock); + </pre> +</blockquote> + +<h2>E.8 <code>H5_API_UNLOCK_END</code></h2> + +<blockquote> + <pre> + #define H5_API_UNLOCK_END } + </pre> +</blockquote> + + +<h2>E.9 <code>H5_API_SET_CANCEL</code></h2> + +<blockquote> + <pre> + #define H5_API_SET_CANCEL \ + if (H5_IS_API(FUNC)) { \ + H5_cancel_count_dec(); \ + } + </pre> +</blockquote> + +<h2>By Chee Wai Lee</h2> +<h4>By Bill Wendling</h4> + +</body> +</html> diff --git a/doxygen/examples/VFL.html b/doxygen/examples/VFL.html new file mode 100644 index 0000000..9776f96 --- /dev/null +++ b/doxygen/examples/VFL.html @@ -0,0 +1,1601 @@ +<HTML> +<HEAD> +<!-- This HTML file has been created by texi2html 1.51 + from VFL.texi on 18 November 1999 --> + +<TITLE>HDF5 Virtual File Layer</TITLE> +</HEAD> + + +<!-- + * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * + * Copyright by The HDF Group. * + * Copyright by the Board of Trustees of the University of Illinois. * + * All rights reserved. * + * * + * This file is part of HDF5. The full HDF5 copyright notice, including * + * terms governing use, modification, and redistribution, is contained in * + * the files COPYING and Copyright.html. COPYING can be found at the root * + * of the source code distribution tree; Copyright.html can be found at the * + * root level of an installed copy of the electronic HDF5 document set and * + * is linked from the top-level documents page. It can also be found at * + * http://hdfgroup.org/HDF5/doc/Copyright.html. If you do not have * + * access to either file, you may request a copy from help@hdfgroup.org. * + * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * + --> + + +<BODY> + +<strong>Revision History</strong> +<p>Initial document, 18 November 1999.</p> + +<p>Updated on 10/24/00, Quincey Koziol</p> + +<p>Added the section “Programming Note for C++ Developers Using C +Functions,” 08/23/2012, Mark Evans + + + +<P> +<P><HR><P> +<H1>Table of Contents</H1> +<UL> +<LI><A NAME="TOC1" HREF="#SEC1">Introduction</A> +<LI><A NAME="TOC2" HREF="#SEC2">Using a File Driver</A> +<UL> +<LI><A NAME="TOC3" HREF="#SEC3">Driver Header Files</A> +<LI><A NAME="TOC4" HREF="#SEC4">Creating and Opening Files</A> +<LI><A NAME="TOC5" HREF="#SEC5">Performing I/O</A> +<LI><A NAME="TOC6" HREF="#SEC6">File Driver Interchangeability</A> +</UL> +<LI><A NAME="TOC7" HREF="#SEC7">Implementation of a Driver</A> +<UL> +<LI><A NAME="TOC8" HREF="#SEC8">Mode Functions</A> +<LI><A NAME="TOC9" HREF="#SEC9">File Functions</A> +<UL> +<LI><A NAME="TOC10" HREF="#SEC10">Opening Files</A> +<LI><A NAME="TOC11" HREF="#SEC11">Closing Files</A> +<LI><A NAME="TOC12" HREF="#SEC12">File Keys</A> +<LI><A NAME="TOC13" HREF="#SEC13">Saving Modes Across Opens</A> +</UL> +<LI><A NAME="TOC14" HREF="#SEC14">Address Space Functions</A> +<UL> +<LI><A NAME="TOC15" HREF="#SEC15">Userblock and Superblock</A> +<LI><A NAME="TOC16" HREF="#SEC16">Allocation of Format Regions</A> +<LI><A NAME="TOC17" HREF="#SEC17">Freeing Format Regions</A> +<LI><A NAME="TOC18" HREF="#SEC18">Querying Address Range</A> +</UL> +<LI><A NAME="TOC19" HREF="#SEC19">Data Functions</A> +<UL> +<LI><A NAME="TOC20" HREF="#SEC20">Contiguous I/O Functions</A> +<LI><A NAME="TOC21" HREF="#SEC21">Flushing Cached Data</A> +</UL> +<LI><A NAME="TOC22" HREF="#SEC22">Optimization Functions</A> +<LI><A NAME="TOC23" HREF="#SEC23">Registration of a Driver</A> + <ul> + <li><a name="TOCProgNote" href="#SECProgNote"> + Programming Note for C++ Developers Using C Functions</a> + </li> + </ul> +<LI><A NAME="TOC24" HREF="#SEC24">Querying Driver Information</A> +</UL> +<LI><A NAME="TOC25" HREF="#SEC25">Miscellaneous</A> +</UL> +<P><HR><P> + + +<H1><A NAME="SEC1" HREF="#TOC1">Introduction</A></H1> + +<P> +The HDF5 file format describes how HDF5 data structures and dataset raw +data are mapped to a linear <STRONG>format address space</STRONG> and the HDF5 +library implements that bidirectional mapping in terms of an +API. However, the HDF5 format specifications do <EM>not</EM> indicate how +the format address space is mapped onto storage and HDF (version 5 and +earlier) simply mapped the format address space directly onto a single +file by convention. + +</P> +<P> +Since early versions of HDF5 it became apparent that users want the ability to +map the format address space onto different types of storage (a single file, +multiple files, local memory, global memory, network distributed global +memory, a network protocol, <I>etc</I>.) with various types of maps. For +instance, some users want to be able to handle very large format address +spaces on operating systems that support only 2GB files by partitioning the +format address space into equal-sized parts each served by a separate +file. Other users want the same multi-file storage capability but want to +partition the address space according to purpose (raw data in one file, object +headers in another, global heap in a third, <I>etc.</I>) in order to improve I/O +speeds. + +</P> +<P> +In fact, the number of storage variations is probably larger than the +number of methods that the HDF5 team is capable of implementing and +supporting. Therefore, a <STRONG>Virtual File Layer</STRONG> API is being +implemented which will allow application teams or departments to design +and implement their own mapping between the HDF5 format address space +and storage, with each mapping being a separate <STRONG>file driver</STRONG> +(possibly written in terms of other file drivers). The HDF5 team will +provide a small set of useful file drivers which will also serve as +examples for those who which to write their own: + +</P> +<DL COMPACT> + +<DT><CODE>H5FD_SEC2</CODE> +<DD> +This is the default driver which uses Posix file-system functions like +<CODE>read</CODE> and <CODE>write</CODE> to perform I/O to a single file. All I/O +requests are unbuffered although the driver does optimize file seeking +operations to some extent. + +<DT><CODE>H5FD_STDIO</CODE> +<DD> +This driver uses functions from <TT>`stdio.h'</TT> to perform buffered I/O +to a single file. + +<DT><CODE>H5FD_CORE</CODE> +<DD> +This driver performs I/O directly to memory and can be used to create small +temporary files that never exist on permanent storage. This type of storage is +generally very fast since the I/O consists only of memory-to-memory copy +operations. + +<DT><CODE>H5FD_MPIIO</CODE> +<DD> +This is the driver of choice for accessing files in parallel using MPI and +MPI-IO. It is only predefined if the library is compiled with parallel I/O +support. + +<DT><CODE>H5FD_FAMILY</CODE> +<DD> +Large format address spaces are partitioned into more manageable pieces and +sent to separate storage locations using an underlying driver of the user's +choice. The <CODE>h5repart</CODE> tool can be used to change the sizes of the +family members when stored as files or to convert a family of files to a +single file or vice versa. + +<DT><CODE>H5FD_SPLIT</CODE> +<DD> +The format address space is split into meta data and raw data and each is +mapped onto separate storage using underlying drivers of the user's +choice. The meta data storage can be read by itself (for limited +functionality) or both files can be accessed together. +</DL> + + + +<H1><A NAME="SEC2" HREF="#TOC2">Using a File Driver</A></H1> + +<P> +Most application writers will use a driver defined by the HDF5 library or +contributed by another programming team. This chapter describes how existing +drivers are used. + +</P> + + + +<H2><A NAME="SEC3" HREF="#TOC3">Driver Header Files</A></H2> + +<P> +Each file driver is defined in its own public header file which should +be included by any application which plans to use that driver. The +predefined drivers are in header files whose names begin with +<SAMP>`H5FD'</SAMP> followed by the driver name and <SAMP>`.h'</SAMP>. The <TT>`hdf5.h'</TT> +header file includes all the predefined driver header files. + +</P> +<P> +Once the appropriate header file is included a symbol of the form +<SAMP>`H5FD_'</SAMP> followed by the upper-case driver name will be the driver +identification number.