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    82. 

  82. <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en">
    83. 

  83. <div class="titlepage">
    84. 

  84. <div>
    85. 

  85. <div><h1 class="title">
    86. 

  86. <a name="userman"></a>bzip2 and libbzip2, version 1.0.5</h1></div>
    87. 

  87. <div><h2 class="subtitle">A program and library for data compression</h2></div>
    88. 

  88. <div><div class="authorgroup"><div class="author">
    89. 

  89. <h3 class="author">
    90. 

  90. <span class="firstname">Julian</span> <span class="surname">Seward</span>
    91. 

  91. </h3>
    92. 

  92. <div class="affiliation"><span class="orgname">http://www.bzip.org<br></span></div>
    93. 

  93. </div></div></div>
    94. 

  94. <div><p class="releaseinfo">Version 1.0.5 of 10 December 2007</p></div>
    95. 

  95. <div><p class="copyright">Copyright Š 1996-2007 Julian Seward</p></div>
    96. 

  96. <div><div class="legalnotice">
    97. 

  97. <a name="id2499833"></a><p>This program, <code class="computeroutput">bzip2</code>, the
    98. 

  98.   associated library <code class="computeroutput">libbzip2</code>, and
    99. 

  99.   all documentation, are copyright Š 1996-2007 Julian Seward.
    100. 

  100.   All rights reserved.</p>
    101. 

  101. <p>Redistribution and use in source and binary forms, with
    102. 

  102.   or without modification, are permitted provided that the
    103. 

  103.   following conditions are met:</p>
    104. 

  104. <div class="itemizedlist"><ul type="bullet">
    105. 

  105. <li style="list-style-type: disc"><p>Redistributions of source code must retain the
    106. 

  106.    above copyright notice, this list of conditions and the
    107. 

  107.    following disclaimer.</p></li>
    108. 

  108. <li style="list-style-type: disc"><p>The origin of this software must not be
    109. 

  109.    misrepresented; you must not claim that you wrote the original
    110. 

  110.    software.  If you use this software in a product, an
    111. 

  111.    acknowledgment in the product documentation would be
    112. 

  112.    appreciated but is not required.</p></li>
    113. 

  113. <li style="list-style-type: disc"><p>Altered source versions must be plainly marked
    114. 

  114.    as such, and must not be misrepresented as being the original
    115. 

  115.    software.</p></li>
    116. 

  116. <li style="list-style-type: disc"><p>The name of the author may not be used to
    117. 

  117.    endorse or promote products derived from this software without
    118. 

  118.    specific prior written permission.</p></li>
    119. 

  119. </ul></div>
    120. 

  120. <p>THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY
    121. 

  121.   EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
    122. 

  122.   THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
    123. 

  123.   PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
    124. 

  124.   AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
    125. 

  125.   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
    126. 

  126.   TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    127. 

  127.   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
    128. 

  128.   ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    129. 

  129.   LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
    130. 

  130.   IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
    131. 

  131.   THE POSSIBILITY OF SUCH DAMAGE.</p>
    132. 

  132. <p>PATENTS: To the best of my knowledge,
    133. 

  133.  <code class="computeroutput">bzip2</code> and
    134. 

  134.  <code class="computeroutput">libbzip2</code> do not use any patented
    135. 

  135.  algorithms.  However, I do not have the resources to carry
    136. 

  136.  out a patent search.  Therefore I cannot give any guarantee of
    137. 

  137.  the above statement.
    138. 

  138.  </p>
    139. 

  139. </div></div>
    140. 

  140. </div>
    141. 

  141. <hr>
    142. 

  142. </div>
    143. 

  143. <div class="toc">
    144. 

  144. <p><b>Table of Contents</b></p>
    145. 

  145. <dl>
    146. 

  146. <dt><span class="chapter"><a href="#intro">1. Introduction</a></span></dt>
    147. 

  147. <dt><span class="chapter"><a href="#using">2. How to use bzip2</a></span></dt>
    148. 

  148. <dd><dl>
    149. 

  149. <dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt>
    150. 

  150. <dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt>
    151. 

  151. <dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt>
    152. 

  152. <dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt>
    153. 

  153. <dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt>
    154. 

  154. <dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt>
    155. 

  155. <dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt>
    156. 

  156. <dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt>
    157. 

  157. <dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt>
    158. 

  158. </dl></dd>
    159. 

  159. <dt><span class="chapter"><a href="#libprog">3. 
    160. 

  160. Programming with <code class="computeroutput">libbzip2</code>
    161. 

  161. </a></span></dt>
    162. 

  162. <dd><dl>
    163. 

  163. <dt><span class="sect1"><a href="#top-level">3.1. Top-level structure</a></span></dt>
    164. 

  164. <dd><dl>
    165. 

  165. <dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt>
    166. 

  166. <dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt>
    167. 

  167. <dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt>
    168. 

  168. </dl></dd>
    169. 

  169. <dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt>
    170. 

  170. <dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt>
    171. 

  171. <dd><dl>
    172. 

  172. <dt><span class="sect2"><a href="#bzcompress-init">3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></a></span></dt>
    173. 

  173. <dt><span class="sect2"><a href="#bzCompress">3.3.2. <code class="computeroutput">BZ2_bzCompress</code></a></span></dt>
    174. 

  174. <dt><span class="sect2"><a href="#bzCompress-end">3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></a></span></dt>
    175. 

  175. <dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></a></span></dt>
    176. 

  176. <dt><span class="sect2"><a href="#bzDecompress">3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></a></span></dt>
    177. 

  177. <dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></a></span></dt>
    178. 

  178. </dl></dd>
    179. 

  179. <dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt>
    180. 

  180. <dd><dl>
    181. 

  181. <dt><span class="sect2"><a href="#bzreadopen">3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></a></span></dt>
    182. 

  182. <dt><span class="sect2"><a href="#bzread">3.4.2. <code class="computeroutput">BZ2_bzRead</code></a></span></dt>
    183. 

  183. <dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></a></span></dt>
    184. 

  184. <dt><span class="sect2"><a href="#bzreadclose">3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></a></span></dt>
    185. 

  185. <dt><span class="sect2"><a href="#bzwriteopen">3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></a></span></dt>
    186. 

  186. <dt><span class="sect2"><a href="#bzwrite">3.4.6. <code class="computeroutput">BZ2_bzWrite</code></a></span></dt>
    187. 

  187. <dt><span class="sect2"><a href="#bzwriteclose">3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></a></span></dt>
    188. 

  188. <dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt>
    189. 

  189. <dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt>
    190. 

  190. </dl></dd>
    191. 

  191. <dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt>
    192. 

  192. <dd><dl>
    193. 

  193. <dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></a></span></dt>
    194. 

  194. <dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></a></span></dt>
    195. 

  195. </dl></dd>
    196. 

  196. <dt><span class="sect1"><a href="#zlib-compat">3.6. <code class="computeroutput">zlib</code> compatibility functions</a></span></dt>
    197. 

  197. <dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</a></span></dt>
    198. 

  198. <dd><dl>
    199. 

  199. <dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of <code class="computeroutput">stdio</code></a></span></dt>
    200. 

  200. <dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt>
    201. 

  201. </dl></dd>
    202. 

  202. <dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt>
    203. 

  203. </dl></dd>
    204. 

  204. <dt><span class="chapter"><a href="#misc">4. Miscellanea</a></span></dt>
    205. 

  205. <dd><dl>
    206. 

  206. <dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt>
    207. 

  207. <dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt>
    208. 

  208. <dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt>
    209. 

  209. <dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt>
    210. 

  210. <dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt>
    211. 

  211. </dl></dd>
    212. 

  212. </dl>
    213. 

  213. </div>
    214. 

  214. <div class="chapter" lang="en">
    215. 

  215. <div class="titlepage"><div><div><h2 class="title">
    216. 

  216. <a name="intro"></a>1. Introduction</h2></div></div></div>
    217. 

  217. <p><code class="computeroutput">bzip2</code> compresses files
    218. 

  218. using the Burrows-Wheeler block-sorting text compression
    219. 

  219. algorithm, and Huffman coding.  Compression is generally
    220. 

  220. considerably better than that achieved by more conventional
    221. 

  221. LZ77/LZ78-based compressors, and approaches the performance of
    222. 

  222. the PPM family of statistical compressors.</p>
    223. 

  223. <p><code class="computeroutput">bzip2</code> is built on top of
    224. 

  224. <code class="computeroutput">libbzip2</code>, a flexible library for
    225. 

  225. handling compressed data in the
    226. 

  226. <code class="computeroutput">bzip2</code> format.  This manual
    227. 

  227. describes both how to use the program and how to work with the
    228. 

  228. library interface.  Most of the manual is devoted to this
    229. 

  229. library, not the program, which is good news if your interest is
    230. 

  230. only in the program.</p>
    231. 

  231. <div class="itemizedlist"><ul type="bullet">
    232. 

  232. <li style="list-style-type: disc"><p><a href="#using">How to use bzip2</a> describes how to use
    233. 

  233.  <code class="computeroutput">bzip2</code>; this is the only part
    234. 

  234.  you need to read if you just want to know how to operate the
    235. 

  235.  program.</p></li>
    236. 

  236. <li style="list-style-type: disc"><p><a href="#libprog">Programming with libbzip2</a> describes the
    237. 

  237.  programming interfaces in detail, and</p></li>
    238. 

  238. <li style="list-style-type: disc"><p><a href="#misc">Miscellanea</a> records some
    239. 

  239.  miscellaneous notes which I thought ought to be recorded
    240. 

  240.  somewhere.</p></li>
    241. 

  241. </ul></div>
    242. 

  242. </div>
    243. 

  243. <div class="chapter" lang="en">
    244. 

  244. <div class="titlepage"><div><div><h2 class="title">
    245. 

  245. <a name="using"></a>2. How to use bzip2</h2></div></div></div>
    246. 

  246. <div class="toc">
    247. 

  247. <p><b>Table of Contents</b></p>
    248. 

  248. <dl>
    249. 

  249. <dt><span class="sect1"><a href="#name">2.1. NAME</a></span></dt>
    250. 

  250. <dt><span class="sect1"><a href="#synopsis">2.2. SYNOPSIS</a></span></dt>
    251. 

  251. <dt><span class="sect1"><a href="#description">2.3. DESCRIPTION</a></span></dt>
    252. 

  252. <dt><span class="sect1"><a href="#options">2.4. OPTIONS</a></span></dt>
    253. 

  253. <dt><span class="sect1"><a href="#memory-management">2.5. MEMORY MANAGEMENT</a></span></dt>
    254. 

  254. <dt><span class="sect1"><a href="#recovering">2.6. RECOVERING DATA FROM DAMAGED FILES</a></span></dt>
    255. 

  255. <dt><span class="sect1"><a href="#performance">2.7. PERFORMANCE NOTES</a></span></dt>
    256. 

  256. <dt><span class="sect1"><a href="#caveats">2.8. CAVEATS</a></span></dt>
    257. 

  257. <dt><span class="sect1"><a href="#author">2.9. AUTHOR</a></span></dt>
    258. 

  258. </dl>
    259. 

  259. </div>
    260. 

  260. <p>This chapter contains a copy of the
    261. 

  261. <code class="computeroutput">bzip2</code> man page, and nothing
    262. 

  262. else.</p>
    263. 

  263. <div class="sect1" lang="en">
    264. 

  264. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    265. 

  265. <a name="name"></a>2.1. NAME</h2></div></div></div>
    266. 

  266. <div class="itemizedlist"><ul type="bullet">
    267. 

  267. <li style="list-style-type: disc"><p><code class="computeroutput">bzip2</code>,
    268. 

  268.   <code class="computeroutput">bunzip2</code> - a block-sorting file
    269. 

  269.   compressor, v1.0.4</p></li>
    270. 

  270. <li style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> -
    271. 

  271.    decompresses files to stdout</p></li>
    272. 

  272. <li style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code> -
    273. 

  273.    recovers data from damaged bzip2 files</p></li>
    274. 

  274. </ul></div>
    275. 

  275. </div>
    276. 

  276. <div class="sect1" lang="en">
    277. 

  277. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    278. 

  278. <a name="synopsis"></a>2.2. SYNOPSIS</h2></div></div></div>
    279. 

  279. <div class="itemizedlist"><ul type="bullet">
    280. 

  280. <li style="list-style-type: disc"><p><code class="computeroutput">bzip2</code> [
    281. 

  281.   -cdfkqstvzVL123456789 ] [ filenames ...  ]</p></li>
    282. 

  282. <li style="list-style-type: disc"><p><code class="computeroutput">bunzip2</code> [
    283. 

  283.   -fkvsVL ] [ filenames ...  ]</p></li>
    284. 

  284. <li style="list-style-type: disc"><p><code class="computeroutput">bzcat</code> [ -s ] [
    285. 

  285.   filenames ...  ]</p></li>
    286. 

  286. <li style="list-style-type: disc"><p><code class="computeroutput">bzip2recover</code>
    287. 

  287.   filename</p></li>
    288. 

  288. </ul></div>
    289. 

  289. </div>
    290. 

  290. <div class="sect1" lang="en">
    291. 

  291. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    292. 

  292. <a name="description"></a>2.3. DESCRIPTION</h2></div></div></div>
    293. 

  293. <p><code class="computeroutput">bzip2</code> compresses files
    294. 

  294. using the Burrows-Wheeler block sorting text compression
    295. 

  295. algorithm, and Huffman coding.  Compression is generally
    296. 

  296. considerably better than that achieved by more conventional
    297. 

  297. LZ77/LZ78-based compressors, and approaches the performance of
    298. 

  298. the PPM family of statistical compressors.</p>
    299. 

  299. <p>The command-line options are deliberately very similar to
    300. 

  300. those of GNU <code class="computeroutput">gzip</code>, but they are
    301. 

  301. not identical.</p>
    302. 

  302. <p><code class="computeroutput">bzip2</code> expects a list of
    303. 

  303. file names to accompany the command-line flags.  Each file is
    304. 

  304. replaced by a compressed version of itself, with the name
    305. 

  305. <code class="computeroutput">original_name.bz2</code>.  Each
    306. 

  306. compressed file has the same modification date, permissions, and,
    307. 

  307. when possible, ownership as the corresponding original, so that
    308. 

  308. these properties can be correctly restored at decompression time.
    309. 

  309. File name handling is naive in the sense that there is no
    310. 

  310. mechanism for preserving original file names, permissions,
    311. 

  311. ownerships or dates in filesystems which lack these concepts, or
    312. 

  312. have serious file name length restrictions, such as
    313. 

  313. MS-DOS.</p>
    314. 

  314. <p><code class="computeroutput">bzip2</code> and
    315. 

  315. <code class="computeroutput">bunzip2</code> will by default not
    316. 

  316. overwrite existing files.  If you want this to happen, specify
    317. 

  317. the <code class="computeroutput">-f</code> flag.</p>
    318. 

  318. <p>If no file names are specified,
    319. 

  319. <code class="computeroutput">bzip2</code> compresses from standard
    320. 

  320. input to standard output.  In this case,
    321. 

  321. <code class="computeroutput">bzip2</code> will decline to write
    322. 

  322. compressed output to a terminal, as this would be entirely
    323. 

  323. incomprehensible and therefore pointless.</p>
    324. 

  324. <p><code class="computeroutput">bunzip2</code> (or
    325. 

  325. <code class="computeroutput">bzip2 -d</code>) decompresses all
    326. 

  326. specified files.  Files which were not created by
    327. 

  327. <code class="computeroutput">bzip2</code> will be detected and
    328. 

  328. ignored, and a warning issued.
    329. 

  329. <code class="computeroutput">bzip2</code> attempts to guess the
    330. 

  330. filename for the decompressed file from that of the compressed
    331. 

  331. file as follows:</p>
    332. 

  332. <div class="itemizedlist"><ul type="bullet">
    333. 

  333. <li style="list-style-type: disc"><p><code class="computeroutput">filename.bz2 </code>
    334. 

  334.   becomes
    335. 

  335.   <code class="computeroutput">filename</code></p></li>
    336. 

  336. <li style="list-style-type: disc"><p><code class="computeroutput">filename.bz </code>
    337. 

  337.   becomes
    338. 

  338.   <code class="computeroutput">filename</code></p></li>
    339. 

  339. <li style="list-style-type: disc"><p><code class="computeroutput">filename.tbz2</code>
    340. 

  340.   becomes
    341. 

  341.   <code class="computeroutput">filename.tar</code></p></li>
    342. 

  342. <li style="list-style-type: disc"><p><code class="computeroutput">filename.tbz </code>
    343. 

  343.   becomes
    344. 

  344.   <code class="computeroutput">filename.tar</code></p></li>
    345. 

  345. <li style="list-style-type: disc"><p><code class="computeroutput">anyothername </code>
    346. 

  346.   becomes
    347. 

  347.   <code class="computeroutput">anyothername.out</code></p></li>
    348. 

  348. </ul></div>
    349. 

  349. <p>If the file does not end in one of the recognised endings,
    350. 

  350. <code class="computeroutput">.bz2</code>,
    351. 

  351. <code class="computeroutput">.bz</code>,
    352. 

  352. <code class="computeroutput">.tbz2</code> or
    353. 

  353. <code class="computeroutput">.tbz</code>,
    354. 

  354. <code class="computeroutput">bzip2</code> complains that it cannot
    355. 

  355. guess the name of the original file, and uses the original name
    356. 

  356. with <code class="computeroutput">.out</code> appended.</p>
    357. 

  357. <p>As with compression, supplying no filenames causes
    358. 

  358. decompression from standard input to standard output.</p>
    359. 

  359. <p><code class="computeroutput">bunzip2</code> will correctly
    360. 

  360. decompress a file which is the concatenation of two or more
    361. 

  361. compressed files.  The result is the concatenation of the
    362. 

  362. corresponding uncompressed files.  Integrity testing
    363. 

  363. (<code class="computeroutput">-t</code>) of concatenated compressed
    364. 

  364. files is also supported.</p>
    365. 

  365. <p>You can also compress or decompress files to the standard
    366. 

  366. output by giving the <code class="computeroutput">-c</code> flag.
    367. 

  367. Multiple files may be compressed and decompressed like this.  The
    368. 

  368. resulting outputs are fed sequentially to stdout.  Compression of
    369. 

  369. multiple files in this manner generates a stream containing
    370. 

  370. multiple compressed file representations.  Such a stream can be
    371. 

  371. decompressed correctly only by
    372. 

  372. <code class="computeroutput">bzip2</code> version 0.9.0 or later.
    373. 

  373. Earlier versions of <code class="computeroutput">bzip2</code> will
    374. 

  374. stop after decompressing the first file in the stream.</p>
    375. 

  375. <p><code class="computeroutput">bzcat</code> (or
    376. 

  376. <code class="computeroutput">bzip2 -dc</code>) decompresses all
    377. 

  377. specified files to the standard output.</p>
    378. 

  378. <p><code class="computeroutput">bzip2</code> will read arguments
    379. 

  379. from the environment variables
    380. 

  380. <code class="computeroutput">BZIP2</code> and
    381. 

  381. <code class="computeroutput">BZIP</code>, in that order, and will
    382. 

  382. process them before any arguments read from the command line.
    383. 

  383. This gives a convenient way to supply default arguments.</p>
    384. 

  384. <p>Compression is always performed, even if the compressed
    385. 

  385. file is slightly larger than the original.  Files of less than
    386. 

  386. about one hundred bytes tend to get larger, since the compression
    387. 

  387. mechanism has a constant overhead in the region of 50 bytes.
    388. 

  388. Random data (including the output of most file compressors) is
    389. 

  389. coded at about 8.05 bits per byte, giving an expansion of around
    390. 

  390. 0.5%.</p>
    391. 

  391. <p>As a self-check for your protection,
    392. 

  392. <code class="computeroutput">bzip2</code> uses 32-bit CRCs to make
    393. 

  393. sure that the decompressed version of a file is identical to the
    394. 

  394. original.  This guards against corruption of the compressed data,
    395. 

  395. and against undetected bugs in
    396. 

  396. <code class="computeroutput">bzip2</code> (hopefully very unlikely).
    397. 

  397. The chances of data corruption going undetected is microscopic,
    398. 

  398. about one chance in four billion for each file processed.  Be
    399. 

  399. aware, though, that the check occurs upon decompression, so it
    400. 

  400. can only tell you that something is wrong.  It can't help you
    401. 

  401. recover the original uncompressed data.  You can use
    402. 

  402. <code class="computeroutput">bzip2recover</code> to try to recover
    403. 

  403. data from damaged files.</p>
    404. 

  404. <p>Return values: 0 for a normal exit, 1 for environmental
    405. 

  405. problems (file not found, invalid flags, I/O errors, etc.), 2
    406. 

  406. to indicate a corrupt compressed file, 3 for an internal
    407. 

  407. consistency error (eg, bug) which caused
    408. 

  408. <code class="computeroutput">bzip2</code> to panic.</p>
    409. 

  409. </div>
    410. 

  410. <div class="sect1" lang="en">
    411. 

  411. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    412. 

  412. <a name="options"></a>2.4. OPTIONS</h2></div></div></div>
    413. 

  413. <div class="variablelist"><dl>
    414. 

  414. <dt><span class="term"><code class="computeroutput">-c --stdout</code></span></dt>
    415. 

  415. <dd><p>Compress or decompress to standard
    416. 

  416.   output.</p></dd>
    417. 

  417. <dt><span class="term"><code class="computeroutput">-d --decompress</code></span></dt>
    418. 

  418. <dd><p>Force decompression.
    419. 

