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82<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en">
83<div class="titlepage">
84<div>
85<div><h1 class="title">
86<a name="userman"></a>bzip2 and libbzip2, version 1.0.4</h1></div>
87<div><h2 class="subtitle">A program and library for data compression</h2></div>
88<div><div class="authorgroup"><div class="author">
89<h3 class="author">
90<span class="firstname">Julian</span> <span class="surname">Seward</span>
91</h3>
92<div class="affiliation"><span class="orgname">http://www.bzip.org<br></span></div>
93</div></div></div>
94<div><p class="releaseinfo">Version 1.0.4 of 20 December 2006</p></div>
95<div><p class="copyright">Copyright © 1996-2006 Julian Seward</p></div>
96<div><div class="legalnotice">
97<a name="id2497666"></a><p>This program, <code class="computeroutput">bzip2</code>, the
98 associated library <code class="computeroutput">libbzip2</code>, and
99 all documentation, are copyright © 1996-2006 Julian Seward.
100 All rights reserved.</p>
101<p>Redistribution and use in source and binary forms, with
102 or without modification, are permitted provided that the
103 following conditions are met:</p>
104<div class="itemizedlist"><ul type="bullet">
105<li style="list-style-type: disc"><p>Redistributions of source code must retain the
106 above copyright notice, this list of conditions and the
107 following disclaimer.</p></li>
108<li style="list-style-type: disc"><p>The origin of this software must not be
109 misrepresented; you must not claim that you wrote the original
110 software. If you use this software in a product, an
111 acknowledgment in the product documentation would be
112 appreciated but is not required.</p></li>
113<li style="list-style-type: disc"><p>Altered source versions must be plainly marked
114 as such, and must not be misrepresented as being the original
115 software.</p></li>
116<li style="list-style-type: disc"><p>The name of the author may not be used to
117 endorse or promote products derived from this software without
118 specific prior written permission.</p></li>
119</ul></div>
120<p>THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY
121 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
122 THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
123 PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
124 AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
125 EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
126 TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
127 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
128 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
129 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
130 IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
131 THE POSSIBILITY OF SUCH DAMAGE.</p>
132<p>PATENTS: To the best of my knowledge,
133 <code class="computeroutput">bzip2</code> and
134 <code class="computeroutput">libbzip2</code> do not use any patented
135 algorithms. However, I do not have the resources to carry
136 out a patent search. Therefore I cannot give any guarantee of
137 the above statement.
138 </p>
139</div></div>
140</div>
141<hr>
142</div>
143<div class="toc">
144<p><b>Table of Contents</b></p>
145<dl>
146<dt><span class="chapter"><a href="#intro">1. Introduction</a></span></dt>
147<dt><span class="chapter"><a href="#using">2. How to use bzip2</a></span></dt>
148<dd><dl>
149<dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt>
150<dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt>
151<dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt>
152<dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt>
153<dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt>
154<dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt>
155<dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt>
156<dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt>
157<dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt>
158</dl></dd>
159<dt><span class="chapter"><a href="#libprog">3.
160Programming with <code class="computeroutput">libbzip2</code>
161</a></span></dt>
162<dd><dl>
163<dt><span class="sect1"><a href="#top-level">3.1. Top-level structure</a></span></dt>
164<dd><dl>
165<dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt>
166<dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt>
167<dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt>
168</dl></dd>
169<dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt>
170<dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt>
171<dd><dl>
172<dt><span class="sect2"><a href="#bzcompress-init">3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></a></span></dt>
173<dt><span class="sect2"><a href="#bzCompress">3.3.2. <code class="computeroutput">BZ2_bzCompress</code></a></span></dt>
174<dt><span class="sect2"><a href="#bzCompress-end">3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></a></span></dt>
175<dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></a></span></dt>
176<dt><span class="sect2"><a href="#bzDecompress">3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></a></span></dt>
177<dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></a></span></dt>
178</dl></dd>
179<dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt>
180<dd><dl>
181<dt><span class="sect2"><a href="#bzreadopen">3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></a></span></dt>
182<dt><span class="sect2"><a href="#bzread">3.4.2. <code class="computeroutput">BZ2_bzRead</code></a></span></dt>
183<dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></a></span></dt>
184<dt><span class="sect2"><a href="#bzreadclose">3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></a></span></dt>
185<dt><span class="sect2"><a href="#bzwriteopen">3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></a></span></dt>
186<dt><span class="sect2"><a href="#bzwrite">3.4.6. <code class="computeroutput">BZ2_bzWrite</code></a></span></dt>
187<dt><span class="sect2"><a href="#bzwriteclose">3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></a></span></dt>
188<dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt>
189<dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt>
190</dl></dd>
191<dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt>
192<dd><dl>
193<dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></a></span></dt>
194<dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></a></span></dt>
195</dl></dd>
196<dt><span class="sect1"><a href="#zlib-compat">3.6. <code class="computeroutput">zlib</code> compatibility functions</a></span></dt>
197<dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</a></span></dt>
198<dd><dl>
199<dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of <code class="computeroutput">stdio</code></a></span></dt>
200<dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt>
201</dl></dd>
202<dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt>
203</dl></dd>
204<dt><span class="chapter"><a href="#misc">4. Miscellanea</a></span></dt>
205<dd><dl>
206<dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt>
207<dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt>
208<dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt>
209<dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt>
210<dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt>
211</dl></dd>
212</dl>
213</div>
214<div class="chapter" lang="en">
215<div class="titlepage"><div><div><h2 class="title">
216<a name="intro"></a>1. Introduction</h2></div></div></div>
217<p><code class="computeroutput">bzip2</code> compresses files
218using the Burrows-Wheeler block-sorting text compression
219algorithm, and Huffman coding. Compression is generally
220considerably better than that achieved by more conventional
221LZ77/LZ78-based compressors, and approaches the performance of
222the PPM family of statistical compressors.</p>
223<p><code class="computeroutput">bzip2</code> is built on top of
224<code class="computeroutput">libbzip2</code>, a flexible library for
225handling compressed data in the
226<code class="computeroutput">bzip2</code> format. This manual
227describes both how to use the program and how to work with the
228library interface. Most of the manual is devoted to this
229library, not the program, which is good news if your interest is
230only in the program.</p>
231<div class="itemizedlist"><ul type="bullet">
232<li style="list-style-type: disc"><p><a href="#using">How to use bzip2</a> describes how to use
233 <code class="computeroutput">bzip2</code>; this is the only part
234 you need to read if you just want to know how to operate the
235 program.</p></li>
236<li style="list-style-type: disc"><p><a href="#libprog">Programming with libbzip2</a> describes the
237 programming interfaces in detail, and</p></li>
238<li style="list-style-type: disc"><p><a href="#misc">Miscellanea</a> records some
239 miscellaneous notes which I thought ought to be recorded
240 somewhere.</p></li>
241</ul></div>
242</div>
243<div class="chapter" lang="en">
244<div class="titlepage"><div><div><h2 class="title">
245<a name="using"></a>2. How to use bzip2</h2></div></div></div>
246<div class="toc">
247<p><b>Table of Contents</b></p>
248<dl>
249<dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt>
250<dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt>
251<dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt>
252<dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt>
253<dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt>
254<dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt>
255<dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt>
256<dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt>
257<dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt>
258</dl>
259</div>
260<p>This chapter contains a copy of the
261<code class="computeroutput">bzip2</code> man page, and nothing
262else.</p>
263<div class="sect1" lang="en">
264<div class="titlepage"><div><div><h2 class="title" style="clear: both">
265<a name="name"></a>2.1. NAME</h2></div></div></div>
266<div class="itemizedlist"><ul type="bullet">
267<li style="list-style-type: disc"><p><code class="computeroutput">bzip2</code>,
268 <code class="computeroutput">bunzip2</code> - a block-sorting file
269 compressor, v1.0.4</p></li>
270<li style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> -
271 decompresses files to stdout</p></li>
272<li style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code> -
273 recovers data from damaged bzip2 files</p></li>
274</ul></div>
275</div>
276<div class="sect1" lang="en">
277<div class="titlepage"><div><div><h2 class="title" style="clear: both">
278<a name="synopsis"></a>2.2. SYNOPSIS</h2></div></div></div>
279<div class="itemizedlist"><ul type="bullet">
280<li style="list-style-type: disc"><p><code class="computeroutput">bzip2</code> [
281 -cdfkqstvzVL123456789 ] [ filenames ... ]</p></li>
282<li style="list-style-type: disc"><p><code class="computeroutput">bunzip2</code> [
283 -fkvsVL ] [ filenames ... ]</p></li>
284<li style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> [ -s ] [
285 filenames ... ]</p></li>
286<li style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code>
287 filename</p></li>
288</ul></div>
289</div>
290<div class="sect1" lang="en">
291<div class="titlepage"><div><div><h2 class="title" style="clear: both">
292<a name="description"></a>2.3. DESCRIPTION</h2></div></div></div>
293<p><code class="computeroutput">bzip2</code> compresses files
294using the Burrows-Wheeler block sorting text compression
295algorithm, and Huffman coding. Compression is generally
296considerably better than that achieved by more conventional
297LZ77/LZ78-based compressors, and approaches the performance of
298the PPM family of statistical compressors.</p>
299<p>The command-line options are deliberately very similar to
300those of GNU <code class="computeroutput">gzip</code>, but they are
301not identical.</p>
302<p><code class="computeroutput">bzip2</code> expects a list of
303file names to accompany the command-line flags. Each file is
304replaced by a compressed version of itself, with the name
305<code class="computeroutput">original_name.bz2</code>. Each
306compressed file has the same modification date, permissions, and,
307when possible, ownership as the corresponding original, so that
308these properties can be correctly restored at decompression time.
309File name handling is naive in the sense that there is no
310mechanism for preserving original file names, permissions,
311ownerships or dates in filesystems which lack these concepts, or
312have serious file name length restrictions, such as
313MS-DOS.</p>
314<p><code class="computeroutput">bzip2</code> and
315<code class="computeroutput">bunzip2</code> will by default not
316overwrite existing files. If you want this to happen, specify
317the <code class="computeroutput">-f</code> flag.</p>
318<p>If no file names are specified,
319<code class="computeroutput">bzip2</code> compresses from standard
320input to standard output. In this case,
321<code class="computeroutput">bzip2</code> will decline to write
322compressed output to a terminal, as this would be entirely
323incomprehensible and therefore pointless.</p>
324<p><code class="computeroutput">bunzip2</code> (or
325<code class="computeroutput">bzip2 -d</code>) decompresses all
326specified files. Files which were not created by
327<code class="computeroutput">bzip2</code> will be detected and
328ignored, and a warning issued.
329<code class="computeroutput">bzip2</code> attempts to guess the
330filename for the decompressed file from that of the compressed
331file as follows:</p>
332<div class="itemizedlist"><ul type="bullet">
333<li style="list-style-type: disc"><p><code class="computeroutput">filename.bz2 </code>
334 becomes
335 <code class="computeroutput">filename</code></p></li>
336<li style="list-style-type: disc"><p><code class="computeroutput">filename.bz </code>
337 becomes
338 <code class="computeroutput">filename</code></p></li>
339<li style="list-style-type: disc"><p><code class="computeroutput">filename.tbz2</code>
340 becomes
341 <code class="computeroutput">filename.tar</code></p></li>
342<li style="list-style-type: disc"><p><code class="computeroutput">filename.tbz </code>
343 becomes
344 <code class="computeroutput">filename.tar</code></p></li>
345<li style="list-style-type: disc"><p><code class="computeroutput">anyothername </code>
346 becomes
347 <code class="computeroutput">anyothername.out</code></p></li>
348</ul></div>
349<p>If the file does not end in one of the recognised endings,
350<code class="computeroutput">.bz2</code>,
351<code class="computeroutput">.bz</code>,
352<code class="computeroutput">.tbz2</code> or
353<code class="computeroutput">.tbz</code>,
354<code class="computeroutput">bzip2</code> complains that it cannot
355guess the name of the original file, and uses the original name
356with <code class="computeroutput">.out</code> appended.</p>
357<p>As with compression, supplying no filenames causes
358decompression from standard input to standard output.</p>
359<p><code class="computeroutput">bunzip2</code> will correctly
360decompress a file which is the concatenation of two or more
361compressed files. The result is the concatenation of the
362corresponding uncompressed files. Integrity testing
363(<code class="computeroutput">-t</code>) of concatenated compressed
364files is also supported.</p>
365<p>You can also compress or decompress files to the standard
366output by giving the <code class="computeroutput">-c</code> flag.
367Multiple files may be compressed and decompressed like this. The
368resulting outputs are fed sequentially to stdout. Compression of
369multiple files in this manner generates a stream containing
370multiple compressed file representations. Such a stream can be
371decompressed correctly only by
372<code class="computeroutput">bzip2</code> version 0.9.0 or later.
373Earlier versions of <code class="computeroutput">bzip2</code> will
374stop after decompressing the first file in the stream.</p>
375<p><code class="computeroutput">bzcat</code> (or
376<code class="computeroutput">bzip2 -dc</code>) decompresses all
377specified files to the standard output.</p>
378<p><code class="computeroutput">bzip2</code> will read arguments
379from the environment variables
380<code class="computeroutput">BZIP2</code> and
381<code class="computeroutput">BZIP</code>, in that order, and will
382process them before any arguments read from the command line.
383This gives a convenient way to supply default arguments.</p>
384<p>Compression is always performed, even if the compressed
385file is slightly larger than the original. Files of less than
386about one hundred bytes tend to get larger, since the compression
387mechanism has a constant overhead in the region of 50 bytes.
388Random data (including the output of most file compressors) is
389coded at about 8.05 bits per byte, giving an expansion of around
3900.5%.</p>
391<p>As a self-check for your protection,
392<code class="computeroutput">bzip2</code> uses 32-bit CRCs to make
393sure that the decompressed version of a file is identical to the
394original. This guards against corruption of the compressed data,
395and against undetected bugs in
396<code class="computeroutput">bzip2</code> (hopefully very unlikely).
397The chances of data corruption going undetected is microscopic,
398about one chance in four billion for each file processed. Be
399aware, though, that the check occurs upon decompression, so it
400can only tell you that something is wrong. It can't help you
401recover the original uncompressed data. You can use
402<code class="computeroutput">bzip2recover</code> to try to recover
403data from damaged files.</p>
404<p>Return values: 0 for a normal exit, 1 for environmental
405problems (file not found, invalid flags, I/O errors, etc.), 2
406to indicate a corrupt compressed file, 3 for an internal
407consistency error (eg, bug) which caused
408<code class="computeroutput">bzip2</code> to panic.</p>
409</div>
410<div class="sect1" lang="en">
411<div class="titlepage"><div><div><h2 class="title" style="clear: both">
412<a name="options"></a>2.4. OPTIONS</h2></div></div></div>
413<div class="variablelist"><dl>
414<dt><span class="term"><code class="computeroutput">-c --stdout</code></span></dt>
415<dd><p>Compress or decompress to standard
416 output.</p></dd>
417<dt><span class="term"><code class="computeroutput">-d --decompress</code></span></dt>
418<dd><p>Force decompression.