<A NAME="DOCF1" HREF="#FOOT1">(1)</A> However, the +value may change if the library is closed (<I>e.g.</I>, by calling +<CODE>H5close</CODE>) and the symbol is referenced again. + +</P> + + +<H2><A NAME="SEC4" HREF="#TOC4">Creating and Opening Files</A></H2> + +<P> +In order to create or open a file one must define the method by which the +storage is accessed<A NAME="DOCF2" HREF="#FOOT2">(2)</A> and does so by creating a file access property list<A NAME="DOCF3" HREF="#FOOT3">(3)</A> which is passed to the <CODE>H5Fcreate</CODE> or +<CODE>H5Fopen</CODE> function. A default file access property list is created by +calling <CODE>H5Pcreate</CODE> and then the file driver information is inserted by +calling a driver initialization function such as <CODE>H5Pset_fapl_family</CODE>: + +</P> + +<PRE> +hid_t fapl = H5Pcreate(H5P_FILE_ACCESS); +size_t member_size = 100*1024*1024; /*100MB*/ +H5Pset_fapl_family(fapl, member_size, H5P_DEFAULT); +hid_t file = H5Fcreate("foo%05d.h5", H5F_ACC_TRUNC, H5P_DEFAULT, fapl); +H5Pclose(fapl); +</PRE> + +<P> +Each file driver will have its own initialization function +whose name is <CODE>H5Pset_fapl_</CODE> followed by the driver name and which +takes a file access property list as the first argument followed by +additional driver-dependent arguments. + +</P> +<P> +An alternative to using the driver initialization function is to set the +driver directly using the <CODE>H5Pset_driver</CODE> function.<A NAME="DOCF4" HREF="#FOOT4">(4)</A> Its second argument is the file driver identifier, which may +have a different numeric value from run to run depending on the order in which +the file drivers are registered with the library. The third argument +encapsulates the additional arguments of the driver initialization +function. This method only works if the file driver writer has made the +driver-specific property list structure a public datatype, which is +often not the case. + +</P> + +<PRE> +hid_t fapl = H5Pcreate(H5P_FILE_ACCESS); +static H5FD_family_fapl_t fa = {100*1024*1024, H5P_DEFAULT}; +H5Pset_driver(fapl, H5FD_FAMILY, &fa); +hid_t file = H5Fcreate("foo.h5", H5F_ACC_TRUNC, H5P_DEFAULT, fapl); +H5Pclose(fapl); +</PRE> + +<P> +It is also possible to query the file driver information from a file access +property list by calling <CODE>H5Pget_driver</CODE> to determine the driver and then +calling a driver-defined query function to obtain the driver information: + +</P> + +<PRE> +hid_t driver = H5Pget_driver(fapl); +if (H5FD_SEC2==driver) { + /*nothing further to get*/ +} else if (H5FD_FAMILY==driver) { + hid_t member_fapl; + haddr_t member_size; + H5Pget_fapl_family(fapl, &member_size, &member_fapl); +} else if (....) { + .... +} +</PRE> + + + +<H2><A NAME="SEC5" HREF="#TOC5">Performing I/O</A></H2> + +<P> +The <CODE>H5Dread</CODE> and <CODE>H5Dwrite</CODE> functions transfer data between +application memory and the file. They both take an optional data transfer +property list which has some general driver-independent properties and +optional driver-defined properties. An application will typically perform I/O +in one of three styles via the <CODE>H5Dread</CODE> or <CODE>H5Dwrite</CODE> function: + +</P> +<P> +Like file access properties in the previous section, data transfer properties +can be set using a driver initialization function or a general purpose +function. For example, to set the MPI-IO driver to use independent access for +I/O operations one would say: + +</P> + +<PRE> +hid_t dxpl = H5Pcreate(H5P_DATA_XFER); +H5Pset_dxpl_mpio(dxpl, H5FD_MPIO_INDEPENDENT); +H5Dread(dataset, type, mspace, fspace, buffer, dxpl); +H5Pclose(dxpl); +</PRE> + +<P> +The alternative is to initialize a driver defined C <CODE>struct</CODE> and pass it +to the <CODE>H5Pset_driver</CODE> function: + +</P> + +<PRE> +hid_t dxpl = H5Pcreate(H5P_DATA_XFER); +static H5FD_mpio_dxpl_t dx = {H5FD_MPIO_INDEPENDENT}; +H5Pset_driver(dxpl, H5FD_MPIO, &dx); +H5Dread(dataset, type, mspace, fspace, buffer, dxpl); +</PRE> + +<P> +The transfer propery list can be queried in a manner similar to the file +access property list: the driver provides a function (or functions) to return +various information about the transfer property list: + +</P> + +<PRE> +hid_t driver = H5Pget_driver(dxpl); +if (H5FD_MPIO==driver) { + H5FD_mpio_xfer_t xfer_mode; + H5Pget_dxpl_mpio(dxpl, &xfer_mode); +} else { + .... +} +</PRE> + + + +<H2><A NAME="SEC6" HREF="#TOC6">File Driver Interchangeability</A></H2> + +<P> +The HDF5 specifications describe two things: the mapping of data onto a linear +<STRONG>format address space</STRONG> and the C API which performs the mapping. +However, the mapping of the format address space onto storage intentionally +falls outside the scope of the HDF5 specs. This is a direct result of the fact +that it is not generally possible to store information about how to access +storage inside the storage itself. For instance, given only the file name +<TT>`/arborea/1225/work/f%03d'</TT> the HDF5 library is unable to tell whether the +name refers to a file on the local file system, a family of files on the local +file system, a file on host <SAMP>`arborea'</SAMP> port 1225, a family of files on a +remote system, <I>etc</I>. + +</P> +<P> +Two ways which library could figure out where the storage is located are: +storage access information can be provided by the user, or the library can try +all known file access methods. This implementation uses the former method. + +</P> +<P> +In general, if a file was created with one driver then it isn't possible to +open it with another driver. There are of course exceptions: a file created +with MPIO could probably be opened with the sec2 driver, any file created +by the sec2 driver could be opened as a family of files with one member, +<I>etc</I>. In fact, sometimes a file must not only be opened with the same +driver but also with the same driver properties. The predefined drivers are +written in such a way that specifying the correct driver is sufficient for +opening a file. + +</P> + + +<H1><A