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82 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book" title="bzip2 and libbzip2, version 1.0.6">
83 <div class="titlepage">
84 <div>
85 <div><h1 class="title">
86 <a name="userman"></a>bzip2 and libbzip2, version 1.0.6</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 1.0.6 of 6 September 2010</p></div>
95 <div><p class="copyright">Copyright © 1996-2010 Julian Seward</p></div>
96 <div><div class="legalnotice" title="Legal Notice">
97 <a name="id537185"></a><p>This program, <code class="computeroutput">bzip2</code>, the
98 associated library <code class="computeroutput">libbzip2</code>, and
99 all documentation, are copyright © 1996-2010 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 class="itemizedlist" type="bullet">
105 <li class="listitem" 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 class="listitem" 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 class="listitem" 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 class="listitem" 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.
160 Programming 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. BZ2_bzCompressInit</a></span></dt>
173 <dt><span class="sect2"><a href="#bzCompress">3.3.2. BZ2_bzCompress</a></span></dt>
174 <dt><span class="sect2"><a href="#bzCompress-end">3.3.3. BZ2_bzCompressEnd</a></span></dt>
175 <dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. BZ2_bzDecompressInit</a></span></dt>
176 <dt><span class="sect2"><a href="#bzDecompress">3.3.5. BZ2_bzDecompress</a></span></dt>
177 <dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. BZ2_bzDecompressEnd</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. BZ2_bzReadOpen</a></span></dt>
182 <dt><span class="sect2"><a href="#bzread">3.4.2. BZ2_bzRead</a></span></dt>
183 <dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. BZ2_bzReadGetUnused</a></span></dt>
184 <dt><span class="sect2"><a href="#bzreadclose">3.4.4. BZ2_bzReadClose</a></span></dt>
185 <dt><span class="sect2"><a href="#bzwriteopen">3.4.5. BZ2_bzWriteOpen</a></span></dt>
186 <dt><span class="sect2"><a href="#bzwrite">3.4.6. BZ2_bzWrite</a></span></dt>
187 <dt><span class="sect2"><a href="#bzwriteclose">3.4.7. BZ2_bzWriteClose</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. BZ2_bzBuffToBuffCompress</a></span></dt>
194 <dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. BZ2_bzBuffToBuffDecompress</a></span></dt>
195 </dl></dd>
196 <dt><span class="sect1"><a href="#zlib-compat">3.6. zlib compatibility functions</a></span></dt>
197 <dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a stdio-free environment</a></span></dt>
198 <dd><dl>
199 <dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of stdio</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" title="1. Introduction">
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
218 using the Burrows-Wheeler block-sorting text compression
219 algorithm, and Huffman coding. Compression is generally
220 considerably better than that achieved by more conventional
221 LZ77/LZ78-based compressors, and approaches the performance of
222 the 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
225 handling compressed data in the
226 <code class="computeroutput">bzip2</code> format. This manual
227 describes both how to use the program and how to work with the
228 library interface. Most of the manual is devoted to this
229 library, not the program, which is good news if your interest is
230 only in the program.</p>
231 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
232 <li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#using" title="2. How to use bzip2">How to use bzip2</a> describes how to use
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 class="listitem" style="list-style-type: disc"><p><a class="xref" href="#libprog" title="3.  Programming with libbzip2">Programming with libbzip2</a> describes the
237 programming interfaces in detail, and</p></li>
238 <li class="listitem" style="list-style-type: disc"><p><a class="xref" href="#misc" title="4. Miscellanea">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" title="2. How to use bzip2">
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
262 else.</p>
263 <div class="sect1" title="2.1. NAME">
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 class="itemizedlist" type="bullet">
267 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzip2</code>,
268 <code class="computeroutput">bunzip2</code> - a block-sorting file
269 compressor, v1.0.6</p></li>
270 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> -
271 decompresses files to stdout</p></li>
272 <li class="listitem" 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" title="2.2. SYNOPSIS">
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 class="itemizedlist" type="bullet">
280 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzip2</code> [
281 -cdfkqstvzVL123456789 ] [ filenames ... ]</p></li>
282 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bunzip2</code> [
283 -fkvsVL ] [ filenames ... ]</p></li>
284 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> [ -s ] [
285 filenames ... ]</p></li>
286 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code>
287 filename</p></li>
288 </ul></div>
289 </div>
290 <div class="sect1" title="2.3. DESCRIPTION">
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
294 using the Burrows-Wheeler block sorting text compression
295 algorithm, and Huffman coding. Compression is generally
296 considerably better than that achieved by more conventional
297 LZ77/LZ78-based compressors, and approaches the performance of
298 the PPM family of statistical compressors.</p>
299 <p>The command-line options are deliberately very similar to
300 those of GNU <code class="computeroutput">gzip</code>, but they are
301 not identical.</p>
302 <p><code class="computeroutput">bzip2</code> expects a list of
303 file names to accompany the command-line flags. Each file is
304 replaced by a compressed version of itself, with the name
305 <code class="computeroutput">original_name.bz2</code>. Each
306 compressed file has the same modification date, permissions, and,
307 when possible, ownership as the corresponding original, so that
308 these properties can be correctly restored at decompression time.
309 File name handling is naive in the sense that there is no
310 mechanism for preserving original file names, permissions,
311 ownerships or dates in filesystems which lack these concepts, or
312 have serious file name length restrictions, such as
313 MS-DOS.</p>
314 <p><code class="computeroutput">bzip2</code> and
315 <code class="computeroutput">bunzip2</code> will by default not
316 overwrite existing files. If you want this to happen, specify
317 the <code class="computeroutput">-f</code> flag.</p>
318 <p>If no file names are specified,
319 <code class="computeroutput">bzip2</code> compresses from standard
320 input to standard output. In this case,
321 <code class="computeroutput">bzip2</code> will decline to write
322 compressed output to a terminal, as this would be entirely
323 incomprehensible and therefore pointless.</p>
324 <p><code class="computeroutput">bunzip2</code> (or
325 <code class="computeroutput">bzip2 -d</code>) decompresses all
326 specified files. Files which were not created by
327 <code class="computeroutput">bzip2</code> will be detected and
328 ignored, and a warning issued.
329 <code class="computeroutput">bzip2</code> attempts to guess the
330 filename for the decompressed file from that of the compressed
331 file as follows:</p>
332 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
333 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">filename.bz2 </code>
334 becomes
335 <code class="computeroutput">filename</code></p></li>
336 <li class="listitem" style="list-style-type: disc"><p><code class="computeroutput">filename.bz </code>
337 becomes
338 <code class="computeroutput">filename</code></p></li>
339 <li class="listitem" 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 class="listitem" 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 class="listitem" 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
355 guess the name of the original file, and uses the original name
356 with <code class="computeroutput">.out</code> appended.</p>
357 <p>As with compression, supplying no filenames causes
358 decompression from standard input to standard output.</p>
359 <p><code class="computeroutput">bunzip2</code> will correctly
360 decompress a file which is the concatenation of two or more
361 compressed files. The result is the concatenation of the
362 corresponding uncompressed files. Integrity testing
363 (<code class="computeroutput">-t</code>) of concatenated compressed
364 files is also supported.</p>
365 <p>You can also compress or decompress files to the standard
366 output by giving the <code class="computeroutput">-c</code> flag.
367 Multiple files may be compressed and decompressed like this. The
368 resulting outputs are fed sequentially to stdout. Compression of
369 multiple files in this manner generates a stream containing
370 multiple compressed file representations. Such a stream can be
371 decompressed correctly only by
372 <code class="computeroutput">bzip2</code> version 0.9.0 or later.
373 Earlier versions of <code class="computeroutput">bzip2</code> will
374 stop 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
377 specified files to the standard output.</p>
378 <p><code class="computeroutput">bzip2</code> will read arguments
379 from the environment variables
380 <code class="computeroutput">BZIP2</code> and
381 <code class="computeroutput">BZIP</code>, in that order, and will
382 process them before any arguments read from the command line.
383 This gives a convenient way to supply default arguments.</p>
384 <p>Compression is always performed, even if the compressed
385 file is slightly larger than the original. Files of less than
386 about one hundred bytes tend to get larger, since the compression
387 mechanism has a constant overhead in the region of 50 bytes.
