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diff --git a/Utilities/cmbzip2/manual.html b/Utilities/cmbzip2/manual.html new file mode 100644 index 0000000..bb44953 --- /dev/null +++ b/Utilities/cmbzip2/manual.html @@ -0,0 +1,2540 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>bzip2 and libbzip2, version 1.0.5</title> +<meta name="generator" content="DocBook XSL Stylesheets V1.69.1"> +<style type="text/css" media="screen">/* Colours: +#74240f dark brown h1, h2, h3, h4 +#336699 medium blue links +#339999 turquoise link hover colour +#202020 almost black general text +#761596 purple md5sum text +#626262 dark gray pre border +#eeeeee very light gray pre background +#f2f2f9 very light blue nav table background +#3366cc medium blue nav table border +*/ + +a, a:link, a:visited, a:active { color: #336699; } +a:hover { color: #339999; } + +body { font: 80%/126% sans-serif; } +h1, h2, h3, h4 { color: #74240f; } + +dt { color: #336699; font-weight: bold } +dd { + margin-left: 1.5em; + padding-bottom: 0.8em; +} + +/* -- ruler -- */ +div.hr_blue { + height: 3px; + background:#ffffff url("/images/hr_blue.png") repeat-x; } +div.hr_blue hr { display:none; } + +/* release styles */ +#release p { margin-top: 0.4em; } +#release .md5sum { color: #761596; } + + +/* ------ styles for docs|manuals|howto ------ */ +/* -- lists -- */ +ul { + margin: 0px 4px 16px 16px; + padding: 0px; + list-style: url("/images/li-blue.png"); +} +ul li { + margin-bottom: 10px; +} +ul ul { + list-style-type: none; + list-style-image: none; + margin-left: 0px; +} + +/* header / footer nav tables */ +table.nav { + border: solid 1px #3366cc; + background: #f2f2f9; + background-color: #f2f2f9; + margin-bottom: 0.5em; +} +/* don't have underlined links in chunked nav menus */ +table.nav a { text-decoration: none; } +table.nav a:hover { text-decoration: underline; } +table.nav td { font-size: 85%; } + +code, tt, pre { font-size: 120%; } +code, tt { color: #761596; } + +div.literallayout, pre.programlisting, pre.screen { + color: #000000; + padding: 0.5em; + background: #eeeeee; + border: 1px solid #626262; + background-color: #eeeeee; + margin: 4px 0px 4px 0px; +} +</style> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en"> +<div class="titlepage"> +<div> +<div><h1 class="title"> +<a name="userman"></a>bzip2 and libbzip2, version 1.0.5</h1></div> +<div><h2 class="subtitle">A program and library for data compression</h2></div> +<div><div class="authorgroup"><div class="author"> +<h3 class="author"> +<span class="firstname">Julian</span> <span class="surname">Seward</span> +</h3> +<div class="affiliation"><span class="orgname">http://www.bzip.org<br></span></div> +</div></div></div> +<div><p class="releaseinfo">Version 1.0.5 of 10 December 2007</p></div> +<div><p class="copyright">Copyright © 1996-2007 Julian Seward</p></div> +<div><div class="legalnotice"> +<a name="id2499833"></a><p>This program, <code class="computeroutput">bzip2</code>, the + associated library <code class="computeroutput">libbzip2</code>, and + all documentation, are copyright © 1996-2007 Julian Seward. + All rights reserved.</p> +<p>Redistribution and use in source and binary forms, with + or without modification, are permitted provided that the + following conditions are met:</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p>Redistributions of source code must retain the + above copyright notice, this list of conditions and the + following disclaimer.</p></li> +<li style="list-style-type: disc"><p>The origin of this software must not be + misrepresented; you must not claim that you wrote the original + software. If you use this software in a product, an + acknowledgment in the product documentation would be + appreciated but is not required.</p></li> +<li style="list-style-type: disc"><p>Altered source versions must be plainly marked + as such, and must not be misrepresented as being the original + software.</p></li> +<li style="list-style-type: disc"><p>The name of the author may not be used to + endorse or promote products derived from this software without + specific prior written permission.</p></li> +</ul></div> +<p>THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY + EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, + EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED + TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND + ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING + IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF + THE POSSIBILITY OF SUCH DAMAGE.</p> +<p>PATENTS: To the best of my knowledge, + <code class="computeroutput">bzip2</code> and + <code class="computeroutput">libbzip2</code> do not use any patented + algorithms. However, I do not have the resources to carry + out a patent search. Therefore I cannot give any guarantee of + the above statement. + </p> +</div></div> +</div> +<hr> +</div> +<div class="toc"> +<p><b>Table of Contents</b></p> +<dl> +<dt><span class="chapter"><a href="#intro">1. Introduction</a></span></dt> +<dt><span class="chapter"><a href="#using">2. How to use bzip2</a></span></dt> +<dd><dl> +<dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt> +<dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt> +<dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt> +<dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt> +<dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt> +<dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt> +<dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt> +<dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt> +<dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt> +</dl></dd> +<dt><span class="chapter"><a href="#libprog">3. +Programming with <code class="computeroutput">libbzip2</code> +</a></span></dt> +<dd><dl> +<dt><span class="sect1"><a href="#top-level">3.1. Top-level structure</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt> +<dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt> +<dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt> +<dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#bzcompress-init">3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></a></span></dt> +<dt><span class="sect2"><a href="#bzCompress">3.3.2. <code class="computeroutput">BZ2_bzCompress</code></a></span></dt> +<dt><span class="sect2"><a href="#bzCompress-end">3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></a></span></dt> +<dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></a></span></dt> +<dt><span class="sect2"><a href="#bzDecompress">3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></a></span></dt> +<dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#bzreadopen">3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></a></span></dt> +<dt><span class="sect2"><a href="#bzread">3.4.2. <code class="computeroutput">BZ2_bzRead</code></a></span></dt> +<dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></a></span></dt> +<dt><span class="sect2"><a href="#bzreadclose">3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></a></span></dt> +<dt><span class="sect2"><a href="#bzwriteopen">3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></a></span></dt> +<dt><span class="sect2"><a href="#bzwrite">3.4.6. <code class="computeroutput">BZ2_bzWrite</code></a></span></dt> +<dt><span class="sect2"><a href="#bzwriteclose">3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></a></span></dt> +<dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt> +<dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></a></span></dt> +<dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#zlib-compat">3.6. <code class="computeroutput">zlib</code> compatibility functions</a></span></dt> +<dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of <code class="computeroutput">stdio</code></a></span></dt> +<dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt> +</dl></dd> +<dt><span class="chapter"><a href="#misc">4. Miscellanea</a></span></dt> +<dd><dl> +<dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt> +<dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt> +<dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt> +<dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt> +<dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt> +</dl></dd> +</dl> +</div> +<div class="chapter" lang="en"> +<div class="titlepage"><div><div><h2 class="title"> +<a name="intro"></a>1. Introduction</h2></div></div></div> +<p><code class="computeroutput">bzip2</code> compresses files +using the Burrows-Wheeler block-sorting text compression +algorithm, and Huffman coding. Compression is generally +considerably better than that achieved by more conventional +LZ77/LZ78-based compressors, and approaches the performance of +the PPM family of statistical compressors.</p> +<p><code class="computeroutput">bzip2</code> is built on top of +<code class="computeroutput">libbzip2</code>, a flexible library for +handling compressed data in the +<code class="computeroutput">bzip2</code> format. This manual +describes both how to use the program and how to work with the +library interface. Most of the manual is devoted to this +library, not the program, which is good news if your interest is +only in the program.</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p><a href="#using">How to use bzip2</a> describes how to use + <code class="computeroutput">bzip2</code>; this is the only part + you need to read if you just want to know how to operate the + program.</p></li> +<li style="list-style-type: disc"><p><a href="#libprog">Programming with libbzip2</a> describes the + programming interfaces in detail, and</p></li> +<li style="list-style-type: disc"><p><a href="#misc">Miscellanea</a> records some + miscellaneous notes which I thought ought to be recorded + somewhere.</p></li> +</ul></div> +</div> +<div class="chapter" lang="en"> +<div class="titlepage"><div><div><h2 class="title"> +<a name="using"></a>2. How to use bzip2</h2></div></div></div> +<div class="toc"> +<p><b>Table of Contents</b></p> +<dl> +<dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt> +<dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt> +<dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt> +<dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt> +<dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt> +<dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt> +<dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt> +<dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt> +<dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt> +</dl> +</div> +<p>This chapter contains a copy of the +<code class="computeroutput">bzip2</code> man page, and nothing +else.</p> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="name"></a>2.1. NAME</h2></div></div></div> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p><code class="computeroutput">bzip2</code>, + <code class="computeroutput">bunzip2</code> - a block-sorting file + compressor, v1.0.4</p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> - + decompresses files to stdout</p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code> - + recovers data from damaged bzip2 files</p></li> +</ul></div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="synopsis"></a>2.2. SYNOPSIS</h2></div></div></div> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p><code class="computeroutput">bzip2</code> [ + -cdfkqstvzVL123456789 ] [ filenames ... ]</p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">bunzip2</code> [ + -fkvsVL ] [ filenames ... ]</p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> [ -s ] [ + filenames ... ]</p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code> + filename</p></li> +</ul></div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="description"></a>2.3. DESCRIPTION</h2></div></div></div> +<p><code class="computeroutput">bzip2</code> compresses files +using the Burrows-Wheeler block sorting text compression +algorithm, and Huffman coding. Compression is generally +considerably better than that achieved by more conventional +LZ77/LZ78-based compressors, and approaches the performance of +the PPM family of statistical compressors.</p> +<p>The command-line options are deliberately very similar to +those of GNU <code class="computeroutput">gzip</code>, but they are +not identical.</p> +<p><code class="computeroutput">bzip2</code> expects a list of +file names to accompany the command-line flags. Each file is +replaced by a compressed version of itself, with the name +<code class="computeroutput">original_name.bz2</code>. Each +compressed file has the same modification date, permissions, and, +when possible, ownership as the corresponding original, so that +these properties can be correctly restored at decompression time. +File name handling is naive in the sense that there is no +mechanism for preserving original file names, permissions, +ownerships or dates in filesystems which lack these concepts, or +have serious file name length restrictions, such as +MS-DOS.</p> +<p><code class="computeroutput">bzip2</code> and +<code class="computeroutput">bunzip2</code> will by default not +overwrite existing files. If you want this to happen, specify +the <code class="computeroutput">-f</code> flag.</p> +<p>If no file names are specified, +<code class="computeroutput">bzip2</code> compresses from standard +input to standard output. In this case, +<code class="computeroutput">bzip2</code> will decline to write +compressed output to a terminal, as this would be entirely +incomprehensible and therefore pointless.</p> +<p><code class="computeroutput">bunzip2</code> (or +<code class="computeroutput">bzip2 -d</code>) decompresses all +specified files. Files which were not created by +<code class="computeroutput">bzip2</code> will be detected and +ignored, and a warning issued. +<code class="computeroutput">bzip2</code> attempts to guess the +filename for the decompressed file from that of the compressed +file as follows:</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p><code class="computeroutput">filename.bz2 </code> + becomes + <code class="computeroutput">filename</code></p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">filename.bz </code> + becomes + <code class="computeroutput">filename</code></p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">filename.tbz2</code> + becomes + <code class="computeroutput">filename.tar</code></p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">filename.tbz </code> + becomes + <code class="computeroutput">filename.tar</code></p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">anyothername </code> + becomes + <code class="computeroutput">anyothername.out</code></p></li> +</ul></div> +<p>If the file does not end in one of the recognised endings, +<code class="computeroutput">.bz2</code>, +<code class="computeroutput">.bz</code>, +<code class="computeroutput">.tbz2</code> or +<code class="computeroutput">.tbz</code>, +<code class="computeroutput">bzip2</code> complains that it cannot +guess the name of the original file, and uses the original name +with <code class="computeroutput">.out</code> appended.