  419.   <code class="computeroutput">bzip2</code>,
    420. 

  420.   <code class="computeroutput">bunzip2</code> and
    421. 

  421.   <code class="computeroutput">bzcat</code> are really the same
    422. 

  422.   program, and the decision about what actions to take is done on
    423. 

  423.   the basis of which name is used.  This flag overrides that
    424. 

  424.   mechanism, and forces bzip2 to decompress.</p></dd>
    425. 

  425. <dt><span class="term"><code class="computeroutput">-z --compress</code></span></dt>
    426. 

  426. <dd><p>The complement to
    427. 

  427.   <code class="computeroutput">-d</code>: forces compression,
    428. 

  428.   regardless of the invokation name.</p></dd>
    429. 

  429. <dt><span class="term"><code class="computeroutput">-t --test</code></span></dt>
    430. 

  430. <dd><p>Check integrity of the specified file(s), but
    431. 

  431.   don't decompress them.  This really performs a trial
    432. 

  432.   decompression and throws away the result.</p></dd>
    433. 

  433. <dt><span class="term"><code class="computeroutput">-f --force</code></span></dt>
    434. 

  434. <dd>
    435. 

  435. <p>Force overwrite of output files.  Normally,
    436. 

  436.   <code class="computeroutput">bzip2</code> will not overwrite
    437. 

  437.   existing output files.  Also forces
    438. 

  438.   <code class="computeroutput">bzip2</code> to break hard links to
    439. 

  439.   files, which it otherwise wouldn't do.</p>
    440. 

  440. <p><code class="computeroutput">bzip2</code> normally declines
    441. 

  441.   to decompress files which don't have the correct magic header
    442. 

  442.   bytes. If forced (<code class="computeroutput">-f</code>),
    443. 

  443.   however, it will pass such files through unmodified. This is
    444. 

  444.   how GNU <code class="computeroutput">gzip</code> behaves.</p>
    445. 

  445. </dd>
    446. 

  446. <dt><span class="term"><code class="computeroutput">-k --keep</code></span></dt>
    447. 

  447. <dd><p>Keep (don't delete) input files during
    448. 

  448.   compression or decompression.</p></dd>
    449. 

  449. <dt><span class="term"><code class="computeroutput">-s --small</code></span></dt>
    450. 

  450. <dd>
    451. 

  451. <p>Reduce memory usage, for compression,
    452. 

  452.   decompression and testing.  Files are decompressed and tested
    453. 

  453.   using a modified algorithm which only requires 2.5 bytes per
    454. 

  454.   block byte.  This means any file can be decompressed in 2300k
    455. 

  455.   of memory, albeit at about half the normal speed.</p>
    456. 

  456. <p>During compression, <code class="computeroutput">-s</code>
    457. 

  457.   selects a block size of 200k, which limits memory use to around
    458. 

  458.   the same figure, at the expense of your compression ratio.  In
    459. 

  459.   short, if your machine is low on memory (8 megabytes or less),
    460. 

  460.   use <code class="computeroutput">-s</code> for everything.  See
    461. 

  461.   <a href="#memory-management">MEMORY MANAGEMENT</a> below.</p>
    462. 

  462. </dd>
    463. 

  463. <dt><span class="term"><code class="computeroutput">-q --quiet</code></span></dt>
    464. 

  464. <dd><p>Suppress non-essential warning messages.
    465. 

  465.   Messages pertaining to I/O errors and other critical events
    466. 

  466.   will not be suppressed.</p></dd>
    467. 

  467. <dt><span class="term"><code class="computeroutput">-v --verbose</code></span></dt>
    468. 

  468. <dd><p>Verbose mode -- show the compression ratio for
    469. 

  469.   each file processed.  Further
    470. 

  470.   <code class="computeroutput">-v</code>'s increase the verbosity
    471. 

  471.   level, spewing out lots of information which is primarily of
    472. 

  472.   interest for diagnostic purposes.</p></dd>
    473. 

  473. <dt><span class="term"><code class="computeroutput">-L --license -V --version</code></span></dt>
    474. 

  474. <dd><p>Display the software version, license terms and
    475. 

  475.   conditions.</p></dd>
    476. 

  476. <dt><span class="term"><code class="computeroutput">-1</code> (or
    477. 

  477.  <code class="computeroutput">--fast</code>) to
    478. 

  478.  <code class="computeroutput">-9</code> (or
    479. 

  479.  <code class="computeroutput">-best</code>)</span></dt>
    480. 

  480. <dd><p>Set the block size to 100 k, 200 k ...  900 k
    481. 

  481.   when compressing.  Has no effect when decompressing.  See <a href="#memory-management">MEMORY MANAGEMENT</a> below.  The
    482. 

  482.   <code class="computeroutput">--fast</code> and
    483. 

  483.   <code class="computeroutput">--best</code> aliases are primarily
    484. 

  484.   for GNU <code class="computeroutput">gzip</code> compatibility.
    485. 

  485.   In particular, <code class="computeroutput">--fast</code> doesn't
    486. 

  486.   make things significantly faster.  And
    487. 

  487.   <code class="computeroutput">--best</code> merely selects the
    488. 

  488.   default behaviour.</p></dd>
    489. 

  489. <dt><span class="term"><code class="computeroutput">--</code></span></dt>
    490. 

  490. <dd><p>Treats all subsequent arguments as file names,
    491. 

  491.   even if they start with a dash.  This is so you can handle
    492. 

  492.   files with names beginning with a dash, for example:
    493. 

  493.   <code class="computeroutput">bzip2 --
    494. 

  494.   -myfilename</code>.</p></dd>
    495. 

  495. <dt>
    496. 

  496. <span class="term"><code class="computeroutput">--repetitive-fast</code>, </span><span class="term"><code class="computeroutput">--repetitive-best</code></span>
    497. 

  497. </dt>
    498. 

  498. <dd><p>These flags are redundant in versions 0.9.5 and
    499. 

  499.   above.  They provided some coarse control over the behaviour of
    500. 

  500.   the sorting algorithm in earlier versions, which was sometimes
    501. 

  501.   useful.  0.9.5 and above have an improved algorithm which
    502. 

  502.   renders these flags irrelevant.</p></dd>
    503. 

  503. </dl></div>
    504. 

  504. </div>
    505. 

  505. <div class="sect1" lang="en">
    506. 

  506. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    507. 

  507. <a name="memory-management"></a>2.5. MEMORY MANAGEMENT</h2></div></div></div>
    508. 

  508. <p><code class="computeroutput">bzip2</code> compresses large
    509. 

  509. files in blocks.  The block size affects both the compression
    510. 

  510. ratio achieved, and the amount of memory needed for compression
    511. 

  511. and decompression.  The flags <code class="computeroutput">-1</code>
    512. 

  512. through <code class="computeroutput">-9</code> specify the block
    513. 

  513. size to be 100,000 bytes through 900,000 bytes (the default)
    514. 

  514. respectively.  At decompression time, the block size used for
    515. 

  515. compression is read from the header of the compressed file, and
    516. 

  516. <code class="computeroutput">bunzip2</code> then allocates itself
    517. 

  517. just enough memory to decompress the file.  Since block sizes are
    518. 

  518. stored in compressed files, it follows that the flags
    519. 

  519. <code class="computeroutput">-1</code> to
    520. 

  520. <code class="computeroutput">-9</code> are irrelevant to and so
    521. 

  521. ignored during decompression.</p>
    522. 

  522. <p>Compression and decompression requirements, in bytes, can be
    523. 

  523. estimated as:</p>
    524. 

  524. <pre class="programlisting">Compression:   400k + ( 8 x block size )
    525. 

  525. 

  526. Decompression: 100k + ( 4 x block size ), or
    527. 

  527.                100k + ( 2.5 x block size )</pre>
    528. 

  528. <p>Larger block sizes give rapidly diminishing marginal
    529. 

  529. returns.  Most of the compression comes from the first two or
    530. 

  530. three hundred k of block size, a fact worth bearing in mind when
    531. 

  531. using <code class="computeroutput">bzip2</code> on small machines.
    532. 

  532. It is also important to appreciate that the decompression memory
    533. 

  533. requirement is set at compression time by the choice of block
    534. 

  534. size.</p>
    535. 

  535. <p>For files compressed with the default 900k block size,
    536. 

  536. <code class="computeroutput">bunzip2</code> will require about 3700
    537. 

  537. kbytes to decompress.  To support decompression of any file on a
    538. 

  538. 4 megabyte machine, <code class="computeroutput">bunzip2</code> has
    539. 

  539. an option to decompress using approximately half this amount of
    540. 

  540. memory, about 2300 kbytes.  Decompression speed is also halved,
    541. 

  541. so you should use this option only where necessary.  The relevant
    542. 

  542. flag is <code class="computeroutput">-s</code>.</p>
    543. 

  543. <p>In general, try and use the largest block size memory
    544. 

  544. constraints allow, since that maximises the compression achieved.
    545. 

  545. Compression and decompression speed are virtually unaffected by
    546. 

  546. block size.</p>
    547. 

  547. <p>Another significant point applies to files which fit in a
    548. 

  548. single block -- that means most files you'd encounter using a
    549. 

  549. large block size.  The amount of real memory touched is
    550. 

  550. proportional to the size of the file, since the file is smaller
    551. 

  551. than a block.  For example, compressing a file 20,000 bytes long
    552. 

  552. with the flag <code class="computeroutput">-9</code> will cause the
    553. 

  553. compressor to allocate around 7600k of memory, but only touch
    554. 

  554. 400k + 20000 * 8 = 560 kbytes of it.  Similarly, the decompressor
    555. 

  555. will allocate 3700k but only touch 100k + 20000 * 4 = 180
    556. 

  556. kbytes.</p>
    557. 

  557. <p>Here is a table which summarises the maximum memory usage
    558. 

  558. for different block sizes.  Also recorded is the total compressed
    559. 

  559. size for 14 files of the Calgary Text Compression Corpus
    560. 

  560. totalling 3,141,622 bytes.  This column gives some feel for how
    561. 

  561. compression varies with block size.  These figures tend to
    562. 

  562. understate the advantage of larger block sizes for larger files,
    563. 

  563. since the Corpus is dominated by smaller files.</p>
    564. 

  564. <pre class="programlisting">        Compress   Decompress   Decompress   Corpus
    565. 

  565. Flag     usage      usage       -s usage     Size
    566. 

  566. 

  567.  -1      1200k       500k         350k      914704
    568. 

  568.  -2      2000k       900k         600k      877703
    569. 

  569.  -3      2800k      1300k         850k      860338
    570. 

  570.  -4      3600k      1700k        1100k      846899
    571. 

  571.  -5      4400k      2100k        1350k      845160
    572. 

  572.  -6      5200k      2500k        1600k      838626
    573. 

  573.  -7      6100k      2900k        1850k      834096
    574. 

  574.  -8      6800k      3300k        2100k      828642
    575. 

  575.  -9      7600k      3700k        2350k      828642</pre>
    576. 

  576. </div>
    577. 

  577. <div class="sect1" lang="en">
    578. 

  578. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    579. 

  579. <a name="recovering"></a>2.6. RECOVERING DATA FROM DAMAGED FILES</h2></div></div></div>
    580. 

  580. <p><code class="computeroutput">bzip2</code> compresses files in
    581. 

  581. blocks, usually 900kbytes long.  Each block is handled
    582. 

  582. independently.  If a media or transmission error causes a
    583. 

  583. multi-block <code class="computeroutput">.bz2</code> file to become
    584. 

  584. damaged, it may be possible to recover data from the undamaged
    585. 

  585. blocks in the file.</p>
    586. 

  586. <p>The compressed representation of each block is delimited by
    587. 

  587. a 48-bit pattern, which makes it possible to find the block
    588. 

  588. boundaries with reasonable certainty.  Each block also carries
    589. 

  589. its own 32-bit CRC, so damaged blocks can be distinguished from
    590. 

  590. undamaged ones.</p>
    591. 

  591. <p><code class="computeroutput">bzip2recover</code> is a simple
    592. 

  592. program whose purpose is to search for blocks in
    593. 

  593. <code class="computeroutput">.bz2</code> files, and write each block
    594. 

  594. out into its own <code class="computeroutput">.bz2</code> file.  You
    595. 

  595. can then use <code class="computeroutput">bzip2 -t</code> to test
    596. 

  596. the integrity of the resulting files, and decompress those which
    597. 

  597. are undamaged.</p>
    598. 

  598. <p><code class="computeroutput">bzip2recover</code> takes a
    599. 

  599. single argument, the name of the damaged file, and writes a
    600. 

  600. number of files <code class="computeroutput">rec0001file.bz2</code>,
    601. 

  601. <code class="computeroutput">rec0002file.bz2</code>, etc, containing
    602. 

  602. the extracted blocks.  The output filenames are designed so that
    603. 

  603. the use of wildcards in subsequent processing -- for example,
    604. 

  604. <code class="computeroutput">bzip2 -dc rec*file.bz2 &gt;
    605. 

  605. recovered_data</code> -- lists the files in the correct
    606. 

  606. order.</p>
    607. 

  607. <p><code class="computeroutput">bzip2recover</code> should be of
    608. 

  608. most use dealing with large <code class="computeroutput">.bz2</code>
    609. 

  609. files, as these will contain many blocks.  It is clearly futile
    610. 

  610. to use it on damaged single-block files, since a damaged block
    611. 

  611. cannot be recovered.  If you wish to minimise any potential data
    612. 

  612. loss through media or transmission errors, you might consider
    613. 

  613. compressing with a smaller block size.</p>
    614. 

  614. </div>
    615. 

  615. <div class="sect1" lang="en">
    616. 

  616. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    617. 

  617. <a name="performance"></a>2.7. PERFORMANCE NOTES</h2></div></div></div>
    618. 

  618. <p>The sorting phase of compression gathers together similar
    619. 

  619. strings in the file.  Because of this, files containing very long
    620. 

  620. runs of repeated symbols, like "aabaabaabaab ..."  (repeated
    621. 

  621. several hundred times) may compress more slowly than normal.
    622. 

  622. Versions 0.9.5 and above fare much better than previous versions
    623. 

  623. in this respect.  The ratio between worst-case and average-case
    624. 

  624. compression time is in the region of 10:1.  For previous
    625. 

  625. versions, this figure was more like 100:1.  You can use the
    626. 

  626. <code class="computeroutput">-vvvv</code> option to monitor progress
    627. 

  627. in great detail, if you want.</p>
    628. 

  628. <p>Decompression speed is unaffected by these
    629. 

  629. phenomena.</p>
    630. 

  630. <p><code class="computeroutput">bzip2</code> usually allocates
    631. 

  631. several megabytes of memory to operate in, and then charges all
    632. 

  632. over it in a fairly random fashion.  This means that performance,
    633. 

  633. both for compressing and decompressing, is largely determined by
    634. 

  634. the speed at which your machine can service cache misses.
    635. 

  635. Because of this, small changes to the code to reduce the miss
    636. 

  636. rate have been observed to give disproportionately large
    637. 

  637. performance improvements.  I imagine
    638. 

  638. <code class="computeroutput">bzip2</code> will perform best on
    639. 

  639. machines with very large caches.</p>
    640. 

  640. </div>
    641. 

  641. <div class="sect1" lang="en">
    642. 

  642. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    643. 

  643. <a name="caveats"></a>2.8. CAVEATS</h2></div></div></div>
    644. 

  644. <p>I/O error messages are not as helpful as they could be.
    645. 

  645. <code class="computeroutput">bzip2</code> tries hard to detect I/O
    646. 

  646. errors and exit cleanly, but the details of what the problem is
    647. 

  647. sometimes seem rather misleading.</p>
    648. 

  648. <p>This manual page pertains to version 1.0.5 of
    649. 

  649. <code class="computeroutput">bzip2</code>.  Compressed data created by
    650. 

  650. this version is entirely forwards and backwards compatible with the
    651. 

  651. previous public releases, versions 0.1pl2, 0.9.0 and 0.9.5, 1.0.0,
    652. 

  652. 1.0.1, 1.0.2 and 1.0.3, but with the following exception: 0.9.0 and
    653. 

  653. above can correctly decompress multiple concatenated compressed files.
    654. 

  654. 0.1pl2 cannot do this; it will stop after decompressing just the first
    655. 

  655. file in the stream.</p>
    656. 

  656. <p><code class="computeroutput">bzip2recover</code> versions
    657. 

  657. prior to 1.0.2 used 32-bit integers to represent bit positions in
    658. 

  658. compressed files, so it could not handle compressed files more
    659. 

  659. than 512 megabytes long.  Versions 1.0.2 and above use 64-bit ints
    660. 

  660. on some platforms which support them (GNU supported targets, and
    661. 

  661. Windows). To establish whether or not
    662. 

  662. <code class="computeroutput">bzip2recover</code> was built with such
    663. 

  663. a limitation, run it without arguments. In any event you can
    664. 

  664. build yourself an unlimited version if you can recompile it with
    665. 

  665. <code class="computeroutput">MaybeUInt64</code> set to be an
    666. 

  666. unsigned 64-bit integer.</p>
    667. 

  667. </div>
    668. 

  668. <div class="sect1" lang="en">
    669. 

  669. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    670. 

  670. <a name="author"></a>2.9. AUTHOR</h2></div></div></div>
    671. 

  671. <p>Julian Seward,
    672. 

  672. <code class="computeroutput">jseward@bzip.org</code></p>
    673. 

  673. <p>The ideas embodied in
    674. 

  674. <code class="computeroutput">bzip2</code> are due to (at least) the
    675. 

  675. following people: Michael Burrows and David Wheeler (for the
    676. 

  676. block sorting transformation), David Wheeler (again, for the
    677. 

  677. Huffman coder), Peter Fenwick (for the structured coding model in
    678. 

  678. the original <code class="computeroutput">bzip</code>, and many
    679. 

  679. refinements), and Alistair Moffat, Radford Neal and Ian Witten
    680. 

  680. (for the arithmetic coder in the original
    681. 

  681. <code class="computeroutput">bzip</code>).  I am much indebted for
    682. 

  682. their help, support and advice.  See the manual in the source
    683. 

  683. distribution for pointers to sources of documentation.  Christian
    684. 

  684. von Roques encouraged me to look for faster sorting algorithms,
    685. 

  685. so as to speed up compression.  Bela Lubkin encouraged me to
    686. 

  686. improve the worst-case compression performance.  
    687. 

  687. Donna Robinson XMLised the documentation.
    688. 

  688. Many people sent
    689. 

  689. patches, helped with portability problems, lent machines, gave
    690. 

  690. advice and were generally helpful.</p>
    691. 

  691. </div>
    692. 

  692. </div>
    693. 

  693. <div class="chapter" lang="en">
    694. 

  694. <div class="titlepage"><div><div><h2 class="title">
    695. 

  695. <a name="libprog"></a>3. 
    696. 

  696. Programming with <code class="computeroutput">libbzip2</code>
    697. 

  697. </h2></div></div></div>
    698. 

  698. <div class="toc">
    699. 

  699. <p><b>Table of Contents</b></p>
    700. 

  700. <dl>
    701. 

  701. <dt><span class="sect1"><a href="#top-level">3.1. Top-level structure</a></span></dt>
    702. 

  702. <dd><dl>
    703. 

  703. <dt><span class="sect2"><a href="#ll-summary">3.1.1. Low-level summary</a></span></dt>
    704. 

  704. <dt><span class="sect2"><a href="#hl-summary">3.1.2. High-level summary</a></span></dt>
    705. 

  705. <dt><span class="sect2"><a href="#util-fns-summary">3.1.3. Utility functions summary</a></span></dt>
    706. 

  706. </dl></dd>
    707. 

  707. <dt><span class="sect1"><a href="#err-handling">3.2. Error handling</a></span></dt>
    708. 

  708. <dt><span class="sect1"><a href="#low-level">3.3. Low-level interface</a></span></dt>
    709. 

  709. <dd><dl>
    710. 

  710. <dt><span class="sect2"><a href="#bzcompress-init">3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></a></span></dt>
    711. 

  711. <dt><span class="sect2"><a href="#bzCompress">3.3.2. <code class="computeroutput">BZ2_bzCompress</code></a></span></dt>
    712. 

  712. <dt><span class="sect2"><a href="#bzCompress-end">3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></a></span></dt>
    713. 

  713. <dt><span class="sect2"><a href="#bzDecompress-init">3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></a></span></dt>
    714. 

  714. <dt><span class="sect2"><a href="#bzDecompress">3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></a></span></dt>
    715. 

  715. <dt><span class="sect2"><a href="#bzDecompress-end">3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></a></span></dt>
    716. 

  716. </dl></dd>
    717. 

  717. <dt><span class="sect1"><a href="#hl-interface">3.4. High-level interface</a></span></dt>
    718. 

  718. <dd><dl>
    719. 

  719. <dt><span class="sect2"><a href="#bzreadopen">3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></a></span></dt>
    720. 

  720. <dt><span class="sect2"><a href="#bzread">3.4.2. <code class="computeroutput">BZ2_bzRead</code></a></span></dt>
    721. 

  721. <dt><span class="sect2"><a href="#bzreadgetunused">3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></a></span></dt>
    722. 

  722. <dt><span class="sect2"><a href="#bzreadclose">3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></a></span></dt>
    723. 

  723. <dt><span class="sect2"><a href="#bzwriteopen">3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></a></span></dt>
    724. 

  724. <dt><span class="sect2"><a href="#bzwrite">3.4.6. <code class="computeroutput">BZ2_bzWrite</code></a></span></dt>
    725. 

  725. <dt><span class="sect2"><a href="#bzwriteclose">3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></a></span></dt>
    726. 