419 <code class="computeroutput">bzip2</code>,
420 <code class="computeroutput">bunzip2</code> and
421 <code class="computeroutput">bzcat</code> are really the same
422 program, and the decision about what actions to take is done on
423 the basis of which name is used. This flag overrides that
424 mechanism, and forces bzip2 to decompress.</p></dd>
425<dt><span class="term"><code class="computeroutput">-z --compress</code></span></dt>
426<dd><p>The complement to
427 <code class="computeroutput">-d</code>: forces compression,
428 regardless of the invokation name.</p></dd>
429<dt><span class="term"><code class="computeroutput">-t --test</code></span></dt>
430<dd><p>Check integrity of the specified file(s), but
431 don't decompress them. This really performs a trial
432 decompression and throws away the result.</p></dd>
433<dt><span class="term"><code class="computeroutput">-f --force</code></span></dt>
434<dd>
435<p>Force overwrite of output files. Normally,
436 <code class="computeroutput">bzip2</code> will not overwrite
437 existing output files. Also forces
438 <code class="computeroutput">bzip2</code> to break hard links to
439 files, which it otherwise wouldn't do.</p>
440<p><code class="computeroutput">bzip2</code> normally declines
441 to decompress files which don't have the correct magic header
442 bytes. If forced (<code class="computeroutput">-f</code>),
443 however, it will pass such files through unmodified. This is
444 how GNU <code class="computeroutput">gzip</code> behaves.</p>
445</dd>
446<dt><span class="term"><code class="computeroutput">-k --keep</code></span></dt>
447<dd><p>Keep (don't delete) input files during
448 compression or decompression.</p></dd>
449<dt><span class="term"><code class="computeroutput">-s --small</code></span></dt>
450<dd>
451<p>Reduce memory usage, for compression,
452 decompression and testing. Files are decompressed and tested
453 using a modified algorithm which only requires 2.5 bytes per
454 block byte. This means any file can be decompressed in 2300k
455 of memory, albeit at about half the normal speed.</p>
456<p>During compression, <code class="computeroutput">-s</code>
457 selects a block size of 200k, which limits memory use to around
458 the same figure, at the expense of your compression ratio. In
459 short, if your machine is low on memory (8 megabytes or less),
460 use <code class="computeroutput">-s</code> for everything. See
461 <a href="#memory-management">MEMORY MANAGEMENT</a> below.</p>
462</dd>
463<dt><span class="term"><code class="computeroutput">-q --quiet</code></span></dt>
464<dd><p>Suppress non-essential warning messages.
465 Messages pertaining to I/O errors and other critical events
466 will not be suppressed.</p></dd>
467<dt><span class="term"><code class="computeroutput">-v --verbose</code></span></dt>
468<dd><p>Verbose mode -- show the compression ratio for
469 each file processed. Further
470 <code class="computeroutput">-v</code>'s increase the verbosity
471 level, spewing out lots of information which is primarily of
472 interest for diagnostic purposes.</p></dd>
473<dt><span class="term"><code class="computeroutput">-L --license -V --version</code></span></dt>
474<dd><p>Display the software version, license terms and
475 conditions.</p></dd>
476<dt><span class="term"><code class="computeroutput">-1</code> (or
477 <code class="computeroutput">--fast</code>) to
478 <code class="computeroutput">-9</code> (or
479 <code class="computeroutput">-best</code>)</span></dt>
480<dd><p>Set the block size to 100 k, 200 k ... 900 k
481 when compressing. Has no effect when decompressing. See <a href="#memory-management">MEMORY MANAGEMENT</a> below. The
482 <code class="computeroutput">--fast</code> and
483 <code class="computeroutput">--best</code> aliases are primarily
484 for GNU <code class="computeroutput">gzip</code> compatibility.
485 In particular, <code class="computeroutput">--fast</code> doesn't
486 make things significantly faster. And
487 <code class="computeroutput">--best</code> merely selects the
488 default behaviour.</p></dd>
489<dt><span class="term"><code class="computeroutput">--</code></span></dt>
490<dd><p>Treats all subsequent arguments as file names,
491 even if they start with a dash. This is so you can handle
492 files with names beginning with a dash, for example:
493 <code class="computeroutput">bzip2 --
494 -myfilename</code>.</p></dd>
495<dt>
496<span class="term"><code class="computeroutput">--repetitive-fast</code>, </span><span class="term"><code class="computeroutput">--repetitive-best</code></span>
497</dt>
498<dd><p>These flags are redundant in versions 0.9.5 and
499 above. They provided some coarse control over the behaviour of
500 the sorting algorithm in earlier versions, which was sometimes
501 useful. 0.9.5 and above have an improved algorithm which
502 renders these flags irrelevant.</p></dd>
503</dl></div>
504</div>
505<div class="sect1" lang="en">
506<div class="titlepage"><div><div><h2 class="title" style="clear: both">
507<a name="memory-management"></a>2.5. MEMORY MANAGEMENT</h2></div></div></div>
508<p><code class="computeroutput">bzip2</code> compresses large
509files in blocks. The block size affects both the compression
510ratio achieved, and the amount of memory needed for compression
511and decompression. The flags <code class="computeroutput">-1</code>
512through <code class="computeroutput">-9</code> specify the block
513size to be 100,000 bytes through 900,000 bytes (the default)
514respectively. At decompression time, the block size used for
515compression is read from the header of the compressed file, and
516<code class="computeroutput">bunzip2</code> then allocates itself
517just enough memory to decompress the file. Since block sizes are
518stored in compressed files, it follows that the flags
519<code class="computeroutput">-1</code> to
520<code class="computeroutput">-9</code> are irrelevant to and so
521ignored during decompression.</p>
522<p>Compression and decompression requirements, in bytes, can be
523estimated as:</p>
524<pre class="programlisting">Compression: 400k + ( 8 x block size )
525
526Decompression: 100k + ( 4 x block size ), or
527 100k + ( 2.5 x block size )</pre>
528<p>Larger block sizes give rapidly diminishing marginal
529returns. Most of the compression comes from the first two or
530three hundred k of block size, a fact worth bearing in mind when
531using <code class="computeroutput">bzip2</code> on small machines.
532It is also important to appreciate that the decompression memory
533requirement is set at compression time by the choice of block
534size.</p>
535<p>For files compressed with the default 900k block size,
536<code class="computeroutput">bunzip2</code> will require about 3700
537kbytes to decompress. To support decompression of any file on a
5384 megabyte machine, <code class="computeroutput">bunzip2</code> has
539an option to decompress using approximately half this amount of
540memory, about 2300 kbytes. Decompression speed is also halved,
541so you should use this option only where necessary. The relevant
542flag is <code class="computeroutput">-s</code>.</p>
543<p>In general, try and use the largest block size memory
544constraints allow, since that maximises the compression achieved.
545Compression and decompression speed are virtually unaffected by
546block size.</p>
547<p>Another significant point applies to files which fit in a
548single block -- that means most files you'd encounter using a
549large block size. The amount of real memory touched is
550proportional to the size of the file, since the file is smaller
551than a block. For example, compressing a file 20,000 bytes long
552with the flag <code class="computeroutput">-9</code> will cause the
553compressor to allocate around 7600k of memory, but only touch
554400k + 20000 * 8 = 560 kbytes of it. Similarly, the decompressor
555will allocate 3700k but only touch 100k + 20000 * 4 = 180
556kbytes.</p>
557<p>Here is a table which summarises the maximum memory usage
558for different block sizes. Also recorded is the total compressed
559size for 14 files of the Calgary Text Compression Corpus
560totalling 3,141,622 bytes. This column gives some feel for how
561compression varies with block size. These figures tend to
562understate the advantage of larger block sizes for larger files,
563since the Corpus is dominated by smaller files.</p>
564<pre class="programlisting"> Compress Decompress Decompress Corpus
565Flag usage usage -s usage Size
566
567 -1 1200k 500k 350k 914704
568 -2 2000k 900k 600k 877703
569 -3 2800k 1300k 850k 860338
570 -4 3600k 1700k 1100k 846899
571 -5 4400k 2100k 1350k 845160
572 -6 5200k 2500k 1600k 838626
573 -7 6100k 2900k 1850k 834096
574 -8 6800k 3300k 2100k 828642
575 -9 7600k 3700k 2350k 828642</pre>
576</div>
577<div class="sect1" lang="en">
578<div class="titlepage"><div><div><h2 class="title" style="clear: both">
579<a name="recovering"></a>2.6. RECOVERING DATA FROM DAMAGED FILES</h2></div></div></div>
580<p><code class="computeroutput">bzip2</code> compresses files in
581blocks, usually 900kbytes long. Each block is handled
582independently. If a media or transmission error causes a
583multi-block <code class="computeroutput">.bz2</code> file to become
584damaged, it may be possible to recover data from the undamaged
585blocks in the file.</p>
586<p>The compressed representation of each block is delimited by
587a 48-bit pattern, which makes it possible to find the block
588boundaries with reasonable certainty. Each block also carries
589its own 32-bit CRC, so damaged blocks can be distinguished from
590undamaged ones.</p>
591<p><code class="computeroutput">bzip2recover</code> is a simple
592program whose purpose is to search for blocks in
593<code class="computeroutput">.bz2</code> files, and write each block
594out into its own <code class="computeroutput">.bz2</code> file. You
595can then use <code class="computeroutput">bzip2 -t</code> to test
596the integrity of the resulting files, and decompress those which
597are undamaged.</p>
598<p><code class="computeroutput">bzip2recover</code> takes a
599single argument, the name of the damaged file, and writes a
600number of files <code class="computeroutput">rec0001file.bz2</code>,
601<code class="computeroutput">rec0002file.bz2</code>, etc, containing
602the extracted blocks. The output filenames are designed so that
603the use of wildcards in subsequent processing -- for example,
604<code class="computeroutput">bzip2 -dc rec*file.bz2 &gt;
605recovered_data</code> -- lists the files in the correct
606order.</p>
607<p><code class="computeroutput">bzip2recover</code> should be of
608most use dealing with large <code class="computeroutput">.bz2</code>
609files, as these will contain many blocks. It is clearly futile
610to use it on damaged single-block files, since a damaged block
611cannot be recovered. If you wish to minimise any potential data
612loss through media or transmission errors, you might consider
613compressing with a smaller block size.</p>
614</div>
615<div class="sect1" lang="en">
616<div class="titlepage"><div><div><h2 class="title" style="clear: both">
617<a name="performance"></a>2.7. PERFORMANCE NOTES</h2></div></div></div>
618<p>The sorting phase of compression gathers together similar
619strings in the file. Because of this, files containing very long
620runs of repeated symbols, like "aabaabaabaab ..." (repeated
621several hundred times) may compress more slowly than normal.
622Versions 0.9.5 and above fare much better than previous versions
623in this respect. The ratio between worst-case and average-case
624compression time is in the region of 10:1. For previous
625versions, this figure was more like 100:1. You can use the
626<code class="computeroutput">-vvvv</code> option to monitor progress
627in great detail, if you want.</p>
628<p>Decompression speed is unaffected by these
629phenomena.</p>
630<p><code class="computeroutput">bzip2</code> usually allocates
631several megabytes of memory to operate in, and then charges all
632over it in a fairly random fashion. This means that performance,
633both for compressing and decompressing, is largely determined by
634the speed at which your machine can service cache misses.
635Because of this, small changes to the code to reduce the miss
636rate have been observed to give disproportionately large
637performance improvements. I imagine
638<code class="computeroutput">bzip2</code> will perform best on
639machines with very large caches.</p>
640</div>
641<div class="sect1" lang="en">
642<div class="titlepage"><div><div><h2 class="title" style="clear: both">
643<a name="caveats"></a>2.8. CAVEATS</h2></div></div></div>
644<p>I/O error messages are not as helpful as they could be.
645<code class="computeroutput">bzip2</code> tries hard to detect I/O
646errors and exit cleanly, but the details of what the problem is
647sometimes seem rather misleading.</p>
648<p>This manual page pertains to version 1.0.4 of
649<code class="computeroutput">bzip2</code>. Compressed data created by
650this version is entirely forwards and backwards compatible with the
651previous public releases, versions 0.1pl2, 0.9.0 and 0.9.5, 1.0.0,
6521.0.1, 1.0.2 and 1.0.3, but with the following exception: 0.9.0 and
653above can correctly decompress multiple concatenated compressed files.
6540.1pl2 cannot do this; it will stop after decompressing just the first
655file in the stream.</p>
656<p><code class="computeroutput">bzip2recover</code> versions
657prior to 1.0.2 used 32-bit integers to represent bit positions in
658compressed files, so it could not handle compressed files more
659than 512 megabytes long. Versions 1.0.2 and above use 64-bit ints
660on some platforms which support them (GNU supported targets, and
661Windows). To establish whether or not
662<code class="computeroutput">bzip2recover</code> was built with such
663a limitation, run it without arguments. In any event you can
664build yourself an unlimited version if you can recompile it with
665<code class="computeroutput">MaybeUInt64</code> set to be an
666unsigned 64-bit integer.</p>
667</div>
668<div class="sect1" lang="en">
669<div class="titlepage"><div><div><h2 class="title" style="clear: both">
670<a name="author"></a>2.9. AUTHOR</h2></div></div></div>
671<p>Julian Seward,
672<code class="computeroutput">jseward@bzip.org</code></p>
673<p>The ideas embodied in
674<code class="computeroutput">bzip2</code> are due to (at least) the
675following people: Michael Burrows and David Wheeler (for the
676block sorting transformation), David Wheeler (again, for the
677Huffman coder), Peter Fenwick (for the structured coding model in
678the original <code class="computeroutput">bzip</code>, and many
679refinements), and Alistair Moffat, Radford Neal and Ian Witten
680(for the arithmetic coder in the original
681<code class="computeroutput">bzip</code>). I am much indebted for
682their help, support and advice. See the manual in the source
683distribution for pointers to sources of documentation. Christian
684von Roques encouraged me to look for faster sorting algorithms,
685so as to speed up compression. Bela Lubkin encouraged me to
686improve the worst-case compression performance.
687Donna Robinson XMLised the documentation.
688Many people sent
689patches, helped with portability problems, lent machines, gave
690advice and were generally helpful.</p>
691</div>
692</div>
693<div class="chapter" lang="en">
694<div class="titlepage"><div><div><h2 class="title">
695<a name="libprog"></a>3. 