NAME="SEC7" HREF="#TOC7">Implementation of a Driver</A></H1> + +<P> +A driver is simply a collection of functions and data structures which are +registered with the HDF5 library at runtime. The functions fall into these +categories: + +</P> + +<UL> +<LI>Functions which operate on modes + +<LI>Functions which operate on files + +<LI>Functions which operate on the address space + +<LI>Functions which operate on data + +<LI>Functions for driver initialization + +<LI>Optimization functions + +</UL> + + + +<H2><A NAME="SEC8" HREF="#TOC8">Mode Functions</A></H2> + +<P> +Some drivers need information about file access and data transfers which are +very specific to the driver. The information is usually implemented as a pair +of pointers to C structs which are allocated and initialized as part of an +HDF5 property list and passed down to various driver functions. There are two +classes of settings: file access modes that describe how to access the file +through the driver, and data transfer modes which are settings that control +I/O operations. Each file opened by a particular driver may have a different +access mode; each dataset I/O request for a particular file may have a +different data transfer mode. + +</P> +<P> +Since each driver has its own particular requirements for various settings, +each driver is responsible for defining the mode structures that it +needs. Higher layers of the library treat the structures as opaque but must be +able to copy and free them. Thus, the driver provides either the size of the +structure or a pair of function pointers for each of the mode types. + +</P> +<P> +<STRONG>Example:</STRONG> The family driver needs to know how the format address +space is partitioned and the file access property list to use for the +family members. + +</P> + +<PRE> +/* Driver-specific file access properties */ +typedef struct H5FD_family_fapl_t { + hsize_t memb_size; /*size of each member */ + hid_t memb_fapl_id; /*file access property list of each memb*/ +} H5FD_family_fapl_t; + +/* Driver specific data transfer properties */ +typedef struct H5FD_family_dxpl_t { + hid_t memb_dxpl_id; /*data xfer property list of each memb */ +} H5FD_family_dxpl_t; +</PRE> + +<P> +In order to copy or free one of these structures the member file access +or data transfer properties must also be copied or freed. This is done +by providing a copy and close function for each structure: + +</P> +<P> +<STRONG>Example:</STRONG> The file access property list copy and close functions +for the family driver: + +</P> + +<PRE> +static void * +H5FD_family_fapl_copy(const void *_old_fa) +{ + const H5FD_family_fapl_t *old_fa = (const H5FD_family_fapl_t*)_old_fa; + H5FD_family_fapl_t *new_fa = malloc(sizeof(H5FD_family_fapl_t)); + assert(new_fa); + + memcpy(new_fa, old_fa, sizeof(H5FD_family_fapl_t)); + new_fa->memb_fapl_id = H5Pcopy(old_fa->memb_fapl_id); + return new_fa; +} + +static herr_t +H5FD_family_fapl_free(void *_fa) +{ + H5FD_family_fapl_t *fa = (H5FD_family_fapl_t*)_fa; + H5Pclose(fa->memb_fapl_id); + free(fa); + return 0; +} +</PRE> + +<P> +Generally when a file is created or opened the file access properties +for the driver are copied into the file pointer which is returned and +they may be modified from their original value (for instance, the file +family driver modifies the member size property when opening an existing +family). In order to support the <CODE>H5Fget_access_plist</CODE> function the +driver must provide a <CODE>fapl_get</CODE> callback which creates a copy of +the driver-specific properties based on a particular file. + +</P> +<P> +<STRONG>Example:</STRONG> The file family driver copies the member size file +access property list into the return value: + +</P> + +<PRE> +static void * +H5FD_family_fapl_get(H5FD_t *_file) +{ + H5FD_family_t *file = (H5FD_family_t*)_file; + H5FD_family_fapl_t *fa = calloc(1, sizeof(H5FD_family_fapl_t*)); + + fa->memb_size = file->memb_size; + fa->memb_fapl_id = H5Pcopy(file->memb_fapl_id); + return fa; +} +</PRE> + + + +<H2><A NAME="SEC9" HREF="#TOC9">File Functions</A></H2> + +<P> +The higher layers of the library expect files to have a name and allow the +file to be accessed in various modes. The driver must be able to create a new +file, replace an existing file, or open an existing file. Opening or creating +a file should return a handle, a pointer to a specialization of the +<CODE>H5FD_t</CODE> struct, which allows read-only or read-write access and which +will be passed to the other driver functions as they are +called.<A NAME="DOCF5" HREF="#FOOT5">(5)</A> + +</P> + +<PRE> +typedef struct { + /* Public fields */ + H5FD_class_t *cls; /*class data defined below*/ + + /* Private fields -- driver-defined */ + +} H5FD_t; +</PRE> + +<P> +<STRONG>Example:</STRONG> The family driver requires handles to the underlying +storage, the size of the members for this particular file (which might be +different than the member size specified in the file access property list if +an existing file family is being opened), the name used to open the file in +case additional members must be created, and the flags to use for creating +those additional members. The <CODE>eoa</CODE> member caches the size of the format +address space so the family members don't have to be queried in order to find +it. + +</P> + +<PRE> +/* The description of a file belonging to this driver. */ +typedef struct H5FD_family_t { + H5FD_t pub; /*public stuff, must be first */ + hid_t memb_fapl_id; /*file access property list for members */ + hsize_t memb_size; /*maximum size of each member file */ + int nmembs; /*number of family members */ + int amembs; /*number of member slots allocated */ + H5FD_t **memb; /*dynamic array of member pointers */ + haddr_t eoa; /*end of allocated addresses */ + char *name; /*name generator printf format */ + unsigned flags; /*flags for opening additional members */ +} H5FD_family_t; +</PRE> + +<P> +<STRONG>Example:</STRONG> The sec2 driver needs to keep track of the underlying Unix +file descriptor and also the end of format address space and current Unix file +size. It also keeps track of the current file position and last operation +(read, write, or unknown) in order to optimize calls to <CODE>lseek</CODE>. The +<CODE>device</CODE> and <CODE>inode</CODE> fields are defined on Unix in order to uniquely +identify the file and will be discussed below. + +</P> + +<PRE> +typedef struct H5FD_sec2_t { + H5FD_t pub; /*public stuff, must be first */ + int fd; /*the unix file */ + haddr_t eoa; /*end of allocated region */ + haddr_t eof; /*end of file; current file size*/ + haddr_t pos; /*current file I/O position */ + int op; /*last operation */ + dev_t device; /*file device number */ + ino_t inode; /*file i-node number */ +} H5FD_sec2_t; +</PRE> + + + +<H3><A NAME="SEC10" HREF="#TOC10">Opening Files</A></H3> + +<P> +All drivers must define a function for opening/creating a file. This +function should have a prototype which is: + +</P> +<P> +<DL> +<DT><U>Function:</U> static H5FD_t * <B>open</B> <I>(const