  726. <dt><span class="sect2"><a href="#embed">3.4.8. Handling embedded compressed data streams</a></span></dt>
    727. 

  727. <dt><span class="sect2"><a href="#std-rdwr">3.4.9. Standard file-reading/writing code</a></span></dt>
    728. 

  728. </dl></dd>
    729. 

  729. <dt><span class="sect1"><a href="#util-fns">3.5. Utility functions</a></span></dt>
    730. 

  730. <dd><dl>
    731. 

  731. <dt><span class="sect2"><a href="#bzbufftobuffcompress">3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></a></span></dt>
    732. 

  732. <dt><span class="sect2"><a href="#bzbufftobuffdecompress">3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></a></span></dt>
    733. 

  733. </dl></dd>
    734. 

  734. <dt><span class="sect1"><a href="#zlib-compat">3.6. <code class="computeroutput">zlib</code> compatibility functions</a></span></dt>
    735. 

  735. <dt><span class="sect1"><a href="#stdio-free">3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</a></span></dt>
    736. 

  736. <dd><dl>
    737. 

  737. <dt><span class="sect2"><a href="#stdio-bye">3.7.1. Getting rid of <code class="computeroutput">stdio</code></a></span></dt>
    738. 

  738. <dt><span class="sect2"><a href="#critical-error">3.7.2. Critical error handling</a></span></dt>
    739. 

  739. </dl></dd>
    740. 

  740. <dt><span class="sect1"><a href="#win-dll">3.8. Making a Windows DLL</a></span></dt>
    741. 

  741. </dl>
    742. 

  742. </div>
    743. 

  743. <p>This chapter describes the programming interface to
    744. 

  744. <code class="computeroutput">libbzip2</code>.</p>
    745. 

  745. <p>For general background information, particularly about
    746. 

  746. memory use and performance aspects, you'd be well advised to read
    747. 

  747. <a href="#using">How to use bzip2</a> as well.</p>
    748. 

  748. <div class="sect1" lang="en">
    749. 

  749. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    750. 

  750. <a name="top-level"></a>3.1. Top-level structure</h2></div></div></div>
    751. 

  751. <p><code class="computeroutput">libbzip2</code> is a flexible
    752. 

  752. library for compressing and decompressing data in the
    753. 

  753. <code class="computeroutput">bzip2</code> data format.  Although
    754. 

  754. packaged as a single entity, it helps to regard the library as
    755. 

  755. three separate parts: the low level interface, and the high level
    756. 

  756. interface, and some utility functions.</p>
    757. 

  757. <p>The structure of
    758. 

  758. <code class="computeroutput">libbzip2</code>'s interfaces is similar
    759. 

  759. to that of Jean-loup Gailly's and Mark Adler's excellent
    760. 

  760. <code class="computeroutput">zlib</code> library.</p>
    761. 

  761. <p>All externally visible symbols have names beginning
    762. 

  762. <code class="computeroutput">BZ2_</code>.  This is new in version
    763. 

  763. 1.0.  The intention is to minimise pollution of the namespaces of
    764. 

  764. library clients.</p>
    765. 

  765. <p>To use any part of the library, you need to
    766. 

  766. <code class="computeroutput">#include &lt;bzlib.h&gt;</code>
    767. 

  767. into your sources.</p>
    768. 

  768. <div class="sect2" lang="en">
    769. 

  769. <div class="titlepage"><div><div><h3 class="title">
    770. 

  770. <a name="ll-summary"></a>3.1.1. Low-level summary</h3></div></div></div>
    771. 

  771. <p>This interface provides services for compressing and
    772. 

  772. decompressing data in memory.  There's no provision for dealing
    773. 

  773. with files, streams or any other I/O mechanisms, just straight
    774. 

  774. memory-to-memory work.  In fact, this part of the library can be
    775. 

  775. compiled without inclusion of
    776. 

  776. <code class="computeroutput">stdio.h</code>, which may be helpful
    777. 

  777. for embedded applications.</p>
    778. 

  778. <p>The low-level part of the library has no global variables
    779. 

  779. and is therefore thread-safe.</p>
    780. 

  780. <p>Six routines make up the low level interface:
    781. 

  781. <code class="computeroutput">BZ2_bzCompressInit</code>,
    782. 

  782. <code class="computeroutput">BZ2_bzCompress</code>, and
    783. 

  783. <code class="computeroutput">BZ2_bzCompressEnd</code> for
    784. 

  784. compression, and a corresponding trio
    785. 

  785. <code class="computeroutput">BZ2_bzDecompressInit</code>,
    786. 

  786. <code class="computeroutput">BZ2_bzDecompress</code> and
    787. 

  787. <code class="computeroutput">BZ2_bzDecompressEnd</code> for
    788. 

  788. decompression.  The <code class="computeroutput">*Init</code>
    789. 

  789. functions allocate memory for compression/decompression and do
    790. 

  790. other initialisations, whilst the
    791. 

  791. <code class="computeroutput">*End</code> functions close down
    792. 

  792. operations and release memory.</p>
    793. 

  793. <p>The real work is done by
    794. 

  794. <code class="computeroutput">BZ2_bzCompress</code> and
    795. 

  795. <code class="computeroutput">BZ2_bzDecompress</code>.  These
    796. 

  796. compress and decompress data from a user-supplied input buffer to
    797. 

  797. a user-supplied output buffer.  These buffers can be any size;
    798. 

  798. arbitrary quantities of data are handled by making repeated calls
    799. 

  799. to these functions.  This is a flexible mechanism allowing a
    800. 

  800. consumer-pull style of activity, or producer-push, or a mixture
    801. 

  801. of both.</p>
    802. 

  802. </div>
    803. 

  803. <div class="sect2" lang="en">
    804. 

  804. <div class="titlepage"><div><div><h3 class="title">
    805. 

  805. <a name="hl-summary"></a>3.1.2. High-level summary</h3></div></div></div>
    806. 

  806. <p>This interface provides some handy wrappers around the
    807. 

  807. low-level interface to facilitate reading and writing
    808. 

  808. <code class="computeroutput">bzip2</code> format files
    809. 

  809. (<code class="computeroutput">.bz2</code> files).  The routines
    810. 

  810. provide hooks to facilitate reading files in which the
    811. 

  811. <code class="computeroutput">bzip2</code> data stream is embedded
    812. 

  812. within some larger-scale file structure, or where there are
    813. 

  813. multiple <code class="computeroutput">bzip2</code> data streams
    814. 

  814. concatenated end-to-end.</p>
    815. 

  815. <p>For reading files,
    816. 

  816. <code class="computeroutput">BZ2_bzReadOpen</code>,
    817. 

  817. <code class="computeroutput">BZ2_bzRead</code>,
    818. 

  818. <code class="computeroutput">BZ2_bzReadClose</code> and 
    819. 

  819. <code class="computeroutput">BZ2_bzReadGetUnused</code> are
    820. 

  820. supplied.  For writing files,
    821. 

  821. <code class="computeroutput">BZ2_bzWriteOpen</code>,
    822. 

  822. <code class="computeroutput">BZ2_bzWrite</code> and
    823. 

  823. <code class="computeroutput">BZ2_bzWriteFinish</code> are
    824. 

  824. available.</p>
    825. 

  825. <p>As with the low-level library, no global variables are used
    826. 

  826. so the library is per se thread-safe.  However, if I/O errors
    827. 

  827. occur whilst reading or writing the underlying compressed files,
    828. 

  828. you may have to consult <code class="computeroutput">errno</code> to
    829. 

  829. determine the cause of the error.  In that case, you'd need a C
    830. 

  830. library which correctly supports
    831. 

  831. <code class="computeroutput">errno</code> in a multithreaded
    832. 

  832. environment.</p>
    833. 

  833. <p>To make the library a little simpler and more portable,
    834. 

  834. <code class="computeroutput">BZ2_bzReadOpen</code> and
    835. 

  835. <code class="computeroutput">BZ2_bzWriteOpen</code> require you to
    836. 

  836. pass them file handles (<code class="computeroutput">FILE*</code>s)
    837. 

  837. which have previously been opened for reading or writing
    838. 

  838. respectively.  That avoids portability problems associated with
    839. 

  839. file operations and file attributes, whilst not being much of an
    840. 

  840. imposition on the programmer.</p>
    841. 

  841. </div>
    842. 

  842. <div class="sect2" lang="en">
    843. 

  843. <div class="titlepage"><div><div><h3 class="title">
    844. 

  844. <a name="util-fns-summary"></a>3.1.3. Utility functions summary</h3></div></div></div>
    845. 

  845. <p>For very simple needs,
    846. 

  846. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code> and
    847. 

  847. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> are
    848. 

  848. provided.  These compress data in memory from one buffer to
    849. 

  849. another buffer in a single function call.  You should assess
    850. 

  850. whether these functions fulfill your memory-to-memory
    851. 

  851. compression/decompression requirements before investing effort in
    852. 

  852. understanding the more general but more complex low-level
    853. 

  853. interface.</p>
    854. 

  854. <p>Yoshioka Tsuneo
    855. 

  855. (<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>) has
    856. 

  856. contributed some functions to give better
    857. 

  857. <code class="computeroutput">zlib</code> compatibility.  These
    858. 

  858. functions are <code class="computeroutput">BZ2_bzopen</code>,
    859. 

  859. <code class="computeroutput">BZ2_bzread</code>,
    860. 

  860. <code class="computeroutput">BZ2_bzwrite</code>,
    861. 

  861. <code class="computeroutput">BZ2_bzflush</code>,
    862. 

  862. <code class="computeroutput">BZ2_bzclose</code>,
    863. 

  863. <code class="computeroutput">BZ2_bzerror</code> and
    864. 

  864. <code class="computeroutput">BZ2_bzlibVersion</code>.  You may find
    865. 

  865. these functions more convenient for simple file reading and
    866. 

  866. writing, than those in the high-level interface.  These functions
    867. 

  867. are not (yet) officially part of the library, and are minimally
    868. 

  868. documented here.  If they break, you get to keep all the pieces.
    869. 

  869. I hope to document them properly when time permits.</p>
    870. 

  870. <p>Yoshioka also contributed modifications to allow the
    871. 

  871. library to be built as a Windows DLL.</p>
    872. 

  872. </div>
    873. 

  873. </div>
    874. 

  874. <div class="sect1" lang="en">
    875. 

  875. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    876. 

  876. <a name="err-handling"></a>3.2. Error handling</h2></div></div></div>
    877. 

  877. <p>The library is designed to recover cleanly in all
    878. 

  878. situations, including the worst-case situation of decompressing
    879. 

  879. random data.  I'm not 100% sure that it can always do this, so
    880. 

  880. you might want to add a signal handler to catch segmentation
    881. 

  881. violations during decompression if you are feeling especially
    882. 

  882. paranoid.  I would be interested in hearing more about the
    883. 

  883. robustness of the library to corrupted compressed data.</p>
    884. 

  884. <p>Version 1.0.3 more robust in this respect than any
    885. 

  885. previous version.  Investigations with Valgrind (a tool for detecting
    886. 

  886. problems with memory management) indicate
    887. 

  887. that, at least for the few files I tested, all single-bit errors
    888. 

  888. in the decompressed data are caught properly, with no
    889. 

  889. segmentation faults, no uses of uninitialised data, no out of
    890. 

  890. range reads or writes, and no infinite looping in the decompressor.
    891. 

  891. So it's certainly pretty robust, although
    892. 

  892. I wouldn't claim it to be totally bombproof.</p>
    893. 

  893. <p>The file <code class="computeroutput">bzlib.h</code> contains
    894. 

  894. all definitions needed to use the library.  In particular, you
    895. 

  895. should definitely not include
    896. 

  896. <code class="computeroutput">bzlib_private.h</code>.</p>
    897. 

  897. <p>In <code class="computeroutput">bzlib.h</code>, the various
    898. 

  898. return values are defined.  The following list is not intended as
    899. 

  899. an exhaustive description of the circumstances in which a given
    900. 

  900. value may be returned -- those descriptions are given later.
    901. 

  901. Rather, it is intended to convey the rough meaning of each return
    902. 

  902. value.  The first five actions are normal and not intended to
    903. 

  903. denote an error situation.</p>
    904. 

  904. <div class="variablelist"><dl>
    905. 

  905. <dt><span class="term"><code class="computeroutput">BZ_OK</code></span></dt>
    906. 

  906. <dd><p>The requested action was completed
    907. 

  907.    successfully.</p></dd>
    908. 

  908. <dt><span class="term"><code class="computeroutput">BZ_RUN_OK, BZ_FLUSH_OK,
    909. 

  909.     BZ_FINISH_OK</code></span></dt>
    910. 

  910. <dd><p>In 
    911. 

  911.    <code class="computeroutput">BZ2_bzCompress</code>, the requested
    912. 

  912.    flush/finish/nothing-special action was completed
    913. 

  913.    successfully.</p></dd>
    914. 

  914. <dt><span class="term"><code class="computeroutput">BZ_STREAM_END</code></span></dt>
    915. 

  915. <dd><p>Compression of data was completed, or the
    916. 

  916.    logical stream end was detected during
    917. 

  917.    decompression.</p></dd>
    918. 

  918. </dl></div>
    919. 

  919. <p>The following return values indicate an error of some
    920. 

  920. kind.</p>
    921. 

  921. <div class="variablelist"><dl>
    922. 

  922. <dt><span class="term"><code class="computeroutput">BZ_CONFIG_ERROR</code></span></dt>
    923. 

  923. <dd><p>Indicates that the library has been improperly
    924. 

  924.    compiled on your platform -- a major configuration error.
    925. 

  925.    Specifically, it means that
    926. 

  926.    <code class="computeroutput">sizeof(char)</code>,
    927. 

  927.    <code class="computeroutput">sizeof(short)</code> and
    928. 

  928.    <code class="computeroutput">sizeof(int)</code> are not 1, 2 and
    929. 

  929.    4 respectively, as they should be.  Note that the library
    930. 

  930.    should still work properly on 64-bit platforms which follow
    931. 

  931.    the LP64 programming model -- that is, where
    932. 

  932.    <code class="computeroutput">sizeof(long)</code> and
    933. 

  933.    <code class="computeroutput">sizeof(void*)</code> are 8.  Under
    934. 

  934.    LP64, <code class="computeroutput">sizeof(int)</code> is still 4,
    935. 

  935.    so <code class="computeroutput">libbzip2</code>, which doesn't
    936. 

  936.    use the <code class="computeroutput">long</code> type, is
    937. 

  937.    OK.</p></dd>
    938. 

  938. <dt><span class="term"><code class="computeroutput">BZ_SEQUENCE_ERROR</code></span></dt>
    939. 

  939. <dd><p>When using the library, it is important to call
    940. 

  940.    the functions in the correct sequence and with data structures
    941. 

  941.    (buffers etc) in the correct states.
    942. 

  942.    <code class="computeroutput">libbzip2</code> checks as much as it
    943. 

  943.    can to ensure this is happening, and returns
    944. 

  944.    <code class="computeroutput">BZ_SEQUENCE_ERROR</code> if not.
    945. 

  945.    Code which complies precisely with the function semantics, as
    946. 

  946.    detailed below, should never receive this value; such an event
    947. 

  947.    denotes buggy code which you should
    948. 

  948.    investigate.</p></dd>
    949. 

  949. <dt><span class="term"><code class="computeroutput">BZ_PARAM_ERROR</code></span></dt>
    950. 

  950. <dd><p>Returned when a parameter to a function call is
    951. 

  951.    out of range or otherwise manifestly incorrect.  As with
    952. 

  952.    <code class="computeroutput">BZ_SEQUENCE_ERROR</code>, this
    953. 

  953.    denotes a bug in the client code.  The distinction between
    954. 

  954.    <code class="computeroutput">BZ_PARAM_ERROR</code> and
    955. 

  955.    <code class="computeroutput">BZ_SEQUENCE_ERROR</code> is a bit
    956. 

  956.    hazy, but still worth making.</p></dd>
    957. 

  957. <dt><span class="term"><code class="computeroutput">BZ_MEM_ERROR</code></span></dt>
    958. 

  958. <dd><p>Returned when a request to allocate memory
    959. 

  959.    failed.  Note that the quantity of memory needed to decompress
    960. 

  960.    a stream cannot be determined until the stream's header has
    961. 

  961.    been read.  So
    962. 

  962.    <code class="computeroutput">BZ2_bzDecompress</code> and
    963. 

  963.    <code class="computeroutput">BZ2_bzRead</code> may return
    964. 

  964.    <code class="computeroutput">BZ_MEM_ERROR</code> even though some
    965. 

  965.    of the compressed data has been read.  The same is not true
    966. 

  966.    for compression; once
    967. 

  967.    <code class="computeroutput">BZ2_bzCompressInit</code> or
    968. 

  968.    <code class="computeroutput">BZ2_bzWriteOpen</code> have
    969. 

  969.    successfully completed,
    970. 

  970.    <code class="computeroutput">BZ_MEM_ERROR</code> cannot
    971. 

  971.    occur.</p></dd>
    972. 

  972. <dt><span class="term"><code class="computeroutput">BZ_DATA_ERROR</code></span></dt>
    973. 

  973. <dd><p>Returned when a data integrity error is
    974. 

  974.    detected during decompression.  Most importantly, this means
    975. 

  975.    when stored and computed CRCs for the data do not match.  This
    976. 

  976.    value is also returned upon detection of any other anomaly in
    977. 

  977.    the compressed data.</p></dd>
    978. 

  978. <dt><span class="term"><code class="computeroutput">BZ_DATA_ERROR_MAGIC</code></span></dt>
    979. 

  979. <dd><p>As a special case of
    980. 

  980.    <code class="computeroutput">BZ_DATA_ERROR</code>, it is
    981. 

  981.    sometimes useful to know when the compressed stream does not
    982. 

  982.    start with the correct magic bytes (<code class="computeroutput">'B' 'Z'
    983. 

  983.    'h'</code>).</p></dd>
    984. 

  984. <dt><span class="term"><code class="computeroutput">BZ_IO_ERROR</code></span></dt>
    985. 

  985. <dd><p>Returned by
    986. 

  986.    <code class="computeroutput">BZ2_bzRead</code> and
    987. 

  987.    <code class="computeroutput">BZ2_bzWrite</code> when there is an
    988. 

  988.    error reading or writing in the compressed file, and by
    989. 

  989.    <code class="computeroutput">BZ2_bzReadOpen</code> and
    990. 

  990.    <code class="computeroutput">BZ2_bzWriteOpen</code> for attempts
    991. 

  991.    to use a file for which the error indicator (viz,
    992. 

  992.    <code class="computeroutput">ferror(f)</code>) is set.  On
    993. 

  993.    receipt of <code class="computeroutput">BZ_IO_ERROR</code>, the
    994. 

  994.    caller should consult <code class="computeroutput">errno</code>
    995. 

  995.    and/or <code class="computeroutput">perror</code> to acquire
    996. 

  996.    operating-system specific information about the
    997. 

  997.    problem.</p></dd>
    998. 

  998. <dt><span class="term"><code class="computeroutput">BZ_UNEXPECTED_EOF</code></span></dt>
    999. 

  999. <dd><p>Returned by
    1000. 

  1000.    <code class="computeroutput">BZ2_bzRead</code> when the
    1001. 

  1001.    compressed file finishes before the logical end of stream is
    1002. 

  1002.    detected.</p></dd>
    1003. 

  1003. <dt><span class="term"><code class="computeroutput">BZ_OUTBUFF_FULL</code></span></dt>
    1004. 

  1004. <dd><p>Returned by
    1005. 

  1005.    <code class="computeroutput">BZ2_bzBuffToBuffCompress</code> and
    1006. 

  1006.    <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> to
    1007. 

  1007.    indicate that the output data will not fit into the output
    1008. 

  1008.    buffer provided.</p></dd>
    1009. 

  1009. </dl></div>
    1010. 

  1010. </div>
    1011. 

  1011. <div class="sect1" lang="en">
    1012. 

  1012. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    1013. 

  1013. <a name="low-level"></a>3.3. Low-level interface</h2></div></div></div>
    1014. 

  1014. <div class="sect2" lang="en">
    1015. 

  1015. <div class="titlepage"><div><div><h3 class="title">
    1016. 

  1016. <a name="bzcompress-init"></a>3.3.1. <code class="computeroutput">BZ2_bzCompressInit</code></h3></div></div></div>
    1017. 

  1017. <pre class="programlisting">typedef struct {
    1018. 

  1018.   char *next_in;
    1019. 

  1019.   unsigned int avail_in;
    1020. 

  1020.   unsigned int total_in_lo32;
    1021. 

  1021.   unsigned int total_in_hi32;
    1022. 

  1022. 

  1023.   char *next_out;
    1024. 

  1024.   unsigned int avail_out;
    1025. 

  1025.   unsigned int total_out_lo32;
    1026. 

  1026.   unsigned int total_out_hi32;
    1027. 

  1027. 

  1028.   void *state;
    1029. 

  1029. 

  1030.   void *(*bzalloc)(void *,int,int);
    1031. 

  1031.   void (*bzfree)(void *,void *);
    1032. 

  1032.   void *opaque;
    1033. 

  1033. } bz_stream;
    1034. 

  1034. 

  1035. int BZ2_bzCompressInit ( bz_stream *strm, 
    1036. 

  1036.                          int blockSize100k, 
    1037. 

  1037.                          int verbosity,
    1038. 

  1038.                          int workFactor );</pre>
    1039. 

  1039. <p>Prepares for compression.  The
    1040. 