696Programming with <code class="computeroutput">libbzip2</code>
697</h2></div></div></div>
698<div class="toc">
699<p><b>Table of Contents</b></p>
700<dl>
701<dt><span class="sect1"><a href="#top-level">3.1. Top-level structure</a></span></dt>
702<dd><dl>
703<dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt>
704<dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt>
705<dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt>
706</dl></dd>
707<dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt>
708<dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt>
709<dd><dl>
710<dt><span class="sect2"><a href="#bzcompress-init">3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></a></span></dt>
711<dt><span class="sect2"><a href="#bzCompress">3.3.2. <code class="computeroutput">BZ2_bzCompress</code></a></span></dt>
712<dt><span class="sect2"><a href="#bzCompress-end">3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></a></span></dt>
713<dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></a></span></dt>
714<dt><span class="sect2"><a href="#bzDecompress">3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></a></span></dt>
715<dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></a></span></dt>
716</dl></dd>
717<dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt>
718<dd><dl>
719<dt><span class="sect2"><a href="#bzreadopen">3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></a></span></dt>
720<dt><span class="sect2"><a href="#bzread">3.4.2. <code class="computeroutput">BZ2_bzRead</code></a></span></dt>
721<dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></a></span></dt>
722<dt><span class="sect2"><a href="#bzreadclose">3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></a></span></dt>
723<dt><span class="sect2"><a href="#bzwriteopen">3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></a></span></dt>
724<dt><span class="sect2"><a href="#bzwrite">3.4.6. <code class="computeroutput">BZ2_bzWrite</code></a></span></dt>
725<dt><span class="sect2"><a href="#bzwriteclose">3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></a></span></dt>
726<dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt>
727<dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt>
728</dl></dd>
729<dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt>
730<dd><dl>
731<dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></a></span></dt>
732<dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></a></span></dt>
733</dl></dd>
734<dt><span class="sect1"><a href="#zlib-compat">3.6. <code class="computeroutput">zlib</code> compatibility functions</a></span></dt>
735<dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</a></span></dt>
736<dd><dl>
737<dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of <code class="computeroutput">stdio</code></a></span></dt>
738<dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt>
739</dl></dd>
740<dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt>
741</dl>
742</div>
743<p>This chapter describes the programming interface to
744<code class="computeroutput">libbzip2</code>.</p>
745<p>For general background information, particularly about
746memory use and performance aspects, you'd be well advised to read
747<a href="#using">How to use bzip2</a> as well.</p>
748<div class="sect1" lang="en">
749<div class="titlepage"><div><div><h2 class="title" style="clear: both">
750<a name="top-level"></a>3.1. Top-level structure</h2></div></div></div>
751<p><code class="computeroutput">libbzip2</code> is a flexible
752library for compressing and decompressing data in the
753<code class="computeroutput">bzip2</code> data format. Although
754packaged as a single entity, it helps to regard the library as
755three separate parts: the low level interface, and the high level
756interface, and some utility functions.</p>
757<p>The structure of
758<code class="computeroutput">libbzip2</code>'s interfaces is similar
759to that of Jean-loup Gailly's and Mark Adler's excellent
760<code class="computeroutput">zlib</code> library.</p>
761<p>All externally visible symbols have names beginning
762<code class="computeroutput">BZ2_</code>. This is new in version
7631.0. The intention is to minimise pollution of the namespaces of
764library clients.</p>
765<p>To use any part of the library, you need to
766<code class="computeroutput">#include &lt;bzlib.h&gt;</code>
767into your sources.</p>
768<div class="sect2" lang="en">
769<div class="titlepage"><div><div><h3 class="title">
770<a name="ll-summary"></a>3.1.1. Low-level summary</h3></div></div></div>
771<p>This interface provides services for compressing and
772decompressing data in memory. There's no provision for dealing
773with files, streams or any other I/O mechanisms, just straight
774memory-to-memory work. In fact, this part of the library can be
775compiled without inclusion of
776<code class="computeroutput">stdio.h</code>, which may be helpful
777for embedded applications.</p>
778<p>The low-level part of the library has no global variables
779and is therefore thread-safe.</p>
780<p>Six routines make up the low level interface:
781<code class="computeroutput">BZ2_bzCompressInit</code>,
782<code class="computeroutput">BZ2_bzCompress</code>, and
783<code class="computeroutput">BZ2_bzCompressEnd</code> for
784compression, and a corresponding trio
785<code class="computeroutput">BZ2_bzDecompressInit</code>,
786<code class="computeroutput">BZ2_bzDecompress</code> and
787<code class="computeroutput">BZ2_bzDecompressEnd</code> for
788decompression. The <code class="computeroutput">*Init</code>
789functions allocate memory for compression/decompression and do
790other initialisations, whilst the
791<code class="computeroutput">*End</code> functions close down
792operations and release memory.</p>
793<p>The real work is done by
794<code class="computeroutput">BZ2_bzCompress</code> and
795<code class="computeroutput">BZ2_bzDecompress</code>. These
796compress and decompress data from a user-supplied input buffer to
797a user-supplied output buffer. These buffers can be any size;
798arbitrary quantities of data are handled by making repeated calls
799to these functions. This is a flexible mechanism allowing a
800consumer-pull style of activity, or producer-push, or a mixture
801of both.</p>
802</div>
803<div class="sect2" lang="en">
804<div class="titlepage"><div><div><h3 class="title">
805<a name="hl-summary"></a>3.1.2. High-level summary</h3></div></div></div>
806<p>This interface provides some handy wrappers around the
807low-level interface to facilitate reading and writing
808<code class="computeroutput">bzip2</code> format files
809(<code class="computeroutput">.bz2</code> files). The routines
810provide hooks to facilitate reading files in which the
811<code class="computeroutput">bzip2</code> data stream is embedded
812within some larger-scale file structure, or where there are
813multiple <code class="computeroutput">bzip2</code> data streams
814concatenated end-to-end.</p>
815<p>For reading files,
816<code class="computeroutput">BZ2_bzReadOpen</code>,
817<code class="computeroutput">BZ2_bzRead</code>,
818<code class="computeroutput">BZ2_bzReadClose</code> and
819<code class="computeroutput">BZ2_bzReadGetUnused</code> are
820supplied. For writing files,
821<code class="computeroutput">BZ2_bzWriteOpen</code>,
822<code class="computeroutput">BZ2_bzWrite</code> and
823<code class="computeroutput">BZ2_bzWriteFinish</code> are
824available.</p>
825<p>As with the low-level library, no global variables are used
826so the library is per se thread-safe. However, if I/O errors
827occur whilst reading or writing the underlying compressed files,
828you may have to consult <code class="computeroutput">errno</code> to
829determine the cause of the error. In that case, you'd need a C
830library which correctly supports
831<code class="computeroutput">errno</code> in a multithreaded
832environment.</p>
833<p>To make the library a little simpler and more portable,
834<code class="computeroutput">BZ2_bzReadOpen</code> and
835<code class="computeroutput">BZ2_bzWriteOpen</code> require you to
836pass them file handles (<code class="computeroutput">FILE*</code>s)
837which have previously been opened for reading or writing
838respectively. That avoids portability problems associated with
839file operations and file attributes, whilst not being much of an
840imposition on the programmer.</p>
841</div>
842<div class="sect2" lang="en">
843<div class="titlepage"><div><div><h3 class="title">
844<a name="util-fns-summary"></a>3.1.3. Utility functions summary</h3></div></div></div>
845<p>For very simple needs,
846<code class="computeroutput">BZ2_bzBuffToBuffCompress</code> and
847<code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> are
848provided. These compress data in memory from one buffer to
849another buffer in a single function call. You should assess
850whether these functions fulfill your memory-to-memory
851compression/decompression requirements before investing effort in
852understanding the more general but more complex low-level
853interface.</p>
854<p>Yoshioka Tsuneo
855(<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>) has
856contributed some functions to give better
857<code class="computeroutput">zlib</code> compatibility. These
858functions are <code class="computeroutput">BZ2_bzopen</code>,
859<code class="computeroutput">BZ2_bzread</code>,
860<code class="computeroutput">BZ2_bzwrite</code>,
861<code class="computeroutput">BZ2_bzflush</code>,
862<code class="computeroutput">BZ2_bzclose</code>,
863<code class="computeroutput">BZ2_bzerror</code> and
864<code class="computeroutput">BZ2_bzlibVersion</code>. You may find
865these functions more convenient for simple file reading and
866writing, than those in the high-level interface. These functions
867are not (yet) officially part of the library, and are minimally
868documented here. If they break, you get to keep all the pieces.
869I hope to document them properly when time permits.</p>
870<p>Yoshioka also contributed modifications to allow the
871library to be built as a Windows DLL.</p>
872</div>
873</div>
874<div class="sect1" lang="en">
875<div class="titlepage"><div><div><h2 class="title" style="clear: both">
876<a name="err-handling"></a>3.2. Error handling</h2></div></div></div>
877<p>The library is designed to recover cleanly in all
878situations, including the worst-case situation of decompressing
879random data. I'm not 100% sure that it can always do this, so
880you might want to add a signal handler to catch segmentation
881violations during decompression if you are feeling especially
882paranoid. I would be interested in hearing more about the
883robustness of the library to corrupted compressed data.</p>
884<p>Version 1.0.3 more robust in this respect than any
885previous version. Investigations with Valgrind (a tool for detecting
886problems with memory management) indicate
887that, at least for the few files I tested, all single-bit errors
888in the decompressed data are caught properly, with no
889segmentation faults, no uses of uninitialised data, no out of
890range reads or writes, and no infinite looping in the decompressor.
891So it's certainly pretty robust, although
892I wouldn't claim it to be totally bombproof.</p>
893<p>The file <code class="computeroutput">bzlib.h</code> contains
894all definitions needed to use the library. In particular, you
895should definitely not include
896<code class="computeroutput">bzlib_private.h</code>.</p>
897<p>In <code class="computeroutput">bzlib.h</code>, the various
898return values are defined. The following list is not intended as
899an exhaustive description of the circumstances in which a given
900value may be returned -- those descriptions are given later.
901Rather, it is intended to convey the rough meaning of each return
902value. The first five actions are normal and not intended to
903denote an error situation.</p>
904<div class="variablelist"><dl>
905<dt><span class="term"><code class="computeroutput">BZ_OK</code></span></dt>
906<dd><p>The requested action was completed
907 successfully.</p></dd>
908<dt><span class="term"><code class="computeroutput">BZ_RUN_OK, BZ_FLUSH_OK,
909 BZ_FINISH_OK</code></span></dt>
910<dd><p>In
911 <code class="computeroutput">BZ2_bzCompress</code>, the requested
912 flush/finish/nothing-special action was completed
913 successfully.</p></dd>
914<dt><span class="term"><code class="computeroutput">BZ_STREAM_END</code></span></dt>
915<dd><p>Compression of data was completed, or the
916 logical stream end was detected during
917 decompression.</p></dd>
918</dl></div>
919<p>The following return values indicate an error of some
920kind.</p>
921<div class="variablelist"><dl>
922<dt><span class="term"><code class="computeroutput">BZ_CONFIG_ERROR</code></span></dt>
923<dd><p>Indicates that the library has been improperly
924 compiled on your platform -- a major configuration error.
925 Specifically, it means that
926 <code class="computeroutput">sizeof(char)</code>,
927 <code class="computeroutput">sizeof(short)</code> and
928 <code class="computeroutput">sizeof(int)</code> are not 1, 2 and
929 4 respectively, as they should be. Note that the library
930 should still work properly on 64-bit platforms which follow
931 the LP64 programming model -- that is, where
932 <code class="computeroutput">sizeof(long)</code> and
933 <code class="computeroutput">sizeof(void*)</code> are 8. Under
934 LP64, <code class="computeroutput">sizeof(int)</code> is still 4,
935 so <code class="computeroutput">libbzip2</code>, which doesn't
936 use the <code class="computeroutput">long</code> type, is
937 OK.</p></dd>
938<dt><span class="term"><code class="computeroutput">BZ_SEQUENCE_ERROR</code></span></dt>
939<dd><p>When using the library, it is important to call
940 the functions in the correct sequence and with data structures
941 (buffers etc) in the correct states.
942 <code class="computeroutput">libbzip2</code> checks as much as it
943 can to ensure this is happening, and returns
944 <code class="computeroutput">BZ_SEQUENCE_ERROR</code> if not.
945 Code which complies precisely with the function semantics, as
946 detailed below, should never receive this value; such an event
947 denotes buggy code which you should
948 investigate.</p></dd>
949<dt><span class="term"><code class="computeroutput">BZ_PARAM_ERROR</code></span></dt>
950<dd><p>Returned when a parameter to a function call is
951 out of range or otherwise manifestly incorrect. As with
952 <code class="computeroutput">BZ_SEQUENCE_ERROR</code>, this
953 denotes a bug in the client code. The distinction between
954 <code class="computeroutput">BZ_PARAM_ERROR</code> and
955 <code class="computeroutput">BZ_SEQUENCE_ERROR</code> is a bit
956 hazy, but still worth making.</p></dd>
957<dt><span class="term"><code class="computeroutput">BZ_MEM_ERROR</code></span></dt>
958<dd><p>Returned when a request to allocate memory
959 failed. Note that the quantity of memory needed to decompress
960 a stream cannot be determined until the stream's header has
961 been read. So
962 <code class="computeroutput">BZ2_bzDecompress</code> and
963 <code class="computeroutput">BZ2_bzRead</code> may return
964 <code class="computeroutput">BZ_MEM_ERROR</code> even though some
965 of the compressed data has been read. The same is not true
966 for compression; once
967 <code class="computeroutput">BZ2_bzCompressInit</code> or
968 <code class="computeroutput">BZ2_bzWriteOpen</code> have
969 successfully completed,
970 <code class="computeroutput">BZ_MEM_ERROR</code> cannot
971 occur.</p></dd>
972<dt><span class="term"><code class="computeroutput">BZ_DATA_ERROR</code></span></dt>
973<dd><p>Returned when a data integrity error is
974 detected during decompression. Most importantly, this means
975 when stored and computed CRCs for the data do not match. This
976 value is also returned upon detection of any other anomaly in
977 the compressed data.</p></dd>