char *<VAR>name</VAR>, unsigned <VAR>flags</VAR>, hid_t <VAR>fapl</VAR>, haddr_t <VAR>maxaddr</VAR>)</I> +<DD><A NAME="IDX1"></A> + +</P> +<P> +The file name <VAR>name</VAR> and file access property list <VAR>fapl</VAR> are +the same as were specified in the <CODE>H5Fcreate</CODE> or <CODE>H5Fopen</CODE> +call. The <VAR>flags</VAR> are the same as in those calls also except the +flag <CODE>H5F_ACC_CREATE</CODE> is also present if the call was to +<CODE>H5Fcreate</CODE> and they are documented in the <TT>`H5Fpublic.h'</TT> +file. The <VAR>maxaddr</VAR> argument is the maximum format address that the +driver should be prepared to handle (the minimum address is always +zero). +</DL> + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver opens a Unix file with the requested name +and saves information which uniquely identifies the file (the Unix device +number and inode). + +</P> + +<PRE> +static H5FD_t * +H5FD_sec2_open(const char *name, unsigned flags, hid_t fapl_id/*unused*/, + haddr_t maxaddr) +{ + unsigned o_flags; + int fd; + struct stat sb; + H5FD_sec2_t *file=NULL; + + /* Check arguments */ + if (!name || !*name) return NULL; + if (0==maxaddr || HADDR_UNDEF==maxaddr) return NULL; + if (ADDR_OVERFLOW(maxaddr)) return NULL; + + /* Build the open flags */ + o_flags = (H5F_ACC_RDWR & flags) ? O_RDWR : O_RDONLY; + if (H5F_ACC_TRUNC & flags) o_flags |= O_TRUNC; + if (H5F_ACC_CREAT & flags) o_flags |= O_CREAT; + if (H5F_ACC_EXCL & flags) o_flags |= O_EXCL; + + /* Open the file */ + if ((fd=open(name, o_flags, 0666))<0) return NULL; + if (fstat(fd, &sb)<0) { + close(fd); + return NULL; + } + + /* Create the new file struct */ + file = calloc(1, sizeof(H5FD_sec2_t)); + file->fd = fd; + file->eof = sb.st_size; + file->pos = HADDR_UNDEF; + file->op = OP_UNKNOWN; + file->device = sb.st_dev; + file->inode = sb.st_ino; + + return (H5FD_t*)file; +} +</PRE> + + + +<H3><A NAME="SEC11" HREF="#TOC11">Closing Files</A></H3> + +<P> +Closing a file simply means that all cached data should be flushed to the next +lower layer, the file should be closed at the next lower layer, and all +file-related data structures should be freed. All information needed by the +close function is already present in the file handle. + +</P> +<P> +<DL> +<DT><U>Function:</U> static herr_t <B>close</B> <I>(H5FD_t *<VAR>file</VAR>)</I> +<DD><A NAME="IDX2"></A> + +</P> +<P> +The <VAR>file</VAR> argument is the handle which was returned by the <CODE>open</CODE> +function, and the <CODE>close</CODE> should free only memory associated with the +driver-specific part of the handle (the public parts will have already been released by HDF5's virtual file layer). +</DL> + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver just closes the underlying Unix file, +making sure that the actual file size is the same as that known to the +library by writing a zero to the last file position it hasn't been +written by some previous operation (which happens in the same code which +flushes the file contents and is shown below). + +</P> + +<PRE> +static herr_t +H5FD_sec2_close(H5FD_t *_file) +{ + H5FD_sec2_t *file = (H5FD_sec2_t*)_file; + + if (H5FD_sec2_flush(_file)<0) return -1; + if (close(file->fd)<0) return -1; + free(file); + return 0; +} +</PRE> + + + +<H3><A NAME="SEC12" HREF="#TOC12">File Keys</A></H3> + +<P> +Occasionally an application will attempt to open a single file more than one +time in order to obtain multiple handles to the file. HDF5 allows the files to +share information<A NAME="DOCF6" HREF="#FOOT6">(6)</A> but in order to +accomplish this HDF5 must be able to tell when two names refer to the same +file. It does this by associating a driver-defined key with each file opened +by a driver and comparing the key for an open request with the keys for all +other files currently open by the same driver. + +</P> +<P> +<DL> +<DT><U>Function:</U> const int <B>cmp</B> <I>(const H5FD_t *<VAR>f1</VAR>, const H5FD_t *<VAR>f2</VAR>)</I> +<DD><A NAME="IDX3"></A> + +</P> +<P> +The driver may provide a function which compares two files <VAR>f1</VAR> and +<VAR>f2</VAR> belonging to the same driver and returns a negative, positive, or +zero value <I>a la</I> the <CODE>strcmp</CODE> function.<A NAME="DOCF7" HREF="#FOOT7">(7)</A> If this +function is not provided then HDF5 assumes that all calls to the <CODE>open</CODE> +callback return unique files regardless of the arguments and it is up to the +application to avoid doing this if that assumption is incorrect. +</DL> + +</P> +<P> +Each time a file is opened the library calls the <CODE>cmp</CODE> function to +compare that file with all other files currently open by the same driver and +if one of them matches (at most one can match) then the file which was just +opened is closed and the previously opened file is used instead. + +</P> +<P> +Opening a file twice with incompatible flags will result in failure. For +instance, opening a file with the truncate flag is a two step process which +first opens the file without truncation so keys can be compared, and if no +matching file is found already open then the file is closed and immediately +reopened with the truncation flag set (if a matching file is already open then +the truncating open will fail). + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver uses the Unix device and i-node as the +key. They were initialized when the file was opened. + +</P> + +<PRE> +static int +H5FD_sec2_cmp(const H5FD_t *_f1, const H5FD_t *_f2) +{ + const H5FD_sec2_t *f1 = (const H5FD_sec2_t*)_f1; + const H5FD_sec2_t *f2 = (const H5FD_sec2_t*)_f2; + + if (f1->device < f2->device) return -1; + if (f1->device > f2->device) return 1; + + if (f1->inode < f2->inode) return -1; + if (f1->inode > f2->inode) return 1; + + return 0; +} +</PRE> + + + +<H3><A NAME="SEC13" HREF="#TOC13">Saving Modes Across Opens</A></H3> + +<P> +Some drivers may also need to store certain information in the file superblock +in order to be able to reliably open the file at a later date. This is done by +three functions: one to determine how much space will be necessary to store +the information in the superblock, one to encode the information, and one to +decode the information. These functions are optional, but if any one is +defined then the other two must also be defined. + +</P> +<P> +<DL> +<DT><U>Function:</U> static hsize_t <B>sb_size</B> <I>(H5FD_t *<VAR>file</VAR>)</I> +<DD><A NAME="IDX4"></A> +<DT><U>Function:</U> static herr_t <B>sb_encode</B> <I>(H5FD_t *<VAR>file</VAR>, char *<VAR>name</VAR>, unsigned char *<VAR>buf</VAR>)</I> +<DD><A NAME="IDX5"></A> +<DT><U>Function:</U> static herr_t <B>sb_decode</B> <I>(H5FD_t *<VAR>file</VAR>, const char *<VAR>name</VAR>, const unsigned char *<VAR>buf</VAR>)</I> +<DD><A NAME="IDX6"></A> + +</P> +<P> +The <CODE>sb_size</CODE> function returns the number of bytes necessary to encode +information needed later if the file is reopened. The <CODE>sb_encode</CODE> +function encodes information from the file into buffer <VAR>buf</VAR> +allocated by the caller. It also writes an 8-character (plus null +termination) into the <CODE>name</CODE> argument, which should be a unique +identification for the driver. The <CODE>sb_decode</CODE> function looks at +the <VAR>name</VAR> + +</P> +<P> + decodes +data from the buffer <VAR>buf</VAR> and updates the <VAR>file</VAR> argument with the new information, +advancing <VAR>*p</VAR> in the process. +</DL> + +</P> +<P> +The part of this which is somewhat tricky is that the file must be readable +before the superblock information is decoded. File access modes fall outside +the scope of the HDF5 file format, but they are placed inside the boot block +for convenience.