  1040. <code class="computeroutput">bz_stream</code> structure holds all
    1041. 

  1041. data pertaining to the compression activity.  A
    1042. 

  1042. <code class="computeroutput">bz_stream</code> structure should be
    1043. 

  1043. allocated and initialised prior to the call.  The fields of
    1044. 

  1044. <code class="computeroutput">bz_stream</code> comprise the entirety
    1045. 

  1045. of the user-visible data.  <code class="computeroutput">state</code>
    1046. 

  1046. is a pointer to the private data structures required for
    1047. 

  1047. compression.</p>
    1048. 

  1048. <p>Custom memory allocators are supported, via fields
    1049. 

  1049. <code class="computeroutput">bzalloc</code>,
    1050. 

  1050. <code class="computeroutput">bzfree</code>, and
    1051. 

  1051. <code class="computeroutput">opaque</code>.  The value
    1052. 

  1052. <code class="computeroutput">opaque</code> is passed to as the first
    1053. 

  1053. argument to all calls to <code class="computeroutput">bzalloc</code>
    1054. 

  1054. and <code class="computeroutput">bzfree</code>, but is otherwise
    1055. 

  1055. ignored by the library.  The call <code class="computeroutput">bzalloc (
    1056. 

  1056. opaque, n, m )</code> is expected to return a pointer
    1057. 

  1057. <code class="computeroutput">p</code> to <code class="computeroutput">n *
    1058. 

  1058. m</code> bytes of memory, and <code class="computeroutput">bzfree (
    1059. 

  1059. opaque, p )</code> should free that memory.</p>
    1060. 

  1060. <p>If you don't want to use a custom memory allocator, set
    1061. 

  1061. <code class="computeroutput">bzalloc</code>,
    1062. 

  1062. <code class="computeroutput">bzfree</code> and
    1063. 

  1063. <code class="computeroutput">opaque</code> to
    1064. 

  1064. <code class="computeroutput">NULL</code>, and the library will then
    1065. 

  1065. use the standard <code class="computeroutput">malloc</code> /
    1066. 

  1066. <code class="computeroutput">free</code> routines.</p>
    1067. 

  1067. <p>Before calling
    1068. 

  1068. <code class="computeroutput">BZ2_bzCompressInit</code>, fields
    1069. 

  1069. <code class="computeroutput">bzalloc</code>,
    1070. 

  1070. <code class="computeroutput">bzfree</code> and
    1071. 

  1071. <code class="computeroutput">opaque</code> should be filled
    1072. 

  1072. appropriately, as just described.  Upon return, the internal
    1073. 

  1073. state will have been allocated and initialised, and
    1074. 

  1074. <code class="computeroutput">total_in_lo32</code>,
    1075. 

  1075. <code class="computeroutput">total_in_hi32</code>,
    1076. 

  1076. <code class="computeroutput">total_out_lo32</code> and
    1077. 

  1077. <code class="computeroutput">total_out_hi32</code> will have been
    1078. 

  1078. set to zero.  These four fields are used by the library to inform
    1079. 

  1079. the caller of the total amount of data passed into and out of the
    1080. 

  1080. library, respectively.  You should not try to change them.  As of
    1081. 

  1081. version 1.0, 64-bit counts are maintained, even on 32-bit
    1082. 

  1082. platforms, using the <code class="computeroutput">_hi32</code>
    1083. 

  1083. fields to store the upper 32 bits of the count.  So, for example,
    1084. 

  1084. the total amount of data in is <code class="computeroutput">(total_in_hi32
    1085. 

  1085. &lt;&lt; 32) + total_in_lo32</code>.</p>
    1086. 

  1086. <p>Parameter <code class="computeroutput">blockSize100k</code>
    1087. 

  1087. specifies the block size to be used for compression.  It should
    1088. 

  1088. be a value between 1 and 9 inclusive, and the actual block size
    1089. 

  1089. used is 100000 x this figure.  9 gives the best compression but
    1090. 

  1090. takes most memory.</p>
    1091. 

  1091. <p>Parameter <code class="computeroutput">verbosity</code> should
    1092. 

  1092. be set to a number between 0 and 4 inclusive.  0 is silent, and
    1093. 

  1093. greater numbers give increasingly verbose monitoring/debugging
    1094. 

  1094. output.  If the library has been compiled with
    1095. 

  1095. <code class="computeroutput">-DBZ_NO_STDIO</code>, no such output
    1096. 

  1096. will appear for any verbosity setting.</p>
    1097. 

  1097. <p>Parameter <code class="computeroutput">workFactor</code>
    1098. 

  1098. controls how the compression phase behaves when presented with
    1099. 

  1099. worst case, highly repetitive, input data.  If compression runs
    1100. 

  1100. into difficulties caused by repetitive data, the library switches
    1101. 

  1101. from the standard sorting algorithm to a fallback algorithm.  The
    1102. 

  1102. fallback is slower than the standard algorithm by perhaps a
    1103. 

  1103. factor of three, but always behaves reasonably, no matter how bad
    1104. 

  1104. the input.</p>
    1105. 

  1105. <p>Lower values of <code class="computeroutput">workFactor</code>
    1106. 

  1106. reduce the amount of effort the standard algorithm will expend
    1107. 

  1107. before resorting to the fallback.  You should set this parameter
    1108. 

  1108. carefully; too low, and many inputs will be handled by the
    1109. 

  1109. fallback algorithm and so compress rather slowly, too high, and
    1110. 

  1110. your average-to-worst case compression times can become very
    1111. 

  1111. large.  The default value of 30 gives reasonable behaviour over a
    1112. 

  1112. wide range of circumstances.</p>
    1113. 

  1113. <p>Allowable values range from 0 to 250 inclusive.  0 is a
    1114. 

  1114. special case, equivalent to using the default value of 30.</p>
    1115. 

  1115. <p>Note that the compressed output generated is the same
    1116. 

  1116. regardless of whether or not the fallback algorithm is
    1117. 

  1117. used.</p>
    1118. 

  1118. <p>Be aware also that this parameter may disappear entirely in
    1119. 

  1119. future versions of the library.  In principle it should be
    1120. 

  1120. possible to devise a good way to automatically choose which
    1121. 

  1121. algorithm to use.  Such a mechanism would render the parameter
    1122. 

  1122. obsolete.</p>
    1123. 

  1123. <p>Possible return values:</p>
    1124. 

  1124. <pre class="programlisting">BZ_CONFIG_ERROR
    1125. 

  1125.   if the library has been mis-compiled
    1126. 

  1126. BZ_PARAM_ERROR
    1127. 

  1127.   if strm is NULL 
    1128. 

  1128.   or blockSize &lt; 1 or blockSize &gt; 9
    1129. 

  1129.   or verbosity &lt; 0 or verbosity &gt; 4
    1130. 

  1130.   or workFactor &lt; 0 or workFactor &gt; 250
    1131. 

  1131. BZ_MEM_ERROR 
    1132. 

  1132.   if not enough memory is available
    1133. 

  1133. BZ_OK 
    1134. 

  1134.   otherwise</pre>
    1135. 

  1135. <p>Allowable next actions:</p>
    1136. 

  1136. <pre class="programlisting">BZ2_bzCompress
    1137. 

  1137.   if BZ_OK is returned
    1138. 

  1138.   no specific action needed in case of error</pre>
    1139. 

  1139. </div>
    1140. 

  1140. <div class="sect2" lang="en">
    1141. 

  1141. <div class="titlepage"><div><div><h3 class="title">
    1142. 

  1142. <a name="bzCompress"></a>3.3.2. <code class="computeroutput">BZ2_bzCompress</code></h3></div></div></div>
    1143. 

  1143. <pre class="programlisting">int BZ2_bzCompress ( bz_stream *strm, int action );</pre>
    1144. 

  1144. <p>Provides more input and/or output buffer space for the
    1145. 

  1145. library.  The caller maintains input and output buffers, and
    1146. 

  1146. calls <code class="computeroutput">BZ2_bzCompress</code> to transfer
    1147. 

  1147. data between them.</p>
    1148. 

  1148. <p>Before each call to
    1149. 

  1149. <code class="computeroutput">BZ2_bzCompress</code>,
    1150. 

  1150. <code class="computeroutput">next_in</code> should point at the data
    1151. 

  1151. to be compressed, and <code class="computeroutput">avail_in</code>
    1152. 

  1152. should indicate how many bytes the library may read.
    1153. 

  1153. <code class="computeroutput">BZ2_bzCompress</code> updates
    1154. 

  1154. <code class="computeroutput">next_in</code>,
    1155. 

  1155. <code class="computeroutput">avail_in</code> and
    1156. 

  1156. <code class="computeroutput">total_in</code> to reflect the number
    1157. 

  1157. of bytes it has read.</p>
    1158. 

  1158. <p>Similarly, <code class="computeroutput">next_out</code> should
    1159. 

  1159. point to a buffer in which the compressed data is to be placed,
    1160. 

  1160. with <code class="computeroutput">avail_out</code> indicating how
    1161. 

  1161. much output space is available.
    1162. 

  1162. <code class="computeroutput">BZ2_bzCompress</code> updates
    1163. 

  1163. <code class="computeroutput">next_out</code>,
    1164. 

  1164. <code class="computeroutput">avail_out</code> and
    1165. 

  1165. <code class="computeroutput">total_out</code> to reflect the number
    1166. 

  1166. of bytes output.</p>
    1167. 

  1167. <p>You may provide and remove as little or as much data as you
    1168. 

  1168. like on each call of
    1169. 

  1169. <code class="computeroutput">BZ2_bzCompress</code>.  In the limit,
    1170. 

  1170. it is acceptable to supply and remove data one byte at a time,
    1171. 

  1171. although this would be terribly inefficient.  You should always
    1172. 

  1172. ensure that at least one byte of output space is available at
    1173. 

  1173. each call.</p>
    1174. 

  1174. <p>A second purpose of
    1175. 

  1175. <code class="computeroutput">BZ2_bzCompress</code> is to request a
    1176. 

  1176. change of mode of the compressed stream.</p>
    1177. 

  1177. <p>Conceptually, a compressed stream can be in one of four
    1178. 

  1178. states: IDLE, RUNNING, FLUSHING and FINISHING.  Before
    1179. 

  1179. initialisation
    1180. 

  1180. (<code class="computeroutput">BZ2_bzCompressInit</code>) and after
    1181. 

  1181. termination (<code class="computeroutput">BZ2_bzCompressEnd</code>),
    1182. 

  1182. a stream is regarded as IDLE.</p>
    1183. 

  1183. <p>Upon initialisation
    1184. 

  1184. (<code class="computeroutput">BZ2_bzCompressInit</code>), the stream
    1185. 

  1185. is placed in the RUNNING state.  Subsequent calls to
    1186. 

  1186. <code class="computeroutput">BZ2_bzCompress</code> should pass
    1187. 

  1187. <code class="computeroutput">BZ_RUN</code> as the requested action;
    1188. 

  1188. other actions are illegal and will result in
    1189. 

  1189. <code class="computeroutput">BZ_SEQUENCE_ERROR</code>.</p>
    1190. 

  1190. <p>At some point, the calling program will have provided all
    1191. 

  1191. the input data it wants to.  It will then want to finish up -- in
    1192. 

  1192. effect, asking the library to process any data it might have
    1193. 

  1193. buffered internally.  In this state,
    1194. 

  1194. <code class="computeroutput">BZ2_bzCompress</code> will no longer
    1195. 

  1195. attempt to read data from
    1196. 

  1196. <code class="computeroutput">next_in</code>, but it will want to
    1197. 

  1197. write data to <code class="computeroutput">next_out</code>.  Because
    1198. 

  1198. the output buffer supplied by the user can be arbitrarily small,
    1199. 

  1199. the finishing-up operation cannot necessarily be done with a
    1200. 

  1200. single call of
    1201. 

  1201. <code class="computeroutput">BZ2_bzCompress</code>.</p>
    1202. 

  1202. <p>Instead, the calling program passes
    1203. 

  1203. <code class="computeroutput">BZ_FINISH</code> as an action to
    1204. 

  1204. <code class="computeroutput">BZ2_bzCompress</code>.  This changes
    1205. 

  1205. the stream's state to FINISHING.  Any remaining input (ie,
    1206. 

  1206. <code class="computeroutput">next_in[0 .. avail_in-1]</code>) is
    1207. 

  1207. compressed and transferred to the output buffer.  To do this,
    1208. 

  1208. <code class="computeroutput">BZ2_bzCompress</code> must be called
    1209. 

  1209. repeatedly until all the output has been consumed.  At that
    1210. 

  1210. point, <code class="computeroutput">BZ2_bzCompress</code> returns
    1211. 

  1211. <code class="computeroutput">BZ_STREAM_END</code>, and the stream's
    1212. 

  1212. state is set back to IDLE.
    1213. 

  1213. <code class="computeroutput">BZ2_bzCompressEnd</code> should then be
    1214. 

  1214. called.</p>
    1215. 

  1215. <p>Just to make sure the calling program does not cheat, the
    1216. 

  1216. library makes a note of <code class="computeroutput">avail_in</code>
    1217. 

  1217. at the time of the first call to
    1218. 

  1218. <code class="computeroutput">BZ2_bzCompress</code> which has
    1219. 

  1219. <code class="computeroutput">BZ_FINISH</code> as an action (ie, at
    1220. 

  1220. the time the program has announced its intention to not supply
    1221. 

  1221. any more input).  By comparing this value with that of
    1222. 

  1222. <code class="computeroutput">avail_in</code> over subsequent calls
    1223. 

  1223. to <code class="computeroutput">BZ2_bzCompress</code>, the library
    1224. 

  1224. can detect any attempts to slip in more data to compress.  Any
    1225. 

  1225. calls for which this is detected will return
    1226. 

  1226. <code class="computeroutput">BZ_SEQUENCE_ERROR</code>.  This
    1227. 

  1227. indicates a programming mistake which should be corrected.</p>
    1228. 

  1228. <p>Instead of asking to finish, the calling program may ask
    1229. 

  1229. <code class="computeroutput">BZ2_bzCompress</code> to take all the
    1230. 

  1230. remaining input, compress it and terminate the current
    1231. 

  1231. (Burrows-Wheeler) compression block.  This could be useful for
    1232. 

  1232. error control purposes.  The mechanism is analogous to that for
    1233. 

  1233. finishing: call <code class="computeroutput">BZ2_bzCompress</code>
    1234. 

  1234. with an action of <code class="computeroutput">BZ_FLUSH</code>,
    1235. 

  1235. remove output data, and persist with the
    1236. 

  1236. <code class="computeroutput">BZ_FLUSH</code> action until the value
    1237. 

  1237. <code class="computeroutput">BZ_RUN</code> is returned.  As with
    1238. 

  1238. finishing, <code class="computeroutput">BZ2_bzCompress</code>
    1239. 

  1239. detects any attempt to provide more input data once the flush has
    1240. 

  1240. begun.</p>
    1241. 

  1241. <p>Once the flush is complete, the stream returns to the
    1242. 

  1242. normal RUNNING state.</p>
    1243. 

  1243. <p>This all sounds pretty complex, but isn't really.  Here's a
    1244. 

  1244. table which shows which actions are allowable in each state, what
    1245. 

  1245. action will be taken, what the next state is, and what the
    1246. 

  1246. non-error return values are.  Note that you can't explicitly ask
    1247. 

  1247. what state the stream is in, but nor do you need to -- it can be
    1248. 

  1248. inferred from the values returned by
    1249. 

  1249. <code class="computeroutput">BZ2_bzCompress</code>.</p>
    1250. 

  1250. <pre class="programlisting">IDLE/any
    1251. 

  1251.   Illegal.  IDLE state only exists after BZ2_bzCompressEnd or
    1252. 

  1252.   before BZ2_bzCompressInit.
    1253. 

  1253.   Return value = BZ_SEQUENCE_ERROR
    1254. 

  1254. 

  1255. RUNNING/BZ_RUN
    1256. 

  1256.   Compress from next_in to next_out as much as possible.
    1257. 

  1257.   Next state = RUNNING
    1258. 

  1258.   Return value = BZ_RUN_OK
    1259. 

  1259. 

  1260. RUNNING/BZ_FLUSH
    1261. 

  1261.   Remember current value of next_in. Compress from next_in
    1262. 

  1262.   to next_out as much as possible, but do not accept any more input.
    1263. 

  1263.   Next state = FLUSHING
    1264. 

  1264.   Return value = BZ_FLUSH_OK
    1265. 

  1265. 

  1266. RUNNING/BZ_FINISH
    1267. 

  1267.   Remember current value of next_in. Compress from next_in
    1268. 

  1268.   to next_out as much as possible, but do not accept any more input.
    1269. 

  1269.   Next state = FINISHING
    1270. 

  1270.   Return value = BZ_FINISH_OK
    1271. 

  1271. 

  1272. FLUSHING/BZ_FLUSH
    1273. 

  1273.   Compress from next_in to next_out as much as possible, 
    1274. 

  1274.   but do not accept any more input.
    1275. 

  1275.   If all the existing input has been used up and all compressed
    1276. 

  1276.   output has been removed
    1277. 

  1277.     Next state = RUNNING; Return value = BZ_RUN_OK
    1278. 

  1278.   else
    1279. 

  1279.     Next state = FLUSHING; Return value = BZ_FLUSH_OK
    1280. 

  1280. 

  1281. FLUSHING/other     
    1282. 

  1282.   Illegal.
    1283. 

  1283.   Return value = BZ_SEQUENCE_ERROR
    1284. 

  1284. 

  1285. FINISHING/BZ_FINISH
    1286. 

  1286.   Compress from next_in to next_out as much as possible,
    1287. 

  1287.   but to not accept any more input.  
    1288. 

  1288.   If all the existing input has been used up and all compressed
    1289. 

  1289.   output has been removed
    1290. 

  1290.     Next state = IDLE; Return value = BZ_STREAM_END
    1291. 

  1291.   else
    1292. 

  1292.     Next state = FINISHING; Return value = BZ_FINISH_OK
    1293. 

  1293. 

  1294. FINISHING/other
    1295. 

  1295.   Illegal.
    1296. 

  1296.   Return value = BZ_SEQUENCE_ERROR</pre>
    1297. 

  1297. <p>That still looks complicated?  Well, fair enough.  The
    1298. 

  1298. usual sequence of calls for compressing a load of data is:</p>
    1299. 

  1299. <div class="orderedlist"><ol type="1">
    1300. 

  1300. <li><p>Get started with
    1301. 

  1301.   <code class="computeroutput">BZ2_bzCompressInit</code>.</p></li>
    1302. 

  1302. <li><p>Shovel data in and shlurp out its compressed form
    1303. 

  1303.   using zero or more calls of
    1304. 

  1304.   <code class="computeroutput">BZ2_bzCompress</code> with action =
    1305. 

  1305.   <code class="computeroutput">BZ_RUN</code>.</p></li>
    1306. 

  1306. <li><p>Finish up. Repeatedly call
    1307. 

  1307.   <code class="computeroutput">BZ2_bzCompress</code> with action =
    1308. 

  1308.   <code class="computeroutput">BZ_FINISH</code>, copying out the
    1309. 

  1309.   compressed output, until
    1310. 

  1310.   <code class="computeroutput">BZ_STREAM_END</code> is
    1311. 

  1311.   returned.</p></li>
    1312. 

  1312. <li><p>Close up and go home.  Call
    1313. 

  1313.   <code class="computeroutput">BZ2_bzCompressEnd</code>.</p></li>
    1314. 

  1314. </ol></div>
    1315. 

  1315. <p>If the data you want to compress fits into your input
    1316. 

  1316. buffer all at once, you can skip the calls of
    1317. 

  1317. <code class="computeroutput">BZ2_bzCompress ( ..., BZ_RUN )</code>
    1318. 

  1318. and just do the <code class="computeroutput">BZ2_bzCompress ( ..., BZ_FINISH
    1319. 

  1319. )</code> calls.</p>
    1320. 

  1320. <p>All required memory is allocated by
    1321. 

  1321. <code class="computeroutput">BZ2_bzCompressInit</code>.  The
    1322. 

  1322. compression library can accept any data at all (obviously).  So
    1323. 

  1323. you shouldn't get any error return values from the
    1324. 

  1324. <code class="computeroutput">BZ2_bzCompress</code> calls.  If you
    1325. 

  1325. do, they will be
    1326. 

  1326. <code class="computeroutput">BZ_SEQUENCE_ERROR</code>, and indicate
    1327. 

  1327. a bug in your programming.</p>
    1328. 

  1328. <p>Trivial other possible return values:</p>
    1329. 

  1329. <pre class="programlisting">BZ_PARAM_ERROR
    1330. 

  1330.   if strm is NULL, or strm-&gt;s is NULL</pre>
    1331. 

  1331. </div>
    1332. 

  1332. <div class="sect2" lang="en">
    1333. 

  1333. <div class="titlepage"><div><div><h3 class="title">
    1334. 

  1334. <a name="bzCompress-end"></a>3.3.3. <code class="computeroutput">BZ2_bzCompressEnd</code></h3></div></div></div>
    1335. 

  1335. <pre class="programlisting">int BZ2_bzCompressEnd ( bz_stream *strm );</pre>
    1336. 

  1336. <p>Releases all memory associated with a compression
    1337. 

  1337. stream.</p>
    1338. 

  1338. <p>Possible return values:</p>
    1339. 

  1339. <pre class="programlisting">BZ_PARAM_ERROR  if strm is NULL or strm-&gt;s is NULL
    1340. 

  1340. BZ_OK           otherwise</pre>
    1341. 

  1341. </div>
    1342. 