978<dt><span class="term"><code class="computeroutput">BZ_DATA_ERROR_MAGIC</code></span></dt>
979<dd><p>As a special case of
980 <code class="computeroutput">BZ_DATA_ERROR</code>, it is
981 sometimes useful to know when the compressed stream does not
982 start with the correct magic bytes (<code class="computeroutput">'B' 'Z'
983 'h'</code>).</p></dd>
984<dt><span class="term"><code class="computeroutput">BZ_IO_ERROR</code></span></dt>
985<dd><p>Returned by
986 <code class="computeroutput">BZ2_bzRead</code> and
987 <code class="computeroutput">BZ2_bzWrite</code> when there is an
988 error reading or writing in the compressed file, and by
989 <code class="computeroutput">BZ2_bzReadOpen</code> and
990 <code class="computeroutput">BZ2_bzWriteOpen</code> for attempts
991 to use a file for which the error indicator (viz,
992 <code class="computeroutput">ferror(f)</code>) is set. On
993 receipt of <code class="computeroutput">BZ_IO_ERROR</code>, the
994 caller should consult <code class="computeroutput">errno</code>
995 and/or <code class="computeroutput">perror</code> to acquire
996 operating-system specific information about the
997 problem.</p></dd>
998<dt><span class="term"><code class="computeroutput">BZ_UNEXPECTED_EOF</code></span></dt>
999<dd><p>Returned by
1000 <code class="computeroutput">BZ2_bzRead</code> when the
1001 compressed file finishes before the logical end of stream is
1002 detected.</p></dd>
1003<dt><span class="term"><code class="computeroutput">BZ_OUTBUFF_FULL</code></span></dt>
1004<dd><p>Returned by
1005 <code class="computeroutput">BZ2_bzBuffToBuffCompress</code> and
1006 <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> to
1007 indicate that the output data will not fit into the output
1008 buffer provided.</p></dd>
1009</dl></div>
1010</div>
1011<div class="sect1" lang="en">
1012<div class="titlepage"><div><div><h2 class="title" style="clear: both">
1013<a name="low-level"></a>3.3. Low-level interface</h2></div></div></div>
1014<div class="sect2" lang="en">
1015<div class="titlepage"><div><div><h3 class="title">
1016<a name="bzcompress-init"></a>3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></h3></div></div></div>
1017<pre class="programlisting">typedef struct {
1018 char *next_in;
1019 unsigned int avail_in;
1020 unsigned int total_in_lo32;
1021 unsigned int total_in_hi32;
1022
1023 char *next_out;
1024 unsigned int avail_out;
1025 unsigned int total_out_lo32;
1026 unsigned int total_out_hi32;
1027
1028 void *state;
1029
1030 void *(*bzalloc)(void *,int,int);
1031 void (*bzfree)(void *,void *);
1032 void *opaque;
1033} bz_stream;
1034
1035int BZ2_bzCompressInit ( bz_stream *strm,
1036 int blockSize100k,
1037 int verbosity,
1038 int workFactor );</pre>
1039<p>Prepares for compression. The
1040<code class="computeroutput">bz_stream</code> structure holds all
1041data pertaining to the compression activity. A
1042<code class="computeroutput">bz_stream</code> structure should be
1043allocated and initialised prior to the call. The fields of
1044<code class="computeroutput">bz_stream</code> comprise the entirety
1045of the user-visible data. <code class="computeroutput">state</code>
1046is a pointer to the private data structures required for
1047compression.</p>
1048<p>Custom memory allocators are supported, via fields
1049<code class="computeroutput">bzalloc</code>,
1050<code class="computeroutput">bzfree</code>, and
1051<code class="computeroutput">opaque</code>. The value
1052<code class="computeroutput">opaque</code> is passed to as the first
1053argument to all calls to <code class="computeroutput">bzalloc</code>
1054and <code class="computeroutput">bzfree</code>, but is otherwise
1055ignored by the library. The call <code class="computeroutput">bzalloc (
1056opaque, n, m )</code> is expected to return a pointer
1057<code class="computeroutput">p</code> to <code class="computeroutput">n *
1058m</code> bytes of memory, and <code class="computeroutput">bzfree (
1059opaque, p )</code> should free that memory.</p>
1060<p>If you don't want to use a custom memory allocator, set
1061<code class="computeroutput">bzalloc</code>,
1062<code class="computeroutput">bzfree</code> and
1063<code class="computeroutput">opaque</code> to
1064<code class="computeroutput">NULL</code>, and the library will then
1065use the standard <code class="computeroutput">malloc</code> /
1066<code class="computeroutput">free</code> routines.</p>
1067<p>Before calling
1068<code class="computeroutput">BZ2_bzCompressInit</code>, fields
1069<code class="computeroutput">bzalloc</code>,
1070<code class="computeroutput">bzfree</code> and
1071<code class="computeroutput">opaque</code> should be filled
1072appropriately, as just described. Upon return, the internal
1073state will have been allocated and initialised, and
1074<code class="computeroutput">total_in_lo32</code>,
1075<code class="computeroutput">total_in_hi32</code>,
1076<code class="computeroutput">total_out_lo32</code> and
1077<code class="computeroutput">total_out_hi32</code> will have been
1078set to zero. These four fields are used by the library to inform
1079the caller of the total amount of data passed into and out of the
1080library, respectively. You should not try to change them. As of
1081version 1.0, 64-bit counts are maintained, even on 32-bit
1082platforms, using the <code class="computeroutput">_hi32</code>
1083fields to store the upper 32 bits of the count. So, for example,
1084the total amount of data in is <code class="computeroutput">(total_in_hi32
1085&lt;&lt; 32) + total_in_lo32</code>.</p>
1086<p>Parameter <code class="computeroutput">blockSize100k</code>
1087specifies the block size to be used for compression. It should
1088be a value between 1 and 9 inclusive, and the actual block size
1089used is 100000 x this figure. 9 gives the best compression but
1090takes most memory.</p>
1091<p>Parameter <code class="computeroutput">verbosity</code> should
1092be set to a number between 0 and 4 inclusive. 0 is silent, and
1093greater numbers give increasingly verbose monitoring/debugging
1094output. If the library has been compiled with
1095<code class="computeroutput">-DBZ_NO_STDIO</code>, no such output
1096will appear for any verbosity setting.</p>
1097<p>Parameter <code class="computeroutput">workFactor</code>
1098controls how the compression phase behaves when presented with
1099worst case, highly repetitive, input data. If compression runs
1100into difficulties caused by repetitive data, the library switches
1101from the standard sorting algorithm to a fallback algorithm. The
1102fallback is slower than the standard algorithm by perhaps a
1103factor of three, but always behaves reasonably, no matter how bad
1104the input.</p>
1105<p>Lower values of <code class="computeroutput">workFactor</code>
1106reduce the amount of effort the standard algorithm will expend
1107before resorting to the fallback. You should set this parameter
1108carefully; too low, and many inputs will be handled by the
1109fallback algorithm and so compress rather slowly, too high, and
1110your average-to-worst case compression times can become very
1111large. The default value of 30 gives reasonable behaviour over a
1112wide range of circumstances.</p>
1113<p>Allowable values range from 0 to 250 inclusive. 0 is a
1114special case, equivalent to using the default value of 30.</p>
1115<p>Note that the compressed output generated is the same
1116regardless of whether or not the fallback algorithm is
1117used.</p>
1118<p>Be aware also that this parameter may disappear entirely in
1119future versions of the library. In principle it should be
1120possible to devise a good way to automatically choose which
1121algorithm to use. Such a mechanism would render the parameter
1122obsolete.</p>
1123<p>Possible return values:</p>
1124<pre class="programlisting">BZ_CONFIG_ERROR
1125 if the library has been mis-compiled
1126BZ_PARAM_ERROR
1127 if strm is NULL
1128 or blockSize &lt; 1 or blockSize &gt; 9
1129 or verbosity &lt; 0 or verbosity &gt; 4
1130 or workFactor &lt; 0 or workFactor &gt; 250
1131BZ_MEM_ERROR
1132 if not enough memory is available
1133BZ_OK
1134 otherwise</pre>
1135<p>Allowable next actions:</p>
1136<pre class="programlisting">BZ2_bzCompress
1137 if BZ_OK is returned
1138 no specific action needed in case of error</pre>
1139</div>
1140<div class="sect2" lang="en">
1141<div class="titlepage"><div><div><h3 class="title">
1142<a name="bzCompress"></a>3.3.2. <code class="computeroutput">BZ2_bzCompress</code></h3></div></div></div>
1143<pre class="programlisting">int BZ2_bzCompress ( bz_stream *strm, int action );</pre>
1144<p>Provides more input and/or output buffer space for the
1145library. The caller maintains input and output buffers, and
1146calls <code class="computeroutput">BZ2_bzCompress</code> to transfer
1147data between them.</p>
1148<p>Before each call to
1149<code class="computeroutput">BZ2_bzCompress</code>,
1150<code class="computeroutput">next_in</code> should point at the data
1151to be compressed, and <code class="computeroutput">avail_in</code>
1152should indicate how many bytes the library may read.
1153<code class="computeroutput">BZ2_bzCompress</code> updates
1154<code class="computeroutput">next_in</code>,
1155<code class="computeroutput">avail_in</code> and
1156<code class="computeroutput">total_in</code> to reflect the number
1157of bytes it has read.</p>
1158<p>Similarly, <code class="computeroutput">next_out</code> should
1159point to a buffer in which the compressed data is to be placed,
1160with <code class="computeroutput">avail_out</code> indicating how
1161much output space is available.
1162<code class="computeroutput">BZ2_bzCompress</code> updates
1163<code class="computeroutput">next_out</code>,
1164<code class="computeroutput">avail_out</code> and
1165<code class="computeroutput">total_out</code> to reflect the number
1166of bytes output.</p>
1167<p>You may provide and remove as little or as much data as you
1168like on each call of
1169<code class="computeroutput">BZ2_bzCompress</code>. In the limit,
1170it is acceptable to supply and remove data one byte at a time,
1171although this would be terribly inefficient. You should always
1172ensure that at least one byte of output space is available at
1173each call.</p>
1174<p>A second purpose of
1175<code class="computeroutput">BZ2_bzCompress</code> is to request a
1176change of mode of the compressed stream.</p>
1177<p>Conceptually, a compressed stream can be in one of four
1178states: IDLE, RUNNING, FLUSHING and FINISHING. Before
1179initialisation
1180(<code class="computeroutput">BZ2_bzCompressInit</code>) and after
1181termination (<code class="computeroutput">BZ2_bzCompressEnd</code>),
1182a stream is regarded as IDLE.</p>
1183<p>Upon initialisation
1184(<code class="computeroutput">BZ2_bzCompressInit</code>), the stream
1185is placed in the RUNNING state. Subsequent calls to
1186<code class="computeroutput">BZ2_bzCompress</code> should pass
1187<code class="computeroutput">BZ_RUN</code> as the requested action;
1188other actions are illegal and will result in
1189<code class="computeroutput">BZ_SEQUENCE_ERROR</code>.</p>
1190<p>At some point, the calling program will have provided all
1191the input data it wants to. It will then want to finish up -- in
1192effect, asking the library to process any data it might have
1193buffered internally. In this state,
1194<code class="computeroutput">BZ2_bzCompress</code> will no longer
1195attempt to read data from
1196<code class="computeroutput">next_in</code>, but it will want to
1197write data to <code class="computeroutput">next_out</code>. Because
1198the output buffer supplied by the user can be arbitrarily small,
1199the finishing-up operation cannot necessarily be done with a
1200single call of
1201<code class="computeroutput">BZ2_bzCompress</code>.</p>
1202<p>Instead, the calling program passes
1203<code class="computeroutput">BZ_FINISH</code> as an action to
1204<code class="computeroutput">BZ2_bzCompress</code>. This changes
1205the stream's state to FINISHING. Any remaining input (ie,
1206<code class="computeroutput">next_in[0 .. avail_in-1]</code>) is
1207compressed and transferred to the output buffer. To do this,
1208<code class="computeroutput">BZ2_bzCompress</code> must be called
1209repeatedly until all the output has been consumed. At that
1210point, <code class="computeroutput">BZ2_bzCompress</code> returns
1211<code class="computeroutput">BZ_STREAM_END</code>, and the stream's
1212state is set back to IDLE.
1213<code class="computeroutput">BZ2_bzCompressEnd</code> should then be
1214called.</p>
1215<p>Just to make sure the calling program does not cheat, the
1216library makes a note of <code class="computeroutput">avail_in</code>
1217at the time of the first call to
1218<code class="computeroutput">BZ2_bzCompress</code> which has
1219<code class="computeroutput">BZ_FINISH</code> as an action (ie, at
1220the time the program has announced its intention to not supply
1221any more input). By comparing this value with that of
1222<code class="computeroutput">avail_in</code> over subsequent calls
1223to <code class="computeroutput">BZ2_bzCompress</code>, the library
1224can detect any attempts to slip in more data to compress. Any
1225calls for which this is detected will return
1226<code class="computeroutput">BZ_SEQUENCE_ERROR</code>. This
1227indicates a programming mistake which should be corrected.</p>
1228<p>Instead of asking to finish, the calling program may ask
1229<code class="computeroutput">BZ2_bzCompress</code> to take all the
1230remaining input, compress it and terminate the current
1231(Burrows-Wheeler) compression block. This could be useful for
1232error control purposes. The mechanism is analogous to that for
1233finishing: call <code class="computeroutput">BZ2_bzCompress</code>
1234with an action of <code class="computeroutput">BZ_FLUSH</code>,
1235remove output data, and persist with the
1236<code class="computeroutput">BZ_FLUSH</code> action until the value
1237<code class="computeroutput">BZ_RUN</code> is returned. As with
1238finishing, <code class="computeroutput">BZ2_bzCompress</code>
1239detects any attempt to provide more input data once the flush has
1240begun.</p>
1241<p>Once the flush is complete, the stream returns to the
1242normal RUNNING state.</p>
1243<p>This all sounds pretty complex, but isn't really. Here's a
1244table which shows which actions are allowable in each state, what
1245action will be taken, what the next state is, and what the
1246non-error return values are. Note that you can't explicitly ask
1247what state the stream is in, but nor do you need to -- it can be
1248inferred from the values returned by
1249<code class="computeroutput">BZ2_bzCompress</code>.</p>
1250<pre class="programlisting">IDLE/any
1251 Illegal. IDLE state only exists after BZ2_bzCompressEnd or
1252 before BZ2_bzCompressInit.
1253 Return value = BZ_SEQUENCE_ERROR
1254
1255RUNNING/BZ_RUN
1256 Compress from next_in to next_out as much as possible.
1257 Next state = RUNNING
1258 Return value = BZ_RUN_OK
1259
1260RUNNING/BZ_FLUSH
1261 Remember current value of next_in. Compress from next_in
1262 to next_out as much as possible, but do not accept any more input.
1263 Next state = FLUSHING
1264 Return value = BZ_FLUSH_OK
1265
1266RUNNING/BZ_FINISH
1267 Remember current value of next_in. Compress from next_in
1268 to next_out as much as possible, but do not accept any more input.
1269 Next state = FINISHING
1270 Return value = BZ_FINISH_OK
1271
1272FLUSHING/BZ_FLUSH
1273 Compress from next_in to next_out as much as possible,
1274 but do not accept any more input.
1275 If all the existing input has been used up and all compressed
1276 output has been removed
1277 Next state = RUNNING; Return value = BZ_RUN_OK
1278 else
1279 Next state = FLUSHING; Return value = BZ_FLUSH_OK
1280
1281FLUSHING/other
1282 Illegal.
1283 Return value = BZ_SEQUENCE_ERROR
1284
1285FINISHING/BZ_FINISH
1286 Compress from next_in to next_out as much as possible,
1287 but to not accept any more input.