<A NAME="DOCF8" HREF="#FOOT8">(8)</A> + +</P> +<P> +<STRONG>Example:</STRONG> <EM>To be written later.</EM> + +</P> + + +<H2><A NAME="SEC14" HREF="#TOC14">Address Space Functions</A></H2> + +<P> +HDF5 does not assume that a file is a linear address space of bytes. Instead, +the library will call functions to allocate and free portions of the HDF5 +format address space, which in turn map onto functions in the file driver to +allocate and free portions of file address space. The library tells the file +driver how much format address space it wants to allocate and the driver +decides what format address to use and how that format address is mapped onto +the file address space. Usually the format address is chosen so that the file +address can be calculated in constant time for data I/O operations (which are +always specified by format addresses). + +</P> + + + +<H3><A NAME="SEC15" HREF="#TOC15">Userblock and Superblock</A></H3> + +<P> +The HDF5 format allows an optional userblock to appear before the actual HDF5 +data in such a way that if the userblock is <STRONG>sucked out</STRONG> of the file and +everything remaining is shifted downward in the file address space, then the +file is still a valid HDF5 file. The userblock size can be zero or any +multiple of two greater than or equal to 512 and the file superblock begins +immediately after the userblock. + +</P> +<P> +HDF5 allocates space for the userblock and superblock by calling an +allocation function defined below, which must return a chunk of memory at +format address zero on the first call. + +</P> + + +<H3><A NAME="SEC16" HREF="#TOC16">Allocation of Format Regions</A></H3> + +<P> +The library makes many types of allocation requests: + +</P> +<DL COMPACT> + +<DT><CODE>H5FD_MEM_SUPER</CODE> +<DD> +An allocation request for the userblock and/or superblock. +<DT><CODE>H5FD_MEM_BTREE</CODE> +<DD> +An allocation request for a node of a B-tree. +<DT><CODE>H5FD_MEM_DRAW</CODE> +<DD> +An allocation request for the raw data of a dataset. +<DT><CODE>H5FD_MEM_META</CODE> +<DD> +An allocation request for the raw data of a dataset which +the user has indicated will be relatively small. +<DT><CODE>H5FD_MEM_GROUP</CODE> +<DD> +An allocation request for a group leaf node (internal nodes of the group tree +are allocated as H5MF_BTREE). +<DT><CODE>H5FD_MEM_GHEAP</CODE> +<DD> +An allocation request for a global heap collection. Global heaps are used to +store certain types of references such as dataset region references. The set +of all global heap collections can become quite large. +<DT><CODE>H5FD_MEM_LHEAP</CODE> +<DD> +An allocation request for a local heap. Local heaps are used to store the +names which are members of a group. The combined size of all local heaps is a +function of the number of object names in the file. +<DT><CODE>H5FD_MEM_OHDR</CODE> +<DD> +An allocation request for (part of) an object header. Object headers are +relatively small and include meta information about objects (like the data +space and type of a dataset) and attributes. +</DL> + +<P> +When a chunk of memory is freed the library adds it to a free list and +allocation requests are satisfied from the free list before requesting memory +from the file driver. Each type of allocation request enumerated above has its +own free list, but the file driver can specify that certain object types can +share a free list. It does so by providing an array which maps a request type +to a free list. If any value of the map is <CODE>H5MF_DEFAULT</CODE> (zero) then the +object's own free list is used. The special value <CODE>H5MF_NOLIST</CODE> indicates +that the library should not attempt to maintain a free list for that +particular object type, instead calling the file driver each time an object of +that type is freed. + +</P> +<P> +Mappings predefined in the <TT>`H5FDpublic.h'</TT> file are: +<DL COMPACT> + +<DT><CODE>H5FD_FLMAP_SINGLE</CODE> +<DD> +All memory usage types are mapped to a single free list. +<DT><CODE>H5FD_FLMAP_DICHOTOMY</CODE> +<DD> +Memory usage is segregated into meta data and raw data for the purposes of +memory management. +<DT><CODE>H5FD_FLMAP_DEFAULT</CODE> +<DD> +Each memory usage type has its own free list. +</DL> + +<P> +<STRONG>Example:</STRONG> To make a map that manages object headers on one free list +and everything else on another free list one might initialize the map with the +following code: (the use of <CODE>H5FD_MEM_SUPER</CODE> is arbitrary) + +</P> + +<PRE> +H5FD_mem_t mt, map[H5FD_MEM_NTYPES]; + +for (mt=0; mt<H5FD_MEM_NTYPES; mt++) { + map[mt] = (H5FD_MEM_OHDR==mt) ? mt : H5FD_MEM_SUPER; +} +</PRE> + +<P> +If an allocation request cannot be satisfied from the free list then one of +two things happen. If the driver defines an allocation callback then it is +used to allocate space; otherwise new memory is allocated from the end of the +format address space by incrementing the end-of-address marker. + +</P> +<P> +<DL> +<DT><U>Function:</U> static haddr_t <B>alloc</B> <I>(H5FD_t *<VAR>file</VAR>, H5MF_type_t <VAR>type</VAR>, hsize_t <VAR>size</VAR>)</I> +<DD><A NAME="IDX7"></A> + +</P> +<P> +The <VAR>file</VAR> argument is the file from which space is to be allocated, +<VAR>type</VAR> is the type of memory being requested (from the list above) without +being mapped according to the freelist map and <VAR>size</VAR> is the number of +bytes being requested. The library is allowed to allocate large chunks of +storage and manage them in a layer above the file driver (although the current +library doesn't do that). The allocation function should return a format +address for the first byte allocated. The allocated region extends from that +address for <VAR>size</VAR> bytes. If the request cannot be honored then the +undefined address value is returned (<CODE>HADDR_UNDEF</CODE>). The first call to +this function for a file which has never had memory allocated <EM>must</EM> +return a format address of zero or <CODE>HADDR_UNDEF</CODE> since this is how the +library allocates space for the userblock and/or superblock. +</DL> + +</P> + +<P> +<STRONG>Example:</STRONG> <EM>To be written later.