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authorFrank Baker <fbaker@hdfgroup.org>2003-05-06 22:20:37 (GMT)
committerFrank Baker <fbaker@hdfgroup.org>2003-05-06 22:20:37 (GMT)
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[svn-r6815]
Purpose: Update H5Zregister to describe new approach to filter management. Description: H5Zregister -- heavy revisions to reflect new filter-handling approach. Added H5Z_class_t struct, H5Z_can_apply_func_t callback function, and H5Z_set_local_func_t callback function, and rewrote much of the rest. Platforms tested: IE 5, Safari
Diffstat (limited to 'doc/html/RM_H5Z.html')
-rw-r--r--doc/html/RM_H5Z.html209
1 files changed, 159 insertions, 50 deletions
diff --git a/doc/html/RM_H5Z.html b/doc/html/RM_H5Z.html
index 5e377b2..aad57f4 100644
--- a/doc/html/RM_H5Z.html
+++ b/doc/html/RM_H5Z.html
@@ -137,44 +137,145 @@ facilitate moving easily between them.</i>
<dl>
<dt><strong>Name:</strong> <a name="Compression-Register">H5Zregister</a>
<dt><strong>Signature:</strong>
- <dd><em>herr_t</em> <code>H5Zregister</code>(<em>H5Z_filter_t</em> <code>filter</code>,
- <em>const char *</em><code>comment</code>,
- <em>H5Z_func_t</em> <code>function</code>
+ <dd><em>herr_t</em> <code>H5Zregister</code>(<em>const H5Z_class_t</em> <code>filter_class</code>)
)
<dt><strong>Purpose:</strong>
- <dd> Registers new filter.
+ <dd>Registers new filter.
<dt><strong>Description:</strong>
<dd><code>H5Zregister</code> registers a new filter with the
- HDF5 library.
- <p>
- Making a new filter available to an application is a two-step
- process. The first step is to <span class="termEmphasis">define</span>
- the new filter <code>function</code> as described below.
- This step can be skipped only when the filter is predifined, as is
- the case with the Fletcher32 checksum and shuffle filters that
- are distributed with the HDF5 Library.
- This call to <code>H5Zregister</code>,
- <span class="termEmphasis">registering</span> the filter with the
- library, is the second step.
- <p>
- The new filter is specified by the filter identifier
- <code>filter</code>.
- <p>
- <code>comment</code> is used for debugging and may be
- the null pointer.
- <p>
- <code>function</code> is a user-defined function
- which performs the action of the filter.
- <p>
- The statistics associated with a filter are not reset
- by this function; they accumulate over the life of the library.
-
- <p><strong>New filters.</strong> Before a filter can be
- linked into an application with <code>H5Zregister</code>,
- the filter must be defined as described in the HDF5 Library
- header file <code>H5Zpublic.h</code>:
-
- <dir>
+ HDF5 library.
+ <p>
+ Making a new filter available to an application is a two-step
+ process. The first step is to <span class="termEmphasis">define</span>
+ the three filter callback filter functions described below:
+ <code>can_applyr_func</code>, <code>set_local_func</code>, and
+ <code>filter_func</code>.
+ This step can be skipped only when the filter is predefined, as is
+ the case with the Fletcher32 checksum and shuffle filters that
+ are distributed with the HDF5 Library.
+ This call to <code>H5Zregister</code>,
+ <span class="termEmphasis">registering</span> the filter with the
+ library, is the second step.
+ <p>
+ <code>H5Zregister</code> accepts a single parameter,
+ the <code>filter_class</code> data structure,
+ which is defined as follows:
+ <pre>
+ &nbsp; typedef struct H5Z_class_t {
+ &nbsp; H5Z_filter_t filter_id;
+ &nbsp; const char *comment;
+ &nbsp; H5Z_can_apply_func_t can_apply_func;
+ &nbsp; H5Z_set_local_func_t set_local_func;
+ &nbsp; H5Z_func_t filter_func;
+ &nbsp; } H5Z_class_t;
+ </pre>
+
+ <p>
+ <code>filter_id</code> is the identifier for the new filter.
+ <p>
+ <code>comment</code> is used for debugging and may be
+ the null pointer.
+ <p>
+ <code>can_apply_func</code>, described in detail below,
+ is a user-defined callback function which determines whether
+ the combination of the dataset creation property list setting,
+ the datatype, and the dataspace represent a valid combination
+ to apply this filter to.
+ <p>
+ <code>set_local_func</code>, described in detail below,
+ is a user-defined callback function which sets any parameters that
+ are specific to this dataset, based on the combination of the
+ dataset creation property list values, the datatype, and the
+ dataspace.
+ <p>
+ <code>filter_func</code>, described in detail below,
+ is a user-defined callback function which performs the action
+ of the filter.
+ <p>
+ The statistics associated with a filter are not reset
+ by this function; they accumulate over the life of the library.
+
+ <p>
+ <strong>The callback functions</strong>
+ <br>
+ Before <code>H5Zregister</code> can link a filter into an
+ application, three callback functions must be defined
+ as described in the HDF5 Library header file <code>H5Zpublic.h</code>.
+
+ <p>
+ <u>The <i>can apply</i> callback function</u> is defined as follows:<br>
+ <dir>
+ <em>typedef herr_t</em> (*<code>H5Z_can_apply_func_t</code>)
+ (<em>hid_t</em> <code>dcpl_id</code>,
+ <em>hid_t</em> <code>type_id</code>,
+ <em>hid_t</em> <code>space_id</code>)
+ </dir>
+ <p>
+ Before a dataset is created, the <i>can apply</i> callbacks for
+ any filters used in the dataset creation property list are called
+ with the dataset's dataset creation property list, <code>dcpl_id</code>,
+ the dataset's datatype, <code>type_id</code>, and
+ a dataspace describing a chunk, <code>space_id</code>,
+ (for chunked dataset storage).