</p> +<p>As with compression, supplying no filenames causes +decompression from standard input to standard output.</p> +<p><code class="computeroutput">bunzip2</code> will correctly +decompress a file which is the concatenation of two or more +compressed files. The result is the concatenation of the +corresponding uncompressed files. Integrity testing +(<code class="computeroutput">-t</code>) of concatenated compressed +files is also supported.</p> +<p>You can also compress or decompress files to the standard +output by giving the <code class="computeroutput">-c</code> flag. +Multiple files may be compressed and decompressed like this. The +resulting outputs are fed sequentially to stdout. Compression of +multiple files in this manner generates a stream containing +multiple compressed file representations. Such a stream can be +decompressed correctly only by +<code class="computeroutput">bzip2</code> version 0.9.0 or later. +Earlier versions of <code class="computeroutput">bzip2</code> will +stop after decompressing the first file in the stream.</p> +<p><code class="computeroutput">bzcat</code> (or +<code class="computeroutput">bzip2 -dc</code>) decompresses all +specified files to the standard output.</p> +<p><code class="computeroutput">bzip2</code> will read arguments +from the environment variables +<code class="computeroutput">BZIP2</code> and +<code class="computeroutput">BZIP</code>, in that order, and will +process them before any arguments read from the command line. +This gives a convenient way to supply default arguments.</p> +<p>Compression is always performed, even if the compressed +file is slightly larger than the original. Files of less than +about one hundred bytes tend to get larger, since the compression +mechanism has a constant overhead in the region of 50 bytes. +Random data (including the output of most file compressors) is +coded at about 8.05 bits per byte, giving an expansion of around +0.5%.</p> +<p>As a self-check for your protection, +<code class="computeroutput">bzip2</code> uses 32-bit CRCs to make +sure that the decompressed version of a file is identical to the +original. This guards against corruption of the compressed data, +and against undetected bugs in +<code class="computeroutput">bzip2</code> (hopefully very unlikely). +The chances of data corruption going undetected is microscopic, +about one chance in four billion for each file processed. Be +aware, though, that the check occurs upon decompression, so it +can only tell you that something is wrong. It can't help you +recover the original uncompressed data. You can use +<code class="computeroutput">bzip2recover</code> to try to recover +data from damaged files.</p> +<p>Return values: 0 for a normal exit, 1 for environmental +problems (file not found, invalid flags, I/O errors, etc.), 2 +to indicate a corrupt compressed file, 3 for an internal +consistency error (eg, bug) which caused +<code class="computeroutput">bzip2</code> to panic.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="options"></a>2.4. OPTIONS</h2></div></div></div> +<div class="variablelist"><dl> +<dt><span class="term"><code class="computeroutput">-c --stdout</code></span></dt> +<dd><p>Compress or decompress to standard + output.</p></dd> +<dt><span class="term"><code class="computeroutput">-d --decompress</code></span></dt> +<dd><p>Force decompression. + <code class="computeroutput">bzip2</code>, + <code class="computeroutput">bunzip2</code> and + <code class="computeroutput">bzcat</code> are really the same + program, and the decision about what actions to take is done on + the basis of which name is used. This flag overrides that + mechanism, and forces bzip2 to decompress.</p></dd> +<dt><span class="term"><code class="computeroutput">-z --compress</code></span></dt> +<dd><p>The complement to + <code class="computeroutput">-d</code>: forces compression, + regardless of the invokation name.</p></dd> +<dt><span class="term"><code class="computeroutput">-t --test</code></span></dt> +<dd><p>Check integrity of the specified file(s), but + don't decompress them. This really performs a trial + decompression and throws away the result.</p></dd> +<dt><span class="term"><code class="computeroutput">-f --force</code></span></dt> +<dd> +<p>Force overwrite of output files. Normally, + <code class="computeroutput">bzip2</code> will not overwrite + existing output files. Also forces + <code class="computeroutput">bzip2</code> to break hard links to + files, which it otherwise wouldn't do.</p> +<p><code class="computeroutput">bzip2</code> normally declines + to decompress files which don't have the correct magic header + bytes. If forced (<code class="computeroutput">-f</code>), + however, it will pass such files through unmodified. This is + how GNU <code class="computeroutput">gzip</code> behaves.</p> +</dd> +<dt><span class="term"><code class="computeroutput">-k --keep</code></span></dt> +<dd><p>Keep (don't delete) input files during + compression or decompression.</p></dd> +<dt><span class="term"><code class="computeroutput">-s --small</code></span></dt> +<dd> +<p>Reduce memory usage, for compression, + decompression and testing. Files are decompressed and tested + using a modified algorithm which only requires 2.5 bytes per + block byte. This means any file can be decompressed in 2300k + of memory, albeit at about half the normal speed.</p> +<p>During compression, <code class="computeroutput">-s</code> + selects a block size of 200k, which limits memory use to around + the same figure, at the expense of your compression ratio. In + short, if your machine is low on memory (8 megabytes or less), + use <code class="computeroutput">-s</code> for everything. See + <a href="#memory-management">MEMORY MANAGEMENT</a> below.</p> +</dd> +<dt><span class="term"><code class="computeroutput">-q --quiet</code></span></dt> +<dd><p>Suppress non-essential warning messages. + Messages pertaining to I/O errors and other critical events + will not be suppressed.</p></dd> +<dt><span class="term"><code class="computeroutput">-v --verbose</code></span></dt> +<dd><p>Verbose mode -- show the compression ratio for + each file processed. Further + <code class="computeroutput">-v</code>'s increase the verbosity + level, spewing out lots of information which is primarily of + interest for diagnostic purposes.</p></dd> +<dt><span class="term"><code class="computeroutput">-L --license -V --version</code></span></dt> +<dd><p>Display the software version, license terms and + conditions.</p></dd> +<dt><span class="term"><code class="computeroutput">-1</code> (or + <code class="computeroutput">--fast</code>) to + <code class="computeroutput">-9</code> (or + <code class="computeroutput">-best</code>)</span></dt> +<dd><p>Set the block size to 100 k, 200 k ... 900 k + when compressing. Has no effect when decompressing. See <a href="#memory-management">MEMORY MANAGEMENT</a> below. The + <code class="computeroutput">--fast</code> and + <code class="computeroutput">--best</code> aliases are primarily + for GNU <code class="computeroutput">gzip</code> compatibility. + In particular, <code class="computeroutput">--fast</code> doesn't + make things significantly faster. And + <code class="computeroutput">--best</code> merely selects the + default behaviour.</p></dd> +<dt><span class="term"><code class="computeroutput">--</code></span></dt> +<dd><p>Treats all subsequent arguments as file names, + even if they start with a dash. This is so you can handle + files with names beginning with a dash, for example: + <code class="computeroutput">bzip2 -- + -myfilename</code>.</p></dd> +<dt> +<span class="term"><code class="computeroutput">--repetitive-fast</code>, </span><span class="term"><code class="computeroutput">--repetitive-best</code></span> +</dt> +<dd><p>These flags are redundant in versions 0.9.5 and + above. They provided some coarse control over the behaviour of + the sorting algorithm in earlier versions, which was sometimes + useful. 0.9.5 and above have an improved algorithm which + renders these flags irrelevant.</p></dd> +</dl></div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="memory-management"></a>2.5. MEMORY MANAGEMENT</h2></div></div></div> +<p><code class="computeroutput">bzip2</code> compresses large +files in blocks. The block size affects both the compression +ratio achieved, and the amount of memory needed for compression +and decompression. The flags <code class="computeroutput">-1</code> +through <code class="computeroutput">-9</code> specify the block +size to be 100,000 bytes through 900,000 bytes (the default) +respectively. At decompression time, the block size used for +compression is read from the header of the compressed file, and +<code class="computeroutput">bunzip2</code> then allocates itself +just enough memory to decompress the file. Since block sizes are +stored in compressed files, it follows that the flags +<code class="computeroutput">-1</code> to +<code class="computeroutput">-9</code> are irrelevant to and so +ignored during decompression.</p> +<p>Compression and decompression requirements, in bytes, can be +estimated as:</p> +<pre class="programlisting">Compression: 400k + ( 8 x block size ) + +Decompression: 100k + ( 4 x block size ), or + 100k + ( 2.5 x block size )</pre> +<p>Larger block sizes give rapidly diminishing marginal +returns. Most of the compression comes from the first two or +three hundred k of block size, a fact worth bearing in mind when +using <code class="computeroutput">bzip2</code> on small machines. +It is also important to appreciate that the decompression memory +requirement is set at compression time by the choice of block +size.</p> +<p>For files compressed with the default 900k block size, +<code class="computeroutput">bunzip2</code> will require about 3700 +kbytes to decompress. To support decompression of any file on a +4 megabyte machine, <code class="computeroutput">bunzip2</code> has +an option to decompress using approximately half this amount of +memory, about 2300 kbytes. Decompression speed is also halved, +so you should use this option only where necessary. The relevant +flag is <code class="computeroutput">-s</code>.</p> +<p>In general, try and use the largest block size memory +constraints allow, since that maximises the compression achieved. +Compression and decompression speed are virtually unaffected by +block size.</p> +<p>Another significant point applies to files which fit in a +single block -- that means most files you'd encounter using a +large block size. The amount of real memory touched is +proportional to the size of the file, since the file is smaller +than a block. For example, compressing a file 20,000 bytes long +with the flag <code class="computeroutput">-9</code> will cause the +compressor to allocate around 7600k of memory, but only touch +400k + 20000 * 8 = 560 kbytes of it. Similarly, the decompressor +will allocate 3700k but only touch 100k + 20000 * 4 = 180 +kbytes.</p> +<p>Here is a table which summarises the maximum memory usage +for different block sizes. Also recorded is the total compressed +size for 14 files of the Calgary Text Compression Corpus +totalling 3,141,622 bytes. This column gives some feel for how +compression varies with block size. These figures tend to +understate the advantage of larger block sizes for larger files, +since the Corpus is dominated by smaller files.</p> +<pre class="programlisting"> Compress Decompress Decompress Corpus +Flag usage usage -s usage Size + + -1 1200k 500k 350k 914704 + -2 2000k 900k 600k 877703 + -3 2800k 1300k 850k 860338 + -4 3600k 1700k 1100k 846899 + -5 4400k 2100k 1350k 845160 + -6 5200k 2500k 1600k 838626 + -7 6100k 2900k 1850k 834096 + -8 6800k 3300k 2100k 828642 + -9 7600k 3700k 2350k 828642</pre> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="recovering"></a>2.6. RECOVERING DATA FROM DAMAGED FILES</h2></div></div></div> +<p><code class="computeroutput">bzip2</code> compresses files in +blocks, usually 900kbytes long. Each block is handled +independently. If a media or transmission error causes a +multi-block <code class="computeroutput">.bz2</code> file to become +damaged, it may be possible to recover data from the undamaged +blocks in the file.</p> +<p>The compressed representation of each block is delimited by +a 48-bit pattern, which makes it possible to find the block +boundaries with reasonable certainty. Each block also carries +its own 32-bit CRC, so damaged blocks can be distinguished from +undamaged ones.</p> +<p><code class="computeroutput">bzip2recover</code> is a simple +program whose purpose is to search for blocks in +<code class="computeroutput">.bz2</code> files, and write each block +out into its own <code class="computeroutput">.bz2</code> file. You +can then use <code class="computeroutput">bzip2 -t</code> to test +the integrity of the resulting files, and decompress those which +are undamaged.</p> +<p><code class="computeroutput">bzip2recover</code> takes a +single argument, the name of the damaged file, and writes a +number of files <code class="computeroutput">rec0001file.bz2</code>, +<code class="computeroutput">rec0002file.bz2</code>, etc, containing +the extracted blocks. The output filenames are designed so that +the use of wildcards in subsequent processing -- for example, +<code class="computeroutput">bzip2 -dc rec*file.bz2 > +recovered_data</code> -- lists the files in the correct +order.</p> +<p><code class="computeroutput">bzip2recover</code> should be of +most use dealing with large <code class="computeroutput">.bz2</code> +files, as these will contain many blocks. It is clearly futile +to use it on damaged single-block files, since a damaged block +cannot be recovered. If you wish to minimise any potential data +loss through media or transmission errors, you might consider +compressing with a smaller block size.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="performance"></a>2.7. PERFORMANCE NOTES</h2></div></div></div> +<p>The sorting phase of compression gathers together similar +strings in the file. Because of this, files containing very long +runs of repeated symbols, like "aabaabaabaab ..." (repeated +several hundred times) may compress more slowly than normal. +Versions 0.9.5 and above fare much better than previous versions +in this respect. The ratio between worst-case and average-case +compression time is in the region of 10:1. For previous +versions, this figure was more like 100:1. You can use the +<code class="computeroutput">-vvvv</code> option to monitor progress +in great detail, if you want.</p> +<p>Decompression speed is unaffected by these +phenomena.