388 Random data (including the output of most file compressors) is
389 coded at about 8.05 bits per byte, giving an expansion of around
390 0.5%.</p>
391 <p>As a self-check for your protection,
392 <code class="computeroutput">bzip2</code> uses 32-bit CRCs to make
393 sure that the decompressed version of a file is identical to the
394 original. This guards against corruption of the compressed data,
395 and against undetected bugs in
396 <code class="computeroutput">bzip2</code> (hopefully very unlikely).
397 The chances of data corruption going undetected is microscopic,
398 about one chance in four billion for each file processed. Be
399 aware, though, that the check occurs upon decompression, so it
400 can only tell you that something is wrong. It can't help you
401 recover the original uncompressed data. You can use
402 <code class="computeroutput">bzip2recover</code> to try to recover
403 data from damaged files.</p>
404 <p>Return values: 0 for a normal exit, 1 for environmental
405 problems (file not found, invalid flags, I/O errors, etc.), 2
406 to indicate a corrupt compressed file, 3 for an internal
407 consistency error (eg, bug) which caused
408 <code class="computeroutput">bzip2</code> to panic.</p>
409 </div>
410 <div class="sect1" title="2.4. OPTIONS">
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 class="xref" href="#memory-management" title="2.5. 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 class="xref" href="#memory-management" title="2.5. 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" title="2.5. MEMORY MANAGEMENT">
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
509 files in blocks. The block size affects both the compression
510 ratio achieved, and the amount of memory needed for compression
511 and decompression. The flags <code class="computeroutput">-1</code>
512 through <code class="computeroutput">-9</code> specify the block
513 size to be 100,000 bytes through 900,000 bytes (the default)
514 respectively. At decompression time, the block size used for
515 compression is read from the header of the compressed file, and
516 <code class="computeroutput">bunzip2</code> then allocates itself
517 just enough memory to decompress the file. Since block sizes are
518 stored 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
521 ignored during decompression.</p>
522 <p>Compression and decompression requirements, in bytes, can be
523 estimated as:</p>
524 <pre class="programlisting">Compression: 400k + ( 8 x block size )
525
526 Decompression: 100k + ( 4 x block size ), or
527 100k + ( 2.5 x block size )</pre>
528 <p>Larger block sizes give rapidly diminishing marginal
529 returns. Most of the compression comes from the first two or
530 three hundred k of block size, a fact worth bearing in mind when
531 using <code class="computeroutput">bzip2</code> on small machines.
532 It is also important to appreciate that the decompression memory
533 requirement is set at compression time by the choice of block
534 size.</p>
535 <p>For files compressed with the default 900k block size,
536 <code class="computeroutput">bunzip2</code> will require about 3700
537 kbytes to decompress. To support decompression of any file on a
538 4 megabyte machine, <code class="computeroutput">bunzip2</code> has
539 an option to decompress using approximately half this amount of
540 memory, about 2300 kbytes. Decompression speed is also halved,
541 so you should use this option only where necessary. The relevant
542 flag is <code class="computeroutput">-s</code>.</p>
543 <p>In general, try and use the largest block size memory
544 constraints allow, since that maximises the compression achieved.
545 Compression and decompression speed are virtually unaffected by
546 block size.</p>
547 <p>Another significant point applies to files which fit in a
548 single block -- that means most files you'd encounter using a
549 large block size. The amount of real memory touched is
550 proportional to the size of the file, since the file is smaller
551 than a block. For example, compressing a file 20,000 bytes long
552 with the flag <code class="computeroutput">-9</code> will cause the
553 compressor to allocate around 7600k of memory, but only touch
554 400k + 20000 * 8 = 560 kbytes of it. Similarly, the decompressor
555 will allocate 3700k but only touch 100k + 20000 * 4 = 180
556 kbytes.</p>
557 <p>Here is a table which summarises the maximum memory usage
558 for different block sizes. Also recorded is the total compressed
559 size for 14 files of the Calgary Text Compression Corpus
560 totalling 3,141,622 bytes. This column gives some feel for how
561 compression varies with block size. These figures tend to
562 understate the advantage of larger block sizes for larger files,
563 since the Corpus is dominated by smaller files.</p>
564 <pre class="programlisting"> Compress Decompress Decompress Corpus
565 Flag 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" title="2.6. RECOVERING DATA FROM DAMAGED FILES">
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
581 blocks, usually 900kbytes long. Each block is handled
582 independently. If a media or transmission error causes a
583 multi-block <code class="computeroutput">.bz2</code> file to become
584 damaged, it may be possible to recover data from the undamaged
585 blocks in the file.</p>
586 <p>The compressed representation of each block is delimited by
587 a 48-bit pattern, which makes it possible to find the block
588 boundaries with reasonable certainty. Each block also carries
589 its own 32-bit CRC, so damaged blocks can be distinguished from
590 undamaged ones.</p>
591 <p><code class="computeroutput">bzip2recover</code> is a simple
592 program whose purpose is to search for blocks in
593 <code class="computeroutput">.bz2</code> files, and write each block
594 out into its own <code class="computeroutput">.bz2</code> file. You
595 can then use <code class="computeroutput">bzip2 -t</code> to test
596 the integrity of the resulting files, and decompress those which
597 are undamaged.</p>
598 <p><code class="computeroutput">bzip2recover</code> takes a
599 single argument, the name of the damaged file, and writes a
600 number of files <code class="computeroutput">rec0001file.bz2</code>,
601 <code class="computeroutput">rec0002file.bz2</code>, etc, containing
602 the extracted blocks. The output filenames are designed so that
603 the use of wildcards in subsequent processing -- for example,
604 <code class="computeroutput">bzip2 -dc rec*file.bz2 &gt;
605 recovered_data</code> -- lists the files in the correct
606 order.</p>
607 <p><code class="computeroutput">bzip2recover</code> should be of
608 most use dealing with large <code class="computeroutput">.bz2</code>
609 files, as these will contain many blocks. It is clearly futile
610 to use it on damaged single-block files, since a damaged block
611 cannot be recovered. If you wish to minimise any potential data
612 loss through media or transmission errors, you might consider
613 compressing with a smaller block size.</p>
614 </div>
615 <div class="sect1" title="2.7. PERFORMANCE NOTES">
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
619 strings in the file. Because of this, files containing very long
620 runs of repeated symbols, like "aabaabaabaab ..." (repeated
621 several hundred times) may compress more slowly than normal.
622 Versions 0.9.5 and above fare much better than previous versions
623 in this respect. The ratio between worst-case and average-case
624 compression time is in the region of 10:1. For previous
625 versions, this figure was more like 100:1. You can use the
626 <code class="computeroutput">-vvvv</code> option to monitor progress
627 in great detail, if you want.</p>
628 <p>Decompression speed is unaffected by these
629 phenomena.</p>
630 <p><code class="computeroutput">bzip2</code> usually allocates
631 several megabytes of memory to operate in, and then charges all
632 over it in a fairly random fashion. This means that performance,
633 both for compressing and decompressing, is largely determined by
634 the speed at which your machine can service cache misses.
635 Because of this, small changes to the code to reduce the miss
636 rate have been observed to give disproportionately large
637 performance improvements. I imagine
638 <code class="computeroutput">bzip2</code> will perform best on
639 machines with very large caches.</p>
640 </div>
641 <div class="sect1" title="2.8. CAVEATS">
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
646 errors and exit cleanly, but the details of what the problem is
647 sometimes seem rather misleading.</p>
648 <p>This manual page pertains to version 1.0.6 of
649 <code class="computeroutput">bzip2</code>. Compressed data created by
650 this version is entirely forwards and backwards compatible with the
651 previous public releases, versions 0.1pl2, 0.9.0 and 0.9.5, 1.0.0,
652 1.0.1, 1.0.2 and 1.0.3, but with the following exception: 0.9.0 and
653 above can correctly decompress multiple concatenated compressed files.