  1342. <div class="sect2" lang="en">
    1343. 

  1343. <div class="titlepage"><div><div><h3 class="title">
    1344. 

  1344. <a name="bzDecompress-init"></a>3.3.4. <code class="computeroutput">BZ2_bzDecompressInit</code></h3></div></div></div>
    1345. 

  1345. <pre class="programlisting">int BZ2_bzDecompressInit ( bz_stream *strm, int verbosity, int small );</pre>
    1346. 

  1346. <p>Prepares for decompression.  As with
    1347. 

  1347. <code class="computeroutput">BZ2_bzCompressInit</code>, a
    1348. 

  1348. <code class="computeroutput">bz_stream</code> record should be
    1349. 

  1349. allocated and initialised before the call.  Fields
    1350. 

  1350. <code class="computeroutput">bzalloc</code>,
    1351. 

  1351. <code class="computeroutput">bzfree</code> and
    1352. 

  1352. <code class="computeroutput">opaque</code> should be set if a custom
    1353. 

  1353. memory allocator is required, or made
    1354. 

  1354. <code class="computeroutput">NULL</code> for the normal
    1355. 

  1355. <code class="computeroutput">malloc</code> /
    1356. 

  1356. <code class="computeroutput">free</code> routines.  Upon return, the
    1357. 

  1357. internal state will have been initialised, and
    1358. 

  1358. <code class="computeroutput">total_in</code> and
    1359. 

  1359. <code class="computeroutput">total_out</code> will be zero.</p>
    1360. 

  1360. <p>For the meaning of parameter
    1361. 

  1361. <code class="computeroutput">verbosity</code>, see
    1362. 

  1362. <code class="computeroutput">BZ2_bzCompressInit</code>.</p>
    1363. 

  1363. <p>If <code class="computeroutput">small</code> is nonzero, the
    1364. 

  1364. library will use an alternative decompression algorithm which
    1365. 

  1365. uses less memory but at the cost of decompressing more slowly
    1366. 

  1366. (roughly speaking, half the speed, but the maximum memory
    1367. 

  1367. requirement drops to around 2300k).  See <a href="#using">How to use bzip2</a>
    1368. 

  1368. for more information on memory management.</p>
    1369. 

  1369. <p>Note that the amount of memory needed to decompress a
    1370. 

  1370. stream cannot be determined until the stream's header has been
    1371. 

  1371. read, so even if
    1372. 

  1372. <code class="computeroutput">BZ2_bzDecompressInit</code> succeeds, a
    1373. 

  1373. subsequent <code class="computeroutput">BZ2_bzDecompress</code>
    1374. 

  1374. could fail with
    1375. 

  1375. <code class="computeroutput">BZ_MEM_ERROR</code>.</p>
    1376. 

  1376. <p>Possible return values:</p>
    1377. 

  1377. <pre class="programlisting">BZ_CONFIG_ERROR
    1378. 

  1378.   if the library has been mis-compiled
    1379. 

  1379. BZ_PARAM_ERROR
    1380. 

  1380.   if ( small != 0 &amp;&amp; small != 1 )
    1381. 

  1381.   or (verbosity &lt;; 0 || verbosity &gt; 4)
    1382. 

  1382. BZ_MEM_ERROR
    1383. 

  1383.   if insufficient memory is available</pre>
    1384. 

  1384. <p>Allowable next actions:</p>
    1385. 

  1385. <pre class="programlisting">BZ2_bzDecompress
    1386. 

  1386.   if BZ_OK was returned
    1387. 

  1387.   no specific action required in case of error</pre>
    1388. 

  1388. </div>
    1389. 

  1389. <div class="sect2" lang="en">
    1390. 

  1390. <div class="titlepage"><div><div><h3 class="title">
    1391. 

  1391. <a name="bzDecompress"></a>3.3.5. <code class="computeroutput">BZ2_bzDecompress</code></h3></div></div></div>
    1392. 

  1392. <pre class="programlisting">int BZ2_bzDecompress ( bz_stream *strm );</pre>
    1393. 

  1393. <p>Provides more input and/out output buffer space for the
    1394. 

  1394. library.  The caller maintains input and output buffers, and uses
    1395. 

  1395. <code class="computeroutput">BZ2_bzDecompress</code> to transfer
    1396. 

  1396. data between them.</p>
    1397. 

  1397. <p>Before each call to
    1398. 

  1398. <code class="computeroutput">BZ2_bzDecompress</code>,
    1399. 

  1399. <code class="computeroutput">next_in</code> should point at the
    1400. 

  1400. compressed data, and <code class="computeroutput">avail_in</code>
    1401. 

  1401. should indicate how many bytes the library may read.
    1402. 

  1402. <code class="computeroutput">BZ2_bzDecompress</code> updates
    1403. 

  1403. <code class="computeroutput">next_in</code>,
    1404. 

  1404. <code class="computeroutput">avail_in</code> and
    1405. 

  1405. <code class="computeroutput">total_in</code> to reflect the number
    1406. 

  1406. of bytes it has read.</p>
    1407. 

  1407. <p>Similarly, <code class="computeroutput">next_out</code> should
    1408. 

  1408. point to a buffer in which the uncompressed output is to be
    1409. 

  1409. placed, with <code class="computeroutput">avail_out</code>
    1410. 

  1410. indicating how much output space is available.
    1411. 

  1411. <code class="computeroutput">BZ2_bzCompress</code> updates
    1412. 

  1412. <code class="computeroutput">next_out</code>,
    1413. 

  1413. <code class="computeroutput">avail_out</code> and
    1414. 

  1414. <code class="computeroutput">total_out</code> to reflect the number
    1415. 

  1415. of bytes output.</p>
    1416. 

  1416. <p>You may provide and remove as little or as much data as you
    1417. 

  1417. like on each call of
    1418. 

  1418. <code class="computeroutput">BZ2_bzDecompress</code>.  In the limit,
    1419. 

  1419. it is acceptable to supply and remove data one byte at a time,
    1420. 

  1420. although this would be terribly inefficient.  You should always
    1421. 

  1421. ensure that at least one byte of output space is available at
    1422. 

  1422. each call.</p>
    1423. 

  1423. <p>Use of <code class="computeroutput">BZ2_bzDecompress</code> is
    1424. 

  1424. simpler than
    1425. 

  1425. <code class="computeroutput">BZ2_bzCompress</code>.</p>
    1426. 

  1426. <p>You should provide input and remove output as described
    1427. 

  1427. above, and repeatedly call
    1428. 

  1428. <code class="computeroutput">BZ2_bzDecompress</code> until
    1429. 

  1429. <code class="computeroutput">BZ_STREAM_END</code> is returned.
    1430. 

  1430. Appearance of <code class="computeroutput">BZ_STREAM_END</code>
    1431. 

  1431. denotes that <code class="computeroutput">BZ2_bzDecompress</code>
    1432. 

  1432. has detected the logical end of the compressed stream.
    1433. 

  1433. <code class="computeroutput">BZ2_bzDecompress</code> will not
    1434. 

  1434. produce <code class="computeroutput">BZ_STREAM_END</code> until all
    1435. 

  1435. output data has been placed into the output buffer, so once
    1436. 

  1436. <code class="computeroutput">BZ_STREAM_END</code> appears, you are
    1437. 

  1437. guaranteed to have available all the decompressed output, and
    1438. 

  1438. <code class="computeroutput">BZ2_bzDecompressEnd</code> can safely
    1439. 

  1439. be called.</p>
    1440. 

  1440. <p>If case of an error return value, you should call
    1441. 

  1441. <code class="computeroutput">BZ2_bzDecompressEnd</code> to clean up
    1442. 

  1442. and release memory.</p>
    1443. 

  1443. <p>Possible return values:</p>
    1444. 

  1444. <pre class="programlisting">BZ_PARAM_ERROR
    1445. 

  1445.   if strm is NULL or strm-&gt;s is NULL
    1446. 

  1446.   or strm-&gt;avail_out &lt; 1
    1447. 

  1447. BZ_DATA_ERROR
    1448. 

  1448.   if a data integrity error is detected in the compressed stream
    1449. 

  1449. BZ_DATA_ERROR_MAGIC
    1450. 

  1450.   if the compressed stream doesn't begin with the right magic bytes
    1451. 

  1451. BZ_MEM_ERROR
    1452. 

  1452.   if there wasn't enough memory available
    1453. 

  1453. BZ_STREAM_END
    1454. 

  1454.   if the logical end of the data stream was detected and all
    1455. 

  1455.   output in has been consumed, eg s--&gt;avail_out &gt; 0
    1456. 

  1456. BZ_OK
    1457. 

  1457.   otherwise</pre>
    1458. 

  1458. <p>Allowable next actions:</p>
    1459. 

  1459. <pre class="programlisting">BZ2_bzDecompress
    1460. 

  1460.   if BZ_OK was returned
    1461. 

  1461. BZ2_bzDecompressEnd
    1462. 

  1462.   otherwise</pre>
    1463. 

  1463. </div>
    1464. 

  1464. <div class="sect2" lang="en">
    1465. 

  1465. <div class="titlepage"><div><div><h3 class="title">
    1466. 

  1466. <a name="bzDecompress-end"></a>3.3.6. <code class="computeroutput">BZ2_bzDecompressEnd</code></h3></div></div></div>
    1467. 

  1467. <pre class="programlisting">int BZ2_bzDecompressEnd ( bz_stream *strm );</pre>
    1468. 

  1468. <p>Releases all memory associated with a decompression
    1469. 

  1469. stream.</p>
    1470. 

  1470. <p>Possible return values:</p>
    1471. 

  1471. <pre class="programlisting">BZ_PARAM_ERROR
    1472. 

  1472.   if strm is NULL or strm-&gt;s is NULL
    1473. 

  1473. BZ_OK
    1474. 

  1474.   otherwise</pre>
    1475. 

  1475. <p>Allowable next actions:</p>
    1476. 

  1476. <pre class="programlisting">  None.</pre>
    1477. 

  1477. </div>
    1478. 

  1478. </div>
    1479. 

  1479. <div class="sect1" lang="en">
    1480. 

  1480. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    1481. 

  1481. <a name="hl-interface"></a>3.4. High-level interface</h2></div></div></div>
    1482. 

  1482. <p>This interface provides functions for reading and writing
    1483. 

  1483. <code class="computeroutput">bzip2</code> format files.  First, some
    1484. 

  1484. general points.</p>
    1485. 

  1485. <div class="itemizedlist"><ul type="bullet">
    1486. 

  1486. <li style="list-style-type: disc"><p>All of the functions take an
    1487. 

  1487.   <code class="computeroutput">int*</code> first argument,
    1488. 

  1488.   <code class="computeroutput">bzerror</code>.  After each call,
    1489. 

  1489.   <code class="computeroutput">bzerror</code> should be consulted
    1490. 

  1490.   first to determine the outcome of the call.  If
    1491. 

  1491.   <code class="computeroutput">bzerror</code> is
    1492. 

  1492.   <code class="computeroutput">BZ_OK</code>, the call completed
    1493. 

  1493.   successfully, and only then should the return value of the
    1494. 

  1494.   function (if any) be consulted.  If
    1495. 

  1495.   <code class="computeroutput">bzerror</code> is
    1496. 

  1496.   <code class="computeroutput">BZ_IO_ERROR</code>, there was an
    1497. 

  1497.   error reading/writing the underlying compressed file, and you
    1498. 

  1498.   should then consult <code class="computeroutput">errno</code> /
    1499. 

  1499.   <code class="computeroutput">perror</code> to determine the cause
    1500. 

  1500.   of the difficulty.  <code class="computeroutput">bzerror</code>
    1501. 

  1501.   may also be set to various other values; precise details are
    1502. 

  1502.   given on a per-function basis below.</p></li>
    1503. 

  1503. <li style="list-style-type: disc"><p>If <code class="computeroutput">bzerror</code> indicates
    1504. 

  1504.   an error (ie, anything except
    1505. 

  1505.   <code class="computeroutput">BZ_OK</code> and
    1506. 

  1506.   <code class="computeroutput">BZ_STREAM_END</code>), you should
    1507. 

  1507.   immediately call
    1508. 

  1508.   <code class="computeroutput">BZ2_bzReadClose</code> (or
    1509. 

  1509.   <code class="computeroutput">BZ2_bzWriteClose</code>, depending on
    1510. 

  1510.   whether you are attempting to read or to write) to free up all
    1511. 

  1511.   resources associated with the stream.  Once an error has been
    1512. 

  1512.   indicated, behaviour of all calls except
    1513. 

  1513.   <code class="computeroutput">BZ2_bzReadClose</code>
    1514. 

  1514.   (<code class="computeroutput">BZ2_bzWriteClose</code>) is
    1515. 

  1515.   undefined.  The implication is that (1)
    1516. 

  1516.   <code class="computeroutput">bzerror</code> should be checked
    1517. 

  1517.   after each call, and (2) if
    1518. 

  1518.   <code class="computeroutput">bzerror</code> indicates an error,
    1519. 

  1519.   <code class="computeroutput">BZ2_bzReadClose</code>
    1520. 

  1520.   (<code class="computeroutput">BZ2_bzWriteClose</code>) should then
    1521. 

  1521.   be called to clean up.</p></li>
    1522. 

  1522. <li style="list-style-type: disc"><p>The <code class="computeroutput">FILE*</code> arguments
    1523. 

  1523.   passed to <code class="computeroutput">BZ2_bzReadOpen</code> /
    1524. 

  1524.   <code class="computeroutput">BZ2_bzWriteOpen</code> should be set
    1525. 

  1525.   to binary mode.  Most Unix systems will do this by default, but
    1526. 

  1526.   other platforms, including Windows and Mac, will not.  If you
    1527. 

  1527.   omit this, you may encounter problems when moving code to new
    1528. 

  1528.   platforms.</p></li>
    1529. 

  1529. <li style="list-style-type: disc"><p>Memory allocation requests are handled by
    1530. 

  1530.   <code class="computeroutput">malloc</code> /
    1531. 

  1531.   <code class="computeroutput">free</code>.  At present there is no
    1532. 

  1532.   facility for user-defined memory allocators in the file I/O
    1533. 

  1533.   functions (could easily be added, though).</p></li>
    1534. 

  1534. </ul></div>
    1535. 

  1535. <div class="sect2" lang="en">
    1536. 

  1536. <div class="titlepage"><div><div><h3 class="title">
    1537. 

  1537. <a name="bzreadopen"></a>3.4.1. <code class="computeroutput">BZ2_bzReadOpen</code></h3></div></div></div>
    1538. 

  1538. <pre class="programlisting">typedef void BZFILE;
    1539. 

  1539. 

  1540. BZFILE *BZ2_bzReadOpen( int *bzerror, FILE *f, 
    1541. 

  1541.                         int verbosity, int small,
    1542. 

  1542.                         void *unused, int nUnused );</pre>
    1543. 

  1543. <p>Prepare to read compressed data from file handle
    1544. 

  1544. <code class="computeroutput">f</code>.
    1545. 

  1545. <code class="computeroutput">f</code> should refer to a file which
    1546. 

  1546. has been opened for reading, and for which the error indicator
    1547. 

  1547. (<code class="computeroutput">ferror(f)</code>)is not set.  If
    1548. 

  1548. <code class="computeroutput">small</code> is 1, the library will try
    1549. 

  1549. to decompress using less memory, at the expense of speed.</p>
    1550. 

  1550. <p>For reasons explained below,
    1551. 

  1551. <code class="computeroutput">BZ2_bzRead</code> will decompress the
    1552. 

  1552. <code class="computeroutput">nUnused</code> bytes starting at
    1553. 

  1553. <code class="computeroutput">unused</code>, before starting to read
    1554. 

  1554. from the file <code class="computeroutput">f</code>.  At most
    1555. 

  1555. <code class="computeroutput">BZ_MAX_UNUSED</code> bytes may be
    1556. 

  1556. supplied like this.  If this facility is not required, you should
    1557. 

  1557. pass <code class="computeroutput">NULL</code> and
    1558. 

  1558. <code class="computeroutput">0</code> for
    1559. 

  1559. <code class="computeroutput">unused</code> and
    1560. 

  1560. n<code class="computeroutput">Unused</code> respectively.</p>
    1561. 

  1561. <p>For the meaning of parameters
    1562. 

  1562. <code class="computeroutput">small</code> and
    1563. 

  1563. <code class="computeroutput">verbosity</code>, see
    1564. 

  1564. <code class="computeroutput">BZ2_bzDecompressInit</code>.</p>
    1565. 

  1565. <p>The amount of memory needed to decompress a file cannot be
    1566. 

  1566. determined until the file's header has been read.  So it is
    1567. 

  1567. possible that <code class="computeroutput">BZ2_bzReadOpen</code>
    1568. 

  1568. returns <code class="computeroutput">BZ_OK</code> but a subsequent
    1569. 

  1569. call of <code class="computeroutput">BZ2_bzRead</code> will return
    1570. 

  1570. <code class="computeroutput">BZ_MEM_ERROR</code>.</p>
    1571. 

  1571. <p>Possible assignments to
    1572. 

  1572. <code class="computeroutput">bzerror</code>:</p>
    1573. 

  1573. <pre class="programlisting">BZ_CONFIG_ERROR
    1574. 

  1574.   if the library has been mis-compiled
    1575. 

  1575. BZ_PARAM_ERROR
    1576. 

  1576.   if f is NULL
    1577. 

  1577.   or small is neither 0 nor 1
    1578. 

  1578.   or ( unused == NULL &amp;&amp; nUnused != 0 )
    1579. 

  1579.   or ( unused != NULL &amp;&amp; !(0 &lt;= nUnused &lt;= BZ_MAX_UNUSED) )
    1580. 

  1580. BZ_IO_ERROR
    1581. 

  1581.   if ferror(f) is nonzero
    1582. 

  1582. BZ_MEM_ERROR
    1583. 

  1583.   if insufficient memory is available
    1584. 

  1584. BZ_OK
    1585. 

  1585.   otherwise.</pre>
    1586. 

  1586. <p>Possible return values:</p>
    1587. 

  1587. <pre class="programlisting">Pointer to an abstract BZFILE
    1588. 

  1588.   if bzerror is BZ_OK
    1589. 

  1589. NULL
    1590. 

  1590.   otherwise</pre>
    1591. 

  1591. <p>Allowable next actions:</p>
    1592. 

  1592. <pre class="programlisting">BZ2_bzRead
    1593. 

  1593.   if bzerror is BZ_OK
    1594. 

  1594. BZ2_bzClose
    1595. 

  1595.   otherwise</pre>
    1596. 

  1596. </div>
    1597. 

  1597. <div class="sect2" lang="en">
    1598. 

  1598. <div class="titlepage"><div><div><h3 class="title">
    1599. 

  1599. <a name="bzread"></a>3.4.2. <code class="computeroutput">BZ2_bzRead</code></h3></div></div></div>
    1600. 

  1600. <pre class="programlisting">int BZ2_bzRead ( int *bzerror, BZFILE *b, void *buf, int len );</pre>
    1601. 

  1601. <p>Reads up to <code class="computeroutput">len</code>
    1602. 

  1602. (uncompressed) bytes from the compressed file
    1603. 

  1603. <code class="computeroutput">b</code> into the buffer
    1604. 

  1604. <code class="computeroutput">buf</code>.  If the read was
    1605. 

  1605. successful, <code class="computeroutput">bzerror</code> is set to
    1606. 

  1606. <code class="computeroutput">BZ_OK</code> and the number of bytes
    1607. 

  1607. read is returned.  If the logical end-of-stream was detected,
    1608. 

  1608. <code class="computeroutput">bzerror</code> will be set to
    1609. 

  1609. <code class="computeroutput">BZ_STREAM_END</code>, and the number of
    1610. 

  1610. bytes read is returned.  All other
    1611. 

  1611. <code class="computeroutput">bzerror</code> values denote an
    1612. 

  1612. error.</p>
    1613. 

  1613. <p><code class="computeroutput">BZ2_bzRead</code> will supply
    1614. 

  1614. <code class="computeroutput">len</code> bytes, unless the logical
    1615. 

  1615. stream end is detected or an error occurs.  Because of this, it
    1616. 

  1616. is possible to detect the stream end by observing when the number
    1617. 

  1617. of bytes returned is less than the number requested.
    1618. 

  1618. Nevertheless, this is regarded as inadvisable; you should instead
    1619. 

  1619. check <code class="computeroutput">bzerror</code> after every call
    1620. 

  1620. and watch out for
    1621. 

  1621. <code class="computeroutput">BZ_STREAM_END</code>.</p>
    1622. 

  1622. <p>Internally, <code class="computeroutput">BZ2_bzRead</code>
    1623. 

  1623. copies data from the compressed file in chunks of size
    1624. 

  1624. <code class="computeroutput">BZ_MAX_UNUSED</code> bytes before
    1625. 

  1625. decompressing it.  If the file contains more bytes than strictly
    1626. 

  1626. needed to reach the logical end-of-stream,
    1627. 

  1627. <code class="computeroutput">BZ2_bzRead</code> will almost certainly
    1628. 

  1628. read some of the trailing data before signalling
    1629. 

  1629. <code class="computeroutput">BZ_SEQUENCE_END</code>.  To collect the
    1630. 

  1630. read but unused data once
    1631. 

  1631. <code class="computeroutput">BZ_SEQUENCE_END</code> has appeared,
    1632. 

  1632. call <code class="computeroutput">BZ2_bzReadGetUnused</code>
    1633. 

  1633. immediately before
    1634. 

  1634. <code class="computeroutput">BZ2_bzReadClose</code>.</p>
    1635. 