</p> +<p><code class="computeroutput">bzip2</code> usually allocates +several megabytes of memory to operate in, and then charges all +over it in a fairly random fashion. This means that performance, +both for compressing and decompressing, is largely determined by +the speed at which your machine can service cache misses. +Because of this, small changes to the code to reduce the miss +rate have been observed to give disproportionately large +performance improvements. I imagine +<code class="computeroutput">bzip2</code> will perform best on +machines with very large caches.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="caveats"></a>2.8. CAVEATS</h2></div></div></div> +<p>I/O error messages are not as helpful as they could be. +<code class="computeroutput">bzip2</code> tries hard to detect I/O +errors and exit cleanly, but the details of what the problem is +sometimes seem rather misleading.</p> +<p>This manual page pertains to version 1.0.5 of +<code class="computeroutput">bzip2</code>. Compressed data created by +this version is entirely forwards and backwards compatible with the +previous public releases, versions 0.1pl2, 0.9.0 and 0.9.5, 1.0.0, +1.0.1, 1.0.2 and 1.0.3, but with the following exception: 0.9.0 and +above can correctly decompress multiple concatenated compressed files. +0.1pl2 cannot do this; it will stop after decompressing just the first +file in the stream.</p> +<p><code class="computeroutput">bzip2recover</code> versions +prior to 1.0.2 used 32-bit integers to represent bit positions in +compressed files, so it could not handle compressed files more +than 512 megabytes long. Versions 1.0.2 and above use 64-bit ints +on some platforms which support them (GNU supported targets, and +Windows). To establish whether or not +<code class="computeroutput">bzip2recover</code> was built with such +a limitation, run it without arguments. In any event you can +build yourself an unlimited version if you can recompile it with +<code class="computeroutput">MaybeUInt64</code> set to be an +unsigned 64-bit integer.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="author"></a>2.9. AUTHOR</h2></div></div></div> +<p>Julian Seward, +<code class="computeroutput">jseward@bzip.org</code></p> +<p>The ideas embodied in +<code class="computeroutput">bzip2</code> are due to (at least) the +following people: Michael Burrows and David Wheeler (for the +block sorting transformation), David Wheeler (again, for the +Huffman coder), Peter Fenwick (for the structured coding model in +the original <code class="computeroutput">bzip</code>, and many +refinements), and Alistair Moffat, Radford Neal and Ian Witten +(for the arithmetic coder in the original +<code class="computeroutput">bzip</code>). I am much indebted for +their help, support and advice. See the manual in the source +distribution for pointers to sources of documentation. Christian +von Roques encouraged me to look for faster sorting algorithms, +so as to speed up compression. Bela Lubkin encouraged me to +improve the worst-case compression performance. +Donna Robinson XMLised the documentation. +Many people sent +patches, helped with portability problems, lent machines, gave +advice and were generally helpful.</p> +</div> +</div> +<div class="chapter" lang="en"> +<div class="titlepage"><div><div><h2 class="title"> +<a name="libprog"></a>3. +Programming with <code class="computeroutput">libbzip2</code> +</h2></div></div></div> +<div class="toc"> +<p><b>Table of Contents</b></p> +<dl> +<dt><span class="sect1"><a href="#top-level">3.1. Top-level structure</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt> +<dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt> +<dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt> +<dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#bzcompress-init">3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></a></span></dt> +<dt><span class="sect2"><a href="#bzCompress">3.3.2. <code class="computeroutput">BZ2_bzCompress</code></a></span></dt> +<dt><span class="sect2"><a href="#bzCompress-end">3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></a></span></dt> +<dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></a></span></dt> +<dt><span class="sect2"><a href="#bzDecompress">3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></a></span></dt> +<dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#bzreadopen">3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></a></span></dt> +<dt><span class="sect2"><a href="#bzread">3.4.2. <code class="computeroutput">BZ2_bzRead</code></a></span></dt> +<dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></a></span></dt> +<dt><span class="sect2"><a href="#bzreadclose">3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></a></span></dt> +<dt><span class="sect2"><a href="#bzwriteopen">3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></a></span></dt> +<dt><span class="sect2"><a href="#bzwrite">3.4.6. <code class="computeroutput">BZ2_bzWrite</code></a></span></dt> +<dt><span class="sect2"><a href="#bzwriteclose">3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></a></span></dt> +<dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt> +<dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></a></span></dt> +<dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#zlib-compat">3.6. <code class="computeroutput">zlib</code> compatibility functions</a></span></dt> +<dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</a></span></dt> +<dd><dl> +<dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of <code class="computeroutput">stdio</code></a></span></dt> +<dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt> +</dl></dd> +<dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt> +</dl> +</div> +<p>This chapter describes the programming interface to +<code class="computeroutput">libbzip2</code>.</p> +<p>For general background information, particularly about +memory use and performance aspects, you'd be well advised to read +<a href="#using">How to use bzip2</a> as well.</p> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="top-level"></a>3.1. Top-level structure</h2></div></div></div> +<p><code class="computeroutput">libbzip2</code> is a flexible +library for compressing and decompressing data in the +<code class="computeroutput">bzip2</code> data format. Although +packaged as a single entity, it helps to regard the library as +three separate parts: the low level interface, and the high level +interface, and some utility functions.</p> +<p>The structure of +<code class="computeroutput">libbzip2</code>'s interfaces is similar +to that of Jean-loup Gailly's and Mark Adler's excellent +<code class="computeroutput">zlib</code> library.</p> +<p>All externally visible symbols have names beginning +<code class="computeroutput">BZ2_</code>. This is new in version +1.0. The intention is to minimise pollution of the namespaces of +library clients.</p> +<p>To use any part of the library, you need to +<code class="computeroutput">#include <bzlib.h></code> +into your sources.</p> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="ll-summary"></a>3.1.1. Low-level summary</h3></div></div></div> +<p>This interface provides services for compressing and +decompressing data in memory. There's no provision for dealing +with files, streams or any other I/O mechanisms, just straight +memory-to-memory work. In fact, this part of the library can be +compiled without inclusion of +<code class="computeroutput">stdio.h</code>, which may be helpful +for embedded applications.</p> +<p>The low-level part of the library has no global variables +and is therefore thread-safe.</p> +<p>Six routines make up the low level interface: +<code class="computeroutput">BZ2_bzCompressInit</code>, +<code class="computeroutput">BZ2_bzCompress</code>, and +<code class="computeroutput">BZ2_bzCompressEnd</code> for +compression, and a corresponding trio +<code class="computeroutput">BZ2_bzDecompressInit</code>, +<code class="computeroutput">BZ2_bzDecompress</code> and +<code class="computeroutput">BZ2_bzDecompressEnd</code> for +decompression. The <code class="computeroutput">*Init</code> +functions allocate memory for compression/decompression and do +other initialisations, whilst the +<code class="computeroutput">*End</code> functions close down +operations and release memory.</p> +<p>The real work is done by +<code class="computeroutput">BZ2_bzCompress</code> and +<code class="computeroutput">BZ2_bzDecompress</code>. These +compress and decompress data from a user-supplied input buffer to +a user-supplied output buffer. These buffers can be any size; +arbitrary quantities of data are handled by making repeated calls +to these functions. This is a flexible mechanism allowing a +consumer-pull style of activity, or producer-push, or a mixture +of both.</p> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="hl-summary"></a>3.1.2. High-level summary</h3></div></div></div> +<p>This interface provides some handy wrappers around the +low-level interface to facilitate reading and writing +<code class="computeroutput">bzip2</code> format files +(<code class="computeroutput">.bz2</code> files). The routines +provide hooks to facilitate reading files in which the +<code class="computeroutput">bzip2</code> data stream is embedded +within some larger-scale file structure, or where there are +multiple <code class="computeroutput">bzip2</code> data streams +concatenated end-to-end.</p> +<p>For reading files, +<code class="computeroutput">BZ2_bzReadOpen</code>, +<code class="computeroutput">BZ2_bzRead</code>, +<code class="computeroutput">BZ2_bzReadClose</code> and +<code class="computeroutput">BZ2_bzReadGetUnused</code> are +supplied. For writing files, +<code class="computeroutput">BZ2_bzWriteOpen</code>, +<code class="computeroutput">BZ2_bzWrite</code> and +<code class="computeroutput">BZ2_bzWriteFinish</code> are +available.</p> +<p>As with the low-level library, no global variables are used +so the library is per se thread-safe. However, if I/O errors +occur whilst reading or writing the underlying compressed files, +you may have to consult <code class="computeroutput">errno</code> to +determine the cause of the error. In that case, you'd need a C +library which correctly supports +<code class="computeroutput">errno</code> in a multithreaded +environment.</p> +<p>To make the library a little simpler and more portable, +<code class="computeroutput">BZ2_bzReadOpen</code> and +<code class="computeroutput">BZ2_bzWriteOpen</code> require you to +pass them file handles (<code class="computeroutput">FILE*</code>s) +which have previously been opened for reading or writing +respectively. That avoids portability problems associated with +file operations and file attributes, whilst not being much of an +imposition on the programmer.</p> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="util-fns-summary"></a>3.1.3. Utility functions summary</h3></div></div></div> +<p>For very simple needs, +<code class="computeroutput">BZ2_bzBuffToBuffCompress</code> and +<code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> are +provided. These compress data in memory from one buffer to +another buffer in a single function call. You should assess +whether these functions fulfill your memory-to-memory +compression/decompression requirements before investing effort in +understanding the more general but more complex low-level +interface.</p> +<p>Yoshioka Tsuneo +(<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>) has +contributed some functions to give better +<code class="computeroutput">zlib</code> compatibility. These +functions are <code class="computeroutput">BZ2_bzopen</code>, +<code class="computeroutput">BZ2_bzread</code>, +<code class="computeroutput">BZ2_bzwrite</code>, +<code class="computeroutput">BZ2_bzflush</code>, +<code class="computeroutput">BZ2_bzclose</code>, +<code class="computeroutput">BZ2_bzerror</code> and +<code class="computeroutput">BZ2_bzlibVersion</code>. You may find +these functions more convenient for simple file reading and +writing, than those in the high-level interface. These functions +are not (yet) officially part of the library, and are minimally +documented here. If they break, you get to keep all the pieces. +I hope to document them properly when time permits.</p> +<p>Yoshioka also contributed modifications to allow the +library to be built as a Windows DLL.</p> +</div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="err-handling"></a>3.2. Error handling</h2></div></div></div> +<p>The library is designed to recover cleanly in all +situations, including the worst-case situation of decompressing +random data. I'm not 100% sure that it can always do this, so +you might want to add a signal handler to catch segmentation +violations during decompression if you are feeling especially +paranoid. I would be interested in hearing more about the +robustness of the library to corrupted compressed data.</p> +<p>Version 1.0.3 more robust in this respect than any +previous version. Investigations with Valgrind (a tool for detecting +problems with memory management) indicate +that, at least for the few files I tested, all single-bit errors +in the decompressed data are caught properly, with no +segmentation faults, no uses of uninitialised data, no out of +range reads or writes, and no infinite looping in the decompressor. +So it's certainly pretty robust, although +I wouldn't claim it to be totally bombproof.</p> +<p>The file <code class="computeroutput">bzlib.h</code> contains +all definitions needed to use the library. In particular, you +should definitely not include +<code class="computeroutput">bzlib_private.h</code>.</p> +<p>In <code class="computeroutput">bzlib.h</code>, the various +return values are defined. The following list is not intended as +an exhaustive description of the circumstances in which a given +value may be returned -- those descriptions are given later. +Rather, it is intended to convey the rough meaning of each return +value. The first five actions are normal and not intended to +denote an error situation.</p> +<div class="variablelist"><dl> +<dt><span class="term"><code class="computeroutput">BZ_OK</code></span></dt> +<dd><p>The requested action was completed + successfully.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_RUN_OK, BZ_FLUSH_OK, + BZ_FINISH_OK</code></span></dt> +<dd><p>In + <code class="computeroutput">BZ2_bzCompress</code>, the requested + flush/finish/nothing-special action was completed + successfully.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_STREAM_END</code></span></dt> +<dd><p>Compression of data was completed, or the + logical stream end was detected during + decompression.</p></dd> +</dl></div> +<p>The following return values indicate an error of some +kind.