654 0.1pl2 cannot do this; it will stop after decompressing just the first
655 file in the stream.</p>
656 <p><code class="computeroutput">bzip2recover</code> versions
657 prior to 1.0.2 used 32-bit integers to represent bit positions in
658 compressed files, so it could not handle compressed files more
659 than 512 megabytes long. Versions 1.0.2 and above use 64-bit ints
660 on some platforms which support them (GNU supported targets, and
661 Windows). To establish whether or not
662 <code class="computeroutput">bzip2recover</code> was built with such
663 a limitation, run it without arguments. In any event you can
664 build yourself an unlimited version if you can recompile it with
665 <code class="computeroutput">MaybeUInt64</code> set to be an
666 unsigned 64-bit integer.</p>
667 </div>
668 <div class="sect1" title="2.9. AUTHOR">
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
675 following people: Michael Burrows and David Wheeler (for the
676 block sorting transformation), David Wheeler (again, for the
677 Huffman coder), Peter Fenwick (for the structured coding model in
678 the original <code class="computeroutput">bzip</code>, and many
679 refinements), 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
682 their help, support and advice. See the manual in the source
683 distribution for pointers to sources of documentation. Christian
684 von Roques encouraged me to look for faster sorting algorithms,
685 so as to speed up compression. Bela Lubkin encouraged me to
686 improve the worst-case compression performance.
687 Donna Robinson XMLised the documentation.
688 Many people sent
689 patches, helped with portability problems, lent machines, gave
690 advice and were generally helpful.</p>
691 </div>
692 </div>
693 <div class="chapter" title="3.  Programming with libbzip2">
694 <div class="titlepage"><div><div><h2 class="title">
695 <a name="libprog"></a>3. 
696 Programming 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. BZ2_bzCompressInit</a></span></dt>
711 <dt><span class="sect2"><a href="#bzCompress">3.3.2. BZ2_bzCompress</a></span></dt>
712 <dt><span class="sect2"><a href="#bzCompress-end">3.3.3. BZ2_bzCompressEnd</a></span></dt>
713 <dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. BZ2_bzDecompressInit</a></span></dt>
714 <dt><span class="sect2"><a href="#bzDecompress">3.3.5. BZ2_bzDecompress</a></span></dt>
715 <dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. BZ2_bzDecompressEnd</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. BZ2_bzReadOpen</a></span></dt>
720 <dt><span class="sect2"><a href="#bzread">3.4.2. BZ2_bzRead</a></span></dt>
721 <dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. BZ2_bzReadGetUnused</a></span></dt>
722 <dt><span class="sect2"><a href="#bzreadclose">3.4.4. BZ2_bzReadClose</a></span></dt>
723 <dt><span class="sect2"><a href="#bzwriteopen">3.4.5. BZ2_bzWriteOpen</a></span></dt>
724 <dt><span class="sect2"><a href="#bzwrite">3.4.6. BZ2_bzWrite</a></span></dt>
725 <dt><span class="sect2"><a href="#bzwriteclose">3.4.7. BZ2_bzWriteClose</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. BZ2_bzBuffToBuffCompress</a></span></dt>
732 <dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. BZ2_bzBuffToBuffDecompress</a></span></dt>
733 </dl></dd>
734 <dt><span class="sect1"><a href="#zlib-compat">3.6. zlib compatibility functions</a></span></dt>
735 <dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a stdio-free environment</a></span></dt>
736 <dd><dl>
737 <dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of stdio</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
746 memory use and performance aspects, you'd be well advised to read
747 <a class="xref" href="#using" title="2. How to use bzip2">How to use bzip2</a> as well.</p>
748 <div class="sect1" title="3.1. Top-level structure">
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
752 library for compressing and decompressing data in the
753 <code class="computeroutput">bzip2</code> data format. Although
754 packaged as a single entity, it helps to regard the library as
755 three separate parts: the low level interface, and the high level
756 interface, and some utility functions.</p>
757 <p>The structure of
758 <code class="computeroutput">libbzip2</code>'s interfaces is similar
759 to 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
763 1.0. The intention is to minimise pollution of the namespaces of
764 library clients.</p>
765 <p>To use any part of the library, you need to
766 <code class="computeroutput">#include &lt;bzlib.h&gt;</code>
767 into your sources.</p>
768 <div class="sect2" title="3.1.1. Low-level summary">
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
772 decompressing data in memory. There's no provision for dealing
773 with files, streams or any other I/O mechanisms, just straight
774 memory-to-memory work. In fact, this part of the library can be
775 compiled without inclusion of
776 <code class="computeroutput">stdio.h</code>, which may be helpful
777 for embedded applications.</p>
778 <p>The low-level part of the library has no global variables
779 and 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
784 compression, 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
788 decompression. The <code class="computeroutput">*Init</code>
789 functions allocate memory for compression/decompression and do
790 other initialisations, whilst the
791 <code class="computeroutput">*End</code> functions close down
792 operations 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
796 compress and decompress data from a user-supplied input buffer to
797 a user-supplied output buffer. These buffers can be any size;
798 arbitrary quantities of data are handled by making repeated calls
799 to these functions. This is a flexible mechanism allowing a
800 consumer-pull style of activity, or producer-push, or a mixture
801 of both.</p>
802 </div>
803 <div class="sect2" title="3.1.2. High-level summary">
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
807 low-level interface to facilitate reading and writing
808 <code class="computeroutput">bzip2</code> format files
809 (<code class="computeroutput">.bz2</code> files). The routines
810 provide hooks to facilitate reading files in which the
811 <code class="computeroutput">bzip2</code> data stream is embedded
812 within some larger-scale file structure, or where there are
813 multiple <code class="computeroutput">bzip2</code> data streams
814 concatenated 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
820 supplied. 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
824 available.</p>
825 <p>As with the low-level library, no global variables are used
826 so the library is per se thread-safe. However, if I/O errors
827 occur whilst reading or writing the underlying compressed files,
828 you may have to consult <code class="computeroutput">errno</code> to
829 determine the cause of the error. In that case, you'd need a C
830 library which correctly supports
831 <code class="computeroutput">errno</code> in a multithreaded
832 environment.</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
836 pass them file handles (<code class="computeroutput">FILE*</code>s)
837 which have previously been opened for reading or writing
838 respectively. That avoids portability problems associated with
839 file operations and file attributes, whilst not being much of an
840 imposition on the programmer.</p>
841 </div>
842 <div class="sect2" title="3.1.3. Utility functions summary">
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
848 provided. These compress data in memory from one buffer to
849 another buffer in a single function call. You should assess
850 whether these functions fulfill your memory-to-memory
851 compression/decompression requirements before investing effort in
852 understanding the more general but more complex low-level
853 interface.</p>
854 <p>Yoshioka Tsuneo
855 (<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>) has
856 contributed some functions to give better
857 <code class="computeroutput">zlib</code> compatibility. These
858 functions 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
865 these functions more convenient for simple file reading and
866 writing, than those in the high-level interface. These functions
867 are not (yet) officially part of the library, and are minimally
868 documented here. If they break, you get to keep all the pieces.
869 I hope to document them properly when time permits.</p>
870 <p>Yoshioka also contributed modifications to allow the
871 library to be built as a Windows DLL.</p>
872 </div>
873 </div>
874 <div class="sect1" title="3.2. Error handling">
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
878 situations, including the worst-case situation of decompressing
879 random data. I'm not 100% sure that it can always do this, so
880 you might want to add a signal handler to catch segmentation
881 violations during decompression if you are feeling especially
882 paranoid. I would be interested in hearing more about the
883 robustness of the library to corrupted compressed data.</p>
884 <p>Version 1.0.3 more robust in this respect than any
885 previous version. Investigations with Valgrind (a tool for detecting
886 problems with memory management) indicate
887 that, at least for the few files I tested, all single-bit errors
888 in the decompressed data are caught properly, with no
889 segmentation faults, no uses of uninitialised data, no out of
890 range reads or writes, and no infinite looping in the decompressor.
891 So it's certainly pretty robust, although
892 I wouldn't claim it to be totally bombproof.</p>
893 <p>The file <code class="computeroutput">bzlib.h</code> contains
894 all definitions needed to use the library. In particular, you
895 should definitely not include
896 <code class="computeroutput">bzlib_private.h</code>.</p>
897 <p>In <code class="computeroutput">bzlib.h</code>, the various
898 return values are defined. The following list is not intended as
899 an exhaustive description of the circumstances in which a given
900 value may be returned -- those descriptions are given later.