</EM> + +</P> + + +<H3><A NAME="SEC17" HREF="#TOC17">Freeing Format Regions</A></H3> + +<P> +When the library is finished using a certain region of the format address +space it will return the space to the free list according to the type of +memory being freed and the free list map described above. If the free list has +been disabled for a particular memory usage type (according to the free list +map) and the driver defines a <CODE>free</CODE> callback then it will be +invoked. The <CODE>free</CODE> callback is also invoked for all entries on the free +list when the file is closed. + +</P> +<P> +<DL> +<DT><U>Function:</U> static herr_t <B>free</B> <I>(H5FD_t *<VAR>file</VAR>, H5MF_type_t <VAR>type</VAR>, haddr_t <VAR>addr</VAR>, hsize_t <VAR>size</VAR>)</I> +<DD><A NAME="IDX8"></A> + +</P> +<P> +The <VAR>file</VAR> argument is the file for which space is being freed; <VAR>type</VAR> +is the type of object being freed (from the list above) without being mapped +according to the freelist map; <VAR>addr</VAR> is the first format address to free; +and <VAR>size</VAR> is the size in bytes of the region being freed. The region +being freed may refer to just part of the region originally allocated and/or +may cross allocation boundaries provided all regions being freed have the same +usage type. However, the library will never attempt to free regions which have +already been freed or which have never been allocated. +</DL> + +</P> +<P> +A driver may choose to not define the <CODE>free</CODE> function, in which case +format addresses will be leaked. This isn't normally a huge problem since the +library contains a simple free list of its own and freeing parts of the format +address space is not a common occurrence. + +</P> +<P> +<STRONG>Example:</STRONG> <EM>To be written later.</EM> + +</P> + + +<H3><A NAME="SEC18" HREF="#TOC18">Querying Address Range</A></H3> + +<P> +Each file driver must have some mechanism for setting and querying the end of +address, or <STRONG>EOA</STRONG>, marker. The EOA marker is the first format address +after the last format address ever allocated. If the last part of the +allocated address range is freed then the driver may optionally decrease the +eoa marker. + +</P> +<P> +<DL> +<DT><U>Function:</U> static haddr_t <B>get_eoa</B> <I>(H5FD_t *<VAR>file</VAR>)</I> +<DD><A NAME="IDX9"></A> + +</P> +<P> +This function returns the current value of the EOA marker for the specified +file. +</DL> + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver just returns the current eoa marker value +which is cached in the file structure: + +</P> + +<PRE> +static haddr_t +H5FD_sec2_get_eoa(H5FD_t *_file) +{ + H5FD_sec2_t *file = (H5FD_sec2_t*)_file; + return file->eoa; +} +</PRE> + +<P> +The eoa marker is initially zero when a file is opened and the library may set +it to some other value shortly after the file is opened (after the superblock +is read and the saved eoa marker is determined) or when allocating additional +memory in the absence of an <CODE>alloc</CODE> callback (described above). + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver simply caches the eoa marker in the file +structure and does not extend the underlying Unix file. When the file is +flushed or closed then the Unix file size is extended to match the eoa marker. + +</P> + +<PRE> +static herr_t +H5FD_sec2_set_eoa(H5FD_t *_file, haddr_t addr) +{ + H5FD_sec2_t *file = (H5FD_sec2_t*)_file; + file->eoa = addr; + return 0; +} +</PRE> + + + +<H2><A NAME="SEC19" HREF="#TOC19">Data Functions</A></H2> + +<P> +These functions operate on data, transferring a region of the format address +space between memory and files. + +</P> + + + +<H3><A NAME="SEC20" HREF="#TOC20">Contiguous I/O Functions</A></H3> + +<P> +A driver must specify two functions to transfer data from the library to the +file and vice versa. + +</P> +<P> +<DL> +<DT><U>Function:</U> static herr_t <B>read</B> <I>(H5FD_t *<VAR>file</VAR>, H5FD_mem_t <VAR>type</VAR>, hid_t <VAR>dxpl</VAR>, haddr_t <VAR>addr</VAR>, hsize_t <VAR>size</VAR>, void *<VAR>buf</VAR>)</I> +<DD><A NAME="IDX10"></A> +<DT><U>Function:</U> static herr_t <B>write</B> <I>(H5FD_t *<VAR>file</VAR>, H5FD_mem_t <VAR>type</VAR>, hid_t <VAR>dxpl</VAR>, haddr_t <VAR>addr</VAR>, hsize_t <VAR>size</VAR>, const void *<VAR>buf</VAR>)</I> +<DD><A NAME="IDX11"></A> + +</P> +<P> +The <CODE>read</CODE> function reads data from file <VAR>file</VAR> beginning at address +<VAR>addr</VAR> and continuing for <VAR>size</VAR> bytes into the buffer <VAR>buf</VAR> +supplied by the caller. The <CODE>write</CODE> function transfers data in the +opposite direction. Both functions take a data transfer property list +<VAR>dxpl</VAR> which indicates the fine points of how the data is to be +transferred and which comes directly from the <CODE>H5Dread</CODE> or +<CODE>H5Dwrite</CODE> function. Both functions receive <VAR>type</VAR> of +data being written, which may allow a driver to tune it's behavior for +different kinds of data. +</DL> + +</P> +<P> +Both functions should return a negative value if they fail to transfer the +requested data, or non-negative if they succeed. The library will never +attempt to read from unallocated regions of the format address space. + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver just makes system calls. It tries not to +call <CODE>lseek</CODE> if the current operation is the same as the previous +operation and the file position is correct. It also fills the output buffer +with zeros when reading between the current EOF and EOA markers and restarts +system calls which were interrupted. + +</P> + +<PRE> +static herr_t +H5FD_sec2_read(H5FD_t *_file, H5FD_mem_t type/*unused*/, hid_t dxpl_id/*unused*/, + haddr_t addr, hsize_t size, void *buf/*out*/) +{ + H5FD_sec2_t *file = (H5FD_sec2_t*)_file; + ssize_t nbytes; + + assert(file && file->pub.cls); + assert(buf); + + /* Check for overflow conditions */ + if (REGION_OVERFLOW(addr, size)) return -1; + if (addr+size>file->eoa) return -1; + + /* Seek to the correct location */ + if ((addr!=file->pos || OP_READ!=file->op) && + file_seek(file->fd, (file_offset_t)addr, SEEK_SET)<0) { + file->pos = HADDR_UNDEF; + file->op = OP_UNKNOWN; + return -1; + } + + /* + * Read data, being careful of interrupted system calls, partial results, + * and the end of the file. + */ + while (size>0) { + do nbytes = read(file->fd, buf, size); + while (-1==nbytes && EINTR==errno); + if (-1==nbytes) { + /* error */ + file->pos = HADDR_UNDEF; + file->op = OP_UNKNOWN; + return -1; + } + if (0==nbytes) { + /* end of file but not end of format address space */ + memset(buf, 0, size); + size = 0; + } + assert(nbytes>=0); + assert((hsize_t)nbytes<=size); + size -= (hsize_t)nbytes; + addr += (haddr_t)nbytes; + buf = (char*)buf + nbytes; + } + + /* Update current position */ + file->pos = addr; + file->op = OP_READ; + return 0; +} +</PRE> + +<P> +<STRONG>Example:</STRONG> The sec2 <CODE>write</CODE> callback is similar except it updates +the file EOF marker when extending the file. + +</P> + + +<H3><A NAME="SEC21" HREF="#TOC21">Flushing Cached Data</A></H3> + +<P> +Some drivers may desire to cache data in memory in order to make larger I/O +requests to the underlying file and thus improving bandwidth. Such drivers +should register a cache flushing function so that the library can insure that +data has been flushed out of the drivers in response to the application +calling <CODE>H5Fflush</CODE>. + +</P> +<P> +<DL> +<DT><U>Function:</U> static herr_t <B>flush</B> <I>(H5FD_t *<VAR>file</VAR>)</I> +<DD><A NAME="IDX12"></A> + +</P> +<P> +Flush all data for file <VAR>file</VAR> to storage. +</DL> + +</P> +<P> +<STRONG>Example:</STRONG> The sec2 driver doesn't cache any data but it also doesn't +extend the Unix file as agressively as it should. Therefore, when finalizing a +file it should write a zero to the last byte of the allocated region so that +when reopening the file later the EOF marker will be at least as large as the +EOA marker saved in the superblock (otherwise HDF5 will refuse to open the +file, claiming that the data appears to be truncated). + +</P> + +<PRE> +static herr_t +H5FD_sec2_flush(H5FD_t *_file) +{ + H5FD_sec2_t *file = (H5FD_sec2_t*)_file; + + if (file->eoa>file->eof) { + if (-1==file_seek(file->fd, file->eoa-1, SEEK_SET)) return -1; + if (write(file->fd, "", 1)!