  1635. <p>Possible assignments to
    1636. 

  1636. <code class="computeroutput">bzerror</code>:</p>
    1637. 

  1637. <pre class="programlisting">BZ_PARAM_ERROR
    1638. 

  1638.   if b is NULL or buf is NULL or len &lt; 0
    1639. 

  1639. BZ_SEQUENCE_ERROR
    1640. 

  1640.   if b was opened with BZ2_bzWriteOpen
    1641. 

  1641. BZ_IO_ERROR
    1642. 

  1642.   if there is an error reading from the compressed file
    1643. 

  1643. BZ_UNEXPECTED_EOF
    1644. 

  1644.   if the compressed file ended before 
    1645. 

  1645.   the logical end-of-stream was detected
    1646. 

  1646. BZ_DATA_ERROR
    1647. 

  1647.   if a data integrity error was detected in the compressed stream
    1648. 

  1648. BZ_DATA_ERROR_MAGIC
    1649. 

  1649.   if the stream does not begin with the requisite header bytes 
    1650. 

  1650.   (ie, is not a bzip2 data file).  This is really 
    1651. 

  1651.   a special case of BZ_DATA_ERROR.
    1652. 

  1652. BZ_MEM_ERROR
    1653. 

  1653.   if insufficient memory was available
    1654. 

  1654. BZ_STREAM_END
    1655. 

  1655.   if the logical end of stream was detected.
    1656. 

  1656. BZ_OK
    1657. 

  1657.   otherwise.</pre>
    1658. 

  1658. <p>Possible return values:</p>
    1659. 

  1659. <pre class="programlisting">number of bytes read
    1660. 

  1660.   if bzerror is BZ_OK or BZ_STREAM_END
    1661. 

  1661. undefined
    1662. 

  1662.   otherwise</pre>
    1663. 

  1663. <p>Allowable next actions:</p>
    1664. 

  1664. <pre class="programlisting">collect data from buf, then BZ2_bzRead or BZ2_bzReadClose
    1665. 

  1665.   if bzerror is BZ_OK
    1666. 

  1666. collect data from buf, then BZ2_bzReadClose or BZ2_bzReadGetUnused
    1667. 

  1667.   if bzerror is BZ_SEQUENCE_END
    1668. 

  1668. BZ2_bzReadClose
    1669. 

  1669.   otherwise</pre>
    1670. 

  1670. </div>
    1671. 

  1671. <div class="sect2" lang="en">
    1672. 

  1672. <div class="titlepage"><div><div><h3 class="title">
    1673. 

  1673. <a name="bzreadgetunused"></a>3.4.3. <code class="computeroutput">BZ2_bzReadGetUnused</code></h3></div></div></div>
    1674. 

  1674. <pre class="programlisting">void BZ2_bzReadGetUnused( int* bzerror, BZFILE *b, 
    1675. 

  1675.                           void** unused, int* nUnused );</pre>
    1676. 

  1676. <p>Returns data which was read from the compressed file but
    1677. 

  1677. was not needed to get to the logical end-of-stream.
    1678. 

  1678. <code class="computeroutput">*unused</code> is set to the address of
    1679. 

  1679. the data, and <code class="computeroutput">*nUnused</code> to the
    1680. 

  1680. number of bytes.  <code class="computeroutput">*nUnused</code> will
    1681. 

  1681. be set to a value between <code class="computeroutput">0</code> and
    1682. 

  1682. <code class="computeroutput">BZ_MAX_UNUSED</code> inclusive.</p>
    1683. 

  1683. <p>This function may only be called once
    1684. 

  1684. <code class="computeroutput">BZ2_bzRead</code> has signalled
    1685. 

  1685. <code class="computeroutput">BZ_STREAM_END</code> but before
    1686. 

  1686. <code class="computeroutput">BZ2_bzReadClose</code>.</p>
    1687. 

  1687. <p>Possible assignments to
    1688. 

  1688. <code class="computeroutput">bzerror</code>:</p>
    1689. 

  1689. <pre class="programlisting">BZ_PARAM_ERROR
    1690. 

  1690.   if b is NULL
    1691. 

  1691.   or unused is NULL or nUnused is NULL
    1692. 

  1692. BZ_SEQUENCE_ERROR
    1693. 

  1693.   if BZ_STREAM_END has not been signalled
    1694. 

  1694.   or if b was opened with BZ2_bzWriteOpen
    1695. 

  1695. BZ_OK
    1696. 

  1696.   otherwise</pre>
    1697. 

  1697. <p>Allowable next actions:</p>
    1698. 

  1698. <pre class="programlisting">BZ2_bzReadClose</pre>
    1699. 

  1699. </div>
    1700. 

  1700. <div class="sect2" lang="en">
    1701. 

  1701. <div class="titlepage"><div><div><h3 class="title">
    1702. 

  1702. <a name="bzreadclose"></a>3.4.4. <code class="computeroutput">BZ2_bzReadClose</code></h3></div></div></div>
    1703. 

  1703. <pre class="programlisting">void BZ2_bzReadClose ( int *bzerror, BZFILE *b );</pre>
    1704. 

  1704. <p>Releases all memory pertaining to the compressed file
    1705. 

  1705. <code class="computeroutput">b</code>.
    1706. 

  1706. <code class="computeroutput">BZ2_bzReadClose</code> does not call
    1707. 

  1707. <code class="computeroutput">fclose</code> on the underlying file
    1708. 

  1708. handle, so you should do that yourself if appropriate.
    1709. 

  1709. <code class="computeroutput">BZ2_bzReadClose</code> should be called
    1710. 

  1710. to clean up after all error situations.</p>
    1711. 

  1711. <p>Possible assignments to
    1712. 

  1712. <code class="computeroutput">bzerror</code>:</p>
    1713. 

  1713. <pre class="programlisting">BZ_SEQUENCE_ERROR
    1714. 

  1714.   if b was opened with BZ2_bzOpenWrite
    1715. 

  1715. BZ_OK
    1716. 

  1716.   otherwise</pre>
    1717. 

  1717. <p>Allowable next actions:</p>
    1718. 

  1718. <pre class="programlisting">none</pre>
    1719. 

  1719. </div>
    1720. 

  1720. <div class="sect2" lang="en">
    1721. 

  1721. <div class="titlepage"><div><div><h3 class="title">
    1722. 

  1722. <a name="bzwriteopen"></a>3.4.5. <code class="computeroutput">BZ2_bzWriteOpen</code></h3></div></div></div>
    1723. 

  1723. <pre class="programlisting">BZFILE *BZ2_bzWriteOpen( int *bzerror, FILE *f, 
    1724. 

  1724.                          int blockSize100k, int verbosity,
    1725. 

  1725.                          int workFactor );</pre>
    1726. 

  1726. <p>Prepare to write compressed data to file handle
    1727. 

  1727. <code class="computeroutput">f</code>.
    1728. 

  1728. <code class="computeroutput">f</code> should refer to a file which
    1729. 

  1729. has been opened for writing, and for which the error indicator
    1730. 

  1730. (<code class="computeroutput">ferror(f)</code>)is not set.</p>
    1731. 

  1731. <p>For the meaning of parameters
    1732. 

  1732. <code class="computeroutput">blockSize100k</code>,
    1733. 

  1733. <code class="computeroutput">verbosity</code> and
    1734. 

  1734. <code class="computeroutput">workFactor</code>, see
    1735. 

  1735. <code class="computeroutput">BZ2_bzCompressInit</code>.</p>
    1736. 

  1736. <p>All required memory is allocated at this stage, so if the
    1737. 

  1737. call completes successfully,
    1738. 

  1738. <code class="computeroutput">BZ_MEM_ERROR</code> cannot be signalled
    1739. 

  1739. by a subsequent call to
    1740. 

  1740. <code class="computeroutput">BZ2_bzWrite</code>.</p>
    1741. 

  1741. <p>Possible assignments to
    1742. 

  1742. <code class="computeroutput">bzerror</code>:</p>
    1743. 

  1743. <pre class="programlisting">BZ_CONFIG_ERROR
    1744. 

  1744.   if the library has been mis-compiled
    1745. 

  1745. BZ_PARAM_ERROR
    1746. 

  1746.   if f is NULL
    1747. 

  1747.   or blockSize100k &lt; 1 or blockSize100k &gt; 9
    1748. 

  1748. BZ_IO_ERROR
    1749. 

  1749.   if ferror(f) is nonzero
    1750. 

  1750. BZ_MEM_ERROR
    1751. 

  1751.   if insufficient memory is available
    1752. 

  1752. BZ_OK
    1753. 

  1753.   otherwise</pre>
    1754. 

  1754. <p>Possible return values:</p>
    1755. 

  1755. <pre class="programlisting">Pointer to an abstract BZFILE
    1756. 

  1756.   if bzerror is BZ_OK
    1757. 

  1757. NULL
    1758. 

  1758.   otherwise</pre>
    1759. 

  1759. <p>Allowable next actions:</p>
    1760. 

  1760. <pre class="programlisting">BZ2_bzWrite
    1761. 

  1761.   if bzerror is BZ_OK
    1762. 

  1762.   (you could go directly to BZ2_bzWriteClose, but this would be pretty pointless)
    1763. 

  1763. BZ2_bzWriteClose
    1764. 

  1764.   otherwise</pre>
    1765. 

  1765. </div>
    1766. 

  1766. <div class="sect2" lang="en">
    1767. 

  1767. <div class="titlepage"><div><div><h3 class="title">
    1768. 

  1768. <a name="bzwrite"></a>3.4.6. <code class="computeroutput">BZ2_bzWrite</code></h3></div></div></div>
    1769. 

  1769. <pre class="programlisting">void BZ2_bzWrite ( int *bzerror, BZFILE *b, void *buf, int len );</pre>
    1770. 

  1770. <p>Absorbs <code class="computeroutput">len</code> bytes from the
    1771. 

  1771. buffer <code class="computeroutput">buf</code>, eventually to be
    1772. 

  1772. compressed and written to the file.</p>
    1773. 

  1773. <p>Possible assignments to
    1774. 

  1774. <code class="computeroutput">bzerror</code>:</p>
    1775. 

  1775. <pre class="programlisting">BZ_PARAM_ERROR
    1776. 

  1776.   if b is NULL or buf is NULL or len &lt; 0
    1777. 

  1777. BZ_SEQUENCE_ERROR
    1778. 

  1778.   if b was opened with BZ2_bzReadOpen
    1779. 

  1779. BZ_IO_ERROR
    1780. 

  1780.   if there is an error writing the compressed file.
    1781. 

  1781. BZ_OK
    1782. 

  1782.   otherwise</pre>
    1783. 

  1783. </div>
    1784. 

  1784. <div class="sect2" lang="en">
    1785. 

  1785. <div class="titlepage"><div><div><h3 class="title">
    1786. 

  1786. <a name="bzwriteclose"></a>3.4.7. <code class="computeroutput">BZ2_bzWriteClose</code></h3></div></div></div>
    1787. 

  1787. <pre class="programlisting">void BZ2_bzWriteClose( int *bzerror, BZFILE* f,
    1788. 

  1788.                        int abandon,
    1789. 

  1789.                        unsigned int* nbytes_in,
    1790. 

  1790.                        unsigned int* nbytes_out );
    1791. 

  1791. 

  1792. void BZ2_bzWriteClose64( int *bzerror, BZFILE* f,
    1793. 

  1793.                          int abandon,
    1794. 

  1794.                          unsigned int* nbytes_in_lo32,
    1795. 

  1795.                          unsigned int* nbytes_in_hi32,
    1796. 

  1796.                          unsigned int* nbytes_out_lo32,
    1797. 

  1797.                          unsigned int* nbytes_out_hi32 );</pre>
    1798. 

  1798. <p>Compresses and flushes to the compressed file all data so
    1799. 

  1799. far supplied by <code class="computeroutput">BZ2_bzWrite</code>.
    1800. 

  1800. The logical end-of-stream markers are also written, so subsequent
    1801. 

  1801. calls to <code class="computeroutput">BZ2_bzWrite</code> are
    1802. 

  1802. illegal.  All memory associated with the compressed file
    1803. 

  1803. <code class="computeroutput">b</code> is released.
    1804. 

  1804. <code class="computeroutput">fflush</code> is called on the
    1805. 

  1805. compressed file, but it is not
    1806. 

  1806. <code class="computeroutput">fclose</code>'d.</p>
    1807. 

  1807. <p>If <code class="computeroutput">BZ2_bzWriteClose</code> is
    1808. 

  1808. called to clean up after an error, the only action is to release
    1809. 

  1809. the memory.  The library records the error codes issued by
    1810. 

  1810. previous calls, so this situation will be detected automatically.
    1811. 

  1811. There is no attempt to complete the compression operation, nor to
    1812. 

  1812. <code class="computeroutput">fflush</code> the compressed file.  You
    1813. 

  1813. can force this behaviour to happen even in the case of no error,
    1814. 

  1814. by passing a nonzero value to
    1815. 

  1815. <code class="computeroutput">abandon</code>.</p>
    1816. 

  1816. <p>If <code class="computeroutput">nbytes_in</code> is non-null,
    1817. 

  1817. <code class="computeroutput">*nbytes_in</code> will be set to be the
    1818. 

  1818. total volume of uncompressed data handled.  Similarly,
    1819. 

  1819. <code class="computeroutput">nbytes_out</code> will be set to the
    1820. 

  1820. total volume of compressed data written.  For compatibility with
    1821. 

  1821. older versions of the library,
    1822. 

  1822. <code class="computeroutput">BZ2_bzWriteClose</code> only yields the
    1823. 

  1823. lower 32 bits of these counts.  Use
    1824. 

  1824. <code class="computeroutput">BZ2_bzWriteClose64</code> if you want
    1825. 

  1825. the full 64 bit counts.  These two functions are otherwise
    1826. 

  1826. absolutely identical.</p>
    1827. 

  1827. <p>Possible assignments to
    1828. 

  1828. <code class="computeroutput">bzerror</code>:</p>
    1829. 

  1829. <pre class="programlisting">BZ_SEQUENCE_ERROR
    1830. 

  1830.   if b was opened with BZ2_bzReadOpen
    1831. 

  1831. BZ_IO_ERROR
    1832. 

  1832.   if there is an error writing the compressed file
    1833. 

  1833. BZ_OK
    1834. 

  1834.   otherwise</pre>
    1835. 

  1835. </div>
    1836. 

  1836. <div class="sect2" lang="en">
    1837. 

  1837. <div class="titlepage"><div><div><h3 class="title">
    1838. 

  1838. <a name="embed"></a>3.4.8. Handling embedded compressed data streams</h3></div></div></div>
    1839. 

  1839. <p>The high-level library facilitates use of
    1840. 

  1840. <code class="computeroutput">bzip2</code> data streams which form
    1841. 

  1841. some part of a surrounding, larger data stream.</p>
    1842. 

  1842. <div class="itemizedlist"><ul type="bullet">
    1843. 

  1843. <li style="list-style-type: disc"><p>For writing, the library takes an open file handle,
    1844. 

  1844.   writes compressed data to it,
    1845. 

  1845.   <code class="computeroutput">fflush</code>es it but does not
    1846. 

  1846.   <code class="computeroutput">fclose</code> it.  The calling
    1847. 

  1847.   application can write its own data before and after the
    1848. 

  1848.   compressed data stream, using that same file handle.</p></li>
    1849. 

  1849. <li style="list-style-type: disc"><p>Reading is more complex, and the facilities are not as
    1850. 

  1850.   general as they could be since generality is hard to reconcile
    1851. 

  1851.   with efficiency.  <code class="computeroutput">BZ2_bzRead</code>
    1852. 

  1852.   reads from the compressed file in blocks of size
    1853. 

  1853.   <code class="computeroutput">BZ_MAX_UNUSED</code> bytes, and in
    1854. 

  1854.   doing so probably will overshoot the logical end of compressed
    1855. 

  1855.   stream.  To recover this data once decompression has ended,
    1856. 

  1856.   call <code class="computeroutput">BZ2_bzReadGetUnused</code> after
    1857. 

  1857.   the last call of <code class="computeroutput">BZ2_bzRead</code>
    1858. 

  1858.   (the one returning
    1859. 

  1859.   <code class="computeroutput">BZ_STREAM_END</code>) but before
    1860. 

  1860.   calling
    1861. 

  1861.   <code class="computeroutput">BZ2_bzReadClose</code>.</p></li>
    1862. 

  1862. </ul></div>
    1863. 

  1863. <p>This mechanism makes it easy to decompress multiple
    1864. 

  1864. <code class="computeroutput">bzip2</code> streams placed end-to-end.
    1865. 

  1865. As the end of one stream, when
    1866. 

  1866. <code class="computeroutput">BZ2_bzRead</code> returns
    1867. 

  1867. <code class="computeroutput">BZ_STREAM_END</code>, call
    1868. 

  1868. <code class="computeroutput">BZ2_bzReadGetUnused</code> to collect
    1869. 

  1869. the unused data (copy it into your own buffer somewhere).  That
    1870. 

  1870. data forms the start of the next compressed stream.  To start
    1871. 

  1871. uncompressing that next stream, call
    1872. 

  1872. <code class="computeroutput">BZ2_bzReadOpen</code> again, feeding in
    1873. 

  1873. the unused data via the <code class="computeroutput">unused</code> /
    1874. 

  1874. <code class="computeroutput">nUnused</code> parameters.  Keep doing
    1875. 

  1875. this until <code class="computeroutput">BZ_STREAM_END</code> return
    1876. 

  1876. coincides with the physical end of file
    1877. 

  1877. (<code class="computeroutput">feof(f)</code>).  In this situation
    1878. 

  1878. <code class="computeroutput">BZ2_bzReadGetUnused</code> will of
    1879. 

  1879. course return no data.</p>
    1880. 

  1880. <p>This should give some feel for how the high-level interface
    1881. 

  1881. can be used.  If you require extra flexibility, you'll have to
    1882. 

  1882. bite the bullet and get to grips with the low-level
    1883. 

  1883. interface.</p>
    1884. 

  1884. </div>
    1885. 

  1885. <div class="sect2" lang="en">
    1886. 

  1886. <div class="titlepage"><div><div><h3 class="title">
    1887. 

  1887. <a name="std-rdwr"></a>3.4.9. Standard file-reading/writing code</h3></div></div></div>
    1888. 

  1888. <p>Here's how you'd write data to a compressed file:</p>
    1889. 

  1889. <pre class="programlisting">FILE*   f;
    1890. 

  1890. BZFILE* b;
    1891. 

  1891. int     nBuf;
    1892. 

  1892. char    buf[ /* whatever size you like */ ];
    1893. 

  1893. int     bzerror;
    1894. 

  1894. int     nWritten;
    1895. 

  1895. 

  1896. f = fopen ( "myfile.bz2", "w" );
    1897. 

  1897. if ( !f ) {
    1898. 

  1898.  /* handle error */
    1899. 

  1899. }
    1900. 

  1900. b = BZ2_bzWriteOpen( &amp;bzerror, f, 9 );
    1901. 

  1901. if (bzerror != BZ_OK) {
    1902. 

  1902.  BZ2_bzWriteClose ( b );
    1903. 

  1903.  /* handle error */
    1904. 

  1904. }
    1905. 

  1905. 

  1906. while ( /* condition */ ) {
    1907. 

  1907.  /* get data to write into buf, and set nBuf appropriately */
    1908. 

  1908.  nWritten = BZ2_bzWrite ( &amp;bzerror, b, buf, nBuf );
    1909. 

  1909.  if (bzerror == BZ_IO_ERROR) { 
    1910. 

  1910.    BZ2_bzWriteClose ( &amp;bzerror, b );
    1911. 

  1911.    /* handle error */
    1912. 

  1912.  }
    1913. 

  1913. }
    1914. 

  1914. 

  1915. BZ2_bzWriteClose( &amp;bzerror, b );
    1916. 

  1916. if (bzerror == BZ_IO_ERROR) {
    1917. 

  1917.  /* handle error */
    1918. 

  1918. }</pre>
    1919. 

  1919. <p>And to read from a compressed file:</p>
    1920. 

  1920. <pre class="programlisting">FILE*   f;
    1921. 

  1921. BZFILE* b;
    1922. 

  1922. int     nBuf;
    1923. 

  1923. char    buf[ /* whatever size you like */ ];
    1924. 

  1924. int     bzerror;
    1925. 

  1925. int     nWritten;
    1926. 

  1926. 

  1927. f = fopen ( "myfile.bz2", "r" );
    1928. 

  1928. if ( !f ) {
    1929. 

  1929.   /* handle error */
    1930. 

  1930. }
    1931. 

  1931. b = BZ2_bzReadOpen ( &amp;bzerror, f, 0, NULL, 0 );
    1932. 

  1932. if ( bzerror != BZ_OK ) {
    1933. 

  1933.   BZ2_bzReadClose ( &amp;bzerror, b );
    1934. 

  1934.   /* handle error */
    1935. 

  1935. }
    1936. 

  1936. 

  1937. bzerror = BZ_OK;
    1938. 

  1938. while ( bzerror == BZ_OK &amp;&amp; /* arbitrary other conditions */) {
    1939. 

  1939.   nBuf = BZ2_bzRead ( &amp;bzerror, b, buf, /* size of buf */ );
    1940. 

  1940.   if ( bzerror == BZ_OK ) {
    1941. 

  1941.     /* do something with buf[0 .. nBuf-1] */
    1942. 

  1942.   }
    1943. 

  1943. }
    1944. 

  1944. if ( bzerror != BZ_STREAM_END ) {
    1945. 