1288 If all the existing input has been used up and all compressed
1289 output has been removed
1290 Next state = IDLE; Return value = BZ_STREAM_END
1291 else
1292 Next state = FINISHING; Return value = BZ_FINISH_OK
1293
1294FINISHING/other
1295 Illegal.
1296 Return value = BZ_SEQUENCE_ERROR</pre>
1297<p>That still looks complicated? Well, fair enough. The
1298usual sequence of calls for compressing a load of data is:</p>
1299<div class="orderedlist"><ol type="1">
1300<li><p>Get started with
1301 <code class="computeroutput">BZ2_bzCompressInit</code>.</p></li>
1302<li><p>Shovel data in and shlurp out its compressed form
1303 using zero or more calls of
1304 <code class="computeroutput">BZ2_bzCompress</code> with action =
1305 <code class="computeroutput">BZ_RUN</code>.</p></li>
1306<li><p>Finish up. Repeatedly call
1307 <code class="computeroutput">BZ2_bzCompress</code> with action =
1308 <code class="computeroutput">BZ_FINISH</code>, copying out the
1309 compressed output, until
1310 <code class="computeroutput">BZ_STREAM_END</code> is
1311 returned.</p></li>
1312<li><p>Close up and go home. Call
1313 <code class="computeroutput">BZ2_bzCompressEnd</code>.</p></li>
1314</ol></div>
1315<p>If the data you want to compress fits into your input
1316buffer all at once, you can skip the calls of
1317<code class="computeroutput">BZ2_bzCompress ( ..., BZ_RUN )</code>
1318and just do the <code class="computeroutput">BZ2_bzCompress ( ..., BZ_FINISH
1319)</code> calls.</p>
1320<p>All required memory is allocated by
1321<code class="computeroutput">BZ2_bzCompressInit</code>. The
1322compression library can accept any data at all (obviously). So
1323you shouldn't get any error return values from the
1324<code class="computeroutput">BZ2_bzCompress</code> calls. If you
1325do, they will be
1326<code class="computeroutput">BZ_SEQUENCE_ERROR</code>, and indicate
1327a bug in your programming.</p>
1328<p>Trivial other possible return values:</p>
1329<pre class="programlisting">BZ_PARAM_ERROR
1330 if strm is NULL, or strm-&gt;s is NULL</pre>
1331</div>
1332<div class="sect2" lang="en">
1333<div class="titlepage"><div><div><h3 class="title">
1334<a name="bzCompress-end"></a>3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></h3></div></div></div>
1335<pre class="programlisting">int BZ2_bzCompressEnd ( bz_stream *strm );</pre>
1336<p>Releases all memory associated with a compression
1337stream.</p>
1338<p>Possible return values:</p>
1339<pre class="programlisting">BZ_PARAM_ERROR if strm is NULL or strm-&gt;s is NULL
1340BZ_OK otherwise</pre>
1341</div>
1342<div class="sect2" lang="en">
1343<div class="titlepage"><div><div><h3 class="title">
1344<a name="bzDecompress-init"></a>3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></h3></div></div></div>
1345<pre class="programlisting">int BZ2_bzDecompressInit ( bz_stream *strm, int verbosity, int small );</pre>
1346<p>Prepares for decompression. As with
1347<code class="computeroutput">BZ2_bzCompressInit</code>, a
1348<code class="computeroutput">bz_stream</code> record should be
1349allocated and initialised before the call. Fields
1350<code class="computeroutput">bzalloc</code>,
1351<code class="computeroutput">bzfree</code> and
1352<code class="computeroutput">opaque</code> should be set if a custom
1353memory allocator is required, or made
1354<code class="computeroutput">NULL</code> for the normal
1355<code class="computeroutput">malloc</code> /
1356<code class="computeroutput">free</code> routines. Upon return, the
1357internal state will have been initialised, and
1358<code class="computeroutput">total_in</code> and
1359<code class="computeroutput">total_out</code> will be zero.</p>
1360<p>For the meaning of parameter
1361<code class="computeroutput">verbosity</code>, see
1362<code class="computeroutput">BZ2_bzCompressInit</code>.</p>
1363<p>If <code class="computeroutput">small</code> is nonzero, the
1364library will use an alternative decompression algorithm which
1365uses less memory but at the cost of decompressing more slowly
1366(roughly speaking, half the speed, but the maximum memory
1367requirement drops to around 2300k). See <a href="#using">How to use bzip2</a>
1368for more information on memory management.</p>
1369<p>Note that the amount of memory needed to decompress a
1370stream cannot be determined until the stream's header has been
1371read, so even if
1372<code class="computeroutput">BZ2_bzDecompressInit</code> succeeds, a
1373subsequent <code class="computeroutput">BZ2_bzDecompress</code>
1374could fail with
1375<code class="computeroutput">BZ_MEM_ERROR</code>.</p>
1376<p>Possible return values:</p>
1377<pre class="programlisting">BZ_CONFIG_ERROR
1378 if the library has been mis-compiled
1379BZ_PARAM_ERROR
1380 if ( small != 0 &amp;&amp; small != 1 )
1381 or (verbosity &lt;; 0 || verbosity &gt; 4)
1382BZ_MEM_ERROR
1383 if insufficient memory is available</pre>
1384<p>Allowable next actions:</p>
1385<pre class="programlisting">BZ2_bzDecompress
1386 if BZ_OK was returned
1387 no specific action required in case of error</pre>
1388</div>
1389<div class="sect2" lang="en">
1390<div class="titlepage"><div><div><h3 class="title">
1391<a name="bzDecompress"></a>3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></h3></div></div></div>
1392<pre class="programlisting">int BZ2_bzDecompress ( bz_stream *strm );</pre>
1393<p>Provides more input and/out output buffer space for the
1394library. The caller maintains input and output buffers, and uses
1395<code class="computeroutput">BZ2_bzDecompress</code> to transfer
1396data between them.</p>
1397<p>Before each call to
1398<code class="computeroutput">BZ2_bzDecompress</code>,
1399<code class="computeroutput">next_in</code> should point at the
1400compressed data, and <code class="computeroutput">avail_in</code>
1401should indicate how many bytes the library may read.
1402<code class="computeroutput">BZ2_bzDecompress</code> updates
1403<code class="computeroutput">next_in</code>,
1404<code class="computeroutput">avail_in</code> and
1405<code class="computeroutput">total_in</code> to reflect the number
1406of bytes it has read.</p>
1407<p>Similarly, <code class="computeroutput">next_out</code> should
1408point to a buffer in which the uncompressed output is to be
1409placed, with <code class="computeroutput">avail_out</code>
1410indicating how much output space is available.
1411<code class="computeroutput">BZ2_bzCompress</code> updates
1412<code class="computeroutput">next_out</code>,
1413<code class="computeroutput">avail_out</code> and
1414<code class="computeroutput">total_out</code> to reflect the number
1415of bytes output.</p>
1416<p>You may provide and remove as little or as much data as you
1417like on each call of
1418<code class="computeroutput">BZ2_bzDecompress</code>. In the limit,
1419it is acceptable to supply and remove data one byte at a time,
1420although this would be terribly inefficient. You should always
1421ensure that at least one byte of output space is available at
1422each call.</p>
1423<p>Use of <code class="computeroutput">BZ2_bzDecompress</code> is
1424simpler than
1425<code class="computeroutput">BZ2_bzCompress</code>.</p>
1426<p>You should provide input and remove output as described
1427above, and repeatedly call
1428<code class="computeroutput">BZ2_bzDecompress</code> until
1429<code class="computeroutput">BZ_STREAM_END</code> is returned.
1430Appearance of <code class="computeroutput">BZ_STREAM_END</code>
1431denotes that <code class="computeroutput">BZ2_bzDecompress</code>
1432has detected the logical end of the compressed stream.
1433<code class="computeroutput">BZ2_bzDecompress</code> will not
1434produce <code class="computeroutput">BZ_STREAM_END</code> until all
1435output data has been placed into the output buffer, so once
1436<code class="computeroutput">BZ_STREAM_END</code> appears, you are
1437guaranteed to have available all the decompressed output, and
1438<code class="computeroutput">BZ2_bzDecompressEnd</code> can safely
1439be called.</p>
1440<p>If case of an error return value, you should call
1441<code class="computeroutput">BZ2_bzDecompressEnd</code> to clean up
1442and release memory.</p>
1443<p>Possible return values:</p>
1444<pre class="programlisting">BZ_PARAM_ERROR
1445 if strm is NULL or strm-&gt;s is NULL
1446 or strm-&gt;avail_out &lt; 1
1447BZ_DATA_ERROR
1448 if a data integrity error is detected in the compressed stream
1449BZ_DATA_ERROR_MAGIC
1450 if the compressed stream doesn't begin with the right magic bytes
1451BZ_MEM_ERROR
1452 if there wasn't enough memory available
1453BZ_STREAM_END
1454 if the logical end of the data stream was detected and all
1455 output in has been consumed, eg s--&gt;avail_out &gt; 0
1456BZ_OK
1457 otherwise</pre>
1458<p>Allowable next actions:</p>
1459<pre class="programlisting">BZ2_bzDecompress
1460 if BZ_OK was returned
1461BZ2_bzDecompressEnd
1462 otherwise</pre>
1463</div>
1464<div class="sect2" lang="en">
1465<div class="titlepage"><div><div><h3 class="title">
1466<a name="bzDecompress-end"></a>3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></h3></div></div></div>
1467<pre class="programlisting">int BZ2_bzDecompressEnd ( bz_stream *strm );</pre>
1468<p>Releases all memory associated with a decompression
1469stream.</p>
1470<p>Possible return values:</p>
1471<pre class="programlisting">BZ_PARAM_ERROR
1472 if strm is NULL or strm-&gt;s is NULL
1473BZ_OK
1474 otherwise</pre>
1475<p>Allowable next actions:</p>
1476<pre class="programlisting"> None.</pre>
1477</div>
1478</div>
1479<div class="sect1" lang="en">
1480<div class="titlepage"><div><div><h2 class="title" style="clear: both">
1481<a name="hl-interface"></a>3.4. High-level interface</h2></div></div></div>
1482<p>This interface provides functions for reading and writing
1483<code class="computeroutput">bzip2</code> format files. First, some
1484general points.</p>
1485<div class="itemizedlist"><ul type="bullet">
1486<li style="list-style-type: disc"><p>All of the functions take an
1487 <code class="computeroutput">int*</code> first argument,
1488 <code class="computeroutput">bzerror</code>. After each call,
1489 <code class="computeroutput">bzerror</code> should be consulted
1490 first to determine the outcome of the call. If
1491 <code class="computeroutput">bzerror</code> is
1492 <code class="computeroutput">BZ_OK</code>, the call completed
1493 successfully, and only then should the return value of the
1494 function (if any) be consulted. If
1495 <code class="computeroutput">bzerror</code> is
1496 <code class="computeroutput">BZ_IO_ERROR</code>, there was an
1497 error reading/writing the underlying compressed file, and you
1498 should then consult <code class="computeroutput">errno</code> /
1499 <code class="computeroutput">perror</code> to determine the cause
1500 of the difficulty. <code class="computeroutput">bzerror</code>
1501 may also be set to various other values; precise details are
1502 given on a per-function basis below.</p></li>
1503<li style="list-style-type: disc"><p>If <code class="computeroutput">bzerror</code> indicates
1504 an error (ie, anything except
1505 <code class="computeroutput">BZ_OK</code> and
1506 <code class="computeroutput">BZ_STREAM_END</code>), you should
1507 immediately call
1508 <code class="computeroutput">BZ2_bzReadClose</code> (or
1509 <code class="computeroutput">BZ2_bzWriteClose</code>, depending on
1510 whether you are attempting to read or to write) to free up all
1511 resources associated with the stream. Once an error has been
1512 indicated, behaviour of all calls except
1513 <code class="computeroutput">BZ2_bzReadClose</code>
1514 (<code class="computeroutput">BZ2_bzWriteClose</code>) is
1515 undefined. The implication is that (1)
1516 <code class="computeroutput">bzerror</code> should be checked
1517 after each call, and (2) if
1518 <code class="computeroutput">bzerror</code> indicates an error,
1519 <code class="computeroutput">BZ2_bzReadClose</code>
1520 (<code class="computeroutput">BZ2_bzWriteClose</code>) should then
1521 be called to clean up.</p></li>
1522<li style="list-style-type: disc"><p>The <code class="computeroutput">FILE*</code> arguments
1523 passed to <code class="computeroutput">BZ2_bzReadOpen</code> /
1524 <code class="computeroutput">BZ2_bzWriteOpen</code> should be set
1525 to binary mode. Most Unix systems will do this by default, but
1526 other platforms, including Windows and Mac, will not. If you
1527 omit this, you may encounter problems when moving code to new
1528 platforms.</p></li>
1529<li style="list-style-type: disc"><p>Memory allocation requests are handled by
1530 <code class="computeroutput">malloc</code> /
1531 <code class="computeroutput">free</code>. At present there is no
1532 facility for user-defined memory allocators in the file I/O
1533 functions (could easily be added, though).</p></li>
1534</ul></div>
1535<div class="sect2" lang="en">
1536<div class="titlepage"><div><div><h3 class="title">
1537<a name="bzreadopen"></a>3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></h3></div></div></div>
1538<pre class="programlisting">typedef void BZFILE;
1539
1540BZFILE *BZ2_bzReadOpen( int *bzerror, FILE *f,
1541 int verbosity, int small,
1542 void *unused, int nUnused );</pre>
1543<p>Prepare to read compressed data from file handle
1544<code class="computeroutput">f</code>.
1545<code class="computeroutput">f</code> should refer to a file which
1546has been opened for reading, and for which the error indicator
1547(<code class="computeroutput">ferror(f)</code>)is not set. If
1548<code class="computeroutput">small</code> is 1, the library will try
1549to decompress using less memory, at the expense of speed.</p>
1550<p>For reasons explained below,
1551<code class="computeroutput">BZ2_bzRead</code> will decompress the
1552<code class="computeroutput">nUnused</code> bytes starting at
1553<code class="computeroutput">unused</code>, before starting to read
1554from the file <code class="computeroutput">f</code>. At most
1555<code class="computeroutput">BZ_MAX_UNUSED</code> bytes may be
1556supplied like this. If this facility is not required, you should
1557pass <code class="computeroutput">NULL</code> and
1558<code class="computeroutput">0</code> for
1559<code class="computeroutput">unused</code> and
1560n<code class="computeroutput">Unused</code> respectively.</p>
1561<p>For the meaning of parameters
1562<code class="computeroutput">small</code> and
1563<code class="computeroutput">verbosity</code>, see
1564<code class="computeroutput">BZ2_bzDecompressInit</code>.</p>
1565<p>The amount of memory needed to decompress a file cannot be
1566determined until the file's header has been read. So it is
1567possible that <code class="computeroutput">BZ2_bzReadOpen</code>
1568returns <code class="computeroutput">BZ_OK</code> but a subsequent
1569call of <code class="computeroutput">BZ2_bzRead</code> will return
1570<code class="computeroutput">BZ_MEM_ERROR</code>.</p>
1571<p>Possible assignments to
1572<code class="computeroutput">bzerror</code>:</p>
1573<pre class="programlisting">BZ_CONFIG_ERROR
1574 if the library has been mis-compiled
1575BZ_PARAM_ERROR
1576 if f is NULL
1577 or small is neither 0 nor 1
1578 or ( unused == NULL &amp;&amp; nUnused != 0 )
1579 or ( unused != NULL &amp;&amp; !(0 &lt;= nUnused &lt;= BZ_MAX_UNUSED) )
1580BZ_IO_ERROR
1581 if ferror(f) is nonzero
1582BZ_MEM_ERROR
1583 if insufficient memory is available
1584BZ_OK
1585 otherwise.</pre>
1586<p>Possible return values:</p>
1587<pre class="programlisting">Pointer to an abstract BZFILE
1588 if bzerror is BZ_OK
1589NULL
1590 otherwise</pre>
1591<p>Allowable next actions:</p>
1592<pre class="programlisting">BZ2_bzRead
1593 if bzerror is BZ_OK
1594BZ2_bzClose
1595 otherwise</pre>
1596</div>
1597<div class="sect2" lang="en">
1598<div class="titlepage"><div><div><h3 class="title">
1599<a name="bzread"></a>3.4.2. <code class="computeroutput">BZ2_bzRead</code></h3></div></div></div>
1600<pre class="programlisting">int BZ2_bzRead ( int *bzerror, BZFILE *b, void *buf, int len );</pre>
1601<p>Reads up to <code class="computeroutput">len</code>
1602(uncompressed) bytes from the compressed file
1603<code class="computeroutput">b</code> into the buffer
1604<code class="computeroutput">buf</code>. If the read was
1605successful, <code class="computeroutput">bzerror</code> is set to
1606<code class="computeroutput">BZ_OK</code> and the number of bytes
1607read is returned. If the logical end-of-stream was detected,
1608<code class="computeroutput">bzerror</code> will be set to
1609<code class="computeroutput">BZ_STREAM_END</code>, and the number of
1610bytes read is returned. All other
1611<code class="computeroutput">bzerror</code> values denote an
1612error.</p>
1613<p><code class="computeroutput">BZ2_bzRead</code> will supply
1614<code class="computeroutput">len</code> bytes, unless the logical
1615stream end is detected or an error occurs. Because of this, it
1616is possible to detect the stream end by observing when the number
1617of bytes returned is less than the number requested.
