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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">
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<div class="titlepage">
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<div>
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<div><h1 class="title">
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<a name="userman"></a>bzip2 and libbzip2, version 1.0.6</h1></div>
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<div><h2 class="subtitle">A program and library for data compression</h2></div>
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<div><div class="authorgroup"><div class="author">
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<h3 class="author">
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<span class="firstname">Julian</span> <span class="surname">Seward</span>
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</h3>
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<div class="affiliation"><span class="orgname">http://www.bzip.org<br></span></div>
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</div></div></div>
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<div><p class="releaseinfo">Version 1.0.6 of 6 September 2010</p></div>
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<div><p class="copyright">Copyright <20> 1996-2010 Julian Seward</p></div>
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<div><div class="legalnotice" title="Legal Notice">
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<a name="id537185"></a><p>This program, <code class="computeroutput">bzip2</code>, the
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associated library <code class="computeroutput">libbzip2</code>, and
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all documentation, are copyright <20> 1996-2010 Julian Seward.
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All rights reserved.</p>
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<p>Redistribution and use in source and binary forms, with
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or without modification, are permitted provided that the
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following conditions are met:</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="bullet">
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<li class="listitem" style="list-style-type: disc"><p>Redistributions of source code must retain the
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|
above copyright notice, this list of conditions and the
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|
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following disclaimer.</p></li>
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|
<li class="listitem" style="list-style-type: disc"><p>The origin of this software must not be
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|
misrepresented; you must not claim that you wrote the original
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|
software. If you use this software in a product, an
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|
acknowledgment in the product documentation would be
|
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|
appreciated but is not required.</p></li>
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|
<li class="listitem" style="list-style-type: disc"><p>Altered source versions must be plainly marked
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|
as such, and must not be misrepresented as being the original
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|
software.</p></li>
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|
<li class="listitem" style="list-style-type: disc"><p>The name of the author may not be used to
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endorse or promote products derived from this software without
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specific prior written permission.</p></li>
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|
</ul></div>
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<p>THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY
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EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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|
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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|
AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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|
|
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
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|
TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
|
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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|
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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|
|
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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|
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,
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|
<code class="computeroutput">bzip2</code> and
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|
<code class="computeroutput">libbzip2</code> do not use any patented
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algorithms. However, I do not have the resources to carry
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out a patent search. Therefore I cannot give any guarantee of
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the above statement.
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|
</p>
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|
</div></div>
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</div>
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<hr>
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</div>
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<div class="toc">
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<p><b>Table of Contents</b></p>
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<dl>
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<dt><span class="chapter"><a href="#intro">1. Introduction</a></span></dt>
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<dt><span class="chapter"><a href="#using">2. How to use bzip2</a></span></dt>
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|
<dd><dl>
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|