</p> +<div class="variablelist"><dl> +<dt><span class="term"><code class="computeroutput">BZ_CONFIG_ERROR</code></span></dt> +<dd><p>Indicates that the library has been improperly + compiled on your platform -- a major configuration error. + Specifically, it means that + <code class="computeroutput">sizeof(char)</code>, + <code class="computeroutput">sizeof(short)</code> and + <code class="computeroutput">sizeof(int)</code> are not 1, 2 and + 4 respectively, as they should be. Note that the library + should still work properly on 64-bit platforms which follow + the LP64 programming model -- that is, where + <code class="computeroutput">sizeof(long)</code> and + <code class="computeroutput">sizeof(void*)</code> are 8. Under + LP64, <code class="computeroutput">sizeof(int)</code> is still 4, + so <code class="computeroutput">libbzip2</code>, which doesn't + use the <code class="computeroutput">long</code> type, is + OK.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_SEQUENCE_ERROR</code></span></dt> +<dd><p>When using the library, it is important to call + the functions in the correct sequence and with data structures + (buffers etc) in the correct states. + <code class="computeroutput">libbzip2</code> checks as much as it + can to ensure this is happening, and returns + <code class="computeroutput">BZ_SEQUENCE_ERROR</code> if not. + Code which complies precisely with the function semantics, as + detailed below, should never receive this value; such an event + denotes buggy code which you should + investigate.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_PARAM_ERROR</code></span></dt> +<dd><p>Returned when a parameter to a function call is + out of range or otherwise manifestly incorrect. As with + <code class="computeroutput">BZ_SEQUENCE_ERROR</code>, this + denotes a bug in the client code. The distinction between + <code class="computeroutput">BZ_PARAM_ERROR</code> and + <code class="computeroutput">BZ_SEQUENCE_ERROR</code> is a bit + hazy, but still worth making.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_MEM_ERROR</code></span></dt> +<dd><p>Returned when a request to allocate memory + failed. Note that the quantity of memory needed to decompress + a stream cannot be determined until the stream's header has + been read. So + <code class="computeroutput">BZ2_bzDecompress</code> and + <code class="computeroutput">BZ2_bzRead</code> may return + <code class="computeroutput">BZ_MEM_ERROR</code> even though some + of the compressed data has been read. The same is not true + for compression; once + <code class="computeroutput">BZ2_bzCompressInit</code> or + <code class="computeroutput">BZ2_bzWriteOpen</code> have + successfully completed, + <code class="computeroutput">BZ_MEM_ERROR</code> cannot + occur.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_DATA_ERROR</code></span></dt> +<dd><p>Returned when a data integrity error is + detected during decompression. Most importantly, this means + when stored and computed CRCs for the data do not match. This + value is also returned upon detection of any other anomaly in + the compressed data.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_DATA_ERROR_MAGIC</code></span></dt> +<dd><p>As a special case of + <code class="computeroutput">BZ_DATA_ERROR</code>, it is + sometimes useful to know when the compressed stream does not + start with the correct magic bytes (<code class="computeroutput">'B' 'Z' + 'h'</code>).</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_IO_ERROR</code></span></dt> +<dd><p>Returned by + <code class="computeroutput">BZ2_bzRead</code> and + <code class="computeroutput">BZ2_bzWrite</code> when there is an + error reading or writing in the compressed file, and by + <code class="computeroutput">BZ2_bzReadOpen</code> and + <code class="computeroutput">BZ2_bzWriteOpen</code> for attempts + to use a file for which the error indicator (viz, + <code class="computeroutput">ferror(f)</code>) is set. On + receipt of <code class="computeroutput">BZ_IO_ERROR</code>, the + caller should consult <code class="computeroutput">errno</code> + and/or <code class="computeroutput">perror</code> to acquire + operating-system specific information about the + problem.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_UNEXPECTED_EOF</code></span></dt> +<dd><p>Returned by + <code class="computeroutput">BZ2_bzRead</code> when the + compressed file finishes before the logical end of stream is + detected.</p></dd> +<dt><span class="term"><code class="computeroutput">BZ_OUTBUFF_FULL</code></span></dt> +<dd><p>Returned by + <code class="computeroutput">BZ2_bzBuffToBuffCompress</code> and + <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> to + indicate that the output data will not fit into the output + buffer provided.</p></dd> +</dl></div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="low-level"></a>3.3. Low-level interface</h2></div></div></div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzcompress-init"></a>3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></h3></div></div></div> +<pre class="programlisting">typedef struct { + char *next_in; + unsigned int avail_in; + unsigned int total_in_lo32; + unsigned int total_in_hi32; + + char *next_out; + unsigned int avail_out; + unsigned int total_out_lo32; + unsigned int total_out_hi32; + + void *state; + + void *(*bzalloc)(void *,int,int); + void (*bzfree)(void *,void *); + void *opaque; +} bz_stream; + +int BZ2_bzCompressInit ( bz_stream *strm, + int blockSize100k, + int verbosity, + int workFactor );</pre> +<p>Prepares for compression. The +<code class="computeroutput">bz_stream</code> structure holds all +data pertaining to the compression activity. A +<code class="computeroutput">bz_stream</code> structure should be +allocated and initialised prior to the call. The fields of +<code class="computeroutput">bz_stream</code> comprise the entirety +of the user-visible data. <code class="computeroutput">state</code> +is a pointer to the private data structures required for +compression.</p> +<p>Custom memory allocators are supported, via fields +<code class="computeroutput">bzalloc</code>, +<code class="computeroutput">bzfree</code>, and +<code class="computeroutput">opaque</code>. The value +<code class="computeroutput">opaque</code> is passed to as the first +argument to all calls to <code class="computeroutput">bzalloc</code> +and <code class="computeroutput">bzfree</code>, but is otherwise +ignored by the library. The call <code class="computeroutput">bzalloc ( +opaque, n, m )</code> is expected to return a pointer +<code class="computeroutput">p</code> to <code class="computeroutput">n * +m</code> bytes of memory, and <code class="computeroutput">bzfree ( +opaque, p )</code> should free that memory.</p> +<p>If you don't want to use a custom memory allocator, set +<code class="computeroutput">bzalloc</code>, +<code class="computeroutput">bzfree</code> and +<code class="computeroutput">opaque</code> to +<code class="computeroutput">NULL</code>, and the library will then +use the standard <code class="computeroutput">malloc</code> / +<code class="computeroutput">free</code> routines.</p> +<p>Before calling +<code class="computeroutput">BZ2_bzCompressInit</code>, fields +<code class="computeroutput">bzalloc</code>, +<code class="computeroutput">bzfree</code> and +<code class="computeroutput">opaque</code> should be filled +appropriately, as just described. Upon return, the internal +state will have been allocated and initialised, and +<code class="computeroutput">total_in_lo32</code>, +<code class="computeroutput">total_in_hi32</code>, +<code class="computeroutput">total_out_lo32</code> and +<code class="computeroutput">total_out_hi32</code> will have been +set to zero. These four fields are used by the library to inform +the caller of the total amount of data passed into and out of the +library, respectively. You should not try to change them. As of +version 1.0, 64-bit counts are maintained, even on 32-bit +platforms, using the <code class="computeroutput">_hi32</code> +fields to store the upper 32 bits of the count. So, for example, +the total amount of data in is <code class="computeroutput">(total_in_hi32 +<< 32) + total_in_lo32</code>.</p> +<p>Parameter <code class="computeroutput">blockSize100k</code> +specifies the block size to be used for compression. It should +be a value between 1 and 9 inclusive, and the actual block size +used is 100000 x this figure. 9 gives the best compression but +takes most memory.</p> +<p>Parameter <code class="computeroutput">verbosity</code> should +be set to a number between 0 and 4 inclusive. 0 is silent, and +greater numbers give increasingly verbose monitoring/debugging +output. If the library has been compiled with +<code class="computeroutput">-DBZ_NO_STDIO</code>, no such output +will appear for any verbosity setting.</p> +<p>Parameter <code class="computeroutput">workFactor</code> +controls how the compression phase behaves when presented with +worst case, highly repetitive, input data. If compression runs +into difficulties caused by repetitive data, the library switches +from the standard sorting algorithm to a fallback algorithm. The +fallback is slower than the standard algorithm by perhaps a +factor of three, but always behaves reasonably, no matter how bad +the input.</p> +<p>Lower values of <code class="computeroutput">workFactor</code> +reduce the amount of effort the standard algorithm will expend +before resorting to the fallback. You should set this parameter +carefully; too low, and many inputs will be handled by the +fallback algorithm and so compress rather slowly, too high, and +your average-to-worst case compression times can become very +large. The default value of 30 gives reasonable behaviour over a +wide range of circumstances.</p> +<p>Allowable values range from 0 to 250 inclusive. 0 is a +special case, equivalent to using the default value of 30.</p> +<p>Note that the compressed output generated is the same +regardless of whether or not the fallback algorithm is +used.</p> +<p>Be aware also that this parameter may disappear entirely in +future versions of the library. In principle it should be +possible to devise a good way to automatically choose which +algorithm to use. Such a mechanism would render the parameter +obsolete.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_CONFIG_ERROR + if the library has been mis-compiled +BZ_PARAM_ERROR + if strm is NULL + or blockSize < 1 or blockSize > 9 + or verbosity < 0 or verbosity > 4 + or workFactor < 0 or workFactor > 250 +BZ_MEM_ERROR + if not enough memory is available +BZ_OK + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">BZ2_bzCompress + if BZ_OK is returned + no specific action needed in case of error</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzCompress"></a>3.3.2. <code class="computeroutput">BZ2_bzCompress</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzCompress ( bz_stream *strm, int action );</pre> +<p>Provides more input and/or output buffer space for the +library. The caller maintains input and output buffers, and +calls <code class="computeroutput">BZ2_bzCompress</code> to transfer +data between them.</p> +<p>Before each call to +<code class="computeroutput">BZ2_bzCompress</code>, +<code class="computeroutput">next_in</code> should point at the data +to be compressed, and <code class="computeroutput">avail_in</code> +should indicate how many bytes the library may read. +<code class="computeroutput">BZ2_bzCompress</code> updates +<code class="computeroutput">next_in</code>, +<code class="computeroutput">avail_in</code> and +<code class="computeroutput">total_in</code> to reflect the number +of bytes it has read.</p> +<p>Similarly, <code class="computeroutput">next_out</code> should +point to a buffer in which the compressed data is to be placed, +with <code class="computeroutput">avail_out</code> indicating how +much output space is available. +<code class="computeroutput">BZ2_bzCompress</code> updates +<code class="computeroutput">next_out</code>, +<code class="computeroutput">avail_out</code> and +<code class="computeroutput">total_out</code> to reflect the number +of bytes output.</p> +<p>You may provide and remove as little or as much data as you +like on each call of +<code class="computeroutput">BZ2_bzCompress</code>. In the limit, +it is acceptable to supply and remove data one byte at a time, +although this would be terribly inefficient. You should always +ensure that at least one byte of output space is available at +each call.</p> +<p>A second purpose of +<code class="computeroutput">BZ2_bzCompress</code> is to request a +change of mode of the compressed stream.</p> +<p>Conceptually, a compressed stream can be in one of four +states: IDLE, RUNNING, FLUSHING and FINISHING. Before +initialisation +(<code class="computeroutput">BZ2_bzCompressInit</code>) and after +termination (<code class="computeroutput">BZ2_bzCompressEnd</code>), +a stream is regarded as IDLE.</p> +<p>Upon initialisation +(<code class="computeroutput">BZ2_bzCompressInit</code>), the stream +is placed in the RUNNING state. Subsequent calls to +<code class="computeroutput">BZ2_bzCompress</code> should pass +<code class="computeroutput">BZ_RUN</code> as the requested action; +other actions are illegal and will result in +<code class="computeroutput">BZ_SEQUENCE_ERROR</code>.</p> +<p>At some point, the calling program will have provided all +the input data it wants to. It will then want to finish up -- in +effect, asking the library to process any data it might have +buffered internally. In this state, +<code class="computeroutput">BZ2_bzCompress</code> will no longer +attempt to read data from +<code class="computeroutput">next_in</code>, but it will want to +write data to <code class="computeroutput">next_out</code>. Because +the output buffer supplied by the user can be arbitrarily small, +the finishing-up operation cannot necessarily be done with a +single call of +<code class="computeroutput">BZ2_bzCompress</code>.</p> +<p>Instead, the calling program passes +<code class="computeroutput">BZ_FINISH</code> as an action to +<code class="computeroutput">BZ2_bzCompress</code>. This changes +the stream's state to FINISHING. Any remaining input (ie, +<code class="computeroutput">next_in[0 .. avail_in-1]</code>) is +compressed and transferred to the output buffer. To do this, +<code class="computeroutput">BZ2_bzCompress</code> must be called +repeatedly until all the output has been consumed. At that +point, <code class="computeroutput">BZ2_bzCompress</code> returns +<code class="computeroutput">BZ_STREAM_END</code>, and the stream's +state is set back to IDLE. +<code class="computeroutput">BZ2_bzCompressEnd</code> should then be +called.