901 Rather, it is intended to convey the rough meaning of each return
902 value. The first five actions are normal and not intended to
903 denote 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
920 kind.</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" title="3.3. Low-level interface">
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" title="3.3.1. BZ2_bzCompressInit">
1015 <div class="titlepage"><div><div><h3 class="title">
1016 <a name="bzcompress-init"></a>3.3.1. BZ2_bzCompressInit</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
1035 int 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
1041 data pertaining to the compression activity. A
1042 <code class="computeroutput">bz_stream</code> structure should be
1043 allocated and initialised prior to the call. The fields of
1044 <code class="computeroutput">bz_stream</code> comprise the entirety
1045 of the user-visible data. <code class="computeroutput">state</code>
1046 is a pointer to the private data structures required for
1047 compression.</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
1053 argument to all calls to <code class="computeroutput">bzalloc</code>
1054 and <code class="computeroutput">bzfree</code>, but is otherwise
1055 ignored by the library. The call <code class="computeroutput">bzalloc (
1056 opaque, n, m )</code> is expected to return a pointer
1057 <code class="computeroutput">p</code> to <code class="computeroutput">n *
1058 m</code> bytes of memory, and <code class="computeroutput">bzfree (
1059 opaque, 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
1065 use 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
1072 appropriately, as just described. Upon return, the internal
1073 state 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
1078 set to zero. These four fields are used by the library to inform
1079 the caller of the total amount of data passed into and out of the
1080 library, respectively. You should not try to change them. As of
1081 version 1.0, 64-bit counts are maintained, even on 32-bit
1082 platforms, using the <code class="computeroutput">_hi32</code>
1083 fields to store the upper 32 bits of the count. So, for example,
1084 the 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>
1087 specifies the block size to be used for compression. It should
1088 be a value between 1 and 9 inclusive, and the actual block size
1089 used is 100000 x this figure. 9 gives the best compression but
1090 takes most memory.</p>
1091 <p>Parameter <code class="computeroutput">verbosity</code> should
1092 be set to a number between 0 and 4 inclusive. 0 is silent, and
1093 greater numbers give increasingly verbose monitoring/debugging
1094 output. If the library has been compiled with
1095 <code class="computeroutput">-DBZ_NO_STDIO</code>, no such output
1096 will appear for any verbosity setting.</p>
1097 <p>Parameter <code class="computeroutput">workFactor</code>
1098 controls how the compression phase behaves when presented with
1099 worst case, highly repetitive, input data. If compression runs
1100 into difficulties caused by repetitive data, the library switches
1101 from the standard sorting algorithm to a fallback algorithm. The
1102 fallback is slower than the standard algorithm by perhaps a
1103 factor of three, but always behaves reasonably, no matter how bad
1104 the input.</p>
1105 <p>Lower values of <code class="computeroutput">workFactor</code>
1106 reduce the amount of effort the standard algorithm will expend
1107 before resorting to the fallback. You should set this parameter
1108 carefully; too low, and many inputs will be handled by the
1109 fallback algorithm and so compress rather slowly, too high, and
1110 your average-to-worst case compression times can become very
1111 large. The default value of 30 gives reasonable behaviour over a
1112 wide range of circumstances.</p>
1113 <p>Allowable values range from 0 to 250 inclusive. 0 is a
1114 special case, equivalent to using the default value of 30.</p>
1115 <p>Note that the compressed output generated is the same
1116 regardless of whether or not the fallback algorithm is
1117 used.</p>
1118 <p>Be aware also that this parameter may disappear entirely in
1119 future versions of the library. In principle it should be
1120 possible to devise a good way to automatically choose which
1121 algorithm to use. Such a mechanism would render the parameter
1122 obsolete.</p>
1123 <p>Possible return values:</p>
1124 <pre class="programlisting">BZ_CONFIG_ERROR
1125 if the library has been mis-compiled
1126 BZ_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
1131 BZ_MEM_ERROR
1132 if not enough memory is available
1133 BZ_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" title="3.3.2. BZ2_bzCompress">
1141 <div class="titlepage"><div><div><h3 class="title">
1142 <a name="bzCompress"></a>3.3.2. BZ2_bzCompress</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
1145 library. The caller maintains input and output buffers, and
1146 calls <code class="computeroutput">BZ2_bzCompress</code> to transfer
1147 data 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
1151 to be compressed, and <code class="computeroutput">avail_in</code>
1152 should 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
1157 of bytes it has read.</p>
1158 <p>Similarly, <code class="computeroutput">next_out</code> should
1159 point to a buffer in which the compressed data is to be placed,
1160 with <code class="computeroutput">avail_out</code> indicating how
1161 much 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
1166 of bytes output.</p>
1167 <p>You may provide and remove as little or as much data as you
1168 like on each call of
1169 <code class="computeroutput">BZ2_bzCompress</code>. In the limit,
1170 it is acceptable to supply and remove data one byte at a time,
1171 although this would be terribly inefficient. You should always
1172 ensure that at least one byte of output space is available at
1173 each call.</p>
1174 <p>A second purpose of
1175 <code class="computeroutput">BZ2_bzCompress</code> is to request a
1176 change of mode of the compressed stream.</p>
1177 <p>Conceptually, a compressed stream can be in one of four
1178 states: IDLE, RUNNING, FLUSHING and FINISHING. Before
1179 initialisation
1180 (<code class="computeroutput">BZ2_bzCompressInit</code>) and after
1181 termination (<code class="computeroutput">BZ2_bzCompressEnd</code>),
1182 a stream is regarded as IDLE.</p>
1183 <p>Upon initialisation
1184 (<code class="computeroutput">BZ2_bzCompressInit</code>), the stream
1185 is 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;
1188 other 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
1191 the input data it wants to. It will then want to finish up -- in
1192 effect, asking the library to process any data it might have
1193 buffered internally. In this state,
1194 <code class="computeroutput">BZ2_bzCompress</code> will no longer
1195 attempt to read data from
1196 <code class="computeroutput">next_in</code>, but it will want to
1197 write data to <code class="computeroutput">next_out</code>. Because
1198 the output buffer supplied by the user can be arbitrarily small,
1199 the finishing-up operation cannot necessarily be done with a
1200 single 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
1205 the stream's state to FINISHING. Any remaining input (ie,
1206 <code class="computeroutput">next_in[0 .. avail_in-1]</code>) is
1207 compressed and transferred to the output buffer. To do this,
1208 <code class="computeroutput">BZ2_bzCompress</code> must be called
1209 repeatedly until all the output has been consumed. At that
1210 point, <code class="computeroutput">BZ2_bzCompress</code> returns
1211 <code class="computeroutput">BZ_STREAM_END</code>, and the stream's
1212 state is set back to IDLE.