  1945.    BZ2_bzReadClose ( &amp;bzerror, b );
    1946. 

  1946.    /* handle error */
    1947. 

  1947. } else {
    1948. 

  1948.    BZ2_bzReadClose ( &amp;bzerror, b );
    1949. 

  1949. }</pre>
    1950. 

  1950. </div>
    1951. 

  1951. </div>
    1952. 

  1952. <div class="sect1" lang="en">
    1953. 

  1953. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    1954. 

  1954. <a name="util-fns"></a>3.5. Utility functions</h2></div></div></div>
    1955. 

  1955. <div class="sect2" lang="en">
    1956. 

  1956. <div class="titlepage"><div><div><h3 class="title">
    1957. 

  1957. <a name="bzbufftobuffcompress"></a>3.5.1. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code></h3></div></div></div>
    1958. 

  1958. <pre class="programlisting">int BZ2_bzBuffToBuffCompress( char*         dest,
    1959. 

  1959.                               unsigned int* destLen,
    1960. 

  1960.                               char*         source,
    1961. 

  1961.                               unsigned int  sourceLen,
    1962. 

  1962.                               int           blockSize100k,
    1963. 

  1963.                               int           verbosity,
    1964. 

  1964.                               int           workFactor );</pre>
    1965. 

  1965. <p>Attempts to compress the data in <code class="computeroutput">source[0
    1966. 

  1966. .. sourceLen-1]</code> into the destination buffer,
    1967. 

  1967. <code class="computeroutput">dest[0 .. *destLen-1]</code>.  If the
    1968. 

  1968. destination buffer is big enough,
    1969. 

  1969. <code class="computeroutput">*destLen</code> is set to the size of
    1970. 

  1970. the compressed data, and <code class="computeroutput">BZ_OK</code>
    1971. 

  1971. is returned.  If the compressed data won't fit,
    1972. 

  1972. <code class="computeroutput">*destLen</code> is unchanged, and
    1973. 

  1973. <code class="computeroutput">BZ_OUTBUFF_FULL</code> is
    1974. 

  1974. returned.</p>
    1975. 

  1975. <p>Compression in this manner is a one-shot event, done with a
    1976. 

  1976. single call to this function.  The resulting compressed data is a
    1977. 

  1977. complete <code class="computeroutput">bzip2</code> format data
    1978. 

  1978. stream.  There is no mechanism for making additional calls to
    1979. 

  1979. provide extra input data.  If you want that kind of mechanism,
    1980. 

  1980. use the low-level interface.</p>
    1981. 

  1981. <p>For the meaning of parameters
    1982. 

  1982. <code class="computeroutput">blockSize100k</code>,
    1983. 

  1983. <code class="computeroutput">verbosity</code> and
    1984. 

  1984. <code class="computeroutput">workFactor</code>, see
    1985. 

  1985. <code class="computeroutput">BZ2_bzCompressInit</code>.</p>
    1986. 

  1986. <p>To guarantee that the compressed data will fit in its
    1987. 

  1987. buffer, allocate an output buffer of size 1% larger than the
    1988. 

  1988. uncompressed data, plus six hundred extra bytes.</p>
    1989. 

  1989. <p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code>
    1990. 

  1990. will not write data at or beyond
    1991. 

  1991. <code class="computeroutput">dest[*destLen]</code>, even in case of
    1992. 

  1992. buffer overflow.</p>
    1993. 

  1993. <p>Possible return values:</p>
    1994. 

  1994. <pre class="programlisting">BZ_CONFIG_ERROR
    1995. 

  1995.   if the library has been mis-compiled
    1996. 

  1996. BZ_PARAM_ERROR
    1997. 

  1997.   if dest is NULL or destLen is NULL
    1998. 

  1998.   or blockSize100k &lt; 1 or blockSize100k &gt; 9
    1999. 

  1999.   or verbosity &lt; 0 or verbosity &gt; 4
    2000. 

  2000.   or workFactor &lt; 0 or workFactor &gt; 250
    2001. 

  2001. BZ_MEM_ERROR
    2002. 

  2002.   if insufficient memory is available 
    2003. 

  2003. BZ_OUTBUFF_FULL
    2004. 

  2004.   if the size of the compressed data exceeds *destLen
    2005. 

  2005. BZ_OK
    2006. 

  2006.   otherwise</pre>
    2007. 

  2007. </div>
    2008. 

  2008. <div class="sect2" lang="en">
    2009. 

  2009. <div class="titlepage"><div><div><h3 class="title">
    2010. 

  2010. <a name="bzbufftobuffdecompress"></a>3.5.2. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></h3></div></div></div>
    2011. 

  2011. <pre class="programlisting">int BZ2_bzBuffToBuffDecompress( char*         dest,
    2012. 

  2012.                                 unsigned int* destLen,
    2013. 

  2013.                                 char*         source,
    2014. 

  2014.                                 unsigned int  sourceLen,
    2015. 

  2015.                                 int           small,
    2016. 

  2016.                                 int           verbosity );</pre>
    2017. 

  2017. <p>Attempts to decompress the data in <code class="computeroutput">source[0
    2018. 

  2018. .. sourceLen-1]</code> into the destination buffer,
    2019. 

  2019. <code class="computeroutput">dest[0 .. *destLen-1]</code>.  If the
    2020. 

  2020. destination buffer is big enough,
    2021. 

  2021. <code class="computeroutput">*destLen</code> is set to the size of
    2022. 

  2022. the uncompressed data, and <code class="computeroutput">BZ_OK</code>
    2023. 

  2023. is returned.  If the compressed data won't fit,
    2024. 

  2024. <code class="computeroutput">*destLen</code> is unchanged, and
    2025. 

  2025. <code class="computeroutput">BZ_OUTBUFF_FULL</code> is
    2026. 

  2026. returned.</p>
    2027. 

  2027. <p><code class="computeroutput">source</code> is assumed to hold
    2028. 

  2028. a complete <code class="computeroutput">bzip2</code> format data
    2029. 

  2029. stream.
    2030. 

  2030. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code> tries
    2031. 

  2031. to decompress the entirety of the stream into the output
    2032. 

  2032. buffer.</p>
    2033. 

  2033. <p>For the meaning of parameters
    2034. 

  2034. <code class="computeroutput">small</code> and
    2035. 

  2035. <code class="computeroutput">verbosity</code>, see
    2036. 

  2036. <code class="computeroutput">BZ2_bzDecompressInit</code>.</p>
    2037. 

  2037. <p>Because the compression ratio of the compressed data cannot
    2038. 

  2038. be known in advance, there is no easy way to guarantee that the
    2039. 

  2039. output buffer will be big enough.  You may of course make
    2040. 

  2040. arrangements in your code to record the size of the uncompressed
    2041. 

  2041. data, but such a mechanism is beyond the scope of this
    2042. 

  2042. library.</p>
    2043. 

  2043. <p><code class="computeroutput">BZ2_bzBuffToBuffDecompress</code>
    2044. 

  2044. will not write data at or beyond
    2045. 

  2045. <code class="computeroutput">dest[*destLen]</code>, even in case of
    2046. 

  2046. buffer overflow.</p>
    2047. 

  2047. <p>Possible return values:</p>
    2048. 

  2048. <pre class="programlisting">BZ_CONFIG_ERROR
    2049. 

  2049.   if the library has been mis-compiled
    2050. 

  2050. BZ_PARAM_ERROR
    2051. 

  2051.   if dest is NULL or destLen is NULL
    2052. 

  2052.   or small != 0 &amp;&amp; small != 1
    2053. 

  2053.   or verbosity &lt; 0 or verbosity &gt; 4
    2054. 

  2054. BZ_MEM_ERROR
    2055. 

  2055.   if insufficient memory is available 
    2056. 

  2056. BZ_OUTBUFF_FULL
    2057. 

  2057.   if the size of the compressed data exceeds *destLen
    2058. 

  2058. BZ_DATA_ERROR
    2059. 

  2059.   if a data integrity error was detected in the compressed data
    2060. 

  2060. BZ_DATA_ERROR_MAGIC
    2061. 

  2061.   if the compressed data doesn't begin with the right magic bytes
    2062. 

  2062. BZ_UNEXPECTED_EOF
    2063. 

  2063.   if the compressed data ends unexpectedly
    2064. 

  2064. BZ_OK
    2065. 

  2065.   otherwise</pre>
    2066. 

  2066. </div>
    2067. 

  2067. </div>
    2068. 

  2068. <div class="sect1" lang="en">
    2069. 

  2069. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2070. 

  2070. <a name="zlib-compat"></a>3.6. <code class="computeroutput">zlib</code> compatibility functions</h2></div></div></div>
    2071. 

  2071. <p>Yoshioka Tsuneo has contributed some functions to give
    2072. 

  2072. better <code class="computeroutput">zlib</code> compatibility.
    2073. 

  2073. These functions are <code class="computeroutput">BZ2_bzopen</code>,
    2074. 

  2074. <code class="computeroutput">BZ2_bzread</code>,
    2075. 

  2075. <code class="computeroutput">BZ2_bzwrite</code>,
    2076. 

  2076. <code class="computeroutput">BZ2_bzflush</code>,
    2077. 

  2077. <code class="computeroutput">BZ2_bzclose</code>,
    2078. 

  2078. <code class="computeroutput">BZ2_bzerror</code> and
    2079. 

  2079. <code class="computeroutput">BZ2_bzlibVersion</code>.  These
    2080. 

  2080. functions are not (yet) officially part of the library.  If they
    2081. 

  2081. break, you get to keep all the pieces.  Nevertheless, I think
    2082. 

  2082. they work ok.</p>
    2083. 

  2083. <pre class="programlisting">typedef void BZFILE;
    2084. 

  2084. 

  2085. const char * BZ2_bzlibVersion ( void );</pre>
    2086. 

  2086. <p>Returns a string indicating the library version.</p>
    2087. 

  2087. <pre class="programlisting">BZFILE * BZ2_bzopen  ( const char *path, const char *mode );
    2088. 

  2088. BZFILE * BZ2_bzdopen ( int        fd,    const char *mode );</pre>
    2089. 

  2089. <p>Opens a <code class="computeroutput">.bz2</code> file for
    2090. 

  2090. reading or writing, using either its name or a pre-existing file
    2091. 

  2091. descriptor.  Analogous to <code class="computeroutput">fopen</code>
    2092. 

  2092. and <code class="computeroutput">fdopen</code>.</p>
    2093. 

  2093. <pre class="programlisting">int BZ2_bzread  ( BZFILE* b, void* buf, int len );
    2094. 

  2094. int BZ2_bzwrite ( BZFILE* b, void* buf, int len );</pre>
    2095. 

  2095. <p>Reads/writes data from/to a previously opened
    2096. 

  2096. <code class="computeroutput">BZFILE</code>.  Analogous to
    2097. 

  2097. <code class="computeroutput">fread</code> and
    2098. 

  2098. <code class="computeroutput">fwrite</code>.</p>
    2099. 

  2099. <pre class="programlisting">int  BZ2_bzflush ( BZFILE* b );
    2100. 

  2100. void BZ2_bzclose ( BZFILE* b );</pre>
    2101. 

  2101. <p>Flushes/closes a <code class="computeroutput">BZFILE</code>.
    2102. 

  2102. <code class="computeroutput">BZ2_bzflush</code> doesn't actually do
    2103. 

  2103. anything.  Analogous to <code class="computeroutput">fflush</code>
    2104. 

  2104. and <code class="computeroutput">fclose</code>.</p>
    2105. 

  2105. <pre class="programlisting">const char * BZ2_bzerror ( BZFILE *b, int *errnum )</pre>
    2106. 

  2106. <p>Returns a string describing the more recent error status of
    2107. 

  2107. <code class="computeroutput">b</code>, and also sets
    2108. 

  2108. <code class="computeroutput">*errnum</code> to its numerical
    2109. 

  2109. value.</p>
    2110. 

  2110. </div>
    2111. 

  2111. <div class="sect1" lang="en">
    2112. 

  2112. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2113. 

  2113. <a name="stdio-free"></a>3.7. Using the library in a <code class="computeroutput">stdio</code>-free environment</h2></div></div></div>
    2114. 

  2114. <div class="sect2" lang="en">
    2115. 

  2115. <div class="titlepage"><div><div><h3 class="title">
    2116. 

  2116. <a name="stdio-bye"></a>3.7.1. Getting rid of <code class="computeroutput">stdio</code></h3></div></div></div>
    2117. 

  2117. <p>In a deeply embedded application, you might want to use
    2118. 

  2118. just the memory-to-memory functions.  You can do this
    2119. 

  2119. conveniently by compiling the library with preprocessor symbol
    2120. 

  2120. <code class="computeroutput">BZ_NO_STDIO</code> defined.  Doing this
    2121. 

  2121. gives you a library containing only the following eight
    2122. 

  2122. functions:</p>
    2123. 

  2123. <p><code class="computeroutput">BZ2_bzCompressInit</code>,
    2124. 

  2124. <code class="computeroutput">BZ2_bzCompress</code>,
    2125. 

  2125. <code class="computeroutput">BZ2_bzCompressEnd</code>
    2126. 

  2126. <code class="computeroutput">BZ2_bzDecompressInit</code>,
    2127. 

  2127. <code class="computeroutput">BZ2_bzDecompress</code>,
    2128. 

  2128. <code class="computeroutput">BZ2_bzDecompressEnd</code>
    2129. 

  2129. <code class="computeroutput">BZ2_bzBuffToBuffCompress</code>,
    2130. 

  2130. <code class="computeroutput">BZ2_bzBuffToBuffDecompress</code></p>
    2131. 

  2131. <p>When compiled like this, all functions will ignore
    2132. 

  2132. <code class="computeroutput">verbosity</code> settings.</p>
    2133. 

  2133. </div>
    2134. 

  2134. <div class="sect2" lang="en">
    2135. 

  2135. <div class="titlepage"><div><div><h3 class="title">
    2136. 

  2136. <a name="critical-error"></a>3.7.2. Critical error handling</h3></div></div></div>
    2137. 

  2137. <p><code class="computeroutput">libbzip2</code> contains a number
    2138. 

  2138. of internal assertion checks which should, needless to say, never
    2139. 

  2139. be activated.  Nevertheless, if an assertion should fail,
    2140. 

  2140. behaviour depends on whether or not the library was compiled with
    2141. 

  2141. <code class="computeroutput">BZ_NO_STDIO</code> set.</p>
    2142. 

  2142. <p>For a normal compile, an assertion failure yields the
    2143. 

  2143. message:</p>
    2144. 

  2144. <div class="blockquote"><blockquote class="blockquote">
    2145. 

  2145. <p>bzip2/libbzip2: internal error number N.</p>
    2146. 

  2146. <p>This is a bug in bzip2/libbzip2, 1.0.5 of 10 December 2007.
    2147. 

  2147. Please report it to me at: jseward@bzip.org.  If this happened
    2148. 

  2148. when you were using some program which uses libbzip2 as a
    2149. 

  2149. component, you should also report this bug to the author(s)
    2150. 

  2150. of that program.  Please make an effort to report this bug;
    2151. 

  2151. timely and accurate bug reports eventually lead to higher
    2152. 

  2152. quality software.  Thanks.  Julian Seward, 10 December 2007.
    2153. 

  2153. </p>
    2154. 

  2154. </blockquote></div>
    2155. 

  2155. <p>where <code class="computeroutput">N</code> is some error code
    2156. 

  2156. number.  If <code class="computeroutput">N == 1007</code>, it also
    2157. 

  2157. prints some extra text advising the reader that unreliable memory
    2158. 

  2158. is often associated with internal error 1007. (This is a
    2159. 

  2159. frequently-observed-phenomenon with versions 1.0.0/1.0.1).</p>
    2160. 

  2160. <p><code class="computeroutput">exit(3)</code> is then
    2161. 

  2161. called.</p>
    2162. 

  2162. <p>For a <code class="computeroutput">stdio</code>-free library,
    2163. 

  2163. assertion failures result in a call to a function declared
    2164. 

  2164. as:</p>
    2165. 

  2165. <pre class="programlisting">extern void bz_internal_error ( int errcode );</pre>
    2166. 

  2166. <p>The relevant code is passed as a parameter.  You should
    2167. 

  2167. supply such a function.</p>
    2168. 

  2168. <p>In either case, once an assertion failure has occurred, any
    2169. 

  2169. <code class="computeroutput">bz_stream</code> records involved can
    2170. 

  2170. be regarded as invalid.  You should not attempt to resume normal
    2171. 

  2171. operation with them.</p>
    2172. 

  2172. <p>You may, of course, change critical error handling to suit
    2173. 

  2173. your needs.  As I said above, critical errors indicate bugs in
    2174. 

  2174. the library and should not occur.  All "normal" error situations
    2175. 

  2175. are indicated via error return codes from functions, and can be
    2176. 

  2176. recovered from.</p>
    2177. 

  2177. </div>
    2178. 

  2178. </div>
    2179. 

  2179. <div class="sect1" lang="en">
    2180. 

  2180. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2181. 

  2181. <a name="win-dll"></a>3.8. Making a Windows DLL</h2></div></div></div>
    2182. 

  2182. <p>Everything related to Windows has been contributed by
    2183. 

  2183. Yoshioka Tsuneo
    2184. 

  2184. (<code class="computeroutput">tsuneo@rr.iij4u.or.jp</code>), so
    2185. 

  2185. you should send your queries to him (but perhaps Cc: me,
    2186. 

  2186. <code class="computeroutput">jseward@bzip.org</code>).</p>
    2187. 

  2187. <p>My vague understanding of what to do is: using Visual C++
    2188. 

  2188. 5.0, open the project file
    2189. 

  2189. <code class="computeroutput">libbz2.dsp</code>, and build.  That's
    2190. 

  2190. all.</p>
    2191. 

  2191. <p>If you can't open the project file for some reason, make a
    2192. 

  2192. new one, naming these files:
    2193. 

  2193. <code class="computeroutput">blocksort.c</code>,
    2194. 

  2194. <code class="computeroutput">bzlib.c</code>,
    2195. 

  2195. <code class="computeroutput">compress.c</code>,
    2196. 

  2196. <code class="computeroutput">crctable.c</code>,
    2197. 

  2197. <code class="computeroutput">decompress.c</code>,
    2198. 

  2198. <code class="computeroutput">huffman.c</code>,
    2199. 

  2199. <code class="computeroutput">randtable.c</code> and
    2200. 

  2200. <code class="computeroutput">libbz2.def</code>.  You will also need
    2201. 

  2201. to name the header files <code class="computeroutput">bzlib.h</code>
    2202. 

  2202. and <code class="computeroutput">bzlib_private.h</code>.</p>
    2203. 

  2203. <p>If you don't use VC++, you may need to define the
    2204. 

  2204. proprocessor symbol
    2205. 

  2205. <code class="computeroutput">_WIN32</code>.</p>
    2206. 

  2206. <p>Finally, <code class="computeroutput">dlltest.c</code> is a
    2207. 

  2207. sample program using the DLL.  It has a project file,
    2208. 

  2208. <code class="computeroutput">dlltest.dsp</code>.</p>
    2209. 

  2209. <p>If you just want a makefile for Visual C, have a look at
    2210. 

  2210. <code class="computeroutput">makefile.msc</code>.</p>
    2211. 

  2211. <p>Be aware that if you compile
    2212. 

  2212. <code class="computeroutput">bzip2</code> itself on Win32, you must
    2213. 

  2213. set <code class="computeroutput">BZ_UNIX</code> to 0 and
    2214. 

  2214. <code class="computeroutput">BZ_LCCWIN32</code> to 1, in the file
    2215. 

  2215. <code class="computeroutput">bzip2.c</code>, before compiling.
    2216. 

  2216. Otherwise the resulting binary won't work correctly.</p>
    2217. 

  2217. <p>I haven't tried any of this stuff myself, but it all looks
    2218. 

  2218. plausible.</p>
    2219. 

  2219. </div>
    2220. 

  2220. </div>
    2221. 

  2221. <div class="chapter" lang="en">
    2222. 

  2222. <div class="titlepage"><div><div><h2 class="title">
    2223. 

  2223. <a name="misc"></a>4. Miscellanea</h2></div></div></div>
    2224. 

  2224. <div class="toc">
    2225. 

  2225. <p><b>Table of Contents</b></p>
    2226. 

  2226. <dl>
    2227. 

  2227. <dt><span class="sect1"><a href="#limits">4.1. Limitations of the compressed file format</a></span></dt>
    2228. 

  2228. <dt><span class="sect1"><a href="#port-issues">4.2. Portability issues</a></span></dt>
    2229. 

  2229. <dt><span class="sect1"><a href="#bugs">4.3. Reporting bugs</a></span></dt>
    2230. 

  2230. <dt><span class="sect1"><a href="#package">4.4. Did you get the right package?</a></span></dt>
    2231. 

  2231. <dt><span class="sect1"><a href="#reading">4.5. Further Reading</a></span></dt>
    2232. 

  2232. </dl>
    2233. 

  2233. </div>
    2234. 

  2234. <p>These are just some random thoughts of mine.  Your mileage
    2235. 

  2235. may vary.</p>
    2236. 

  2236. <div class="sect1" lang="en">
    2237. 

  2237. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2238. 

  2238. <a name="limits"></a>4.1. Limitations of the compressed file format</h2></div></div></div>
    2239. 

  2239. <p><code class="computeroutput">bzip2-1.0.X</code>,
    2240. 

  2240. <code class="computeroutput">0.9.5</code> and
    2241. 

  2241. <code class="computeroutput">0.9.0</code> use exactly the same file
    2242. 