1618Nevertheless, this is regarded as inadvisable; you should instead
1619check <code class="computeroutput">bzerror</code> after every call
1620and watch out for
1621<code class="computeroutput">BZ_STREAM_END</code>.</p>
1622<p>Internally, <code class="computeroutput">BZ2_bzRead</code>
1623copies data from the compressed file in chunks of size
1624<code class="computeroutput">BZ_MAX_UNUSED</code> bytes before
1625decompressing it. If the file contains more bytes than strictly
1626needed to reach the logical end-of-stream,
1627<code class="computeroutput">BZ2_bzRead</code> will almost certainly
1628read some of the trailing data before signalling
1629<code class="computeroutput">BZ_SEQUENCE_END</code>. To collect the
1630read but unused data once
1631<code class="computeroutput">BZ_SEQUENCE_END</code> has appeared,
1632call <code class="computeroutput">BZ2_bzReadGetUnused</code>
1633immediately before
1634<code class="computeroutput">BZ2_bzReadClose</code>.</p>
1635<p>Possible assignments to
1636<code class="computeroutput">bzerror</code>:</p>
1637<pre class="programlisting">BZ_PARAM_ERROR
1638 if b is NULL or buf is NULL or len &lt; 0
1639BZ_SEQUENCE_ERROR
1640 if b was opened with BZ2_bzWriteOpen
1641BZ_IO_ERROR
1642 if there is an error reading from the compressed file
1643BZ_UNEXPECTED_EOF
1644 if the compressed file ended before
1645 the logical end-of-stream was detected
1646BZ_DATA_ERROR
1647 if a data integrity error was detected in the compressed stream
1648BZ_DATA_ERROR_MAGIC
1649 if the stream does not begin with the requisite header bytes
1650 (ie, is not a bzip2 data file). This is really
1651 a special case of BZ_DATA_ERROR.
1652BZ_MEM_ERROR
1653 if insufficient memory was available
1654BZ_STREAM_END
1655 if the logical end of stream was detected.
1656BZ_OK
1657 otherwise.</pre>
1658<p>Possible return values:</p>
1659<pre class="programlisting">number of bytes read
1660 if bzerror is BZ_OK or BZ_STREAM_END
1661undefined
1662 otherwise</pre>
1663<p>Allowable next actions:</p>
1664<pre class="programlisting">collect data from buf, then BZ2_bzRead or BZ2_bzReadClose
1665 if bzerror is BZ_OK
1666collect data from buf, then BZ2_bzReadClose or BZ2_bzReadGetUnused
1667 if bzerror is BZ_SEQUENCE_END
1668BZ2_bzReadClose
1669 otherwise</pre>
1670</div>
1671<div class="sect2" lang="en">
1672<div class="titlepage"><div><div><h3 class="title">
1673<a name="bzreadgetunused"></a>3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></h3></div></div></div>
1674<pre class="programlisting">void BZ2_bzReadGetUnused( int* bzerror, BZFILE *b,
1675 void** unused, int* nUnused );</pre>
1676<p>Returns data which was read from the compressed file but
1677was not needed to get to the logical end-of-stream.
1678<code class="computeroutput">*unused</code> is set to the address of
1679the data, and <code class="computeroutput">*nUnused</code> to the
1680number of bytes. <code class="computeroutput">*nUnused</code> will
1681be set to a value between <code class="computeroutput">0</code> and
1682<code class="computeroutput">BZ_MAX_UNUSED</code> inclusive.</p>
1683<p>This function may only be called once
1684<code class="computeroutput">BZ2_bzRead</code> has signalled
1685<code class="computeroutput">BZ_STREAM_END</code> but before
1686<code class="computeroutput">BZ2_bzReadClose</code>.</p>
1687<p>Possible assignments to
1688<code class="computeroutput">bzerror</code>:</p>
1689<pre class="programlisting">BZ_PARAM_ERROR
1690 if b is NULL
1691 or unused is NULL or nUnused is NULL
1692BZ_SEQUENCE_ERROR
1693 if BZ_STREAM_END has not been signalled
1694 or if b was opened with BZ2_bzWriteOpen
1695BZ_OK
1696 otherwise</pre>
1697<p>Allowable next actions:</p>
1698<pre class="programlisting">BZ2_bzReadClose</pre>
1699</div>
1700<div class="sect2" lang="en">
1701<div class="titlepage"><div><div><h3 class="title">
1702<a name="bzreadclose"></a>3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></h3></div></div></div>
1703<pre class="programlisting">void BZ2_bzReadClose ( int *bzerror, BZFILE *b );</pre>
1704<p>Releases all memory pertaining to the compressed file
1705<code class="computeroutput">b</code>.
1706<code class="computeroutput">BZ2_bzReadClose</code> does not call
1707<code class="computeroutput">fclose</code> on the underlying file
1708handle, so you should do that yourself if appropriate.
1709<code class="computeroutput">BZ2_bzReadClose</code> should be called
1710to clean up after all error situations.</p>
1711<p>Possible assignments to
1712<code class="computeroutput">bzerror</code>:</p>
1713<pre class="programlisting">BZ_SEQUENCE_ERROR
1714 if b was opened with BZ2_bzOpenWrite
1715BZ_OK
1716 otherwise</pre>
1717<p>Allowable next actions:</p>
1718<pre class="programlisting">none</pre>
1719</div>
1720<div class="sect2" lang="en">
1721<div class="titlepage"><div><div><h3 class="title">
1722<a name="bzwriteopen"></a>3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></h3></div></div></div>
1723<pre class="programlisting">BZFILE *BZ2_bzWriteOpen( int *bzerror, FILE *f,
1724 int blockSize100k, int verbosity,
1725 int workFactor );</pre>
1726<p>Prepare to write compressed data to file handle
1727<code class="computeroutput">f</code>.
1728<code class="computeroutput">f</code> should refer to a file which
1729has been opened for writing, and for which the error indicator
1730(<code class="computeroutput">ferror(f)</code>)is not set.</p>
1731<p>For the meaning of parameters
1732<code class="computeroutput">blockSize100k</code>,
1733<code class="computeroutput">verbosity</code> and
1734<code class="computeroutput">workFactor</code>, see
1735<code class="computeroutput">BZ2_bzCompressInit</code>.</p>
1736<p>All required memory is allocated at this stage, so if the
1737call completes successfully,
1738<code class="computeroutput">BZ_MEM_ERROR</code> cannot be signalled
1739by a subsequent call to
1740<code class="computeroutput">BZ2_bzWrite</code>.</p>
1741<p>Possible assignments to
1742<code class="computeroutput">bzerror</code>:</p>
1743<pre class="programlisting">BZ_CONFIG_ERROR
1744 if the library has been mis-compiled
1745BZ_PARAM_ERROR
1746 if f is NULL
1747 or blockSize100k &lt; 1 or blockSize100k &gt; 9
1748BZ_IO_ERROR
1749 if ferror(f) is nonzero
1750BZ_MEM_ERROR
1751 if insufficient memory is available
1752BZ_OK
1753 otherwise</pre>
1754<p>Possible return values:</p>
1755<pre class="programlisting">Pointer to an abstract BZFILE
1756 if bzerror is BZ_OK
1757NULL
1758 otherwise</pre>
1759<p>Allowable next actions:</p>
1760<pre class="programlisting">BZ2_bzWrite
1761 if bzerror is BZ_OK
1762 (you could go directly to BZ2_bzWriteClose, but this would be pretty pointless)
1763BZ2_bzWriteClose
1764 otherwise</pre>
1765</div>
1766<div class="sect2" lang="en">
1767<div class="titlepage"><div><div><h3 class="title">
1768<a name="bzwrite"></a>3.4.6. <code class="computeroutput">BZ2_bzWrite</code></h3></div></div></div>
1769<pre class="programlisting">void BZ2_bzWrite ( int *bzerror, BZFILE *b, void *buf, int len );</pre>
1770<p>Absorbs <code class="computeroutput">len</code> bytes from the
1771buffer <code class="computeroutput">buf</code>, eventually to be
1772compressed and written to the file.</p>
1773<p>Possible assignments to
1774<code class="computeroutput">bzerror</code>:</p>
1775<pre class="programlisting">BZ_PARAM_ERROR
1776 if b is NULL or buf is NULL or len &lt; 0
1777BZ_SEQUENCE_ERROR
1778 if b was opened with BZ2_bzReadOpen
1779BZ_IO_ERROR
1780 if there is an error writing the compressed file.
1781BZ_OK
1782 otherwise</pre>
1783</div>
1784<div class="sect2" lang="en">
1785<div class="titlepage"><div><div><h3 class="title">
1786<a name="bzwriteclose"></a>3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></h3></div></div></div>
1787<pre class="programlisting">void BZ2_bzWriteClose( int *bzerror, BZFILE* f,
1788 int abandon,
1789 unsigned int* nbytes_in,
1790 unsigned int* nbytes_out );
1791
1792void BZ2_bzWriteClose64( int *bzerror, BZFILE* f,
1793 int abandon,
1794 unsigned int* nbytes_in_lo32,
1795 unsigned int* nbytes_in_hi32,
1796 unsigned int* nbytes_out_lo32,
1797 unsigned int* nbytes_out_hi32 );</pre>
1798<p>Compresses and flushes to the compressed file all data so
1799far supplied by <code class="computeroutput">BZ2_bzWrite</code>.
1800The logical end-of-stream markers are also written, so subsequent
1801calls to <code class="computeroutput">BZ2_bzWrite</code> are
1802illegal. All memory associated with the compressed file
1803<code class="computeroutput">b</code> is released.
1804<code class="computeroutput">fflush</code> is called on the
1805compressed file, but it is not
1806<code class="computeroutput">fclose</code>'d.</p>
1807<p>If <code class="computeroutput">BZ2_bzWriteClose</code> is
1808called to clean up after an error, the only action is to release
1809the memory. The library records the error codes issued by
1810previous calls, so this situation will be detected automatically.
1811There is no attempt to complete the compression operation, nor to
1812<code class="computeroutput">fflush</code> the compressed file. You
1813can force this behaviour to happen even in the case of no error,
1814by passing a nonzero value to
1815<code class="computeroutput">abandon</code>.</p>
1816<p>If <code class="computeroutput">nbytes_in</code> is non-null,
1817<code class="computeroutput">*nbytes_in</code> will be set to be the
1818total volume of uncompressed data handled. Similarly,
1819<code class="computeroutput">nbytes_out</code> will be set to the
1820total volume of compressed data written. For compatibility with
1821older versions of the library,
1822<code class="computeroutput">BZ2_bzWriteClose</code> only yields the
1823lower 32 bits of these counts. Use
1824<code class="computeroutput">BZ2_bzWriteClose64</code> if you want
1825the full 64 bit counts. These two functions are otherwise
1826absolutely identical.</p>
1827<p>Possible assignments to
1828<code class="computeroutput">bzerror</code>:</p>
1829<pre class="programlisting">BZ_SEQUENCE_ERROR
1830 if b was opened with BZ2_bzReadOpen
1831BZ_IO_ERROR
1832 if there is an error writing the compressed file
1833BZ_OK
1834 otherwise</pre>
1835</div>
1836<div class="sect2" lang="en">
1837<div class="titlepage"><div><div><h3 class="title">
1838<a name="embed"></a>3.4.8. Handling embedded compressed data streams</h3></div></div></div>
1839<p>The high-level library facilitates use of
1840<code class="computeroutput">bzip2</code> data streams which form
1841some part of a surrounding, larger data stream.</p>
1842<div class="itemizedlist"><ul type="bullet">
1843<li style="list-style-type: disc"><p>For writing, the library takes an open file handle,
1844 writes compressed data to it,
1845 <code class="computeroutput">fflush</code>es it but does not
1846 <code class="computeroutput">fclose</code> it. The calling
1847 application can write its own data before and after the
1848 compressed data stream, using that same file handle.</p></li>
1849<li style="list-style-type: disc"><p>Reading is more complex, and the facilities are not as
1850 general as they could be since generality is hard to reconcile
1851 with efficiency. <code class="computeroutput">BZ2_bzRead</code>
1852 reads from the compressed file in blocks of size
1853 <code class="computeroutput">BZ_MAX_UNUSED</code> bytes, and in
1854 doing so probably will overshoot the logical end of compressed
1855 stream. To recover this data once decompression has ended,
1856 call <code class="computeroutput">BZ2_bzReadGetUnused</code> after
1857 the last call of <code class="computeroutput">BZ2_bzRead</code>
1858 (the one returning
1859 <code class="computeroutput">BZ_STREAM_END</code>) but before
1860 calling
1861 <code class="computeroutput">BZ2_bzReadClose</code>.</p></li>
1862</ul></div>
1863<p>This mechanism makes it easy to decompress multiple
1864<code class="computeroutput">bzip2</code> streams placed end-to-end.