|
<dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt>
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|
|
<dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt>
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|
|
</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>
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|
|
<dd><dl>
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|
|
<dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt>
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|
<dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt>
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<dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt>
|
|
|
</dl></dd>
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|
<dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt>
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|
<dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt>
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|
<dd><dl>
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|
|
<dt><span class="sect2"><a href="#bzcompress-init">3.3.1. BZ2_bzCompressInit</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzCompress">3.3.2. BZ2_bzCompress</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzCompress-end">3.3.3. BZ2_bzCompressEnd</a></span></dt>
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<dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. BZ2_bzDecompressInit</a></span></dt>
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<dt><span class="sect2"><a href="#bzDecompress">3.3.5. BZ2_bzDecompress</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. BZ2_bzDecompressEnd</a></span></dt>
|
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|
</dl></dd>
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|
<dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt>
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|
<dd><dl>
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|
<dt><span class="sect2"><a href="#bzreadopen">3.4.1. BZ2_bzReadOpen</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzread">3.4.2. BZ2_bzRead</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. BZ2_bzReadGetUnused</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzreadclose">3.4.4. BZ2_bzReadClose</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzwriteopen">3.4.5. BZ2_bzWriteOpen</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzwrite">3.4.6. BZ2_bzWrite</a></span></dt>
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|
<dt><span class="sect2"><a href="#bzwriteclose">3.4.7. BZ2_bzWriteClose</a></span></dt>
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|
<dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt>
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|
<dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt>
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|
</dl></dd>
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|
<dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt>
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|
<dd><dl>
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|
<dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. BZ2_bzBuffToBuffCompress</a></span></dt>
|
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|
<dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. BZ2_bzBuffToBuffDecompress</a></span></dt>
|
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|
</dl></dd>
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|
<dt><span class="sect1"><a href="#zlib-compat">3.6. zlib compatibility functions</a></span></dt>
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|
<dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a stdio-free environment</a></span></dt>
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|
<dd><dl>
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|
<dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of stdio</a></span></dt>
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|
<dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt>
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|
</dl></dd>
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|
<dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt>
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|
</dl></dd>
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|
<dt><span class="chapter"><a href="#misc">4. Miscellanea</a></span></dt>
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<dd><dl>
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<dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt>
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|
<dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt>
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|
<dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt>
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|
<dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt>
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|
<dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt>
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|
</dl></dd>
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|
</dl>
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|
</div>
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<div class="chapter" title="1.<2E>Introduction">
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|
<div class="titlepage"><div><div><h2 class="title">
|
|
|
<a name="intro"></a>1.<2E>Introduction</h2></div></div></div>
|
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|
<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
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|
<code class="computeroutput">bzip2</code> format. This manual
|
|
|
describes both how to use the program and how to work with the
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|
library interface. Most of the manual is devoted to this
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|
library, not the program, which is good news if your interest is
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|
only in the program.</p>
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|
<div class="itemizedlist"><ul class="itemizedlist" type="bullet">
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<li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#using" title="2.<2E>How to use bzip2">How to use bzip2</a> describes how to use
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|