1213 <code class="computeroutput">BZ2_bzCompressEnd</code> should then be
1214 called.</p>
1215 <p>Just to make sure the calling program does not cheat, the
1216 library makes a note of <code class="computeroutput">avail_in</code>
1217 at 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
1220 the time the program has announced its intention to not supply
1221 any more input). By comparing this value with that of
1222 <code class="computeroutput">avail_in</code> over subsequent calls
1223 to <code class="computeroutput">BZ2_bzCompress</code>, the library
1224 can detect any attempts to slip in more data to compress. Any
1225 calls for which this is detected will return
1226 <code class="computeroutput">BZ_SEQUENCE_ERROR</code>. This
1227 indicates 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
1230 remaining input, compress it and terminate the current
1231 (Burrows-Wheeler) compression block. This could be useful for
1232 error control purposes. The mechanism is analogous to that for
1233 finishing: call <code class="computeroutput">BZ2_bzCompress</code>
1234 with an action of <code class="computeroutput">BZ_FLUSH</code>,
1235 remove 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
1238 finishing, <code class="computeroutput">BZ2_bzCompress</code>
1239 detects any attempt to provide more input data once the flush has
1240 begun.</p>
1241 <p>Once the flush is complete, the stream returns to the
1242 normal RUNNING state.</p>
1243 <p>This all sounds pretty complex, but isn't really. Here's a
1244 table which shows which actions are allowable in each state, what
1245 action will be taken, what the next state is, and what the
1246 non-error return values are. Note that you can't explicitly ask
1247 what state the stream is in, but nor do you need to -- it can be
1248 inferred 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
1255 RUNNING/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
1260 RUNNING/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
1266 RUNNING/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
1272 FLUSHING/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
1281 FLUSHING/other
1282 Illegal.
1283 Return value = BZ_SEQUENCE_ERROR
1284
1285 FINISHING/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
1294 FINISHING/other
1295 Illegal.
1296 Return value = BZ_SEQUENCE_ERROR</pre>
1297 <p>That still looks complicated? Well, fair enough. The
1298 usual sequence of calls for compressing a load of data is:</p>
1299 <div class="orderedlist"><ol class="orderedlist" type="1">
1300 <li class="listitem"><p>Get started with
1301 <code class="computeroutput">BZ2_bzCompressInit</code>.</p></li>
1302 <li class="listitem"><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 class="listitem"><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 class="listitem"><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
1316 buffer all at once, you can skip the calls of
1317 <code class="computeroutput">BZ2_bzCompress ( ..., BZ_RUN )</code>
1318 and 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
1322 compression library can accept any data at all (obviously). So
1323 you shouldn't get any error return values from the
1324 <code class="computeroutput">BZ2_bzCompress</code> calls. If you
1325 do, they will be
1326 <code class="computeroutput">BZ_SEQUENCE_ERROR</code>, and indicate
1327 a 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" title="3.3.3. BZ2_bzCompressEnd">
1333 <div class="titlepage"><div><div><h3 class="title">
1334 <a name="bzCompress-end"></a>3.3.3. BZ2_bzCompressEnd</h3></div></div></div>
1335 <pre class="programlisting">int BZ2_bzCompressEnd ( bz_stream *strm );</pre>
1336 <p>Releases all memory associated with a compression
1337 stream.</p>
1338 <p>Possible return values:</p>
1339 <pre class="programlisting">BZ_PARAM_ERROR if strm is NULL or strm-&gt;s is NULL
1340 BZ_OK otherwise</pre>
1341 </div>
1342 <div class="sect2" title="3.3.4. BZ2_bzDecompressInit">
1343 <div class="titlepage"><div><div><h3 class="title">
1344 <a name="bzDecompress-init"></a>3.3.4. BZ2_bzDecompressInit</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
1349 allocated 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
1353 memory 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
1357 internal 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
1364 library will use an alternative decompression algorithm which
1365 uses less memory but at the cost of decompressing more slowly
1366 (roughly speaking, half the speed, but the maximum memory
1367 requirement drops to around 2300k). See <a class="xref" href="#using" title="2. How to use bzip2">How to use bzip2</a>
1368 for more information on memory management.</p>
1369 <p>Note that the amount of memory needed to decompress a
1370 stream cannot be determined until the stream's header has been
1371 read, so even if
1372 <code class="computeroutput">BZ2_bzDecompressInit</code> succeeds, a
1373 subsequent <code class="computeroutput">BZ2_bzDecompress</code>
1374 could 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
1379 BZ_PARAM_ERROR
1380 if ( small != 0 &amp;&amp; small != 1 )
1381 or (verbosity &lt;; 0 || verbosity &gt; 4)
1382 BZ_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" title="3.3.5. BZ2_bzDecompress">
1390 <div class="titlepage"><div><div><h3 class="title">
1391 <a name="bzDecompress"></a>3.3.5. BZ2_bzDecompress</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
1394 library. The caller maintains input and output buffers, and uses
1395 <code class="computeroutput">BZ2_bzDecompress</code> to transfer
1396 data 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
1400 compressed data, and <code class="computeroutput">avail_in</code>
1401 should 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
1406 of bytes it has read.</p>
1407 <p>Similarly, <code class="computeroutput">next_out</code> should
1408 point to a buffer in which the uncompressed output is to be
1409 placed, with <code class="computeroutput">avail_out</code>
1410 indicating 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
1415 of bytes output.</p>
1416 <p>You may provide and remove as little or as much data as you
1417 like on each call of
1418 <code class="computeroutput">BZ2_bzDecompress</code>. In the limit,
1419 it is acceptable to supply and remove data one byte at a time,
1420 although this would be terribly inefficient. You should always
1421 ensure that at least one byte of output space is available at
1422 each call.</p>
1423 <p>Use of <code class="computeroutput">BZ2_bzDecompress</code> is
1424 simpler than
1425 <code class="computeroutput">BZ2_bzCompress</code>.</p>
1426 <p>You should provide input and remove output as described
1427 above, and repeatedly call
1428 <code class="computeroutput">BZ2_bzDecompress</code> until
1429 <code class="computeroutput">BZ_STREAM_END</code> is returned.
1430 Appearance of <code class="computeroutput">BZ_STREAM_END</code>
1431 denotes that <code class="computeroutput">BZ2_bzDecompress</code>
1432 has detected the logical end of the compressed stream.
1433 <code class="computeroutput">BZ2_bzDecompress</code> will not
1434 produce <code class="computeroutput">BZ_STREAM_END</code> until all
1435 output data has been placed into the output buffer, so once
1436 <code class="computeroutput">BZ_STREAM_END</code> appears, you are
1437 guaranteed to have available all the decompressed output, and
1438 <code class="computeroutput">BZ2_bzDecompressEnd</code> can safely
1439 be called.</p>
1440 <p>If case of an error return value, you should call
1441 <code class="computeroutput">BZ2_bzDecompressEnd</code> to clean up
1442 and 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
1447 BZ_DATA_ERROR
1448 if a data integrity error is detected in the compressed stream
1449 BZ_DATA_ERROR_MAGIC
1450 if the compressed stream doesn't begin with the right magic bytes
1451 BZ_MEM_ERROR
1452 if there wasn't enough memory available
1453 BZ_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
1456 BZ_OK
1457 otherwise</pre>
1458 <p>Allowable next actions:</p>
1459 <pre class="programlisting">BZ2_bzDecompress
1460 if BZ_OK was returned
1461 BZ2_bzDecompressEnd
1462 otherwise</pre>
1463 </div>
1464 <div class="sect2" title="3.3.6. BZ2_bzDecompressEnd">
1465 <div class="titlepage"><div><div><h3 class="title">
1466 <a name="bzDecompress-end"></a>3.3.6. BZ2_bzDecompressEnd</h3></div></div></div>
1467 <pre class="programlisting">int BZ2_bzDecompressEnd ( bz_stream *strm );</pre>
1468 <p>Releases all memory associated with a decompression
1469 stream.</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
1473 BZ_OK
1474 otherwise</pre>
1475 <p>Allowable next actions:</p>
1476 <pre class="programlisting"> None.</pre>
1477 </div>
1478 </div>
1479 <div class="sect1" title="3.4. High-level interface">
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
1484 general points.</p>
1485 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
1486 <li class="listitem" 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 class="listitem" 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 class="listitem" 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 class="listitem" 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" title="3.4.1. BZ2_bzReadOpen">
1536 <div class="titlepage"><div><div><h3 class="title">
1537 <a name="bzreadopen"></a>3.4.1. BZ2_bzReadOpen</h3></div></div></div>
1538 <pre class="programlisting">typedef void BZFILE;
1539
1540 BZFILE *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
1546 has 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
1549 to 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
1554 from the file <code class="computeroutput">f</code>. At most
1555 <code class="computeroutput">BZ_MAX_UNUSED</code> bytes may be
1556 supplied like this. If this facility is not required, you should
1557 pass <code class="computeroutput">NULL</code> and
1558 <code class="computeroutput">0</code> for
1559 <code class="computeroutput">unused</code> and
1560 n<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
1566 determined until the file's header has been read. So it is
1567 possible that <code class="computeroutput">BZ2_bzReadOpen</code>
1568 returns <code class="computeroutput">BZ_OK</code> but a subsequent
1569 call 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
1575 BZ_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) )
1580 BZ_IO_ERROR
1581 if ferror(f) is nonzero
1582 BZ_MEM_ERROR
1583 if insufficient memory is available
1584 BZ_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
1589 NULL
1590 otherwise</pre>
1591 <p>Allowable next actions:</p>
1592 <pre class="programlisting">BZ2_bzRead
1593 if bzerror is BZ_OK
1594 BZ2_bzClose
1595 otherwise</pre>
1596 </div>
1597 <div class="sect2" title="3.4.2. BZ2_bzRead">
1598 <div class="titlepage"><div><div><h3 class="title">
1599 <a name="bzread"></a>3.4.2. BZ2_bzRead</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
1605 successful, <code class="computeroutput">bzerror</code> is set to
1606 <code class="computeroutput">BZ_OK</code> and the number of bytes
1607 read 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
1610 bytes read is returned. All other
1611 <code class="computeroutput">bzerror</code> values denote an
1612 error.</p>
1613 <p><code class="computeroutput">BZ2_bzRead</code> will supply
1614 <code class="computeroutput">len</code> bytes, unless the logical
1615 stream end is detected or an error occurs. Because of this, it
1616 is possible to detect the stream end by observing when the number
1617 of bytes returned is less than the number requested.