</p> +<p>Just to make sure the calling program does not cheat, the +library makes a note of <code class="computeroutput">avail_in</code> +at the time of the first call to +<code class="computeroutput">BZ2_bzCompress</code> which has +<code class="computeroutput">BZ_FINISH</code> as an action (ie, at +the time the program has announced its intention to not supply +any more input). By comparing this value with that of +<code class="computeroutput">avail_in</code> over subsequent calls +to <code class="computeroutput">BZ2_bzCompress</code>, the library +can detect any attempts to slip in more data to compress. Any +calls for which this is detected will return +<code class="computeroutput">BZ_SEQUENCE_ERROR</code>. This +indicates a programming mistake which should be corrected.</p> +<p>Instead of asking to finish, the calling program may ask +<code class="computeroutput">BZ2_bzCompress</code> to take all the +remaining input, compress it and terminate the current +(Burrows-Wheeler) compression block. This could be useful for +error control purposes. The mechanism is analogous to that for +finishing: call <code class="computeroutput">BZ2_bzCompress</code> +with an action of <code class="computeroutput">BZ_FLUSH</code>, +remove output data, and persist with the +<code class="computeroutput">BZ_FLUSH</code> action until the value +<code class="computeroutput">BZ_RUN</code> is returned. As with +finishing, <code class="computeroutput">BZ2_bzCompress</code> +detects any attempt to provide more input data once the flush has +begun.</p> +<p>Once the flush is complete, the stream returns to the +normal RUNNING state.</p> +<p>This all sounds pretty complex, but isn't really. Here's a +table which shows which actions are allowable in each state, what +action will be taken, what the next state is, and what the +non-error return values are. Note that you can't explicitly ask +what state the stream is in, but nor do you need to -- it can be +inferred from the values returned by +<code class="computeroutput">BZ2_bzCompress</code>.</p> +<pre class="programlisting">IDLE/any + Illegal. IDLE state only exists after BZ2_bzCompressEnd or + before BZ2_bzCompressInit. + Return value = BZ_SEQUENCE_ERROR + +RUNNING/BZ_RUN + Compress from next_in to next_out as much as possible. + Next state = RUNNING + Return value = BZ_RUN_OK + +RUNNING/BZ_FLUSH + Remember current value of next_in. Compress from next_in + to next_out as much as possible, but do not accept any more input. + Next state = FLUSHING + Return value = BZ_FLUSH_OK + +RUNNING/BZ_FINISH + Remember current value of next_in. Compress from next_in + to next_out as much as possible, but do not accept any more input. + Next state = FINISHING + Return value = BZ_FINISH_OK + +FLUSHING/BZ_FLUSH + Compress from next_in to next_out as much as possible, + but do not accept any more input. + If all the existing input has been used up and all compressed + output has been removed + Next state = RUNNING; Return value = BZ_RUN_OK + else + Next state = FLUSHING; Return value = BZ_FLUSH_OK + +FLUSHING/other + Illegal. + Return value = BZ_SEQUENCE_ERROR + +FINISHING/BZ_FINISH + Compress from next_in to next_out as much as possible, + but to not accept any more input. + If all the existing input has been used up and all compressed + output has been removed + Next state = IDLE; Return value = BZ_STREAM_END + else + Next state = FINISHING; Return value = BZ_FINISH_OK + +FINISHING/other + Illegal. + Return value = BZ_SEQUENCE_ERROR</pre> +<p>That still looks complicated? Well, fair enough. The +usual sequence of calls for compressing a load of data is:</p> +<div class="orderedlist"><ol type="1"> +<li><p>Get started with + <code class="computeroutput">BZ2_bzCompressInit</code>.</p></li> +<li><p>Shovel data in and shlurp out its compressed form + using zero or more calls of + <code class="computeroutput">BZ2_bzCompress</code> with action = + <code class="computeroutput">BZ_RUN</code>.</p></li> +<li><p>Finish up. Repeatedly call + <code class="computeroutput">BZ2_bzCompress</code> with action = + <code class="computeroutput">BZ_FINISH</code>, copying out the + compressed output, until + <code class="computeroutput">BZ_STREAM_END</code> is + returned.</p></li> +<li><p>Close up and go home. Call + <code class="computeroutput">BZ2_bzCompressEnd</code>.</p></li> +</ol></div> +<p>If the data you want to compress fits into your input +buffer all at once, you can skip the calls of +<code class="computeroutput">BZ2_bzCompress ( ..., BZ_RUN )</code> +and just do the <code class="computeroutput">BZ2_bzCompress ( ..., BZ_FINISH +)</code> calls.</p> +<p>All required memory is allocated by +<code class="computeroutput">BZ2_bzCompressInit</code>. The +compression library can accept any data at all (obviously). So +you shouldn't get any error return values from the +<code class="computeroutput">BZ2_bzCompress</code> calls. If you +do, they will be +<code class="computeroutput">BZ_SEQUENCE_ERROR</code>, and indicate +a bug in your programming.</p> +<p>Trivial other possible return values:</p> +<pre class="programlisting">BZ_PARAM_ERROR + if strm is NULL, or strm->s is NULL</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzCompress-end"></a>3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzCompressEnd ( bz_stream *strm );</pre> +<p>Releases all memory associated with a compression +stream.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_PARAM_ERROR if strm is NULL or strm->s is NULL +BZ_OK otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzDecompress-init"></a>3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzDecompressInit ( bz_stream *strm, int verbosity, int small );</pre> +<p>Prepares for decompression. As with +<code class="computeroutput">BZ2_bzCompressInit</code>, a +<code class="computeroutput">bz_stream</code> record should be +allocated and initialised before the call. Fields +<code class="computeroutput">bzalloc</code>, +<code class="computeroutput">bzfree</code> and +<code class="computeroutput">opaque</code> should be set if a custom +memory allocator is required, or made +<code class="computeroutput">NULL</code> for the normal +<code class="computeroutput">malloc</code> / +<code class="computeroutput">free</code> routines. Upon return, the +internal state will have been initialised, and +<code class="computeroutput">total_in</code> and +<code class="computeroutput">total_out</code> will be zero.</p> +<p>For the meaning of parameter +<code class="computeroutput">verbosity</code>, see +<code class="computeroutput">BZ2_bzCompressInit</code>.</p> +<p>If <code class="computeroutput">small</code> is nonzero, the +library will use an alternative decompression algorithm which +uses less memory but at the cost of decompressing more slowly +(roughly speaking, half the speed, but the maximum memory +requirement drops to around 2300k). See <a href="#using">How to use bzip2</a> +for more information on memory management.</p> +<p>Note that the amount of memory needed to decompress a +stream cannot be determined until the stream's header has been +read, so even if +<code class="computeroutput">BZ2_bzDecompressInit</code> succeeds, a +subsequent <code class="computeroutput">BZ2_bzDecompress</code> +could fail with +<code class="computeroutput">BZ_MEM_ERROR</code>.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_CONFIG_ERROR + if the library has been mis-compiled +BZ_PARAM_ERROR + if ( small != 0 && small != 1 ) + or (verbosity <; 0 || verbosity > 4) +BZ_MEM_ERROR + if insufficient memory is available</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">BZ2_bzDecompress + if BZ_OK was returned + no specific action required in case of error</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzDecompress"></a>3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzDecompress ( bz_stream *strm );</pre> +<p>Provides more input and/out output buffer space for the +library. The caller maintains input and output buffers, and uses +<code class="computeroutput">BZ2_bzDecompress</code> to transfer +data between them.</p> +<p>Before each call to +<code class="computeroutput">BZ2_bzDecompress</code>, +<code class="computeroutput">next_in</code> should point at the +compressed data, and <code class="computeroutput">avail_in</code> +should indicate how many bytes the library may read. +<code class="computeroutput">BZ2_bzDecompress</code> updates +<code class="computeroutput">next_in</code>, +<code class="computeroutput">avail_in</code> and +<code class="computeroutput">total_in</code> to reflect the number +of bytes it has read.</p> +<p>Similarly, <code class="computeroutput">next_out</code> should +point to a buffer in which the uncompressed output is to be +placed, with <code class="computeroutput">avail_out</code> +indicating how much output space is available. +<code class="computeroutput">BZ2_bzCompress</code> updates +<code class="computeroutput">next_out</code>, +<code class="computeroutput">avail_out</code> and +<code class="computeroutput">total_out</code> to reflect the number +of bytes output.</p> +<p>You may provide and remove as little or as much data as you +like on each call of +<code class="computeroutput">BZ2_bzDecompress</code>. In the limit, +it is acceptable to supply and remove data one byte at a time, +although this would be terribly inefficient. You should always +ensure that at least one byte of output space is available at +each call.</p> +<p>Use of <code class="computeroutput">BZ2_bzDecompress</code> is +simpler than +<code class="computeroutput">BZ2_bzCompress</code>.</p> +<p>You should provide input and remove output as described +above, and repeatedly call +<code class="computeroutput">BZ2_bzDecompress</code> until +<code class="computeroutput">BZ_STREAM_END</code> is returned. +Appearance of <code class="computeroutput">BZ_STREAM_END</code> +denotes that <code class="computeroutput">BZ2_bzDecompress</code> +has detected the logical end of the compressed stream. +<code class="computeroutput">BZ2_bzDecompress</code> will not +produce <code class="computeroutput">BZ_STREAM_END</code> until all +output data has been placed into the output buffer, so once +<code class="computeroutput">BZ_STREAM_END</code> appears, you are +guaranteed to have available all the decompressed output, and +<code class="computeroutput">BZ2_bzDecompressEnd</code> can safely +be called.</p> +<p>If case of an error return value, you should call +<code class="computeroutput">BZ2_bzDecompressEnd</code> to clean up +and release memory.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_PARAM_ERROR + if strm is NULL or strm->s is NULL + or strm->avail_out < 1 +BZ_DATA_ERROR + if a data integrity error is detected in the compressed stream +BZ_DATA_ERROR_MAGIC + if the compressed stream doesn't begin with the right magic bytes +BZ_MEM_ERROR + if there wasn't enough memory available +BZ_STREAM_END + if the logical end of the data stream was detected and all + output in has been consumed, eg s-->avail_out > 0 +BZ_OK + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">BZ2_bzDecompress + if BZ_OK was returned +BZ2_bzDecompressEnd + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzDecompress-end"></a>3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzDecompressEnd ( bz_stream *strm );</pre> +<p>Releases all memory associated with a decompression +stream.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_PARAM_ERROR + if strm is NULL or strm->s is NULL +BZ_OK + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting"> None.</pre> +</div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="hl-interface"></a>3.4. High-level interface</h2></div></div></div> +<p>This interface provides functions for reading and writing +<code class="computeroutput">bzip2</code> format files. First, some +general points.</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p>All of the functions take an + <code class="computeroutput">int*</code> first argument, + <code class="computeroutput">bzerror</code>. After each call, + <code class="computeroutput">bzerror</code> should be consulted + first to determine the outcome of the call. If + <code class="computeroutput">bzerror</code> is + <code class="computeroutput">BZ_OK</code>, the call completed + successfully, and only then should the return value of the + function (if any) be consulted. If + <code class="computeroutput">bzerror</code> is + <code class="computeroutput">BZ_IO_ERROR</code>, there was an + error reading/writing the underlying compressed file, and you + should then consult <code class="computeroutput">errno</code> / + <code class="computeroutput">perror</code> to determine the cause + of the difficulty. <code class="computeroutput">bzerror</code> + may also be set to various other values; precise details are + given on a per-function basis below.</p></li> +<li style="list-style-type: disc"><p>If <code class="computeroutput">bzerror</code> indicates + an error (ie, anything except + <code class="computeroutput">BZ_OK</code> and + <code class="computeroutput">BZ_STREAM_END</code>), you should + immediately call + <code class="computeroutput">BZ2_bzReadClose</code> (or + <code class="computeroutput">BZ2_bzWriteClose</code>, depending on + whether you are attempting to read or to write) to free up all + resources associated with the stream. Once an error has been + indicated, behaviour of all calls except + <code class="computeroutput">BZ2_bzReadClose</code> + (<code class="computeroutput">BZ2_bzWriteClose</code>) is + undefined. The implication is that (1) + <code class="computeroutput">bzerror</code> should be checked + after each call, and (2) if + <code class="computeroutput">bzerror</code> indicates an error, + <code class="computeroutput">BZ2_bzReadClose</code> + (<code class="computeroutput">BZ2_bzWriteClose</code>) should then + be called to clean up.</p></li> +<li style="list-style-type: disc"><p>The <code class="computeroutput">FILE*</code> arguments + passed to <code class="computeroutput">BZ2_bzReadOpen</code> / + <code class="computeroutput">BZ2_bzWriteOpen</code> should be set + to binary mode. Most Unix systems will do this by default, but + other platforms, including Windows and Mac, will not. If you + omit this, you may encounter problems when moving code to new + platforms.</p></li> +<li style="list-style-type: disc"><p>Memory allocation requests are handled by + <code class="computeroutput">malloc</code> / + <code class="computeroutput">free</code>. At present there is no + facility for user-defined memory allocators in the file I/O + functions (could easily be added, though).</p></li> +</ul></div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzreadopen"></a>3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></h3></div></div></div> +<pre class="programlisting">typedef void BZFILE; + +BZFILE *BZ2_bzReadOpen( int *bzerror, FILE *f, + int verbosity, int small, + void *unused, int nUnused );</pre> +<p>Prepare to read compressed data from file handle +<code class="computeroutput">f</code>. +<code class="computeroutput">f</code> should refer to a file which +has been opened for reading, and for which the error indicator +(<code class="computeroutput">ferror(f)</code>)is not set. If +<code class="computeroutput">small</code> is 1, the library will try +to decompress using less memory, at the expense of speed.