+ <p>
+ This callback must determine whether the combination of the
+ dataset creation property list settings, the datatype, and the
+ dataspace represent a valid combination to which to apply this filter.
+ For example, an invalid combination may involve
+ the filter not operating correctly on certain datatypes,
+ on certain datatype sizes, or on certain sizes of the chunk dataspace.
+ <p>
+ This callback can be the <code>NULL</code> pointer, in which case
+ the library will assume that the filter can be applied to a dataset with
+ any combination of dataset creation property list values, datatypes,
+ and dataspaces.
+ <p>
+ The <i>can apply</i> callback function must return
+ a positive value for a valid combination,
+ zero for an invalid combination, and
+ a negative value for an error.
+
+ <p>
+ <u>The <i>set local</i> callback function</u> is defined as follows:<br>
+ <dir>
+ <em>typedef herr_t</em> (*<code>H5Z_set_local_func_t</code>)
+ (<em>hid_t</em> <code>dcpl_id</code>,
+ <em>hid_t</em> <code>type_id</code>,
+ <em>hid_t</em> <code>space_id</code>)
+ </dir>
+ <p>
+ After the <i>can apply</i> callbacks are checked for a new dataset,
+ the <i>set local</i> callback functions for any filters used in the
+ dataset creation property list are called.
+ These callbacks receive
+ <code>dcpl_id</code>, the dataset's private copy of the dataset
+ creation property list passed in to <code>H5Dcreate</code>
+ (i.e. not the actual property list passed in to <code>H5Dcreate</code>);
+ <code>type_id</code>, the datatype identifier passed in to
+ <code>H5Dcreate</code>,
+ which is not copied and should not be modified; and
+ <code>space_id</code>, a dataspace describing the chunk
+ (for chunked dataset storage), which should also not be modified.
+ <p>
+ The <i>set local</i> callback must set any parameters that are
+ specific to this dataset, based on the combination of the
+ dataset creation property list values, the datatype, and the dataspace.
+ For example, some filters perform different actions based on
+ different datatypes, datatype sizes, numbers of dimensions,
+ or dataspace sizes.
+ <p>
+ The <i>set local</i> callback may be the <code>NULL</code> pointer,
+ in which case, the library will assume that there are
+ no dataset-specific settings for this filter.
+ <p>
+ The <i>set local</i> callback function must return
+ a non-negative value on success and
+ a negative value for an error.
+
+ <p>
+ <u>The <i>filter operation</i> callback function</u>,
+ defining the filter's operation on the data, is defined as follows:
+ <dir>
<em>typedef size_t</em> (*<code>H5Z_func_t</code>)
(<em>unsigned int</em> <code>flags</code>,
<em>size_t</em> <code>cd_nelmts</code>,
@@ -182,34 +283,42 @@ facilitate moving easily between them.</i>
<em>size_t</em> <code>nbytes</code>,
<em>size_t *</em><code>buf_size</code>,
<em>void **</em><code>buf</code>)
- </dir>
+ </dir>
- <p>The parameters <code>flags</code>, <code>cd_nelmts</code>,
+ <p>
+ The parameters <code>flags</code>, <code>cd_nelmts</code>,
and <code>cd_values</code> are the same as for the function
- The additional flag <code>H5Z_FLAG_REVERSE</code> is set when
+ <a href="RM_H5P.html#Property-SetFilter"><code>H5Pset_filter</code></a>.
+ The one exception is that an additional flag,
+ <code>H5Z_FLAG_REVERSE</code>, is set when
the filter is called as part of the input pipeline.
+ <p>
The parameter <code>*buf</code> points to the input buffer
which has a size of <code>*buf_size</code> bytes,
<code>nbytes</code> of which are valid data.
- <p>The filter should perform the transformation in place if
- possible and return the number of valid bytes or zero for
- failure. If the transformation cannot be done in place,
+ <p>
+ The filter should perform the transformation in place if
+ possible. If the transformation cannot be done in place,
then the filter should allocate a new buffer with
<code>malloc()</code> and assign it to <code>*buf</code>,
assigning the allocated size of that buffer to
<code>*buf_size</code>.
The old buffer should be freed by calling <code>free()</code>.
-
+ <p>
+ If successful, the <i>filter operation</i> callback function
+ returns the number of valid bytes of data contained in <code>*buf</code>.
+ In the case of failure, the return value is <code>0</code> (zero)
+ and all pointer arguments are left unchanged.
+<dt><strong>Note:</strong>
+ <dd>The <code>H5Zregister</code> interface is substantially revised
+ from the HDF5 Release 1.4.x series.
+ The <code>H5Z_class_t</code> struct and
+ the <i>set local</i> and <i>can apply</i> callback functions
+ first appeared in HDF5 Release 1.6.
<dt><strong>Parameters:</strong>
<dl>
- <dt><em>H5Z_filter_t</em> <code>method</code>
- <dd>IN: Filter identifier.
- <dt><em>const char *</em><code>comment</code>
- <dd>IN: String associated with the filter;
- used for debugging purposes only.
- May be the null pointer.
- <dt><em>H5Z_func_t</em> <code>function</code>
- <dd>IN: Filter function.
+ <dt><em>const H5Z_class_t</em> <code>filter_class</code>
+ <dd>IN: Struct containing filter-definition information.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns a non-negative value if successful;
@@ -334,7 +443,7 @@ And in this document, the
Describes HDF5 Release 1.5, Unreleased Development Branch
</address><!-- #EndLibraryItem -->
-Last modified: 8 April 2003
+Last modified: 6 May 2003
</body>
</html>