1618 Nevertheless, this is regarded as inadvisable; you should instead
1619 check <code class="computeroutput">bzerror</code> after every call
1620 and watch out for
1621 <code class="computeroutput">BZ_STREAM_END</code>.</p>
1622 <p>Internally, <code class="computeroutput">BZ2_bzRead</code>
1623 copies data from the compressed file in chunks of size
1624 <code class="computeroutput">BZ_MAX_UNUSED</code> bytes before
1625 decompressing it. If the file contains more bytes than strictly
1626 needed to reach the logical end-of-stream,
1627 <code class="computeroutput">BZ2_bzRead</code> will almost certainly
1628 read some of the trailing data before signalling
1629 <code class="computeroutput">BZ_SEQUENCE_END</code>. To collect the
1630 read but unused data once
1631 <code class="computeroutput">BZ_SEQUENCE_END</code> has appeared,
1632 call <code class="computeroutput">BZ2_bzReadGetUnused</code>
1633 immediately 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
1639 BZ_SEQUENCE_ERROR
1640 if b was opened with BZ2_bzWriteOpen
1641 BZ_IO_ERROR
1642 if there is an error reading from the compressed file
1643 BZ_UNEXPECTED_EOF
1644 if the compressed file ended before
1645 the logical end-of-stream was detected
1646 BZ_DATA_ERROR
1647 if a data integrity error was detected in the compressed stream
1648 BZ_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.
1652 BZ_MEM_ERROR
1653 if insufficient memory was available
1654 BZ_STREAM_END
1655 if the logical end of stream was detected.
1656 BZ_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
1661 undefined
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
1666 collect data from buf, then BZ2_bzReadClose or BZ2_bzReadGetUnused
1667 if bzerror is BZ_SEQUENCE_END
1668 BZ2_bzReadClose
1669 otherwise</pre>
1670 </div>
1671 <div class="sect2" title="3.4.3. BZ2_bzReadGetUnused">
1672 <div class="titlepage"><div><div><h3 class="title">
1673 <a name="bzreadgetunused"></a>3.4.3. BZ2_bzReadGetUnused</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
1677 was not needed to get to the logical end-of-stream.
1678 <code class="computeroutput">*unused</code> is set to the address of
1679 the data, and <code class="computeroutput">*nUnused</code> to the
1680 number of bytes. <code class="computeroutput">*nUnused</code> will
1681 be 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
1692 BZ_SEQUENCE_ERROR
1693 if BZ_STREAM_END has not been signalled
1694 or if b was opened with BZ2_bzWriteOpen
1695 BZ_OK
1696 otherwise</pre>
1697 <p>Allowable next actions:</p>
1698 <pre class="programlisting">BZ2_bzReadClose</pre>
1699 </div>
1700 <div class="sect2" title="3.4.4. BZ2_bzReadClose">
1701 <div class="titlepage"><div><div><h3 class="title">
1702 <a name="bzreadclose"></a>3.4.4. BZ2_bzReadClose</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
1708 handle, so you should do that yourself if appropriate.
1709 <code class="computeroutput">BZ2_bzReadClose</code> should be called
1710 to 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
1715 BZ_OK
1716 otherwise</pre>
1717 <p>Allowable next actions:</p>
1718 <pre class="programlisting">none</pre>
1719 </div>
1720 <div class="sect2" title="3.4.5. BZ2_bzWriteOpen">
1721 <div class="titlepage"><div><div><h3 class="title">
1722 <a name="bzwriteopen"></a>3.4.5. BZ2_bzWriteOpen</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
1729 has 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
1737 call completes successfully,
1738 <code class="computeroutput">BZ_MEM_ERROR</code> cannot be signalled
1739 by 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
1745 BZ_PARAM_ERROR
1746 if f is NULL
1747 or blockSize100k &lt; 1 or blockSize100k &gt; 9
1748 BZ_IO_ERROR
1749 if ferror(f) is nonzero
1750 BZ_MEM_ERROR
1751 if insufficient memory is available
1752 BZ_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
1757 NULL
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)
1763 BZ2_bzWriteClose
1764 otherwise</pre>
1765 </div>
1766 <div class="sect2" title="3.4.6. BZ2_bzWrite">
1767 <div class="titlepage"><div><div><h3 class="title">
1768 <a name="bzwrite"></a>3.4.6. BZ2_bzWrite</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
1771 buffer <code class="computeroutput">buf</code>, eventually to be
1772 compressed 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
1777 BZ_SEQUENCE_ERROR
1778 if b was opened with BZ2_bzReadOpen
1779 BZ_IO_ERROR
1780 if there is an error writing the compressed file.
1781 BZ_OK
1782 otherwise</pre>
1783 </div>
1784 <div class="sect2" title="3.4.7. BZ2_bzWriteClose">
1785 <div class="titlepage"><div><div><h3 class="title">
1786 <a name="bzwriteclose"></a>3.4.7. BZ2_bzWriteClose</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
1792 void 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
1799 far supplied by <code class="computeroutput">BZ2_bzWrite</code>.
1800 The logical end-of-stream markers are also written, so subsequent
1801 calls to <code class="computeroutput">BZ2_bzWrite</code> are
1802 illegal. 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
1805 compressed file, but it is not
1806 <code class="computeroutput">fclose</code>'d.</p>
1807 <p>If <code class="computeroutput">BZ2_bzWriteClose</code> is
1808 called to clean up after an error, the only action is to release
1809 the memory. The library records the error codes issued by
1810 previous calls, so this situation will be detected automatically.
1811 There is no attempt to complete the compression operation, nor to
1812 <code class="computeroutput">fflush</code> the compressed file. You
1813 can force this behaviour to happen even in the case of no error,
1814 by 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
1818 total volume of uncompressed data handled. Similarly,
1819 <code class="computeroutput">nbytes_out</code> will be set to the
1820 total volume of compressed data written. For compatibility with
1821 older versions of the library,
1822 <code class="computeroutput">BZ2_bzWriteClose</code> only yields the
1823 lower 32 bits of these counts. Use
1824 <code class="computeroutput">BZ2_bzWriteClose64</code> if you want
1825 the full 64 bit counts. These two functions are otherwise
1826 absolutely 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
1831 BZ_IO_ERROR
1832 if there is an error writing the compressed file
1833 BZ_OK
1834 otherwise</pre>
1835 </div>
1836 <div class="sect2" title="3.4.8. Handling embedded compressed data streams">
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
1841 some part of a surrounding, larger data stream.</p>
1842 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
1843 <li class="listitem" 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 class="listitem" 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.