</p> +<p>For reasons explained below, +<code class="computeroutput">BZ2_bzRead</code> will decompress the +<code class="computeroutput">nUnused</code> bytes starting at +<code class="computeroutput">unused</code>, before starting to read +from the file <code class="computeroutput">f</code>. At most +<code class="computeroutput">BZ_MAX_UNUSED</code> bytes may be +supplied like this. If this facility is not required, you should +pass <code class="computeroutput">NULL</code> and +<code class="computeroutput">0</code> for +<code class="computeroutput">unused</code> and +n<code class="computeroutput">Unused</code> respectively.</p> +<p>For the meaning of parameters +<code class="computeroutput">small</code> and +<code class="computeroutput">verbosity</code>, see +<code class="computeroutput">BZ2_bzDecompressInit</code>.</p> +<p>The amount of memory needed to decompress a file cannot be +determined until the file's header has been read. So it is +possible that <code class="computeroutput">BZ2_bzReadOpen</code> +returns <code class="computeroutput">BZ_OK</code> but a subsequent +call of <code class="computeroutput">BZ2_bzRead</code> will return +<code class="computeroutput">BZ_MEM_ERROR</code>.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_CONFIG_ERROR + if the library has been mis-compiled +BZ_PARAM_ERROR + if f is NULL + or small is neither 0 nor 1 + or ( unused == NULL && nUnused != 0 ) + or ( unused != NULL && !(0 <= nUnused <= BZ_MAX_UNUSED) ) +BZ_IO_ERROR + if ferror(f) is nonzero +BZ_MEM_ERROR + if insufficient memory is available +BZ_OK + otherwise.</pre> +<p>Possible return values:</p> +<pre class="programlisting">Pointer to an abstract BZFILE + if bzerror is BZ_OK +NULL + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">BZ2_bzRead + if bzerror is BZ_OK +BZ2_bzClose + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzread"></a>3.4.2. <code class="computeroutput">BZ2_bzRead</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzRead ( int *bzerror, BZFILE *b, void *buf, int len );</pre> +<p>Reads up to <code class="computeroutput">len</code> +(uncompressed) bytes from the compressed file +<code class="computeroutput">b</code> into the buffer +<code class="computeroutput">buf</code>. If the read was +successful, <code class="computeroutput">bzerror</code> is set to +<code class="computeroutput">BZ_OK</code> and the number of bytes +read is returned. If the logical end-of-stream was detected, +<code class="computeroutput">bzerror</code> will be set to +<code class="computeroutput">BZ_STREAM_END</code>, and the number of +bytes read is returned. All other +<code class="computeroutput">bzerror</code> values denote an +error.</p> +<p><code class="computeroutput">BZ2_bzRead</code> will supply +<code class="computeroutput">len</code> bytes, unless the logical +stream end is detected or an error occurs. Because of this, it +is possible to detect the stream end by observing when the number +of bytes returned is less than the number requested. +Nevertheless, this is regarded as inadvisable; you should instead +check <code class="computeroutput">bzerror</code> after every call +and watch out for +<code class="computeroutput">BZ_STREAM_END</code>.</p> +<p>Internally, <code class="computeroutput">BZ2_bzRead</code> +copies data from the compressed file in chunks of size +<code class="computeroutput">BZ_MAX_UNUSED</code> bytes before +decompressing it. If the file contains more bytes than strictly +needed to reach the logical end-of-stream, +<code class="computeroutput">BZ2_bzRead</code> will almost certainly +read some of the trailing data before signalling +<code class="computeroutput">BZ_SEQUENCE_END</code>. To collect the +read but unused data once +<code class="computeroutput">BZ_SEQUENCE_END</code> has appeared, +call <code class="computeroutput">BZ2_bzReadGetUnused</code> +immediately before +<code class="computeroutput">BZ2_bzReadClose</code>.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_PARAM_ERROR + if b is NULL or buf is NULL or len < 0 +BZ_SEQUENCE_ERROR + if b was opened with BZ2_bzWriteOpen +BZ_IO_ERROR + if there is an error reading from the compressed file +BZ_UNEXPECTED_EOF + if the compressed file ended before + the logical end-of-stream was detected +BZ_DATA_ERROR + if a data integrity error was detected in the compressed stream +BZ_DATA_ERROR_MAGIC + if the stream does not begin with the requisite header bytes + (ie, is not a bzip2 data file). This is really + a special case of BZ_DATA_ERROR. +BZ_MEM_ERROR + if insufficient memory was available +BZ_STREAM_END + if the logical end of stream was detected. +BZ_OK + otherwise.</pre> +<p>Possible return values:</p> +<pre class="programlisting">number of bytes read + if bzerror is BZ_OK or BZ_STREAM_END +undefined + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">collect data from buf, then BZ2_bzRead or BZ2_bzReadClose + if bzerror is BZ_OK +collect data from buf, then BZ2_bzReadClose or BZ2_bzReadGetUnused + if bzerror is BZ_SEQUENCE_END +BZ2_bzReadClose + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzreadgetunused"></a>3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></h3></div></div></div> +<pre class="programlisting">void BZ2_bzReadGetUnused( int* bzerror, BZFILE *b, + void** unused, int* nUnused );</pre> +<p>Returns data which was read from the compressed file but +was not needed to get to the logical end-of-stream. +<code class="computeroutput">*unused</code> is set to the address of +the data, and <code class="computeroutput">*nUnused</code> to the +number of bytes. <code class="computeroutput">*nUnused</code> will +be set to a value between <code class="computeroutput">0</code> and +<code class="computeroutput">BZ_MAX_UNUSED</code> inclusive.</p> +<p>This function may only be called once +<code class="computeroutput">BZ2_bzRead</code> has signalled +<code class="computeroutput">BZ_STREAM_END</code> but before +<code class="computeroutput">BZ2_bzReadClose</code>.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_PARAM_ERROR + if b is NULL + or unused is NULL or nUnused is NULL +BZ_SEQUENCE_ERROR + if BZ_STREAM_END has not been signalled + or if b was opened with BZ2_bzWriteOpen +BZ_OK + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">BZ2_bzReadClose</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzreadclose"></a>3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></h3></div></div></div> +<pre class="programlisting">void BZ2_bzReadClose ( int *bzerror, BZFILE *b );</pre> +<p>Releases all memory pertaining to the compressed file +<code class="computeroutput">b</code>. +<code class="computeroutput">BZ2_bzReadClose</code> does not call +<code class="computeroutput">fclose</code> on the underlying file +handle, so you should do that yourself if appropriate. +<code class="computeroutput">BZ2_bzReadClose</code> should be called +to clean up after all error situations.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_SEQUENCE_ERROR + if b was opened with BZ2_bzOpenWrite +BZ_OK + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">none</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzwriteopen"></a>3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></h3></div></div></div> +<pre class="programlisting">BZFILE *BZ2_bzWriteOpen( int *bzerror, FILE *f, + int blockSize100k, int verbosity, + int workFactor );</pre> +<p>Prepare to write compressed data to file handle +<code class="computeroutput">f</code>. +<code class="computeroutput">f</code> should refer to a file which +has been opened for writing, and for which the error indicator +(<code class="computeroutput">ferror(f)</code>)is not set.</p> +<p>For the meaning of parameters +<code class="computeroutput">blockSize100k</code>, +<code class="computeroutput">verbosity</code> and +<code class="computeroutput">workFactor</code>, see +<code class="computeroutput">BZ2_bzCompressInit</code>.</p> +<p>All required memory is allocated at this stage, so if the +call completes successfully, +<code class="computeroutput">BZ_MEM_ERROR</code> cannot be signalled +by a subsequent call to +<code class="computeroutput">BZ2_bzWrite</code>.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_CONFIG_ERROR + if the library has been mis-compiled +BZ_PARAM_ERROR + if f is NULL + or blockSize100k < 1 or blockSize100k > 9 +BZ_IO_ERROR + if ferror(f) is nonzero +BZ_MEM_ERROR + if insufficient memory is available +BZ_OK + otherwise</pre> +<p>Possible return values:</p> +<pre class="programlisting">Pointer to an abstract BZFILE + if bzerror is BZ_OK +NULL + otherwise</pre> +<p>Allowable next actions:</p> +<pre class="programlisting">BZ2_bzWrite + if bzerror is BZ_OK + (you could go directly to BZ2_bzWriteClose, but this would be pretty pointless) +BZ2_bzWriteClose + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzwrite"></a>3.4.6. <code class="computeroutput">BZ2_bzWrite</code></h3></div></div></div> +<pre class="programlisting">void BZ2_bzWrite ( int *bzerror, BZFILE *b, void *buf, int len );</pre> +<p>Absorbs <code class="computeroutput">len</code> bytes from the +buffer <code class="computeroutput">buf</code>, eventually to be +compressed and written to the file.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_PARAM_ERROR + if b is NULL or buf is NULL or len < 0 +BZ_SEQUENCE_ERROR + if b was opened with BZ2_bzReadOpen +BZ_IO_ERROR + if there is an error writing the compressed file. +BZ_OK + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzwriteclose"></a>3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></h3></div></div></div> +<pre class="programlisting">void BZ2_bzWriteClose( int *bzerror, BZFILE* f, + int abandon, + unsigned int* nbytes_in, + unsigned int* nbytes_out ); + +void BZ2_bzWriteClose64( int *bzerror, BZFILE* f, + int abandon, + unsigned int* nbytes_in_lo32, + unsigned int* nbytes_in_hi32, + unsigned int* nbytes_out_lo32, + unsigned int* nbytes_out_hi32 );</pre> +<p>Compresses and flushes to the compressed file all data so +far supplied by <code class="computeroutput">BZ2_bzWrite</code>. +The logical end-of-stream markers are also written, so subsequent +calls to <code class="computeroutput">BZ2_bzWrite</code> are +illegal. All memory associated with the compressed file +<code class="computeroutput">b</code> is released. +<code class="computeroutput">fflush</code> is called on the +compressed file, but it is not +<code class="computeroutput">fclose</code>'d.</p> +<p>If <code class="computeroutput">BZ2_bzWriteClose</code> is +called to clean up after an error, the only action is to release +the memory. The library records the error codes issued by +previous calls, so this situation will be detected automatically. +There is no attempt to complete the compression operation, nor to +<code class="computeroutput">fflush</code> the compressed file. You +can force this behaviour to happen even in the case of no error, +by passing a nonzero value to +<code class="computeroutput">abandon</code>.</p> +<p>If <code class="computeroutput">nbytes_in</code> is non-null, +<code class="computeroutput">*nbytes_in</code> will be set to be the +total volume of uncompressed data handled. Similarly, +<code class="computeroutput">nbytes_out</code> will be set to the +total volume of compressed data written. For compatibility with +older versions of the library, +<code class="computeroutput">BZ2_bzWriteClose</code> only yields the +lower 32 bits of these counts. Use +<code class="computeroutput">BZ2_bzWriteClose64</code> if you want +the full 64 bit counts. These two functions are otherwise +absolutely identical.</p> +<p>Possible assignments to +<code class="computeroutput">bzerror</code>:</p> +<pre class="programlisting">BZ_SEQUENCE_ERROR + if b was opened with BZ2_bzReadOpen +BZ_IO_ERROR + if there is an error writing the compressed file +BZ_OK + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="embed"></a>3.4.8. Handling embedded compressed data streams</h3></div></div></div> +<p>The high-level library facilitates use of +<code class="computeroutput">bzip2</code> data streams which form +some part of a surrounding, larger data stream.</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p>For writing, the library takes an open file handle, + writes compressed data to it, + <code class="computeroutput">fflush</code>es it but does not + <code class="computeroutput">fclose</code> it. The calling + application can write its own data before and after the + compressed data stream, using that same file handle.</p></li> +<li style="list-style-type: disc"><p>Reading is more complex, and the facilities are not as + general as they could be since generality is hard to reconcile + with efficiency. <code class="computeroutput">BZ2_bzRead</code> + reads from the compressed file in blocks of size + <code class="computeroutput">BZ_MAX_UNUSED</code> bytes, and in + doing so probably will overshoot the logical end of compressed + stream. To recover this data once decompression has ended, + call <code class="computeroutput">BZ2_bzReadGetUnused</code> after + the last call of <code class="computeroutput">BZ2_bzRead</code> + (the one returning + <code class="computeroutput">BZ_STREAM_END</code>) but before + calling + <code class="computeroutput">BZ2_bzReadClose</code>.</p></li> +</ul></div> +<p>This mechanism makes it easy to decompress multiple +<code class="computeroutput">bzip2</code> streams placed end-to-end. +As the end of one stream, when +<code class="computeroutput">BZ2_bzRead</code> returns +<code class="computeroutput">BZ_STREAM_END</code>, call +<code class="computeroutput">BZ2_bzReadGetUnused</code> to collect +the unused data (copy it into your own buffer somewhere). That +data forms the start of the next compressed stream. To start +uncompressing that next stream, call +<code class="computeroutput">BZ2_bzReadOpen</code> again, feeding in +the unused data via the <code class="computeroutput">unused</code> / +<code class="computeroutput">nUnused</code> parameters. Keep doing +this until <code class="computeroutput">BZ_STREAM_END</code> return +coincides with the physical end of file +(<code class="computeroutput">feof(f)</code>). In this situation +<code class="computeroutput">BZ2_bzReadGetUnused</code> will of +course return no data.</p> +<p>This should give some feel for how the high-level interface +can be used. If you require extra flexibility, you'll have to +bite the bullet and get to grips with the low-level +interface.