1865As the end of one stream, when
1866<code class="computeroutput">BZ2_bzRead</code> returns
1867<code class="computeroutput">BZ_STREAM_END</code>, call
1868<code class="computeroutput">BZ2_bzReadGetUnused</code> to collect
1869the unused data (copy it into your own buffer somewhere). That
1870data forms the start of the next compressed stream. To start
1871uncompressing that next stream, call
1872<code class="computeroutput">BZ2_bzReadOpen</code> again, feeding in
1873the unused data via the <code class="computeroutput">unused</code> /
1874<code class="computeroutput">nUnused</code> parameters. Keep doing
1875this until <code class="computeroutput">BZ_STREAM_END</code> return
1876coincides with the physical end of file
1877(<code class="computeroutput">feof(f)</code>). In this situation
1878<code class="computeroutput">BZ2_bzReadGetUnused</code> will of
1879course return no data.</p>
1880<p>This should give some feel for how the high-level interface
1881can be used. If you require extra flexibility, you'll have to
1882bite the bullet and get to grips with the low-level
1883interface.</p>
1884</div>
1885<div class="sect2" lang="en">
1886<div class="titlepage"><div><div><h3 class="title">
1887<a name="std-rdwr"></a>3.4.9. Standard file-reading/writing code</h3></div></div></div>
1888<p>Here's how you'd write data to a compressed file:</p>
1889<pre class="programlisting">FILE* f;
1890BZFILE* b;
1891int nBuf;
1892char buf[ /* whatever size you like */ ];
1893int bzerror;
1894int nWritten;
1895
1896f = fopen ( "myfile.bz2", "w" );
1897if ( !f ) {
1898 /* handle error */
1899}
1900b = BZ2_bzWriteOpen( &amp;bzerror, f, 9 );
1901if (bzerror != BZ_OK) {
1902 BZ2_bzWriteClose ( b );
1903 /* handle error */
1904}
1905
1906while ( /* condition */ ) {
1907 /* get data to write into buf, and set nBuf appropriately */
1908 nWritten = BZ2_bzWrite ( &amp;bzerror, b, buf, nBuf );
1909 if (bzerror == BZ_IO_ERROR) {
1910 BZ2_bzWriteClose ( &amp;bzerror, b );
1911 /* handle error */
1912 }
1913}
1914
1915BZ2_bzWriteClose( &amp;bzerror, b );
1916if (bzerror == BZ_IO_ERROR) {
1917 /* handle error */
1918}</pre>
1919<p>And to read from a compressed file:</p>
1920<pre class="programlisting">FILE* f;
1921BZFILE* b;
1922int nBuf;
1923char buf[ /* whatever size you like */ ];
1924int bzerror;
1925int nWritten;
1926
1927f = fopen ( "myfile.bz2", "r" );
1928if ( !f ) {
1929 /* handle error */
1930}
1931b = BZ2_bzReadOpen ( &amp;bzerror, f, 0, NULL, 0 );
1932if ( bzerror != BZ_OK ) {
1933 BZ2_bzReadClose ( &amp;bzerror, b );
1934 /* handle error */
1935}
1936
1937bzerror = BZ_OK;
1938while ( bzerror == BZ_OK &amp;&amp; /* arbitrary other conditions */) {
1939 nBuf = BZ2_bzRead ( &amp;bzerror, b, buf, /* size of buf */ );
1940 if ( bzerror == BZ_OK ) {
1941 /* do something with buf[0 .. nBuf-1] */
1942 }
1943}
1944if ( bzerror != BZ_STREAM_END ) {
1945 BZ2_bzReadClose ( &amp;bzerror, b );
1946 /* handle error */
1947} else {
1948 BZ2_bzReadClose ( &amp;bzerror, b );
1949}</pre>
1950</div>
1951</div>
1952<div class="sect1" lang="en">
1953<div class="titlepage"><div><div><h2 class="title" style="clear: both">
1954<a name="util-fns"></a>3.5. Utility functions</h2></div></div></div>
1955<div class="sect2" lang="en">
1956<div class="titlepage"><div><div><h3 class="title">
1957<a name="bzbufftobuffcompress"></a>3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></h3></div></div></div>
1958<pre class="programlisting">int BZ2_bzBuffToBuffCompress( char* dest,
1959 unsigned int* destLen,
1960 char* source,
1961 unsigned int sourceLen,
1962 int blockSize100k,
1963 int verbosity,
1964 int workFactor );</pre>
1965<p>Attempts to compress the data in <code class="computeroutput">source[0
1966.. sourceLen-1]</code> into the destination buffer,
1967<code class="computeroutput">dest[0 .. *destLen-1]</code>. If the
1968destination buffer is big enough,
1969<code class="computeroutput">*destLen</code> is set to the size of
1970the compressed data, and <code class="computeroutput">BZ_OK</code>
1971is returned. If the compressed data won't fit,
1972<code class="computeroutput">*destLen</code> is unchanged, and
1973<code class="computeroutput">BZ_OUTBUFF_FULL</code> is
1974returned.</p>
1975<p>Compression in this manner is a one-shot event, done with a
1976single call to this function. The resulting compressed data is a
1977complete <code class="computeroutput">bzip2</code> format data
1978stream. There is no mechanism for making additional calls to
1979provide extra input data. If you want that kind of mechanism,
1980use the low-level interface.</p>
1981<p>For the meaning of parameters
1982<code class="computeroutput">blockSize100k</code>,
1983<code class="computeroutput">verbosity</code> and
1984<code class="computeroutput">workFactor</code>, see
1985<code class="computeroutput">BZ2_bzCompressInit</code>.</p>
1986<p>To guarantee that the compressed data will fit in its
1987buffer, allocate an output buffer of size 1% larger than the
1988uncompressed data, plus six hundred extra bytes.</p>
1989<p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code>
1990will not write data at or beyond
1991<code class="computeroutput">dest[*destLen]</code>, even in case of
1992buffer overflow.</p>
1993<p>Possible return values:</p>
1994<pre class="programlisting">BZ_CONFIG_ERROR
1995 if the library has been mis-compiled
1996BZ_PARAM_ERROR
1997 if dest is NULL or destLen is NULL
1998 or blockSize100k &lt; 1 or blockSize100k &gt; 9
1999 or verbosity &lt; 0 or verbosity &gt; 4
2000 or workFactor &lt; 0 or workFactor &gt; 250
2001BZ_MEM_ERROR
2002 if insufficient memory is available
2003BZ_OUTBUFF_FULL
2004 if the size of the compressed data exceeds *destLen
2005BZ_OK
2006 otherwise</pre>
2007</div>
2008<div class="sect2" lang="en">
2009<div class="titlepage"><div><div><h3 class="title">
2010<a name="bzbufftobuffdecompress"></a>3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></h3></div></div></div>
2011<pre class="programlisting">int BZ2_bzBuffToBuffDecompress( char* dest,
2012 unsigned int* destLen,
2013 char* source,
2014 unsigned int sourceLen,
2015 int small,
2016 int verbosity );</pre>
2017<p>Attempts to decompress the data in <code class="computeroutput">source[0
2018.. sourceLen-1]</code> into the destination buffer,
2019<code class="computeroutput">dest[0 .. *destLen-1]</code>. If the
2020destination buffer is big enough,
2021<code class="computeroutput">*destLen</code> is set to the size of
2022the uncompressed data, and <code class="computeroutput">BZ_OK</code>
2023is returned. If the compressed data won't fit,
2024<code class="computeroutput">*destLen</code> is unchanged, and
2025<code class="computeroutput">BZ_OUTBUFF_FULL</code> is
2026returned.</p>
2027<p><code class="computeroutput">source</code> is assumed to hold
2028a complete <code class="computeroutput">bzip2</code> format data
2029stream.
2030<code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> tries
2031to decompress the entirety of the stream into the output
2032buffer.</p>
2033<p>For the meaning of parameters
2034<code class="computeroutput">small</code> and
2035<code class="computeroutput">verbosity</code>, see
2036<code class="computeroutput">BZ2_bzDecompressInit</code>.</p>
2037<p>Because the compression ratio of the compressed data cannot
2038be known in advance, there is no easy way to guarantee that the
2039output buffer will be big enough. You may of course make
2040arrangements in your code to record the size of the uncompressed
2041data, but such a mechanism is beyond the scope of this
2042library.</p>
2043<p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code>
2044will not write data at or beyond
2045<code class="computeroutput">dest[*destLen]</code>, even in case of
2046buffer overflow.</p>
2047<p>Possible return values:</p>
2048<pre class="programlisting">BZ_CONFIG_ERROR
2049 if the library has been mis-compiled
2050BZ_PARAM_ERROR
2051 if dest is NULL or destLen is NULL
2052 or small != 0 &amp;&amp; small != 1
2053 or verbosity &lt; 0 or verbosity &gt; 4
2054BZ_MEM_ERROR
2055 if insufficient memory is available
2056BZ_OUTBUFF_FULL
2057 if the size of the compressed data exceeds *destLen
2058BZ_DATA_ERROR
2059 if a data integrity error was detected in the compressed data
2060BZ_DATA_ERROR_MAGIC
2061 if the compressed data doesn't begin with the right magic bytes
2062BZ_UNEXPECTED_EOF
2063 if the compressed data ends unexpectedly
2064BZ_OK
2065 otherwise</pre>
2066</div>
2067</div>
2068<div class="sect1" lang="en">
2069<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2070<a name="zlib-compat"></a>3.6. <code class="computeroutput">zlib</code> compatibility functions</h2></div></div></div>
2071<p>Yoshioka Tsuneo has contributed some functions to give
2072better <code class="computeroutput">zlib</code> compatibility.
2073These functions are <code class="computeroutput">BZ2_bzopen</code>,
2074<code class="computeroutput">BZ2_bzread</code>,
2075<code class="computeroutput">BZ2_bzwrite</code>,
2076<code class="computeroutput">BZ2_bzflush</code>,
2077<code class="computeroutput">BZ2_bzclose</code>,
2078<code class="computeroutput">BZ2_bzerror</code> and
2079<code class="computeroutput">BZ2_bzlibVersion</code>. These
2080functions are not (yet) officially part of the library. If they
2081break, you get to keep all the pieces. Nevertheless, I think
2082they work ok.</p>
2083<pre class="programlisting">typedef void BZFILE;
2084
2085const char * BZ2_bzlibVersion ( void );</pre>
2086<p>Returns a string indicating the library version.</p>
2087<pre class="programlisting">BZFILE * BZ2_bzopen ( const char *path, const char *mode );
2088BZFILE * BZ2_bzdopen ( int fd, const char *mode );</pre>
2089<p>Opens a <code class="computeroutput">.bz2</code> file for
2090reading or writing, using either its name or a pre-existing file
2091descriptor. Analogous to <code class="computeroutput">fopen</code>
2092and <code class="computeroutput">fdopen</code>.</p>
2093<pre class="programlisting">int BZ2_bzread ( BZFILE* b, void* buf, int len );
2094int BZ2_bzwrite ( BZFILE* b, void* buf, int len );</pre>
2095<p>Reads/writes data from/to a previously opened
2096<code class="computeroutput">BZFILE</code>. Analogous to
2097<code class="computeroutput">fread</code> and
2098<code class="computeroutput">fwrite</code>.</p>
2099<pre class="programlisting">int BZ2_bzflush ( BZFILE* b );
2100void BZ2_bzclose ( BZFILE* b );</pre>
2101<p>Flushes/closes a <code class="computeroutput">BZFILE</code>.
2102<code class="computeroutput">BZ2_bzflush</code> doesn't actually do
2103anything. Analogous to <code class="computeroutput">fflush</code>
2104and <code class="computeroutput">fclose</code>.</p>
2105<pre class="programlisting">const char * BZ2_bzerror ( BZFILE *b, int *errnum )</pre>
2106<p>Returns a string describing the more recent error status of
2107<code class="computeroutput">b</code>, and also sets
2108<code class="computeroutput">*errnum</code> to its numerical
2109value.</p>
2110</div>
2111<div class="sect1" lang="en">
2112<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2113<a name="stdio-free"></a>3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</h2></div></div></div>
2114<div class="sect2" lang="en">
2115<div class="titlepage"><div><div><h3 class="title">
2116<a name="stdio-bye"></a>3.7.1. Getting rid of <code class="computeroutput">stdio</code></h3></div></div></div>
2117<p>In a deeply embedded application, you might want to use
2118just the memory-to-memory functions. You can do this
2119conveniently by compiling the library with preprocessor symbol
2120<code class="computeroutput">BZ_NO_STDIO</code> defined. Doing this
2121gives you a library containing only the following eight
2122functions:</p>
2123<p><code class="computeroutput">BZ2_bzCompressInit</code>,
2124<code class="computeroutput">BZ2_bzCompress</code>,
2125<code class="computeroutput">BZ2_bzCompressEnd</code>
2126<code class="computeroutput">BZ2_bzDecompressInit</code>,
2127<code class="computeroutput">BZ2_bzDecompress</code>,
2128<code class="computeroutput">BZ2_bzDecompressEnd</code>
2129<code class="computeroutput">BZ2_bzBuffToBuffCompress</code>,
2130<code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></p>
2131<p>When compiled like this, all functions will ignore
2132<code class="computeroutput">verbosity</code> settings.</p>
2133</div>
2134<div class="sect2" lang="en">
2135<div class="titlepage"><div><div><h3 class="title">
2136<a name="critical-error"></a>3.7.2. Critical error handling</h3></div></div></div>
2137<p><code class="computeroutput">libbzip2</code> contains a number
2138of internal assertion checks which should, needless to say, never
2139be activated. Nevertheless, if an assertion should fail,
2140behaviour depends on whether or not the library was compiled with
2141<code class="computeroutput">BZ_NO_STDIO</code> set.</p>
2142<p>For a normal compile, an assertion failure yields the
2143message:</p>
2144<div class="blockquote"><blockquote class="blockquote">
2145<p>bzip2/libbzip2: internal error number N.</p>
2146<p>This is a bug in bzip2/libbzip2, 1.0.4 of 20 December 2006.
2147Please report it to me at: jseward@bzip.org. If this happened
2148when you were using some program which uses libbzip2 as a
2149component, you should also report this bug to the author(s)
2150of that program. Please make an effort to report this bug;
2151timely and accurate bug reports eventually lead to higher
2152quality software. Thanks. Julian Seward, 20 December 2006.
2153</p>
2154</blockquote></div>
2155<p>where <code class="computeroutput">N</code> is some error code
2156number. If <code class="computeroutput">N == 1007</code>, it also
2157prints some extra text advising the reader that unreliable memory
2158is often associated with internal error 1007. (This is a
2159frequently-observed-phenomenon with versions 1.0.0/1.0.1).</p>
2160<p><code class="computeroutput">exit(3)</code> is then
2161called.</p>
2162<p>For a <code class="computeroutput">stdio</code>-free library,
2163assertion failures result in a call to a function declared
2164as:</p>
2165<pre class="programlisting">extern void bz_internal_error ( int errcode );</pre>
2166<p>The relevant code is passed as a parameter. You should
2167supply such a function.</p>
2168<p>In either case, once an assertion failure has occurred, any
2169<code class="computeroutput">bz_stream</code> records involved can
2170be regarded as invalid. You should not attempt to resume normal
2171operation with them.</p>
2172<p>You may, of course, change critical error handling to suit
2173your needs. As I said above, critical errors indicate bugs in
2174the library and should not occur. All "normal" error situations
2175are indicated via error return codes from functions, and can be
2176recovered from.</p>
2177</div>
2178</div>
2179<div class="sect1" lang="en">
2180<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2181<a name="win-dll"></a>3.8. Making a Windows DLL</h2></div></div></div>
2182<p>Everything related to Windows has been contributed by
2183Yoshioka Tsuneo
2184(<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>), so
2185you should send your queries to him (but perhaps Cc: me,
2186<code class="computeroutput">jseward@bzip.org</code>).</p>
2187<p>My vague understanding of what to do is: using Visual C++
21885.0, open the project file
2189<code class="computeroutput">libbz2.dsp</code>, and build. That's
2190all.</p>
2191<p>If you can't open the project file for some reason, make a
2192new one, naming these files:
2193<code class="computeroutput">blocksort.c</code>,
2194<code class="computeroutput">bzlib.c</code>,
2195<code class="computeroutput">compress.c</code>,
2196<code class="computeroutput">crctable.c</code>,
2197<code class="computeroutput">decompress.c</code>,
2198<code class="computeroutput">huffman.c</code>,
2199<code class="computeroutput">randtable.c</code> and
2200<code class="computeroutput">libbz2.def</code>. You will also need
2201to name the header files <code class="computeroutput">bzlib.h</code>
2202and <code class="computeroutput">bzlib_private.h</code>.</p>
2203<p>If you don't use VC++, you may need to define the
2204proprocessor symbol
2205<code class="computeroutput">_WIN32</code>.</p>
2206<p>Finally, <code class="computeroutput">dlltest.c</code> is a
2207sample program using the DLL. It has a project file,
2208<code class="computeroutput">dlltest.dsp</code>.</p>
2209<p>If you just want a makefile for Visual C, have a look at
2210<code class="computeroutput">makefile.msc</code>.</p>
2211<p>Be aware that if you compile
2212<code class="computeroutput">bzip2</code> itself on Win32, you must
2213set <code class="computeroutput">BZ_UNIX</code> to 0 and
2214<code class="computeroutput">BZ_LCCWIN32</code> to 1, in the file
2215<code class="computeroutput">bzip2.c</code>, before compiling.