1865 As 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
1869 the unused data (copy it into your own buffer somewhere). That
1870 data forms the start of the next compressed stream. To start
1871 uncompressing that next stream, call
1872 <code class="computeroutput">BZ2_bzReadOpen</code> again, feeding in
1873 the unused data via the <code class="computeroutput">unused</code> /
1874 <code class="computeroutput">nUnused</code> parameters. Keep doing
1875 this until <code class="computeroutput">BZ_STREAM_END</code> return
1876 coincides 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
1879 course return no data.</p>
1880 <p>This should give some feel for how the high-level interface
1881 can be used. If you require extra flexibility, you'll have to
1882 bite the bullet and get to grips with the low-level
1883 interface.</p>
1884 </div>
1885 <div class="sect2" title="3.4.9. Standard file-reading/writing code">
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;
1890 BZFILE* b;
1891 int nBuf;
1892 char buf[ /* whatever size you like */ ];
1893 int bzerror;
1894 int nWritten;
1895
1896 f = fopen ( "myfile.bz2", "w" );
1897 if ( !f ) {
1898 /* handle error */
1899 }
1900 b = BZ2_bzWriteOpen( &amp;bzerror, f, 9 );
1901 if (bzerror != BZ_OK) {
1902 BZ2_bzWriteClose ( b );
1903 /* handle error */
1904 }
1905
1906 while ( /* 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
1915 BZ2_bzWriteClose( &amp;bzerror, b );
1916 if (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;
1921 BZFILE* b;
1922 int nBuf;
1923 char buf[ /* whatever size you like */ ];
1924 int bzerror;
1925 int nWritten;
1926
1927 f = fopen ( "myfile.bz2", "r" );
1928 if ( !f ) {
1929 /* handle error */
1930 }
1931 b = BZ2_bzReadOpen ( &amp;bzerror, f, 0, NULL, 0 );
1932 if ( bzerror != BZ_OK ) {
1933 BZ2_bzReadClose ( &amp;bzerror, b );
1934 /* handle error */
1935 }
1936
1937 bzerror = BZ_OK;
1938 while ( 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 }
1944 if ( 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" title="3.5. Utility functions">
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" title="3.5.1. BZ2_bzBuffToBuffCompress">
1956 <div class="titlepage"><div><div><h3 class="title">
1957 <a name="bzbufftobuffcompress"></a>3.5.1. BZ2_bzBuffToBuffCompress</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
1968 destination buffer is big enough,
1969 <code class="computeroutput">*destLen</code> is set to the size of
1970 the compressed data, and <code class="computeroutput">BZ_OK</code>
1971 is 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
1974 returned.</p>
1975 <p>Compression in this manner is a one-shot event, done with a
1976 single call to this function. The resulting compressed data is a
1977 complete <code class="computeroutput">bzip2</code> format data
1978 stream. There is no mechanism for making additional calls to
1979 provide extra input data. If you want that kind of mechanism,
1980 use 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
1987 buffer, allocate an output buffer of size 1% larger than the
1988 uncompressed data, plus six hundred extra bytes.</p>
1989 <p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code>
1990 will not write data at or beyond
1991 <code class="computeroutput">dest[*destLen]</code>, even in case of
1992 buffer overflow.</p>
1993 <p>Possible return values:</p>
1994 <pre class="programlisting">BZ_CONFIG_ERROR
1995 if the library has been mis-compiled
1996 BZ_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
2001 BZ_MEM_ERROR
2002 if insufficient memory is available
2003 BZ_OUTBUFF_FULL
2004 if the size of the compressed data exceeds *destLen
2005 BZ_OK
2006 otherwise</pre>
2007 </div>
2008 <div class="sect2" title="3.5.2. BZ2_bzBuffToBuffDecompress">
2009 <div class="titlepage"><div><div><h3 class="title">
2010 <a name="bzbufftobuffdecompress"></a>3.5.2. BZ2_bzBuffToBuffDecompress</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
2020 destination buffer is big enough,
2021 <code class="computeroutput">*destLen</code> is set to the size of
2022 the uncompressed data, and <code class="computeroutput">BZ_OK</code>
2023 is 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
2026 returned.</p>
2027 <p><code class="computeroutput">source</code> is assumed to hold
2028 a complete <code class="computeroutput">bzip2</code> format data
2029 stream.
2030 <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> tries
2031 to decompress the entirety of the stream into the output
2032 buffer.</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
2038 be known in advance, there is no easy way to guarantee that the
2039 output buffer will be big enough. You may of course make
2040 arrangements in your code to record the size of the uncompressed
2041 data, but such a mechanism is beyond the scope of this
2042 library.</p>
2043 <p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code>
2044 will not write data at or beyond
2045 <code class="computeroutput">dest[*destLen]</code>, even in case of
2046 buffer overflow.</p>
2047 <p>Possible return values:</p>
2048 <pre class="programlisting">BZ_CONFIG_ERROR
2049 if the library has been mis-compiled
2050 BZ_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
2054 BZ_MEM_ERROR
2055 if insufficient memory is available
2056 BZ_OUTBUFF_FULL
2057 if the size of the compressed data exceeds *destLen
2058 BZ_DATA_ERROR
2059 if a data integrity error was detected in the compressed data
2060 BZ_DATA_ERROR_MAGIC
2061 if the compressed data doesn't begin with the right magic bytes
2062 BZ_UNEXPECTED_EOF
2063 if the compressed data ends unexpectedly
2064 BZ_OK
2065 otherwise</pre>
2066 </div>
2067 </div>
2068 <div class="sect1" title="3.6. zlib compatibility functions">
2069 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
2070 <a name="zlib-compat"></a>3.6. zlib compatibility functions</h2></div></div></div>
2071 <p>Yoshioka Tsuneo has contributed some functions to give
2072 better <code class="computeroutput">zlib</code> compatibility.
2073 These 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
2080 functions are not (yet) officially part of the library. If they
2081 break, you get to keep all the pieces. Nevertheless, I think
2082 they work ok.</p>
2083 <pre class="programlisting">typedef void BZFILE;
2084
2085 const 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 );
2088 BZFILE * BZ2_bzdopen ( int fd, const char *mode );</pre>
2089 <p>Opens a <code class="computeroutput">.bz2</code> file for
2090 reading or writing, using either its name or a pre-existing file
2091 descriptor. Analogous to <code class="computeroutput">fopen</code>
2092 and <code class="computeroutput">fdopen</code>.</p>
2093 <pre class="programlisting">int BZ2_bzread ( BZFILE* b, void* buf, int len );
2094 int 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 );
2100 void 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
2103 anything. Analogous to <code class="computeroutput">fflush</code>
2104 and <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
2109 value.</p>
2110 </div>
2111 <div class="sect1" title="3.7. Using the library in a stdio-free environment">
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 stdio-free environment</h2></div></div></div>
2114 <div class="sect2" title="3.7.1. Getting rid of stdio">
2115 <div class="titlepage"><div><div><h3 class="title">
2116 <a name="stdio-bye"></a>3.7.1. Getting rid of stdio</h3></div></div></div>
2117 <p>In a deeply embedded application, you might want to use
2118 just the memory-to-memory functions. You can do this
2119 conveniently by compiling the library with preprocessor symbol
2120 <code class="computeroutput">BZ_NO_STDIO</code> defined. Doing this
2121 gives you a library containing only the following eight
2122 functions:</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" title="3.7.2. Critical error handling">
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
2138 of internal assertion checks which should, needless to say, never
2139 be activated. Nevertheless, if an assertion should fail,
2140 behaviour 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
2143 message:</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, 1.0.6 of 6 September 2010.
2147 Please report it to me at: jseward@bzip.org. If this happened
2148 when you were using some program which uses libbzip2 as a
2149 component, you should also report this bug to the author(s)
2150 of that program. Please make an effort to report this bug;
2151 timely and accurate bug reports eventually lead to higher
2152 quality software. Thanks. Julian Seward, 6 September 2010.