=1) return -1; + file->eof = file->eoa; + file->pos = file->eoa; + file->op = OP_WRITE; + } + + return 0; +} +</PRE> + + + +<H2><A NAME="SEC22" HREF="#TOC22">Optimization Functions</A></H2> + +<P> +The library is capable of performing several generic optimizations on I/O, but +these types of optimizations may not be appropriate for a given VFL driver. +</P> + +<P> +Each driver may provide a query function to allow the library to query whether +to enable these optimizations. If a driver lacks a query function, the library +will disable all types of optimizations which can be queried. +</P> + +<P> +<DL> +<DT><U>Function:</U> static herr_t <B>query</B> <I>(const H5FD_t *<VAR>file</VAR>, unsigned long *<VAR>flags</VAR>)</I> +<DD><A NAME="IDX17"></A> +</P> +<P> +This function is called by the library to query which optimizations to enable +for I/O to this driver. These are the flags which are currently defined: + +<UL> +<DL> +<DT>H5FD_FEAT_AGGREGATE_METADATA (0x00000001) +<DD>Defining the H5FD_FEAT_AGGREGATE_METADATA for a VFL driver means that +the library will attempt to allocate a larger block for metadata and +then sub-allocate each metadata request from that larger block. +<DT>H5FD_FEAT_ACCUMULATE_METADATA (0x00000002) +<DD>Defining the H5FD_FEAT_ACCUMULATE_METADATA for a VFL driver means that +the library will attempt to cache metadata as it is written to the file +and build up a larger block of metadata to eventually pass to the VFL +'write' routine. +<DT>H5FD_FEAT_DATA_SIEVE (0x00000004) +<DD>Defining the H5FD_FEAT_DATA_SIEVE for a VFL driver means that +the library will attempt to cache raw data as it is read from/written to +a file in a "data sieve" buffer. See Rajeev Thakur's papers: + <UL> + <DL> + <DT>http://www.mcs.anl.gov/~thakur/papers/romio-coll.ps.gz + <DT>http://www.mcs.anl.gov/~thakur/papers/mpio-high-perf.ps.gz + </DL> + </UL> +</DL> +</UL> +</P> + +</DL> +</P> + +<H2><A NAME="SEC23" HREF="#TOC23">Registration of a Driver</A></H2> + +<P> +Before a driver can be used the HDF5 library needs to be told of its +existence. This is done by registering the driver, which results in a driver +identification number. Instead of passing many arguments to the registration +function, the driver information is entered into a structure and the address +of the structure is passed to the registration function where it is +copied. This allows the HDF5 API to be extended while providing backward +compatibility at the source level. + +</P> +<P> +<DL> +<DT><U>Function:</U> hid_t <B>H5FDregister</B> <I>(H5FD_class_t *<VAR>cls</VAR>)</I> +<DD><A NAME="IDX13"></A> + +</P> +<P> +The driver described by struct <VAR>cls</VAR> is registered with the library and an +ID number for the driver is returned. +</DL> + +</P> +<P> +The <CODE>H5FD_class_t</CODE> type is a struct with the following fields: + +</P> +<DL COMPACT> + +<DT><CODE>const char *name</CODE> +<DD> +A pointer to a constant, null-terminated driver name to be used for debugging +purposes. +<DT><CODE>size_t fapl_size</CODE> +<DD> +The size in bytes of the file access mode structure or zero if the driver +supplies a copy function or doesn't define the structure. +<DT><CODE>void *(*fapl_copy)(const void *fapl)</CODE> +<DD> +An optional function which copies a driver-defined file access mode structure. +This field takes precedence over <CODE>fm_size</CODE> when both are defined. +<DT><CODE>void (*fapl_free)(void *fapl)</CODE> +<DD> +An optional function to free the driver-defined file access mode structure. If +null, then the library calls the C <CODE>free</CODE> function to free the +structure. +<DT><CODE>size_t dxpl_size</CODE> +<DD> +The size in bytes of the data transfer mode structure or zero if the driver +supplies a copy function or doesn't define the structure. +<DT><CODE>void *(*dxpl_copy)(const void *dxpl)</CODE> +<DD> +An optional function which copies a driver-defined data transfer mode +structure. This field takes precedence over <CODE>xm_size</CODE> when both are +defined. +<DT><CODE>void (*dxpl_free)(void *dxpl)</CODE> +<DD> +An optional function to free the driver-defined data transfer mode +structure. If null, then the library calls the C <CODE>free</CODE> function to +free the structure. +<DT><CODE>H5FD_t *(*open)(const char *name, unsigned flags, hid_t fapl, haddr_t maxaddr)</CODE> +<DD> +The function which opens or creates a new file. +<DT><CODE>herr_t (*close)(H5FD_t *file)</CODE> +<DD> +The function which ends access to a file. +<DT><CODE>int (*cmp)(const H5FD_t *f1, const H5FD_t *f2)</CODE> +<DD> +An optional function to determine whether two open files have the same key. If +this function is not present then the library assumes that two files will +never be the same. +<DT><CODE>int (*query)(const H5FD_t *f, unsigned long *flags)</CODE> +<DD> +An optional function to determine which library optimizations a driver can +support. +<DT><CODE>haddr_t (*alloc)(H5FD_t *file, H5FD_mem_t type, hsize_t size)</CODE> +<DD> +An optional function to allocate space in the file. +<DT><CODE>herr_t (*free)(H5FD_t *file, H5FD_mem_t type, haddr_t addr, hsize_t size)</CODE> +<DD> +An optional function to free space in the file. +<DT><CODE>haddr_t (*get_eoa)(H5FD_t *file)</CODE> +<DD> +A function to query how much of the format address space has been allocated. +<DT><CODE>herr_t (*set_eoa)(H5FD_t *file, haddr_t)</CODE> +<DD> +A function to set the end of address space. +<DT><CODE>haddr_t (*get_eof)(H5FD_t *file)</CODE> +<DD> +A function to return the current end-of-file marker value. +<DT><CODE>herr_t (*read)(H5FD_t *file, H5FD_mem_t type, hid_t dxpl, haddr_t addr, hsize_t size, void *buffer)</CODE> +<DD> +A function to read data from a file. +<DT><CODE>herr_t (*write)(H5FD_t *file, H5FD_mem_t type, hid_t dxpl, haddr_t addr, hsize_t size, const void *buffer)</CODE> +<DD> +A function to write data to a file. +<DT><CODE>herr_t (*flush)(H5FD_t *file)</CODE> +<DD> +A function which flushes cached data to the file. +<DT><CODE>H5FD_mem_t fl_map[H5FD_MEM_NTYPES]</CODE> +<DD> +An