</p> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="std-rdwr"></a>3.4.9. Standard file-reading/writing code</h3></div></div></div> +<p>Here's how you'd write data to a compressed file:</p> +<pre class="programlisting">FILE* f; +BZFILE* b; +int nBuf; +char buf[ /* whatever size you like */ ]; +int bzerror; +int nWritten; + +f = fopen ( "myfile.bz2", "w" ); +if ( !f ) { + /* handle error */ +} +b = BZ2_bzWriteOpen( &bzerror, f, 9 ); +if (bzerror != BZ_OK) { + BZ2_bzWriteClose ( b ); + /* handle error */ +} + +while ( /* condition */ ) { + /* get data to write into buf, and set nBuf appropriately */ + nWritten = BZ2_bzWrite ( &bzerror, b, buf, nBuf ); + if (bzerror == BZ_IO_ERROR) { + BZ2_bzWriteClose ( &bzerror, b ); + /* handle error */ + } +} + +BZ2_bzWriteClose( &bzerror, b ); +if (bzerror == BZ_IO_ERROR) { + /* handle error */ +}</pre> +<p>And to read from a compressed file:</p> +<pre class="programlisting">FILE* f; +BZFILE* b; +int nBuf; +char buf[ /* whatever size you like */ ]; +int bzerror; +int nWritten; + +f = fopen ( "myfile.bz2", "r" ); +if ( !f ) { + /* handle error */ +} +b = BZ2_bzReadOpen ( &bzerror, f, 0, NULL, 0 ); +if ( bzerror != BZ_OK ) { + BZ2_bzReadClose ( &bzerror, b ); + /* handle error */ +} + +bzerror = BZ_OK; +while ( bzerror == BZ_OK && /* arbitrary other conditions */) { + nBuf = BZ2_bzRead ( &bzerror, b, buf, /* size of buf */ ); + if ( bzerror == BZ_OK ) { + /* do something with buf[0 .. nBuf-1] */ + } +} +if ( bzerror != BZ_STREAM_END ) { + BZ2_bzReadClose ( &bzerror, b ); + /* handle error */ +} else { + BZ2_bzReadClose ( &bzerror, b ); +}</pre> +</div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="util-fns"></a>3.5. Utility functions</h2></div></div></div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzbufftobuffcompress"></a>3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzBuffToBuffCompress( char* dest, + unsigned int* destLen, + char* source, + unsigned int sourceLen, + int blockSize100k, + int verbosity, + int workFactor );</pre> +<p>Attempts to compress the data in <code class="computeroutput">source[0 +.. sourceLen-1]</code> into the destination buffer, +<code class="computeroutput">dest[0 .. *destLen-1]</code>. If the +destination buffer is big enough, +<code class="computeroutput">*destLen</code> is set to the size of +the compressed data, and <code class="computeroutput">BZ_OK</code> +is returned. If the compressed data won't fit, +<code class="computeroutput">*destLen</code> is unchanged, and +<code class="computeroutput">BZ_OUTBUFF_FULL</code> is +returned.</p> +<p>Compression in this manner is a one-shot event, done with a +single call to this function. The resulting compressed data is a +complete <code class="computeroutput">bzip2</code> format data +stream. There is no mechanism for making additional calls to +provide extra input data. If you want that kind of mechanism, +use the low-level interface.</p> +<p>For the meaning of parameters +<code class="computeroutput">blockSize100k</code>, +<code class="computeroutput">verbosity</code> and +<code class="computeroutput">workFactor</code>, see +<code class="computeroutput">BZ2_bzCompressInit</code>.</p> +<p>To guarantee that the compressed data will fit in its +buffer, allocate an output buffer of size 1% larger than the +uncompressed data, plus six hundred extra bytes.</p> +<p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> +will not write data at or beyond +<code class="computeroutput">dest[*destLen]</code>, even in case of +buffer overflow.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_CONFIG_ERROR + if the library has been mis-compiled +BZ_PARAM_ERROR + if dest is NULL or destLen is NULL + or blockSize100k < 1 or blockSize100k > 9 + or verbosity < 0 or verbosity > 4 + or workFactor < 0 or workFactor > 250 +BZ_MEM_ERROR + if insufficient memory is available +BZ_OUTBUFF_FULL + if the size of the compressed data exceeds *destLen +BZ_OK + otherwise</pre> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="bzbufftobuffdecompress"></a>3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></h3></div></div></div> +<pre class="programlisting">int BZ2_bzBuffToBuffDecompress( char* dest, + unsigned int* destLen, + char* source, + unsigned int sourceLen, + int small, + int verbosity );</pre> +<p>Attempts to decompress the data in <code class="computeroutput">source[0 +.. sourceLen-1]</code> into the destination buffer, +<code class="computeroutput">dest[0 .. *destLen-1]</code>. If the +destination buffer is big enough, +<code class="computeroutput">*destLen</code> is set to the size of +the uncompressed data, and <code class="computeroutput">BZ_OK</code> +is returned. If the compressed data won't fit, +<code class="computeroutput">*destLen</code> is unchanged, and +<code class="computeroutput">BZ_OUTBUFF_FULL</code> is +returned.</p> +<p><code class="computeroutput">source</code> is assumed to hold +a complete <code class="computeroutput">bzip2</code> format data +stream. +<code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> tries +to decompress the entirety of the stream into the output +buffer.</p> +<p>For the meaning of parameters +<code class="computeroutput">small</code> and +<code class="computeroutput">verbosity</code>, see +<code class="computeroutput">BZ2_bzDecompressInit</code>.</p> +<p>Because the compression ratio of the compressed data cannot +be known in advance, there is no easy way to guarantee that the +output buffer will be big enough. You may of course make +arrangements in your code to record the size of the uncompressed +data, but such a mechanism is beyond the scope of this +library.</p> +<p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> +will not write data at or beyond +<code class="computeroutput">dest[*destLen]</code>, even in case of +buffer overflow.</p> +<p>Possible return values:</p> +<pre class="programlisting">BZ_CONFIG_ERROR + if the library has been mis-compiled +BZ_PARAM_ERROR + if dest is NULL or destLen is NULL + or small != 0 && small != 1 + or verbosity < 0 or verbosity > 4 +BZ_MEM_ERROR + if insufficient memory is available +BZ_OUTBUFF_FULL + if the size of the compressed data exceeds *destLen +BZ_DATA_ERROR + if a data integrity error was detected in the compressed data +BZ_DATA_ERROR_MAGIC + if the compressed data doesn't begin with the right magic bytes +BZ_UNEXPECTED_EOF + if the compressed data ends unexpectedly +BZ_OK + otherwise</pre> +</div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="zlib-compat"></a>3.6. <code class="computeroutput">zlib</code> compatibility functions</h2></div></div></div> +<p>Yoshioka Tsuneo has contributed some functions to give +better <code class="computeroutput">zlib</code> compatibility. +These functions are <code class="computeroutput">BZ2_bzopen</code>, +<code class="computeroutput">BZ2_bzread</code>, +<code class="computeroutput">BZ2_bzwrite</code>, +<code class="computeroutput">BZ2_bzflush</code>, +<code class="computeroutput">BZ2_bzclose</code>, +<code class="computeroutput">BZ2_bzerror</code> and +<code class="computeroutput">BZ2_bzlibVersion</code>. These +functions are not (yet) officially part of the library. If they +break, you get to keep all the pieces. Nevertheless, I think +they work ok.</p> +<pre class="programlisting">typedef void BZFILE; + +const char * BZ2_bzlibVersion ( void );</pre> +<p>Returns a string indicating the library version.</p> +<pre class="programlisting">BZFILE * BZ2_bzopen ( const char *path, const char *mode ); +BZFILE * BZ2_bzdopen ( int fd, const char *mode );</pre> +<p>Opens a <code class="computeroutput">.bz2</code> file for +reading or writing, using either its name or a pre-existing file +descriptor. Analogous to <code class="computeroutput">fopen</code> +and <code class="computeroutput">fdopen</code>.</p> +<pre class="programlisting">int BZ2_bzread ( BZFILE* b, void* buf, int len ); +int BZ2_bzwrite ( BZFILE* b, void* buf, int len );</pre> +<p>Reads/writes data from/to a previously opened +<code class="computeroutput">BZFILE</code>. Analogous to +<code class="computeroutput">fread</code> and +<code class="computeroutput">fwrite</code>.</p> +<pre class="programlisting">int BZ2_bzflush ( BZFILE* b ); +void BZ2_bzclose ( BZFILE* b );</pre> +<p>Flushes/closes a <code class="computeroutput">BZFILE</code>. +<code class="computeroutput">BZ2_bzflush</code> doesn't actually do +anything. Analogous to <code class="computeroutput">fflush</code> +and <code class="computeroutput">fclose</code>.</p> +<pre class="programlisting">const char * BZ2_bzerror ( BZFILE *b, int *errnum )</pre> +<p>Returns a string describing the more recent error status of +<code class="computeroutput">b</code>, and also sets +<code class="computeroutput">*errnum</code> to its numerical +value.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="stdio-free"></a>3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</h2></div></div></div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="stdio-bye"></a>3.7.1. Getting rid of <code class="computeroutput">stdio</code></h3></div></div></div> +<p>In a deeply embedded application, you might want to use +just the memory-to-memory functions. You can do this +conveniently by compiling the library with preprocessor symbol +<code class="computeroutput">BZ_NO_STDIO</code> defined. Doing this +gives you a library containing only the following eight +functions:</p> +<p><code class="computeroutput">BZ2_bzCompressInit</code>, +<code class="computeroutput">BZ2_bzCompress</code>, +<code class="computeroutput">BZ2_bzCompressEnd</code> +<code class="computeroutput">BZ2_bzDecompressInit</code>, +<code class="computeroutput">BZ2_bzDecompress</code>, +<code class="computeroutput">BZ2_bzDecompressEnd</code> +<code class="computeroutput">BZ2_bzBuffToBuffCompress</code>, +<code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></p> +<p>When compiled like this, all functions will ignore +<code class="computeroutput">verbosity</code> settings.</p> +</div> +<div class="sect2" lang="en"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="critical-error"></a>3.7.2. Critical error handling</h3></div></div></div> +<p><code class="computeroutput">libbzip2</code> contains a number +of internal assertion checks which should, needless to say, never +be activated. Nevertheless, if an assertion should fail, +behaviour depends on whether or not the library was compiled with +<code class="computeroutput">BZ_NO_STDIO</code> set.</p> +<p>For a normal compile, an assertion failure yields the +message:</p> +<div class="blockquote"><blockquote class="blockquote"> +<p>bzip2/libbzip2: internal error number N.</p> +<p>This is a bug in bzip2/libbzip2, 1.0.5 of 10 December 2007. +Please report it to me at: jseward@bzip.org. If this happened +when you were using some program which uses libbzip2 as a +component, you should also report this bug to the author(s) +of that program. Please make an effort to report this bug; +timely and accurate bug reports eventually lead to higher +quality software. Thanks. Julian Seward, 10 December 2007. +</p> +</blockquote></div> +<p>where <code class="computeroutput">N</code> is some error code +number. If <code class="computeroutput">N == 1007</code>, it also +prints some extra text advising the reader that unreliable memory +is often associated with internal error 1007. (This is a +frequently-observed-phenomenon with versions 1.0.0/1.0.1).</p> +<p><code class="computeroutput">exit(3)</code> is then +called.</p> +<p>For a <code class="computeroutput">stdio</code>-free library, +assertion failures result in a call to a function declared +as:</p> +<pre class="programlisting">extern void bz_internal_error ( int errcode );</pre> +<p>The relevant code is passed as a parameter. You should +supply such a function.</p> +<p>In either case, once an assertion failure has occurred, any +<code class="computeroutput">bz_stream</code> records involved can +be regarded as invalid. You should not attempt to resume normal +operation with them.</p> +<p>You may, of course, change critical error handling to suit +your needs. As I said above, critical errors indicate bugs in +the library and should not occur. All "normal" error situations +are indicated via error return codes from functions, and can be +recovered from.</p> +</div> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="win-dll"></a>3.8. Making a Windows DLL</h2></div></div></div> +<p>Everything related to Windows has been contributed by +Yoshioka Tsuneo +(<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>), so +you should send your queries to him (but perhaps Cc: me, +<code class="computeroutput">jseward@bzip.org</code>).</p> +<p>My vague understanding of what to do is: using Visual C++ +5.0, open the project file +<code class="computeroutput">libbz2.dsp</code>, and build. That's +all.</p> +<p>If you can't open the project file for some reason, make a +new one, naming these files: +<code class="computeroutput">blocksort.c</code>, +<code class="computeroutput">bzlib.c</code>, +<code class="computeroutput">compress.c</code>, +<code class="computeroutput">crctable.c</code>, +<code class="computeroutput">decompress.c</code>, +<code class="computeroutput">huffman.c</code>, +<code class="computeroutput">randtable.c</code> and +<code class="computeroutput">libbz2.def</code>. You will also need +to name the header files <code class="computeroutput">bzlib.h</code> +and <code class="computeroutput">bzlib_private.h</code>.</p> +<p>If you don't use VC++, you may need to define the +proprocessor symbol +<code class="computeroutput">_WIN32</code>.</p> +<p>Finally, <code class="computeroutput">dlltest.c</code> is a +sample program using the DLL. It has a project file, +<code class="computeroutput">dlltest.dsp</code>.</p> +<p>If you just want a makefile for Visual C, have a look at +<code class="computeroutput">makefile.msc</code>.</p> +<p>Be aware that if you compile +<code class="computeroutput">bzip2</code> itself on Win32, you must +set <code class="computeroutput">BZ_UNIX</code> to 0 and +<code class="computeroutput">BZ_LCCWIN32</code> to 1, in the file +<code class="computeroutput">bzip2.c</code>, before compiling. +Otherwise the resulting binary won't work correctly.</p> +<p>I haven't tried any of this stuff myself, but it all looks +plausible.</p> +</div> +</div> +<div class="chapter" lang="en"> +<div class="titlepage"><div><div><h2 class="title"> +<a name="misc"></a>4. Miscellanea</h2></div></div></div> +<div class="toc"> +<p><b>Table of Contents</b></p> +<dl> +<dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt> +<dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt> +<dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt> +<dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt> +<dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt> +</dl> +</div> +<p>These are just some random thoughts of mine. Your mileage +may vary.</p> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="limits"></a>4.1. Limitations of the compressed file format</h2></div></div></div> +<p><code class="computeroutput">bzip2-1.0.X</code>, +<code class="computeroutput">0.9.5</code> and +<code class="computeroutput">0.9.0</code> use exactly the same file +format as the original version, +<code class="computeroutput">bzip2-0.1</code>. This decision was +made in the interests of stability. Creating yet another +incompatible compressed file format would create further +confusion and disruption for users.