2216Otherwise the resulting binary won't work correctly.</p>
2217<p>I haven't tried any of this stuff myself, but it all looks
2218plausible.</p>
2219</div>
2220</div>
2221<div class="chapter" lang="en">
2222<div class="titlepage"><div><div><h2 class="title">
2223<a name="misc"></a>4. Miscellanea</h2></div></div></div>
2224<div class="toc">
2225<p><b>Table of Contents</b></p>
2226<dl>
2227<dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt>
2228<dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt>
2229<dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt>
2230<dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt>
2231<dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt>
2232</dl>
2233</div>
2234<p>These are just some random thoughts of mine. Your mileage
2235may vary.</p>
2236<div class="sect1" lang="en">
2237<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2238<a name="limits"></a>4.1. Limitations of the compressed file format</h2></div></div></div>
2239<p><code class="computeroutput">bzip2-1.0.X</code>,
2240<code class="computeroutput">0.9.5</code> and
2241<code class="computeroutput">0.9.0</code> use exactly the same file
2242format as the original version,
2243<code class="computeroutput">bzip2-0.1</code>. This decision was
2244made in the interests of stability. Creating yet another
2245incompatible compressed file format would create further
2246confusion and disruption for users.</p>
2247<p>Nevertheless, this is not a painless decision. Development
2248work since the release of
2249<code class="computeroutput">bzip2-0.1</code> in August 1997 has
2250shown complexities in the file format which slow down
2251decompression and, in retrospect, are unnecessary. These
2252are:</p>
2253<div class="itemizedlist"><ul type="bullet">
2254<li style="list-style-type: disc"><p>The run-length encoder, which is the first of the
2255 compression transformations, is entirely irrelevant. The
2256 original purpose was to protect the sorting algorithm from the
2257 very worst case input: a string of repeated symbols. But
2258 algorithm steps Q6a and Q6b in the original Burrows-Wheeler
2259 technical report (SRC-124) show how repeats can be handled
2260 without difficulty in block sorting.</p></li>
2261<li style="list-style-type: disc">
2262<p>The randomisation mechanism doesn't really need to be
2263 there. Udi Manber and Gene Myers published a suffix array
2264 construction algorithm a few years back, which can be employed
2265 to sort any block, no matter how repetitive, in O(N log N)
2266 time. Subsequent work by Kunihiko Sadakane has produced a
2267 derivative O(N (log N)^2) algorithm which usually outperforms
2268 the Manber-Myers algorithm.</p>
2269<p>I could have changed to Sadakane's algorithm, but I find
2270 it to be slower than <code class="computeroutput">bzip2</code>'s
2271 existing algorithm for most inputs, and the randomisation
2272 mechanism protects adequately against bad cases. I didn't
2273 think it was a good tradeoff to make. Partly this is due to
2274 the fact that I was not flooded with email complaints about
2275 <code class="computeroutput">bzip2-0.1</code>'s performance on
2276 repetitive data, so perhaps it isn't a problem for real
2277 inputs.</p>
2278<p>Probably the best long-term solution, and the one I have
2279 incorporated into 0.9.5 and above, is to use the existing
2280 sorting algorithm initially, and fall back to a O(N (log N)^2)
2281 algorithm if the standard algorithm gets into
2282 difficulties.</p>
2283</li>
2284<li style="list-style-type: disc"><p>The compressed file format was never designed to be
2285 handled by a library, and I have had to jump though some hoops
2286 to produce an efficient implementation of decompression. It's
2287 a bit hairy. Try passing
2288 <code class="computeroutput">decompress.c</code> through the C
2289 preprocessor and you'll see what I mean. Much of this
2290 complexity could have been avoided if the compressed size of
2291 each block of data was recorded in the data stream.</p></li>
2292<li style="list-style-type: disc"><p>An Adler-32 checksum, rather than a CRC32 checksum,
2293 would be faster to compute.</p></li>
2294</ul></div>
2295<p>It would be fair to say that the
2296<code class="computeroutput">bzip2</code> format was frozen before I
2297properly and fully understood the performance consequences of
2298doing so.</p>
2299<p>Improvements which I was able to incorporate into 0.9.0,
2300despite using the same file format, are:</p>
2301<div class="itemizedlist"><ul type="bullet">
2302<li style="list-style-type: disc"><p>Single array implementation of the inverse BWT. This
2303 significantly speeds up decompression, presumably because it
2304 reduces the number of cache misses.</p></li>
2305<li style="list-style-type: disc"><p>Faster inverse MTF transform for large MTF values.
2306 The new implementation is based on the notion of sliding blocks
2307 of values.</p></li>
2308<li style="list-style-type: disc"><p><code class="computeroutput">bzip2-0.9.0</code> now reads
2309 and writes files with <code class="computeroutput">fread</code>
2310 and <code class="computeroutput">fwrite</code>; version 0.1 used
2311 <code class="computeroutput">putc</code> and
2312 <code class="computeroutput">getc</code>. Duh! Well, you live
2313 and learn.</p></li>
2314</ul></div>
2315<p>Further ahead, it would be nice to be able to do random
2316access into files. This will require some careful design of
2317compressed file formats.</p>
2318</div>
2319<div class="sect1" lang="en">
2320<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2321<a name="port-issues"></a>4.2. Portability issues</h2></div></div></div>
2322<p>After some consideration, I have decided not to use GNU
2323<code class="computeroutput">autoconf</code> to configure 0.9.5 or
23241.0.</p>
2325<p><code class="computeroutput">autoconf</code>, admirable and
2326wonderful though it is, mainly assists with portability problems
2327between Unix-like platforms. But
2328<code class="computeroutput">bzip2</code> doesn't have much in the
2329way of portability problems on Unix; most of the difficulties
2330appear when porting to the Mac, or to Microsoft's operating
2331systems. <code class="computeroutput">autoconf</code> doesn't help
2332in those cases, and brings in a whole load of new
2333complexity.</p>
2334<p>Most people should be able to compile the library and
2335program under Unix straight out-of-the-box, so to speak,
2336especially if you have a version of GNU C available.</p>
2337<p>There are a couple of
2338<code class="computeroutput">__inline__</code> directives in the
2339code. GNU C (<code class="computeroutput">gcc</code>) should be
2340able to handle them. If you're not using GNU C, your C compiler
2341shouldn't see them at all. If your compiler does, for some
2342reason, see them and doesn't like them, just
2343<code class="computeroutput">#define</code>
2344<code class="computeroutput">__inline__</code> to be
2345<code class="computeroutput">/* */</code>. One easy way to do this
2346is to compile with the flag
2347<code class="computeroutput">-D__inline__=</code>, which should be
2348understood by most Unix compilers.</p>
2349<p>If you still have difficulties, try compiling with the
2350macro <code class="computeroutput">BZ_STRICT_ANSI</code> defined.
2351This should enable you to build the library in a strictly ANSI
2352compliant environment. Building the program itself like this is
2353dangerous and not supported, since you remove
2354<code class="computeroutput">bzip2</code>'s checks against
2355compressing directories, symbolic links, devices, and other
2356not-really-a-file entities. This could cause filesystem
2357corruption!</p>
2358<p>One other thing: if you create a
2359<code class="computeroutput">bzip2</code> binary for public distribution,
2360please consider linking it statically (<code class="computeroutput">gcc
2361-static</code>). This avoids all sorts of library-version
2362issues that others may encounter later on.</p>
2363<p>If you build <code class="computeroutput">bzip2</code> on
2364Win32, you must set <code class="computeroutput">BZ_UNIX</code> to 0
2365and <code class="computeroutput">BZ_LCCWIN32</code> to 1, in the
2366file <code class="computeroutput">bzip2.c</code>, before compiling.
2367Otherwise the resulting binary won't work correctly.</p>
2368</div>
2369<div class="sect1" lang="en">
2370<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2371<a name="bugs"></a>4.3. Reporting bugs</h2></div></div></div>
2372<p>I tried pretty hard to make sure
2373<code class="computeroutput">bzip2</code> is bug free, both by
2374design and by testing. Hopefully you'll never need to read this
2375section for real.</p>
2376<p>Nevertheless, if <code class="computeroutput">bzip2</code> dies
2377with a segmentation fault, a bus error or an internal assertion
2378failure, it will ask you to email me a bug report. Experience from
2379years of feedback of bzip2 users indicates that almost all these
2380problems can be traced to either compiler bugs or hardware
2381problems.</p>
2382<div class="itemizedlist"><ul type="bullet">
2383<li style="list-style-type: disc">
2384<p>Recompile the program with no optimisation, and
2385 see if it works. And/or try a different compiler. I heard all
2386 sorts of stories about various flavours of GNU C (and other
2387 compilers) generating bad code for
2388 <code class="computeroutput">bzip2</code>, and I've run across two
2389 such examples myself.</p>
2390<p>2.7.X versions of GNU C are known to generate bad code
2391 from time to time, at high optimisation levels. If you get
2392 problems, try using the flags
2393 <code class="computeroutput">-O2</code>
2394 <code class="computeroutput">-fomit-frame-pointer</code>
2395 <code class="computeroutput">-fno-strength-reduce</code>. You
2396 should specifically <span class="emphasis"><em>not</em></span> use
2397 <code class="computeroutput">-funroll-loops</code>.</p>
2398<p>You may notice that the Makefile runs six tests as part
2399 of the build process. If the program passes all of these, it's
2400 a pretty good (but not 100%) indication that the compiler has
2401 done its job correctly.</p>
2402</li>
2403<li style="list-style-type: disc">
2404<p>If <code class="computeroutput">bzip2</code>
2405 crashes randomly, and the crashes are not repeatable, you may
2406 have a flaky memory subsystem.
2407 <code class="computeroutput">bzip2</code> really hammers your
2408 memory hierarchy, and if it's a bit marginal, you may get these
2409 problems. Ditto if your disk or I/O subsystem is slowly
2410 failing. Yup, this really does happen.</p>
2411<p>Try using a different machine of the same type, and see
2412 if you can repeat the problem.</p>
2413</li>
2414<li style="list-style-type: disc"><p>This isn't really a bug, but ... If
2415 <code class="computeroutput">bzip2</code> tells you your file is
2416 corrupted on decompression, and you obtained the file via FTP,
2417 there is a possibility that you forgot to tell FTP to do a
2418 binary mode transfer. That absolutely will cause the file to
2419 be non-decompressible. You'll have to transfer it
2420 again.</p></li>
2421</ul></div>
2422<p>If you've incorporated
2423<code class="computeroutput">libbzip2</code> into your own program
2424and are getting problems, please, please, please, check that the
2425parameters you are passing in calls to the library, are correct,
2426and in accordance with what the documentation says is allowable.
2427I have tried to make the library robust against such problems,
2428but I'm sure I haven't succeeded.</p>
2429<p>Finally, if the above comments don't help, you'll have to
2430send me a bug report. Now, it's just amazing how many people
2431will send me a bug report saying something like:</p>
2432<pre class="programlisting">bzip2 crashed with segmentation fault on my machine</pre>
2433<p>and absolutely nothing else. Needless to say, a such a
2434report is <span class="emphasis"><em>totally, utterly, completely and
2435comprehensively 100% useless; a waste of your time, my time, and
2436net bandwidth</em></span>. With no details at all, there's no way
2437I can possibly begin to figure out what the problem is.</p>
2438<p>The rules of the game are: facts, facts, facts. Don't omit
2439them because "oh, they won't be relevant". At the bare
2440minimum:</p>
2441<pre class="programlisting">Machine type. Operating system version.
2442Exact version of bzip2 (do bzip2 -V).
2443Exact version of the compiler used.
2444Flags passed to the compiler.</pre>
2445<p>However, the most important single thing that will help me
2446is the file that you were trying to compress or decompress at the
2447time the problem happened. Without that, my ability to do
2448anything more than speculate about the cause, is limited.</p>
2449</div>
2450<div class="sect1" lang="en">
2451<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2452<a name="package"></a>4.4. Did you get the right package?</h2></div></div></div>
2453<p><code class="computeroutput">bzip2</code> is a resource hog.
2454It soaks up large amounts of CPU cycles and memory. Also, it
2455gives very large latencies. In the worst case, you can feed many
2456megabytes of uncompressed data into the library before getting
2457any compressed output, so this probably rules out applications
2458requiring interactive behaviour.</p>
2459<p>These aren't faults of my implementation, I hope, but more
2460an intrinsic property of the Burrows-Wheeler transform
2461(unfortunately). Maybe this isn't what you want.</p>
2462<p>If you want a compressor and/or library which is faster,
2463uses less memory but gets pretty good compression, and has
2464minimal latency, consider Jean-loup Gailly's and Mark Adler's
2465work, <code class="computeroutput">zlib-1.2.1</code> and
2466<code class="computeroutput">gzip-1.2.4</code>. Look for them at
2467<a href="http://www.zlib.org" target="_top">http://www.zlib.org</a> and
2468<a href="http://www.gzip.org" target="_top">http://www.gzip.org</a>
2469respectively.</p>
2470<p>For something faster and lighter still, you might try Markus F
2471X J Oberhumer's <code class="computeroutput">LZO</code> real-time
2472compression/decompression library, at
2473<a href="http://www.oberhumer.com/opensource" target="_top">http://www.oberhumer.com/opensource</a>.</p>
2474</div>
2475<div class="sect1" lang="en">
2476<div class="titlepage"><div><div><h2 class="title" style="clear: both">
2477<a name="reading"></a>4.5. Further Reading</h2></div></div></div>
2478<p><code class="computeroutput">bzip2</code> is not research
2479work, in the sense that it doesn't present any new ideas.
2480Rather, it's an engineering exercise based on existing
2481ideas.</p>
2482<p>Four documents describe essentially all the ideas behind
2483<code class="computeroutput">bzip2</code>:</p>
2484<div class="literallayout"><p>Michael Burrows and D. J. Wheeler:<br>
2485  "A block-sorting lossless data compression algorithm"<br>
2486   10th May 1994. <br>
2487   Digital SRC Research Report 124.<br>
2488   ftp://ftp.digital.com/pub/DEC/SRC/research-reports/SRC-124.ps.gz<br>
2489   If you have trouble finding it, try searching at the<br>
2490   New Zealand Digital Library, http://www.nzdl.org.<br>
2491<br>
2492Daniel S. Hirschberg and Debra A. LeLewer<br>
2493  "Efficient Decoding of Prefix Codes"<br>
2494   Communications of the ACM, April 1990, Vol 33, Number 4.<br>
2495   You might be able to get an electronic copy of this<br>
2496   from the ACM Digital Library.<br>
2497<br>
2498David J. Wheeler<br>
2499   Program bred3.c and accompanying document bred3.ps.<br>
2500   This contains the idea behind the multi-table Huffman coding scheme.<br>
2501   ftp://ftp.cl.cam.ac.uk/users/djw3/<br>
2502<br>
2503Jon L. Bentley and Robert Sedgewick<br>
2504  "Fast Algorithms for Sorting and Searching Strings"<br>
2505   Available from Sedgewick's web page,<br>
2506   www.cs.princeton.edu/~rs<br>
2507</p></div>
2508<p>The following paper gives valuable additional insights into
2509the algorithm, but is not immediately the basis of any code used
2510in bzip2.</p>
2511<div class="literallayout"><p>Peter Fenwick:<br>
2512   Block Sorting Text Compression<br>
2513   Proceedings of the 19th Australasian Computer Science Conference,<br>
2514     Melbourne, Australia.  Jan 31 - Feb 2, 1996.<br>
2515   ftp://ftp.cs.auckland.ac.nz/pub/peter-f/ACSC96paper.ps</p></div>
2516<p>Kunihiko Sadakane's sorting algorithm, mentioned above, is
2517available from:</p>
2518<div class="literallayout"><p>http://naomi.is.s.u-tokyo.ac.jp/~sada/papers/Sada98b.ps.gz<br>
2519</p></div>
2520<p>The Manber-Myers suffix array construction algorithm is
2521described in a paper available from:</p>
2522<div class="literallayout"><p>http://www.cs.arizona.edu/people/gene/PAPERS/suffix.ps<br>
2523</p></div>
2524<p>Finally, the following papers document some
2525investigations I made into the performance of sorting
2526and decompression algorithms:</p>
2527<div class="literallayout"><p>Julian Seward<br>
2528   On the Performance of BWT Sorting Algorithms<br>
2529   Proceedings of the IEEE Data Compression Conference 2000<br>
2530     Snowbird, Utah.  28-30 March 2000.<br>
2531<br>
2532Julian Seward<br>
2533   Space-time Tradeoffs in the Inverse B-W Transform<br>
2534   Proceedings of the IEEE Data Compression Conference 2001<br>
2535     Snowbird, Utah.  27-29 March 2001.<br>
2536</p></div>
2537</div>
2538</div>
2539</div></body>
2540</html>
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