array which maps a file allocation request type to a free list. +</DL> + +<P> +<STRONG>Example:</STRONG> The sec2 driver would be registered as: + +</P> + +<PRE> +static const H5FD_class_t H5FD_sec2_g = { + "sec2", /*name */ + MAXADDR, /*maxaddr */ + NULL, /*sb_size */ + NULL, /*sb_encode */ + NULL, /*sb_decode */ + 0, /*fapl_size */ + NULL, /*fapl_get */ + NULL, /*fapl_copy */ + NULL, /*fapl_free */ + 0, /*dxpl_size */ + NULL, /*dxpl_copy */ + NULL, /*dxpl_free */ + H5FD_sec2_open, /*open */ + H5FD_sec2_close, /*close */ + H5FD_sec2_cmp, /*cmp */ + H5FD_sec2_query, /*query */ + NULL, /*alloc */ + NULL, /*free */ + H5FD_sec2_get_eoa, /*get_eoa */ + H5FD_sec2_set_eoa, /*set_eoa */ + H5FD_sec2_get_eof, /*get_eof */ + H5FD_sec2_read, /*read */ + H5FD_sec2_write, /*write */ + H5FD_sec2_flush, /*flush */ + H5FD_FLMAP_SINGLE, /*fl_map */ +}; + +hid_t +H5FD_sec2_init(void) +{ + if (!H5FD_SEC2_g) { + H5FD_SEC2_g = H5FDregister(&H5FD_sec2_g); + } + return H5FD_SEC2_g; +} +</PRE> + +<P> +A driver can be removed from the library by unregistering it + +</P> +<P> +<DL> +<DT><U>Function:</U> herr_t <B>H5Dunregister</B> <I>(hid_t <VAR>driver</VAR>)</I> +<DD><A NAME="IDX14"></A> +Where <VAR>driver</VAR> is the ID number returned when the driver was registered. +</DL> + +</P> +<P> +Unregistering a driver makes it unusable for creating new file access or data +transfer property lists but doesn't affect any property lists or files that +already use that driver. + +</P> + + + + +<H3><A NAME="SECProgNote" HREF="#TOCProgNote">Programming Note +for C++ Developers Using C Functions</A></H3> + +<p>If a C routine that takes a function pointer as an argument is +called from within C++ code, the C routine should be returned from +normally. </p> + +<p>Examples of this kind of routine include callbacks such as +<code>H5Pset_elink_cb</code> and <code>H5Pset_type_conv_cb</code> +and functions such as <code>H5Tconvert</code> and +<code>H5Ewalk2</code>.</p> + +<p>Exiting the routine in its normal fashion allows the HDF5 C +Library to clean up its work properly. In other words, if the C++ +application jumps out of the routine back to the C++ +“catch” statement, the library is not given the +opportunity to close any temporary data structures that were set +up when the routine was called. The C++ application should save +some state as the routine is started so that any problem that +occurs might be diagnosed.</p> + + + + + + + +<H2><A NAME="SEC24" HREF="#TOC24">Querying Driver Information</A></H2> + +<P> +<DL> +<DT><U>Function:</U> void * <B>H5Pget_driver_data</B> <I>(hid_t <VAR>fapl</VAR>)</I> +<DD><A NAME="IDX15"></A> +<DT><U>Function:</U> void * <B>H5Pget_driver_data</B> <I>(hid_t <VAR>fxpl</VAR>)</I> +<DD><A NAME="IDX16"></A> + +</P> +<P> +This function is intended to be used by driver functions, not applications. +It returns a pointer directly into the file access property list +<CODE><VAR>fapl</VAR></CODE> which is a copy of the driver's file access mode originally +provided to the <CODE>H5Pset_driver</CODE> function. If its argument is a data +transfer property list <CODE>fxpl</CODE> then it returns a pointer to the +driver-specific data transfer information instead. +</DL> + +</P> + + + +<H1><A NAME="SEC25" HREF="#TOC25">Miscellaneous</A></H1> + +<P> +The various private <CODE>H5F_low_*</CODE> functions will be replaced by public +<CODE>H5FD*</CODE> functions so they can be called from drivers. + +</P> +<P> +All private functions <CODE>H5F_addr_*</CODE> which operate on addresses will be +renamed as public functions by removing the first underscore so they can be +called by drivers. + +</P> +<P> +The <CODE>haddr_t</CODE> address data type will be passed by value throughout the +library. The original intent was that this type would eventually be a union of +file address types for the various drivers and may become quite large, but +that was back when drivers were part of HDF5. It will become an alias for an +unsigned integer type (32 or 64 bits depending on how the library was +configured). + +</P> +<P> +The various <CODE>H5F*.c</CODE> driver files will be renamed <CODE>H5FD*.c</CODE> and each +will have a corresponding header file. All driver functions except the +initializer and API will be declared static. + +</P> +<P> +This documentation didn't cover optimization functions which would be useful +to drivers like MPI-IO. Some drivers may be able to perform data pipeline +operations more efficiently than HDF5 and need to be given a chance to +override those parts of the pipeline. The pipeline would be designed to call +various H5FD optimization functions at various points which return one of +three values: the operation is not implemented by the driver, the operation is +implemented but failed in a non-recoverable manner, the operation is +implemented and succeeded. + +</P> +<P> +Various parts of HDF5 check the only the top-level file driver and do +something special if it is the MPI-IO driver. However, we might want to be +able to put the MPI-IO driver under other drivers such as the raw part of a +split driver or under a debug driver whose sole purpose is to accumulate +statistics as it passes all requests through to the MPI-IO driver. Therefore +we will probably need a function which takes a format address and or object +type and returns the driver which would have been used at the lowest level to +process the request. + +</P> + +<P><HR><P> +<H1>Footnotes</H1> +<H3><A NAME="FOOT1" HREF="#DOCF1">(1)</A></H3> +<P>The driver name is by convention and might +not apply to drivers which are not distributed with HDF5. +<H3><A NAME="FOOT2" HREF="#DOCF2">(2)</A></H3> +<P>The access method also indicates how to translate +the storage name to a storage server such as a file, network protocol, or +memory. +<H3><A NAME="FOOT3" HREF="#DOCF3">(3)</A></H3> +<P>The term +"<EM>file</EM> access property list" is a misnomer since storage isn't +required to be a file. +<H3><A NAME="FOOT4" HREF="#DOCF4">(4)</A></H3> +<P>This +function is overloaded to operate on data transfer property lists also, as +described below. +<H3><A NAME="FOOT5" HREF="#DOCF5">(5)</A></H3> +<P>Read-only access is only appropriate when opening an existing +file. +<H3><A NAME="FOOT6" HREF="#DOCF6">(6)</A></H3> +<P>For instance, writing data to one handle will cause +the data to be immediately visible on the other handle. +<H3><A NAME="FOOT7" HREF="#DOCF7">(7)</A></H3> +<P>The ordering is +arbitrary as long as it's consistent within a particular file driver. +<H3><A NAME="FOOT8" HREF="#DOCF8">(8)</A></H3> +<P>File access modes do not describe data, but rather +describe how the HDF5 format address space is mapped to the underlying +file(s). Thus, in general the mapping must be known before the file superblock +can be read. However, the user usually knows enough about the mapping for the +superblock to be readable and once the superblock is read the library can fill +in the missing parts of the mapping. +<P><HR><P> + +<?php include("../ed_libs/Footer2.htm"); ?> + +</BODY> +</HTML> |