</p> +<p>Nevertheless, this is not a painless decision. Development +work since the release of +<code class="computeroutput">bzip2-0.1</code> in August 1997 has +shown complexities in the file format which slow down +decompression and, in retrospect, are unnecessary. These +are:</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p>The run-length encoder, which is the first of the + compression transformations, is entirely irrelevant. The + original purpose was to protect the sorting algorithm from the + very worst case input: a string of repeated symbols. But + algorithm steps Q6a and Q6b in the original Burrows-Wheeler + technical report (SRC-124) show how repeats can be handled + without difficulty in block sorting.</p></li> +<li style="list-style-type: disc"> +<p>The randomisation mechanism doesn't really need to be + there. Udi Manber and Gene Myers published a suffix array + construction algorithm a few years back, which can be employed + to sort any block, no matter how repetitive, in O(N log N) + time. Subsequent work by Kunihiko Sadakane has produced a + derivative O(N (log N)^2) algorithm which usually outperforms + the Manber-Myers algorithm.</p> +<p>I could have changed to Sadakane's algorithm, but I find + it to be slower than <code class="computeroutput">bzip2</code>'s + existing algorithm for most inputs, and the randomisation + mechanism protects adequately against bad cases. I didn't + think it was a good tradeoff to make. Partly this is due to + the fact that I was not flooded with email complaints about + <code class="computeroutput">bzip2-0.1</code>'s performance on + repetitive data, so perhaps it isn't a problem for real + inputs.</p> +<p>Probably the best long-term solution, and the one I have + incorporated into 0.9.5 and above, is to use the existing + sorting algorithm initially, and fall back to a O(N (log N)^2) + algorithm if the standard algorithm gets into + difficulties.</p> +</li> +<li style="list-style-type: disc"><p>The compressed file format was never designed to be + handled by a library, and I have had to jump though some hoops + to produce an efficient implementation of decompression. It's + a bit hairy. Try passing + <code class="computeroutput">decompress.c</code> through the C + preprocessor and you'll see what I mean. Much of this + complexity could have been avoided if the compressed size of + each block of data was recorded in the data stream.</p></li> +<li style="list-style-type: disc"><p>An Adler-32 checksum, rather than a CRC32 checksum, + would be faster to compute.</p></li> +</ul></div> +<p>It would be fair to say that the +<code class="computeroutput">bzip2</code> format was frozen before I +properly and fully understood the performance consequences of +doing so.</p> +<p>Improvements which I was able to incorporate into 0.9.0, +despite using the same file format, are:</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"><p>Single array implementation of the inverse BWT. This + significantly speeds up decompression, presumably because it + reduces the number of cache misses.</p></li> +<li style="list-style-type: disc"><p>Faster inverse MTF transform for large MTF values. + The new implementation is based on the notion of sliding blocks + of values.</p></li> +<li style="list-style-type: disc"><p><code class="computeroutput">bzip2-0.9.0</code> now reads + and writes files with <code class="computeroutput">fread</code> + and <code class="computeroutput">fwrite</code>; version 0.1 used + <code class="computeroutput">putc</code> and + <code class="computeroutput">getc</code>. Duh! Well, you live + and learn.</p></li> +</ul></div> +<p>Further ahead, it would be nice to be able to do random +access into files. This will require some careful design of +compressed file formats.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="port-issues"></a>4.2. Portability issues</h2></div></div></div> +<p>After some consideration, I have decided not to use GNU +<code class="computeroutput">autoconf</code> to configure 0.9.5 or +1.0.</p> +<p><code class="computeroutput">autoconf</code>, admirable and +wonderful though it is, mainly assists with portability problems +between Unix-like platforms. But +<code class="computeroutput">bzip2</code> doesn't have much in the +way of portability problems on Unix; most of the difficulties +appear when porting to the Mac, or to Microsoft's operating +systems. <code class="computeroutput">autoconf</code> doesn't help +in those cases, and brings in a whole load of new +complexity.</p> +<p>Most people should be able to compile the library and +program under Unix straight out-of-the-box, so to speak, +especially if you have a version of GNU C available.</p> +<p>There are a couple of +<code class="computeroutput">__inline__</code> directives in the +code. GNU C (<code class="computeroutput">gcc</code>) should be +able to handle them. If you're not using GNU C, your C compiler +shouldn't see them at all. If your compiler does, for some +reason, see them and doesn't like them, just +<code class="computeroutput">#define</code> +<code class="computeroutput">__inline__</code> to be +<code class="computeroutput">/* */</code>. One easy way to do this +is to compile with the flag +<code class="computeroutput">-D__inline__=</code>, which should be +understood by most Unix compilers.</p> +<p>If you still have difficulties, try compiling with the +macro <code class="computeroutput">BZ_STRICT_ANSI</code> defined. +This should enable you to build the library in a strictly ANSI +compliant environment. Building the program itself like this is +dangerous and not supported, since you remove +<code class="computeroutput">bzip2</code>'s checks against +compressing directories, symbolic links, devices, and other +not-really-a-file entities. This could cause filesystem +corruption!</p> +<p>One other thing: if you create a +<code class="computeroutput">bzip2</code> binary for public distribution, +please consider linking it statically (<code class="computeroutput">gcc +-static</code>). This avoids all sorts of library-version +issues that others may encounter later on.</p> +<p>If you build <code class="computeroutput">bzip2</code> on +Win32, you must set <code class="computeroutput">BZ_UNIX</code> to 0 +and <code class="computeroutput">BZ_LCCWIN32</code> to 1, in the +file <code class="computeroutput">bzip2.c</code>, before compiling. +Otherwise the resulting binary won't work correctly.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="bugs"></a>4.3. Reporting bugs</h2></div></div></div> +<p>I tried pretty hard to make sure +<code class="computeroutput">bzip2</code> is bug free, both by +design and by testing. Hopefully you'll never need to read this +section for real.</p> +<p>Nevertheless, if <code class="computeroutput">bzip2</code> dies +with a segmentation fault, a bus error or an internal assertion +failure, it will ask you to email me a bug report. Experience from +years of feedback of bzip2 users indicates that almost all these +problems can be traced to either compiler bugs or hardware +problems.</p> +<div class="itemizedlist"><ul type="bullet"> +<li style="list-style-type: disc"> +<p>Recompile the program with no optimisation, and + see if it works. And/or try a different compiler. I heard all + sorts of stories about various flavours of GNU C (and other + compilers) generating bad code for + <code class="computeroutput">bzip2</code>, and I've run across two + such examples myself.</p> +<p>2.7.X versions of GNU C are known to generate bad code + from time to time, at high optimisation levels. If you get + problems, try using the flags + <code class="computeroutput">-O2</code> + <code class="computeroutput">-fomit-frame-pointer</code> + <code class="computeroutput">-fno-strength-reduce</code>. You + should specifically <span class="emphasis"><em>not</em></span> use + <code class="computeroutput">-funroll-loops</code>.</p> +<p>You may notice that the Makefile runs six tests as part + of the build process. If the program passes all of these, it's + a pretty good (but not 100%) indication that the compiler has + done its job correctly.</p> +</li> +<li style="list-style-type: disc"> +<p>If <code class="computeroutput">bzip2</code> + crashes randomly, and the crashes are not repeatable, you may + have a flaky memory subsystem. + <code class="computeroutput">bzip2</code> really hammers your + memory hierarchy, and if it's a bit marginal, you may get these + problems. Ditto if your disk or I/O subsystem is slowly + failing. Yup, this really does happen.</p> +<p>Try using a different machine of the same type, and see + if you can repeat the problem.</p> +</li> +<li style="list-style-type: disc"><p>This isn't really a bug, but ... If + <code class="computeroutput">bzip2</code> tells you your file is + corrupted on decompression, and you obtained the file via FTP, + there is a possibility that you forgot to tell FTP to do a + binary mode transfer. That absolutely will cause the file to + be non-decompressible. You'll have to transfer it + again.</p></li> +</ul></div> +<p>If you've incorporated +<code class="computeroutput">libbzip2</code> into your own program +and are getting problems, please, please, please, check that the +parameters you are passing in calls to the library, are correct, +and in accordance with what the documentation says is allowable. +I have tried to make the library robust against such problems, +but I'm sure I haven't succeeded.</p> +<p>Finally, if the above comments don't help, you'll have to +send me a bug report. Now, it's just amazing how many people +will send me a bug report saying something like:</p> +<pre class="programlisting">bzip2 crashed with segmentation fault on my machine</pre> +<p>and absolutely nothing else. Needless to say, a such a +report is <span class="emphasis"><em>totally, utterly, completely and +comprehensively 100% useless; a waste of your time, my time, and +net bandwidth</em></span>. With no details at all, there's no way +I can possibly begin to figure out what the problem is.</p> +<p>The rules of the game are: facts, facts, facts. Don't omit +them because "oh, they won't be relevant". At the bare +minimum:</p> +<pre class="programlisting">Machine type. Operating system version. +Exact version of bzip2 (do bzip2 -V). +Exact version of the compiler used. +Flags passed to the compiler.</pre> +<p>However, the most important single thing that will help me +is the file that you were trying to compress or decompress at the +time the problem happened. Without that, my ability to do +anything more than speculate about the cause, is limited.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="package"></a>4.4. Did you get the right package?</h2></div></div></div> +<p><code class="computeroutput">bzip2</code> is a resource hog. +It soaks up large amounts of CPU cycles and memory. Also, it +gives very large latencies. In the worst case, you can feed many +megabytes of uncompressed data into the library before getting +any compressed output, so this probably rules out applications +requiring interactive behaviour.</p> +<p>These aren't faults of my implementation, I hope, but more +an intrinsic property of the Burrows-Wheeler transform +(unfortunately). Maybe this isn't what you want.</p> +<p>If you want a compressor and/or library which is faster, +uses less memory but gets pretty good compression, and has +minimal latency, consider Jean-loup Gailly's and Mark Adler's +work, <code class="computeroutput">zlib-1.2.1</code> and +<code class="computeroutput">gzip-1.2.4</code>. Look for them at +<a href="http://www.zlib.org" target="_top">http://www.zlib.org</a> and +<a href="http://www.gzip.org" target="_top">http://www.gzip.org</a> +respectively.</p> +<p>For something faster and lighter still, you might try Markus F +X J Oberhumer's <code class="computeroutput">LZO</code> real-time +compression/decompression library, at +<a href="http://www.oberhumer.com/opensource" target="_top">http://www.oberhumer.com/opensource</a>.</p> +</div> +<div class="sect1" lang="en"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="reading"></a>4.5. Further Reading</h2></div></div></div> +<p><code class="computeroutput">bzip2</code> is not research +work, in the sense that it doesn't present any new ideas. +Rather, it's an engineering exercise based on existing +ideas.</p> +<p>Four documents describe essentially all the ideas behind +<code class="computeroutput">bzip2</code>:</p> +<div class="literallayout"><p>Michael Burrows and D. J. Wheeler:<br> + "A block-sorting lossless data compression algorithm"<br> + 10th May 1994. <br> + Digital SRC Research Report 124.<br> + ftp://ftp.digital.com/pub/DEC/SRC/research-reports/SRC-124.ps.gz<br> + If you have trouble finding it, try searching at the<br> + New Zealand Digital Library, http://www.nzdl.org.<br> +<br> +Daniel S. Hirschberg and Debra A. LeLewer<br> + "Efficient Decoding of Prefix Codes"<br> + Communications of the ACM, April 1990, Vol 33, Number 4.<br> + You might be able to get an electronic copy of this<br> + from the ACM Digital Library.<br> +<br> +David J. Wheeler<br> + Program bred3.c and accompanying document bred3.ps.<br> + This contains the idea behind the multi-table Huffman coding scheme.<br> + ftp://ftp.cl.cam.ac.uk/users/djw3/<br> +<br> +Jon L. Bentley and Robert Sedgewick<br> + "Fast Algorithms for Sorting and Searching Strings"<br> + Available from Sedgewick's web page,<br> + www.cs.princeton.edu/~rs<br> +</p></div> +<p>The following paper gives valuable additional insights into +the algorithm, but is not immediately the basis of any code used +in bzip2.</p> +<div class="literallayout"><p>Peter Fenwick:<br> + Block Sorting Text Compression<br> + Proceedings of the 19th Australasian Computer Science Conference,<br> + Melbourne, Australia. Jan 31 - Feb 2, 1996.<br> + ftp://ftp.cs.auckland.ac.nz/pub/peter-f/ACSC96paper.ps</p></div> +<p>Kunihiko Sadakane's sorting algorithm, mentioned above, is +available from:</p> +<div class="literallayout"><p>http://naomi.is.s.u-tokyo.ac.jp/~sada/papers/Sada98b.ps.gz<br> +</p></div> +<p>The Manber-Myers suffix array construction algorithm is +described in a paper available from:</p> +<div class="literallayout"><p>http://www.cs.arizona.edu/people/gene/PAPERS/suffix.ps<br> +</p></div> +<p>Finally, the following papers document some +investigations I made into the performance of sorting +and decompression algorithms:</p> +<div class="literallayout"><p>Julian Seward<br> + On the Performance of BWT Sorting Algorithms<br> + Proceedings of the IEEE Data Compression Conference 2000<br> + Snowbird, Utah. 28-30 March 2000.<br> +<br> +Julian Seward<br> + Space-time Tradeoffs in the Inverse B-W Transform<br> + Proceedings of the IEEE Data Compression Conference 2001<br> + Snowbird, Utah. 27-29 March 2001.<br> +</p></div> +</div> +</div> +</div></body> +</html> |