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| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book" title="bzip2 and libbzip2, version 1.0.6"> |
| <div class="titlepage"> |
| <div> |
| <div><h1 class="title"> |
| <a name="userman"></a>bzip2 and libbzip2, version 1.0.6</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 1.0.6 of 6 September 2010</p></div> |
| <div><p class="copyright">Copyright © 1996-2010 Julian Seward</p></div> |
| <div><div class="legalnotice" title="Legal Notice"> |
| <a name="id537185"></a><p>This program, <code class="computeroutput">bzip2</code>, the |
| associated library <code class="computeroutput">libbzip2</code>, and |
| all documentation, are copyright © 1996-2010 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 class="itemizedlist" type="bullet"> |
| <li class="listitem" 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 class="listitem" 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 class="listitem" 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 class="listitem" 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. BZ2_bzCompressInit</a></span></dt> |
| <dt><span class="sect2"><a href="#bzCompress">3.3.2. BZ2_bzCompress</a></span></dt> |
| <dt><span class="sect2"><a href="#bzCompress-end">3.3.3. BZ2_bzCompressEnd</a></span></dt> |
| <dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. BZ2_bzDecompressInit</a></span></dt> |
| <dt><span class="sect2"><a href="#bzDecompress">3.3.5. BZ2_bzDecompress</a></span></dt> |
| <dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. BZ2_bzDecompressEnd</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. BZ2_bzReadOpen</a></span></dt> |
| <dt><span class="sect2"><a href="#bzread">3.4.2. BZ2_bzRead</a></span></dt> |
| <dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. BZ2_bzReadGetUnused</a></span></dt> |
| <dt><span class="sect2"><a href="#bzreadclose">3.4.4. BZ2_bzReadClose</a></span></dt> |
| <dt><span class="sect2"><a href="#bzwriteopen">3.4.5. BZ2_bzWriteOpen</a></span></dt> |
| <dt><span class="sect2"><a href="#bzwrite">3.4.6. BZ2_bzWrite</a></span></dt> |
| <dt><span class="sect2"><a href="#bzwriteclose">3.4.7. BZ2_bzWriteClose</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. BZ2_bzBuffToBuffCompress</a></span></dt> |
| <dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. BZ2_bzBuffToBuffDecompress</a></span></dt> |
| </dl></dd> |
| <dt><span class="sect1"><a href="#zlib-compat">3.6. zlib compatibility functions</a></span></dt> |
| <dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a stdio-free environment</a></span></dt> |
| <dd><dl> |
| <dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of stdio</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" title="1. Introduction"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#using" title="2. How to use bzip2">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 class="listitem" style="list-style-type: disc"><p><a class="xref" href="#libprog" title="3. Programming with libbzip2">Programming with libbzip2</a> describes the |
| programming interfaces in detail, and</p></li> |
| <li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#misc" title="4. Miscellanea">Miscellanea</a> records some |
| miscellaneous notes which I thought ought to be recorded |
| somewhere.</p></li> |
| </ul></div> |
| </div> |
| <div class="chapter" title="2. How to use bzip2"> |
| <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" title="2.1. NAME"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzip2</code>, |
| <code class="computeroutput">bunzip2</code> - a block-sorting file |
| compressor, v1.0.6</p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> - |
| decompresses files to stdout</p></li> |
| <li class="listitem" 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" title="2.2. SYNOPSIS"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzip2</code> [ |
| -cdfkqstvzVL123456789 ] [ filenames ... ]</p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bunzip2</code> [ |
| -fkvsVL ] [ filenames ... ]</p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> [ -s ] [ |
| filenames ... ]</p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code> |
| filename</p></li> |
| </ul></div> |
| </div> |
| <div class="sect1" title="2.3. DESCRIPTION"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">filename.bz2 </code> |
| becomes |
| <code class="computeroutput">filename</code></p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">filename.bz </code> |
| becomes |
| <code class="computeroutput">filename</code></p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">filename.tbz2</code> |
| becomes |
| <code class="computeroutput">filename.tar</code></p></li> |
| <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">filename.tbz </code> |
| becomes |
| <code class="computeroutput">filename.tar</code></p></li> |
| <li class="listitem" 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" title="2.4. OPTIONS"> |
| <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 class="xref" href="#memory-management" title="2.5. 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 class="xref" href="#memory-management" title="2.5. 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" title="2.5. MEMORY MANAGEMENT"> |
| <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" title="2.6. RECOVERING DATA FROM DAMAGED FILES"> |
| <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" title="2.7. PERFORMANCE NOTES"> |
| <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" title="2.8. CAVEATS"> |
| <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 1.0.6 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" title="2.9. AUTHOR"> |
| <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" title="3. Programming with libbzip2"> |
| <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. BZ2_bzCompressInit</a></span></dt> |
| <dt><span class="sect2"><a href="#bzCompress">3.3.2. BZ2_bzCompress</a></span></dt> |
| <dt><span class="sect2"><a href="#bzCompress-end">3.3.3. BZ2_bzCompressEnd</a></span></dt> |
| <dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. BZ2_bzDecompressInit</a></span></dt> |
| <dt><span class="sect2"><a href="#bzDecompress">3.3.5. BZ2_bzDecompress</a></span></dt> |
| <dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. BZ2_bzDecompressEnd</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. BZ2_bzReadOpen</a></span></dt> |
| <dt><span class="sect2"><a href="#bzread">3.4.2. BZ2_bzRead</a></span></dt> |
| <dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. BZ2_bzReadGetUnused</a></span></dt> |
| <dt><span class="sect2"><a href="#bzreadclose">3.4.4. BZ2_bzReadClose</a></span></dt> |
| <dt><span class="sect2"><a href="#bzwriteopen">3.4.5. BZ2_bzWriteOpen</a></span></dt> |
| <dt><span class="sect2"><a href="#bzwrite">3.4.6. BZ2_bzWrite</a></span></dt> |
| <dt><span class="sect2"><a href="#bzwriteclose">3.4.7. BZ2_bzWriteClose</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. BZ2_bzBuffToBuffCompress</a></span></dt> |
| <dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. BZ2_bzBuffToBuffDecompress</a></span></dt> |
| </dl></dd> |
| <dt><span class="sect1"><a href="#zlib-compat">3.6. zlib compatibility functions</a></span></dt> |
| <dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a stdio-free environment</a></span></dt> |
| <dd><dl> |