<code class="computeroutput">bzip2</code>; this is the only part
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|
|
you need to read if you just want to know how to operate the
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|
|
program.</p></li>
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|
<li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#libprog" title="3.<2E> Programming with libbzip2">Programming with libbzip2</a> describes the
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|
programming interfaces in detail, and</p></li>
|
|
|
<li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#misc" title="4.<2E>Miscellanea">Miscellanea</a> records some
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|
miscellaneous notes which I thought ought to be recorded
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|
somewhere.</p></li>
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|
</ul></div>
|
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</div>
|
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|
<div class="chapter" title="2.<2E>How to use bzip2">
|
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|
<div class="titlepage"><div><div><h2 class="title">
|
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|
<a name="using"></a>2.<2E>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
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|
|
else.</p>
|
|
|
<div class="sect1" title="2.1.<2E>NAME">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="name"></a>2.1.<2E>NAME</h2></div></div></div>
|
|
|
<div class="itemizedlist"><ul class="itemizedlist" type="bullet">
|
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|
<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.<2E>SYNOPSIS">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="synopsis"></a>2.2.<2E>SYNOPSIS</h2></div></div></div>
|
|
|
<div class="itemizedlist"><ul class="itemizedlist" type="bullet">
|
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|
<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.<2E>DESCRIPTION">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="description"></a>2.3.<2E>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.<2E>OPTIONS">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="options"></a>2.4.<2E>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.<2E>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.<2E>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.<2E>MEMORY MANAGEMENT">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="memory-management"></a>2.5.<2E>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.<2E>RECOVERING DATA FROM DAMAGED FILES">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="recovering"></a>2.6.<2E>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.<2E>PERFORMANCE NOTES">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="performance"></a>2.7.<2E>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.<2E>CAVEATS">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="caveats"></a>2.8.<2E>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.<2E>AUTHOR">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="author"></a>2.9.<2E>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.<2E> Programming with libbzip2">
|
|
|
<div class="titlepage"><div><div><h2 class="title">
|
|
|
<a name="libprog"></a>3.<2E>
|
|
|
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.<2E>How to use bzip2">How to use bzip2</a> as well.</p>
|
|
|
<div class="sect1" title="3.1.<2E>Top-level structure">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="top-level"></a>3.1.<2E>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.<2E>Low-level summary">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="ll-summary"></a>3.1.1.<2E>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.<2E>High-level summary">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="hl-summary"></a>3.1.2.<2E>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.<2E>Utility functions summary">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="util-fns-summary"></a>3.1.3.<2E>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.<2E>Error handling">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="err-handling"></a>3.2.<2E>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.<2E>Low-level interface">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="low-level"></a>3.3.<2E>Low-level interface</h2></div></div></div>
|
|
|
<div class="sect2" title="3.3.1.<2E>BZ2_bzCompressInit">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzcompress-init"></a>3.3.1.<2E>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.<2E>BZ2_bzCompress">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzCompress"></a>3.3.2.<2E>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.<2E>BZ2_bzCompressEnd">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzCompress-end"></a>3.3.3.<2E>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.<2E>BZ2_bzDecompressInit">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzDecompress-init"></a>3.3.4.<2E>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.<2E>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.<2E>BZ2_bzDecompress">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzDecompress"></a>3.3.5.<2E>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.<2E>BZ2_bzDecompressEnd">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzDecompress-end"></a>3.3.6.<2E>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.<2E>High-level interface">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="hl-interface"></a>3.4.<2E>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.<2E>BZ2_bzReadOpen">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzreadopen"></a>3.4.1.<2E>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.<2E>BZ2_bzRead">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzread"></a>3.4.2.<2E>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.<2E>BZ2_bzReadGetUnused">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzreadgetunused"></a>3.4.3.<2E>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.<2E>BZ2_bzReadClose">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzreadclose"></a>3.4.4.<2E>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.<2E>BZ2_bzWriteOpen">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzwriteopen"></a>3.4.5.<2E>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.<2E>BZ2_bzWrite">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzwrite"></a>3.4.6.<2E>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.<2E>BZ2_bzWriteClose">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzwriteclose"></a>3.4.7.<2E>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.<2E>Handling embedded compressed data streams">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="embed"></a>3.4.8.<2E>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.<2E>Standard file-reading/writing code">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="std-rdwr"></a>3.4.9.<2E>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.<2E>Utility functions">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="util-fns"></a>3.5.<2E>Utility functions</h2></div></div></div>