2153 </p>
2154 </blockquote></div>
2155 <p>where <code class="computeroutput">N</code> is some error code
2156 number. If <code class="computeroutput">N == 1007</code>, it also
2157 prints some extra text advising the reader that unreliable memory
2158 is often associated with internal error 1007. (This is a
2159 frequently-observed-phenomenon with versions 1.0.0/1.0.1).</p>
2160 <p><code class="computeroutput">exit(3)</code> is then
2161 called.</p>
2162 <p>For a <code class="computeroutput">stdio</code>-free library,
2163 assertion failures result in a call to a function declared
2164 as:</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
2167 supply 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
2170 be regarded as invalid. You should not attempt to resume normal
2171 operation with them.</p>
2172 <p>You may, of course, change critical error handling to suit
2173 your needs. As I said above, critical errors indicate bugs in
2174 the library and should not occur. All "normal" error situations
2175 are indicated via error return codes from functions, and can be
2176 recovered from.</p>
2177 </div>
2178 </div>
2179 <div class="sect1" title="3.8. Making a Windows DLL">
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
2183 Yoshioka Tsuneo
2184 (<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>), so
2185 you 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++
2188 5.0, open the project file
2189 <code class="computeroutput">libbz2.dsp</code>, and build. That's
2190 all.</p>
2191 <p>If you can't open the project file for some reason, make a
2192 new 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
2201 to name the header files <code class="computeroutput">bzlib.h</code>
2202 and <code class="computeroutput">bzlib_private.h</code>.</p>
2203 <p>If you don't use VC++, you may need to define the
2204 proprocessor symbol
2205 <code class="computeroutput">_WIN32</code>.</p>
2206 <p>Finally, <code class="computeroutput">dlltest.c</code> is a
2207 sample 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
2213 set <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.
2216 Otherwise the resulting binary won't work correctly.</p>
2217 <p>I haven't tried any of this stuff myself, but it all looks
2218 plausible.</p>
2219 </div>
2220 </div>
2221 <div class="chapter" title="4. Miscellanea">
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
2235 may vary.</p>
2236 <div class="sect1" title="4.1. Limitations of the compressed file format">
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
2242 format as the original version,
2243 <code class="computeroutput">bzip2-0.1</code>. This decision was
2244 made in the interests of stability. Creating yet another
2245 incompatible compressed file format would create further
2246 confusion and disruption for users.</p>
2247 <p>Nevertheless, this is not a painless decision. Development
2248 work since the release of
2249 <code class="computeroutput">bzip2-0.1</code> in August 1997 has
2250 shown complexities in the file format which slow down
2251 decompression and, in retrospect, are unnecessary. These
2252 are:</p>
2253 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
2254 <li class="listitem" 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 class="listitem" 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 class="listitem" 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 class="listitem" 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
2297 properly and fully understood the performance consequences of
2298 doing so.</p>
2299 <p>Improvements which I was able to incorporate into 0.9.0,
2300 despite using the same file format, are:</p>
2301 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
2302 <li class="listitem" 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 class="listitem" 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 class="listitem" 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
2316 access into files. This will require some careful design of
2317 compressed file formats.</p>
2318 </div>
2319 <div class="sect1" title="4.2. Portability issues">
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
2324 1.0.</p>
2325 <p><code class="computeroutput">autoconf</code>, admirable and
2326 wonderful though it is, mainly assists with portability problems
2327 between Unix-like platforms. But
2328 <code class="computeroutput">bzip2</code> doesn't have much in the
2329 way of portability problems on Unix; most of the difficulties
2330 appear when porting to the Mac, or to Microsoft's operating
2331 systems. <code class="computeroutput">autoconf</code> doesn't help
2332 in those cases, and brings in a whole load of new
2333 complexity.</p>
2334 <p>Most people should be able to compile the library and
2335 program under Unix straight out-of-the-box, so to speak,
2336 especially 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
2339 code. GNU C (<code class="computeroutput">gcc</code>) should be
2340 able to handle them. If you're not using GNU C, your C compiler
2341 shouldn't see them at all. If your compiler does, for some
2342 reason, 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
2346 is to compile with the flag
2347 <code class="computeroutput">-D__inline__=</code>, which should be
2348 understood by most Unix compilers.</p>
2349 <p>If you still have difficulties, try compiling with the
2350 macro <code class="computeroutput">BZ_STRICT_ANSI</code> defined.
2351 This should enable you to build the library in a strictly ANSI
2352 compliant environment. Building the program itself like this is
2353 dangerous and not supported, since you remove
2354 <code class="computeroutput">bzip2</code>'s checks against
2355 compressing directories, symbolic links, devices, and other
2356 not-really-a-file entities. This could cause filesystem
2357 corruption!</p>
2358 <p>One other thing: if you create a
2359 <code class="computeroutput">bzip2</code> binary for public distribution,
2360 please consider linking it statically (<code class="computeroutput">gcc
2361 -static</code>). This avoids all sorts of library-version
2362 issues that others may encounter later on.</p>
2363 <p>If you build <code class="computeroutput">bzip2</code> on
2364 Win32, you must set <code class="computeroutput">BZ_UNIX</code> to 0
2365 and <code class="computeroutput">BZ_LCCWIN32</code> to 1, in the
2366 file <code class="computeroutput">bzip2.c</code>, before compiling.
2367 Otherwise the resulting binary won't work correctly.</p>
2368 </div>
2369 <div class="sect1" title="4.3. Reporting bugs">
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
2374 design and by testing. Hopefully you'll never need to read this
2375 section for real.</p>
2376 <p>Nevertheless, if <code class="computeroutput">bzip2</code> dies
2377 with a segmentation fault, a bus error or an internal assertion
2378 failure, it will ask you to email me a bug report. Experience from
2379 years of feedback of bzip2 users indicates that almost all these
2380 problems can be traced to either compiler bugs or hardware
2381 problems.</p>
2382 <div class="itemizedlist"><ul class="itemizedlist" type="bullet">
2383 <li class="listitem" 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 class="listitem" 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 class="listitem" 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
2424 and are getting problems, please, please, please, check that the
2425 parameters you are passing in calls to the library, are correct,
2426 and in accordance with what the documentation says is allowable.
2427 I have tried to make the library robust against such problems,
2428 but I'm sure I haven't succeeded.</p>
2429 <p>Finally, if the above comments don't help, you'll have to
2430 send me a bug report. Now, it's just amazing how many people
2431 will 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
2434 report is <span class="emphasis"><em>totally, utterly, completely and
2435 comprehensively 100% useless; a waste of your time, my time, and
2436 net bandwidth</em></span>. With no details at all, there's no way
2437 I 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
2439 them because "oh, they won't be relevant". At the bare
2440 minimum:</p>
2441 <pre class="programlisting">Machine type. Operating system version.
2442 Exact version of bzip2 (do bzip2 -V).
2443 Exact version of the compiler used.
2444 Flags passed to the compiler.</pre>
2445 <p>However, the most important single thing that will help me
2446 is the file that you were trying to compress or decompress at the
2447 time the problem happened. Without that, my ability to do
2448 anything more than speculate about the cause, is limited.</p>
2449 </div>
2450 <div class="sect1" title="4.4. Did you get the right package?">
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.
2454 It soaks up large amounts of CPU cycles and memory. Also, it
2455 gives very large latencies. In the worst case, you can feed many
2456 megabytes of uncompressed data into the library before getting
2457 any compressed output, so this probably rules out applications
2458 requiring interactive behaviour.</p>
2459 <p>These aren't faults of my implementation, I hope, but more
2460 an 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,
2463 uses less memory but gets pretty good compression, and has
2464 minimal latency, consider Jean-loup Gailly's and Mark Adler's
2465 work, <code class="computeroutput">zlib-1.2.1</code> and
2466 <code class="computeroutput">gzip-1.2.4</code>. Look for them at
2467 <a class="ulink" href="http://www.zlib.org" target="_top">http://www.zlib.org</a> and
2468 <a class="ulink" href="http://www.gzip.org" target="_top">http://www.gzip.org</a>
2469 respectively.</p>
2470 <p>For something faster and lighter still, you might try Markus F
2471 X J Oberhumer's <code class="computeroutput">LZO</code> real-time
2472 compression/decompression library, at
2473 <a class="ulink" href="http://www.oberhumer.com/opensource" target="_top">http://www.oberhumer.com/opensource</a>.</p>
2474 </div>
2475 <div class="sect1" title="4.5. Further Reading">
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
2479 work, in the sense that it doesn't present any new ideas.
2480 Rather, it's an engineering exercise based on existing
2481 ideas.</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>
2492 Daniel 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>
2498 David 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>
2503 Jon 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
2509 the algorithm, but is not immediately the basis of any code used
2510 in 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
2517 available 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
2521 described 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
2525 investigations I made into the performance of sorting
2526 and 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>
2532 Julian 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>