| <dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of stdio</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 class="xref" href="#using" title="2. How to use bzip2">How to use bzip2</a> as well.</p> |
| <div class="sect1" title="3.1. Top-level structure"> |
| <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" title="3.1.1. Low-level summary"> |
| <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" title="3.1.2. High-level summary"> |
| <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" title="3.1.3. Utility functions summary"> |
| <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" title="3.2. Error handling"> |
| <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" title="3.3. Low-level interface"> |
| <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" title="3.3.1. BZ2_bzCompressInit"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzcompress-init"></a>3.3.1. BZ2_bzCompressInit</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" title="3.3.2. BZ2_bzCompress"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzCompress"></a>3.3.2. BZ2_bzCompress</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 class="orderedlist" type="1"> |
| <li class="listitem"><p>Get started with |
| <code class="computeroutput">BZ2_bzCompressInit</code>.</p></li> |
| <li class="listitem"><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 class="listitem"><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 class="listitem"><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" title="3.3.3. BZ2_bzCompressEnd"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzCompress-end"></a>3.3.3. BZ2_bzCompressEnd</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" title="3.3.4. BZ2_bzDecompressInit"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzDecompress-init"></a>3.3.4. BZ2_bzDecompressInit</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 class="xref" href="#using" title="2. How to use bzip2">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" title="3.3.5. BZ2_bzDecompress"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzDecompress"></a>3.3.5. BZ2_bzDecompress</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" title="3.3.6. BZ2_bzDecompressEnd"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzDecompress-end"></a>3.3.6. BZ2_bzDecompressEnd</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" title="3.4. High-level interface"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" 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 class="listitem" 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 class="listitem" 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 class="listitem" 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" title="3.4.1. BZ2_bzReadOpen"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzreadopen"></a>3.4.1. BZ2_bzReadOpen</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" title="3.4.2. BZ2_bzRead"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzread"></a>3.4.2. BZ2_bzRead</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" title="3.4.3. BZ2_bzReadGetUnused"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzreadgetunused"></a>3.4.3. BZ2_bzReadGetUnused</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" title="3.4.4. BZ2_bzReadClose"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzreadclose"></a>3.4.4. BZ2_bzReadClose</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" title="3.4.5. BZ2_bzWriteOpen"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzwriteopen"></a>3.4.5. BZ2_bzWriteOpen</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" title="3.4.6. BZ2_bzWrite"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzwrite"></a>3.4.6. BZ2_bzWrite</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" title="3.4.7. BZ2_bzWriteClose"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzwriteclose"></a>3.4.7. BZ2_bzWriteClose</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" title="3.4.8. Handling embedded compressed data streams"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" 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 class="listitem" 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" title="3.4.9. Standard file-reading/writing code"> |
| <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" title="3.5. Utility functions"> |
| <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" title="3.5.1. BZ2_bzBuffToBuffCompress"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzbufftobuffcompress"></a>3.5.1. BZ2_bzBuffToBuffCompress</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" title="3.5.2. BZ2_bzBuffToBuffDecompress"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="bzbufftobuffdecompress"></a>3.5.2. BZ2_bzBuffToBuffDecompress</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" title="3.6. zlib compatibility functions"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="zlib-compat"></a>3.6. zlib 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" title="3.7. Using the library in a stdio-free environment"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="stdio-free"></a>3.7. Using the library in a stdio-free environment</h2></div></div></div> |
| <div class="sect2" title="3.7.1. Getting rid of stdio"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="stdio-bye"></a>3.7.1. Getting rid of stdio</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" title="3.7.2. Critical error handling"> |
| <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, 1.0.6 of 6 September 2010. |
| 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, 6 September 2010. |
| </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" title="3.8. Making a Windows DLL"> |
| <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" title="4. Miscellanea"> |
| <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" title="4.1. Limitations of the compressed file format"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" 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 class="listitem" 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 class="listitem" 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 class="listitem" 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 class="itemizedlist" type="bullet"> |
| <li class="listitem" 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 class="listitem" 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 class="listitem" 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" title="4.2. Portability issues"> |
| <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" title="4.3. Reporting bugs"> |
| <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 class="itemizedlist" type="bullet"> |
| <li class="listitem" 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 class="listitem" 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 class="listitem" 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" title="4.4. Did you get the right package?"> |
| <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 class="ulink" href="http://www.zlib.org" target="_top">http://www.zlib.org</a> and |
| <a class="ulink" 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 class="ulink" href="http://www.oberhumer.com/opensource" target="_top">http://www.oberhumer.com/opensource</a>.</p> |
| </div> |
| <div class="sect1" title="4.5. Further Reading"> |
| <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> |