|
|
|
<div class="sect2" title="3.5.1.<2E>BZ2_bzBuffToBuffCompress">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzbufftobuffcompress"></a>3.5.1.<2E>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.<2E>BZ2_bzBuffToBuffDecompress">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="bzbufftobuffdecompress"></a>3.5.2.<2E>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.<2E>zlib compatibility functions">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="zlib-compat"></a>3.6.<2E>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.<2E>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.<2E>Using the library in a stdio-free environment</h2></div></div></div>
|
|
|
<div class="sect2" title="3.7.1.<2E>Getting rid of stdio">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="stdio-bye"></a>3.7.1.<2E>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.<2E>Critical error handling">
|
|
|
<div class="titlepage"><div><div><h3 class="title">
|
|
|
<a name="critical-error"></a>3.7.2.<2E>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.<2E>Making a Windows DLL">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="win-dll"></a>3.8.<2E>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.<2E>Miscellanea">
|
|
|
<div class="titlepage"><div><div><h2 class="title">
|
|
|
<a name="misc"></a>4.<2E>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.<2E>Limitations of the compressed file format">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="limits"></a>4.1.<2E>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.<2E>Portability issues">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="port-issues"></a>4.2.<2E>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.<2E>Reporting bugs">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="bugs"></a>4.3.<2E>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.<2E>Did you get the right package?">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="package"></a>4.4.<2E>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.<2E>Further Reading">
|
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
|
|
<a name="reading"></a>4.5.<2E>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<EFBFBD>Burrows<EFBFBD>and<EFBFBD>D.<2E>J.<2E>Wheeler:<br>
|
|
|
<EFBFBD><EFBFBD>"A<>block-sorting<6E>lossless<73>data<74>compression<6F>algorithm"<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>10th<EFBFBD>May<EFBFBD>1994.<2E><br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Digital<EFBFBD>SRC<EFBFBD>Research<EFBFBD>Report<EFBFBD>124.<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>ftp://ftp.digital.com/pub/DEC/SRC/research-reports/SRC-124.ps.gz<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>If<EFBFBD>you<EFBFBD>have<EFBFBD>trouble<EFBFBD>finding<EFBFBD>it,<2C>try<72>searching<6E>at<61>the<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>New<EFBFBD>Zealand<EFBFBD>Digital<EFBFBD>Library,<2C>http://www.nzdl.org.<br>
|
|
|
<br>
|
|
|
Daniel<EFBFBD>S.<2E>Hirschberg<72>and<6E>Debra<72>A.<2E>LeLewer<br>
|
|
|
<EFBFBD><EFBFBD>"Efficient<6E>Decoding<6E>of<6F>Prefix<69>Codes"<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Communications<EFBFBD>of<EFBFBD>the<EFBFBD>ACM,<2C>April<69>1990,<2C>Vol<6F>33,<2C>Number<65>4.<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>You<EFBFBD>might<EFBFBD>be<EFBFBD>able<EFBFBD>to<EFBFBD>get<EFBFBD>an<EFBFBD>electronic<EFBFBD>copy<EFBFBD>of<EFBFBD>this<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>from<EFBFBD>the<EFBFBD>ACM<EFBFBD>Digital<EFBFBD>Library.<br>
|
|
|
<br>
|
|
|
David<EFBFBD>J.<2E>Wheeler<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Program<EFBFBD>bred3.c<>and<6E>accompanying<6E>document<6E>bred3.ps.<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>This<EFBFBD>contains<EFBFBD>the<EFBFBD>idea<EFBFBD>behind<EFBFBD>the<EFBFBD>multi-table<6C>Huffman<61>coding<6E>scheme.<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>ftp://ftp.cl.cam.ac.uk/users/djw3/<br>
|
|
|
<br>
|
|
|
Jon<EFBFBD>L.<2E>Bentley<65>and<6E>Robert<72>Sedgewick<br>
|
|
|
<EFBFBD><EFBFBD>"Fast<73>Algorithms<6D>for<6F>Sorting<6E>and<6E>Searching<6E>Strings"<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Available<EFBFBD>from<EFBFBD>Sedgewick's<>web<65>page,<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>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<EFBFBD>Fenwick:<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Block<EFBFBD>Sorting<EFBFBD>Text<EFBFBD>Compression<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Proceedings<EFBFBD>of<EFBFBD>the<EFBFBD>19th<EFBFBD>Australasian<EFBFBD>Computer<EFBFBD>Science<EFBFBD>Conference,<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Melbourne,<2C>Australia.<2E><>Jan<61>31<33>-<2D>Feb<65>2,<2C>1996.<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>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<EFBFBD>Seward<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>On<EFBFBD>the<EFBFBD>Performance<EFBFBD>of<EFBFBD>BWT<EFBFBD>Sorting<EFBFBD>Algorithms<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Proceedings<EFBFBD>of<EFBFBD>the<EFBFBD>IEEE<EFBFBD>Data<EFBFBD>Compression<EFBFBD>Conference<EFBFBD>2000<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Snowbird,<2C>Utah.<2E><>28-30<33>March<63>2000.<br>
|
|
|
<br>
|
|
|
Julian<EFBFBD>Seward<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Space-time<6D>Tradeoffs<66>in<69>the<68>Inverse<73>B-W<>Transform<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD>Proceedings<EFBFBD>of<EFBFBD>the<EFBFBD>IEEE<EFBFBD>Data<EFBFBD>Compression<EFBFBD>Conference<EFBFBD>2001<br>
|
|
|
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>Snowbird,<2C>Utah.<2E><>27-29<32>March<63>2001.<br>
|
|
|
</p></div>
|
|
|
</div>
|
|
|
</div>
|
|
|
</div></body>
|
|
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</html>
|