  2242. format as the original version,
    2243. 

  2243. <code class="computeroutput">bzip2-0.1</code>.  This decision was
    2244. 

  2244. made in the interests of stability.  Creating yet another
    2245. 

  2245. incompatible compressed file format would create further
    2246. 

  2246. confusion and disruption for users.</p>
    2247. 

  2247. <p>Nevertheless, this is not a painless decision.  Development
    2248. 

  2248. work since the release of
    2249. 

  2249. <code class="computeroutput">bzip2-0.1</code> in August 1997 has
    2250. 

  2250. shown complexities in the file format which slow down
    2251. 

  2251. decompression and, in retrospect, are unnecessary.  These
    2252. 

  2252. are:</p>
    2253. 

  2253. <div class="itemizedlist"><ul type="bullet">
    2254. 

  2254. <li style="list-style-type: disc"><p>The run-length encoder, which is the first of the
    2255. 

  2255.    compression transformations, is entirely irrelevant.  The
    2256. 

  2256.    original purpose was to protect the sorting algorithm from the
    2257. 

  2257.    very worst case input: a string of repeated symbols.  But
    2258. 

  2258.    algorithm steps Q6a and Q6b in the original Burrows-Wheeler
    2259. 

  2259.    technical report (SRC-124) show how repeats can be handled
    2260. 

  2260.    without difficulty in block sorting.</p></li>
    2261. 

  2261. <li style="list-style-type: disc">
    2262. 

  2262. <p>The randomisation mechanism doesn't really need to be
    2263. 

  2263.    there.  Udi Manber and Gene Myers published a suffix array
    2264. 

  2264.    construction algorithm a few years back, which can be employed
    2265. 

  2265.    to sort any block, no matter how repetitive, in O(N log N)
    2266. 

  2266.    time.  Subsequent work by Kunihiko Sadakane has produced a
    2267. 

  2267.    derivative O(N (log N)^2) algorithm which usually outperforms
    2268. 

  2268.    the Manber-Myers algorithm.</p>
    2269. 

  2269. <p>I could have changed to Sadakane's algorithm, but I find
    2270. 

  2270.    it to be slower than <code class="computeroutput">bzip2</code>'s
    2271. 

  2271.    existing algorithm for most inputs, and the randomisation
    2272. 

  2272.    mechanism protects adequately against bad cases.  I didn't
    2273. 

  2273.    think it was a good tradeoff to make.  Partly this is due to
    2274. 

  2274.    the fact that I was not flooded with email complaints about
    2275. 

  2275.    <code class="computeroutput">bzip2-0.1</code>'s performance on
    2276. 

  2276.    repetitive data, so perhaps it isn't a problem for real
    2277. 

  2277.    inputs.</p>
    2278. 

  2278. <p>Probably the best long-term solution, and the one I have
    2279. 

  2279.    incorporated into 0.9.5 and above, is to use the existing
    2280. 

  2280.    sorting algorithm initially, and fall back to a O(N (log N)^2)
    2281. 

  2281.    algorithm if the standard algorithm gets into
    2282. 

  2282.    difficulties.</p>
    2283. 

  2283. </li>
    2284. 

  2284. <li style="list-style-type: disc"><p>The compressed file format was never designed to be
    2285. 

  2285.    handled by a library, and I have had to jump though some hoops
    2286. 

  2286.    to produce an efficient implementation of decompression.  It's
    2287. 

  2287.    a bit hairy.  Try passing
    2288. 

  2288.    <code class="computeroutput">decompress.c</code> through the C
    2289. 

  2289.    preprocessor and you'll see what I mean.  Much of this
    2290. 

  2290.    complexity could have been avoided if the compressed size of
    2291. 

  2291.    each block of data was recorded in the data stream.</p></li>
    2292. 

  2292. <li style="list-style-type: disc"><p>An Adler-32 checksum, rather than a CRC32 checksum,
    2293. 

  2293.    would be faster to compute.</p></li>
    2294. 

  2294. </ul></div>
    2295. 

  2295. <p>It would be fair to say that the
    2296. 

  2296. <code class="computeroutput">bzip2</code> format was frozen before I
    2297. 

  2297. properly and fully understood the performance consequences of
    2298. 

  2298. doing so.</p>
    2299. 

  2299. <p>Improvements which I was able to incorporate into 0.9.0,
    2300. 

  2300. despite using the same file format, are:</p>
    2301. 

  2301. <div class="itemizedlist"><ul type="bullet">
    2302. 

  2302. <li style="list-style-type: disc"><p>Single array implementation of the inverse BWT.  This
    2303. 

  2303.   significantly speeds up decompression, presumably because it
    2304. 

  2304.   reduces the number of cache misses.</p></li>
    2305. 

  2305. <li style="list-style-type: disc"><p>Faster inverse MTF transform for large MTF values.
    2306. 

  2306.   The new implementation is based on the notion of sliding blocks
    2307. 

  2307.   of values.</p></li>
    2308. 

  2308. <li style="list-style-type: disc"><p><code class="computeroutput">bzip2-0.9.0</code> now reads
    2309. 

  2309.   and writes files with <code class="computeroutput">fread</code>
    2310. 

  2310.   and <code class="computeroutput">fwrite</code>; version 0.1 used
    2311. 

  2311.   <code class="computeroutput">putc</code> and
    2312. 

  2312.   <code class="computeroutput">getc</code>.  Duh!  Well, you live
    2313. 

  2313.   and learn.</p></li>
    2314. 

  2314. </ul></div>
    2315. 

  2315. <p>Further ahead, it would be nice to be able to do random
    2316. 

  2316. access into files.  This will require some careful design of
    2317. 

  2317. compressed file formats.</p>
    2318. 

  2318. </div>
    2319. 

  2319. <div class="sect1" lang="en">
    2320. 

  2320. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2321. 

  2321. <a name="port-issues"></a>4.2. Portability issues</h2></div></div></div>
    2322. 

  2322. <p>After some consideration, I have decided not to use GNU
    2323. 

  2323. <code class="computeroutput">autoconf</code> to configure 0.9.5 or
    2324. 

  2324. 1.0.</p>
    2325. 

  2325. <p><code class="computeroutput">autoconf</code>, admirable and
    2326. 

  2326. wonderful though it is, mainly assists with portability problems
    2327. 

  2327. between Unix-like platforms.  But
    2328. 

  2328. <code class="computeroutput">bzip2</code> doesn't have much in the
    2329. 

  2329. way of portability problems on Unix; most of the difficulties
    2330. 

  2330. appear when porting to the Mac, or to Microsoft's operating
    2331. 

  2331. systems.  <code class="computeroutput">autoconf</code> doesn't help
    2332. 

  2332. in those cases, and brings in a whole load of new
    2333. 

  2333. complexity.</p>
    2334. 

  2334. <p>Most people should be able to compile the library and
    2335. 

  2335. program under Unix straight out-of-the-box, so to speak,
    2336. 

  2336. especially if you have a version of GNU C available.</p>
    2337. 

  2337. <p>There are a couple of
    2338. 

  2338. <code class="computeroutput">__inline__</code> directives in the
    2339. 

  2339. code.  GNU C (<code class="computeroutput">gcc</code>) should be
    2340. 

  2340. able to handle them.  If you're not using GNU C, your C compiler
    2341. 

  2341. shouldn't see them at all.  If your compiler does, for some
    2342. 

  2342. reason, see them and doesn't like them, just
    2343. 

  2343. <code class="computeroutput">#define</code>
    2344. 

  2344. <code class="computeroutput">__inline__</code> to be
    2345. 

  2345. <code class="computeroutput">/* */</code>.  One easy way to do this
    2346. 

  2346. is to compile with the flag
    2347. 

  2347. <code class="computeroutput">-D__inline__=</code>, which should be
    2348. 

  2348. understood by most Unix compilers.</p>
    2349. 

  2349. <p>If you still have difficulties, try compiling with the
    2350. 

  2350. macro <code class="computeroutput">BZ_STRICT_ANSI</code> defined.
    2351. 

  2351. This should enable you to build the library in a strictly ANSI
    2352. 

  2352. compliant environment.  Building the program itself like this is
    2353. 

  2353. dangerous and not supported, since you remove
    2354. 

  2354. <code class="computeroutput">bzip2</code>'s checks against
    2355. 

  2355. compressing directories, symbolic links, devices, and other
    2356. 

  2356. not-really-a-file entities.  This could cause filesystem
    2357. 

  2357. corruption!</p>
    2358. 

  2358. <p>One other thing: if you create a
    2359. 

  2359. <code class="computeroutput">bzip2</code> binary for public distribution,
    2360. 

  2360. please consider linking it statically (<code class="computeroutput">gcc
    2361. 

  2361. -static</code>).  This avoids all sorts of library-version
    2362. 

  2362. issues that others may encounter later on.</p>
    2363. 

  2363. <p>If you build <code class="computeroutput">bzip2</code> on
    2364. 

  2364. Win32, you must set <code class="computeroutput">BZ_UNIX</code> to 0
    2365. 

  2365. and <code class="computeroutput">BZ_LCCWIN32</code> to 1, in the
    2366. 

  2366. file <code class="computeroutput">bzip2.c</code>, before compiling.
    2367. 

  2367. Otherwise the resulting binary won't work correctly.</p>
    2368. 

  2368. </div>
    2369. 

  2369. <div class="sect1" lang="en">
    2370. 

  2370. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2371. 

  2371. <a name="bugs"></a>4.3. Reporting bugs</h2></div></div></div>
    2372. 

  2372. <p>I tried pretty hard to make sure
    2373. 

  2373. <code class="computeroutput">bzip2</code> is bug free, both by
    2374. 

  2374. design and by testing.  Hopefully you'll never need to read this
    2375. 

  2375. section for real.</p>
    2376. 

  2376. <p>Nevertheless, if <code class="computeroutput">bzip2</code> dies
    2377. 

  2377. with a segmentation fault, a bus error or an internal assertion
    2378. 

  2378. failure, it will ask you to email me a bug report.  Experience from
    2379. 

  2379. years of feedback of bzip2 users indicates that almost all these
    2380. 

  2380. problems can be traced to either compiler bugs or hardware
    2381. 

  2381. problems.</p>
    2382. 

  2382. <div class="itemizedlist"><ul type="bullet">
    2383. 

  2383. <li style="list-style-type: disc">
    2384. 

  2384. <p>Recompile the program with no optimisation, and
    2385. 

  2385.   see if it works.  And/or try a different compiler.  I heard all
    2386. 

  2386.   sorts of stories about various flavours of GNU C (and other
    2387. 

  2387.   compilers) generating bad code for
    2388. 

  2388.   <code class="computeroutput">bzip2</code>, and I've run across two
    2389. 

  2389.   such examples myself.</p>
    2390. 

  2390. <p>2.7.X versions of GNU C are known to generate bad code
    2391. 

  2391.   from time to time, at high optimisation levels.  If you get
    2392. 

  2392.   problems, try using the flags
    2393. 

  2393.   <code class="computeroutput">-O2</code>
    2394. 

  2394.   <code class="computeroutput">-fomit-frame-pointer</code>
    2395. 

  2395.   <code class="computeroutput">-fno-strength-reduce</code>.  You
    2396. 

  2396.   should specifically <span class="emphasis"><em>not</em></span> use
    2397. 

  2397.   <code class="computeroutput">-funroll-loops</code>.</p>
    2398. 

  2398. <p>You may notice that the Makefile runs six tests as part
    2399. 

  2399.   of the build process.  If the program passes all of these, it's
    2400. 

  2400.   a pretty good (but not 100%) indication that the compiler has
    2401. 

  2401.   done its job correctly.</p>
    2402. 

  2402. </li>
    2403. 

  2403. <li style="list-style-type: disc">
    2404. 

  2404. <p>If <code class="computeroutput">bzip2</code>
    2405. 

  2405.   crashes randomly, and the crashes are not repeatable, you may
    2406. 

  2406.   have a flaky memory subsystem.
    2407. 

  2407.   <code class="computeroutput">bzip2</code> really hammers your
    2408. 

  2408.   memory hierarchy, and if it's a bit marginal, you may get these
    2409. 

  2409.   problems.  Ditto if your disk or I/O subsystem is slowly
    2410. 

  2410.   failing.  Yup, this really does happen.</p>
    2411. 

  2411. <p>Try using a different machine of the same type, and see
    2412. 

  2412.   if you can repeat the problem.</p>
    2413. 

  2413. </li>
    2414. 

  2414. <li style="list-style-type: disc"><p>This isn't really a bug, but ... If
    2415. 

  2415.   <code class="computeroutput">bzip2</code> tells you your file is
    2416. 

  2416.   corrupted on decompression, and you obtained the file via FTP,
    2417. 

  2417.   there is a possibility that you forgot to tell FTP to do a
    2418. 

  2418.   binary mode transfer.  That absolutely will cause the file to
    2419. 

  2419.   be non-decompressible.  You'll have to transfer it
    2420. 

  2420.   again.</p></li>
    2421. 

  2421. </ul></div>
    2422. 

  2422. <p>If you've incorporated
    2423. 

  2423. <code class="computeroutput">libbzip2</code> into your own program
    2424. 

  2424. and are getting problems, please, please, please, check that the
    2425. 

  2425. parameters you are passing in calls to the library, are correct,
    2426. 

  2426. and in accordance with what the documentation says is allowable.
    2427. 

  2427. I have tried to make the library robust against such problems,
    2428. 

  2428. but I'm sure I haven't succeeded.</p>
    2429. 

  2429. <p>Finally, if the above comments don't help, you'll have to
    2430. 

  2430. send me a bug report.  Now, it's just amazing how many people
    2431. 

  2431. will send me a bug report saying something like:</p>
    2432. 

  2432. <pre class="programlisting">bzip2 crashed with segmentation fault on my machine</pre>
    2433. 

  2433. <p>and absolutely nothing else.  Needless to say, a such a
    2434. 

  2434. report is <span class="emphasis"><em>totally, utterly, completely and
    2435. 

  2435. comprehensively 100% useless; a waste of your time, my time, and
    2436. 

  2436. net bandwidth</em></span>.  With no details at all, there's no way
    2437. 

  2437. I can possibly begin to figure out what the problem is.</p>
    2438. 

  2438. <p>The rules of the game are: facts, facts, facts.  Don't omit
    2439. 

  2439. them because "oh, they won't be relevant".  At the bare
    2440. 

  2440. minimum:</p>
    2441. 

  2441. <pre class="programlisting">Machine type.  Operating system version.  
    2442. 

  2442. Exact version of bzip2 (do bzip2 -V).  
    2443. 

  2443. Exact version of the compiler used.  
    2444. 

  2444. Flags passed to the compiler.</pre>
    2445. 

  2445. <p>However, the most important single thing that will help me
    2446. 

  2446. is the file that you were trying to compress or decompress at the
    2447. 

  2447. time the problem happened.  Without that, my ability to do
    2448. 

  2448. anything more than speculate about the cause, is limited.</p>
    2449. 

  2449. </div>
    2450. 

  2450. <div class="sect1" lang="en">
    2451. 

  2451. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2452. 

  2452. <a name="package"></a>4.4. Did you get the right package?</h2></div></div></div>
    2453. 

  2453. <p><code class="computeroutput">bzip2</code> is a resource hog.
    2454. 

  2454. It soaks up large amounts of CPU cycles and memory.  Also, it
    2455. 

  2455. gives very large latencies.  In the worst case, you can feed many
    2456. 

  2456. megabytes of uncompressed data into the library before getting
    2457. 

  2457. any compressed output, so this probably rules out applications
    2458. 

  2458. requiring interactive behaviour.</p>
    2459. 

  2459. <p>These aren't faults of my implementation, I hope, but more
    2460. 

  2460. an intrinsic property of the Burrows-Wheeler transform
    2461. 

  2461. (unfortunately).  Maybe this isn't what you want.</p>
    2462. 

  2462. <p>If you want a compressor and/or library which is faster,
    2463. 

  2463. uses less memory but gets pretty good compression, and has
    2464. 

  2464. minimal latency, consider Jean-loup Gailly's and Mark Adler's
    2465. 

  2465. work, <code class="computeroutput">zlib-1.2.1</code> and
    2466. 

  2466. <code class="computeroutput">gzip-1.2.4</code>.  Look for them at 
    2467. 

  2467. <a href="http://www.zlib.org" target="_top">http://www.zlib.org</a> and 
    2468. 

  2468. <a href="http://www.gzip.org" target="_top">http://www.gzip.org</a>
    2469. 

  2469. respectively.</p>
    2470. 

  2470. <p>For something faster and lighter still, you might try Markus F
    2471. 

  2471. X J Oberhumer's <code class="computeroutput">LZO</code> real-time
    2472. 

  2472. compression/decompression library, at 
    2473. 

  2473. <a href="http://www.oberhumer.com/opensource" target="_top">http://www.oberhumer.com/opensource</a>.</p>
    2474. 

  2474. </div>
    2475. 

  2475. <div class="sect1" lang="en">
    2476. 

  2476. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    2477. 

  2477. <a name="reading"></a>4.5. Further Reading</h2></div></div></div>
    2478. 

  2478. <p><code class="computeroutput">bzip2</code> is not research
    2479. 

  2479. work, in the sense that it doesn't present any new ideas.
    2480. 

  2480. Rather, it's an engineering exercise based on existing
    2481. 

  2481. ideas.</p>
    2482. 

  2482. <p>Four documents describe essentially all the ideas behind
    2483. 

  2483. <code class="computeroutput">bzip2</code>:</p>
    2484. 

  2484. <div class="literallayout"><p>Michael Burrows and D. J. Wheeler:<br>
    2485. 

  2485.   "A block-sorting lossless data compression algorithm"<br>
    2486. 

  2486.    10th May 1994. <br>
    2487. 

  2487.    Digital SRC Research Report 124.<br>
    2488. 

  2488.    ftp://ftp.digital.com/pub/DEC/SRC/research-reports/SRC-124.ps.gz<br>
    2489. 

  2489.    If you have trouble finding it, try searching at the<br>
    2490. 

  2490.    New Zealand Digital Library, http://www.nzdl.org.<br>
    2491. 

  2491. <br>
    2492. 

  2492. Daniel S. Hirschberg and Debra A. LeLewer<br>
    2493. 

  2493.   "Efficient Decoding of Prefix Codes"<br>
    2494. 

  2494.    Communications of the ACM, April 1990, Vol 33, Number 4.<br>
    2495. 

  2495.    You might be able to get an electronic copy of this<br>
    2496. 

  2496.    from the ACM Digital Library.<br>
    2497. 

  2497. <br>
    2498. 

  2498. David J. Wheeler<br>
    2499. 

  2499.    Program bred3.c and accompanying document bred3.ps.<br>
    2500. 

  2500.    This contains the idea behind the multi-table Huffman coding scheme.<br>
    2501. 

  2501.    ftp://ftp.cl.cam.ac.uk/users/djw3/<br>
    2502. 

  2502. <br>
    2503. 

  2503. Jon L. Bentley and Robert Sedgewick<br>
    2504. 

  2504.   "Fast Algorithms for Sorting and Searching Strings"<br>
    2505. 

  2505.    Available from Sedgewick's web page,<br>
    2506. 

  2506.    www.cs.princeton.edu/~rs<br>
    2507. 

  2507. </p></div>
    2508. 

  2508. <p>The following paper gives valuable additional insights into
    2509. 

  2509. the algorithm, but is not immediately the basis of any code used
    2510. 

  2510. in bzip2.</p>
    2511. 

  2511. <div class="literallayout"><p>Peter Fenwick:<br>
    2512. 

  2512.    Block Sorting Text Compression<br>
    2513. 

  2513.    Proceedings of the 19th Australasian Computer Science Conference,<br>
    2514. 

  2514.      Melbourne, Australia.  Jan 31 - Feb 2, 1996.<br>
    2515. 

  2515.    ftp://ftp.cs.auckland.ac.nz/pub/peter-f/ACSC96paper.ps</p></div>
    2516. 

  2516. <p>Kunihiko Sadakane's sorting algorithm, mentioned above, is
    2517. 

  2517. available from:</p>
    2518. 

  2518. <div class="literallayout"><p>http://naomi.is.s.u-tokyo.ac.jp/~sada/papers/Sada98b.ps.gz<br>
    2519. 

  2519. </p></div>
    2520. 

  2520. <p>The Manber-Myers suffix array construction algorithm is
    2521. 

  2521. described in a paper available from:</p>
    2522. 

  2522. <div class="literallayout"><p>http://www.cs.arizona.edu/people/gene/PAPERS/suffix.ps<br>
    2523. 

  2523. </p></div>
    2524. 

  2524. <p>Finally, the following papers document some
    2525. 

  2525. investigations I made into the performance of sorting
    2526. 

  2526. and decompression algorithms:</p>
    2527. 

  2527. <div class="literallayout"><p>Julian Seward<br>
    2528. 

  2528.    On the Performance of BWT Sorting Algorithms<br>
    2529. 

  2529.    Proceedings of the IEEE Data Compression Conference 2000<br>
    2530. 

  2530.      Snowbird, Utah.  28-30 March 2000.<br>
    2531. 

  2531. <br>
    2532. 

  2532. Julian Seward<br>
    2533. 

  2533.    Space-time Tradeoffs in the Inverse B-W Transform<br>
    2534. 

  2534.    Proceedings of the IEEE Data Compression Conference 2001<br>
    2535. 

  2535.      Snowbird, Utah.  27-29 March 2001.<br>
    2536. 

  2536. </p></div>
    2537. 

  2537. </div>
    2538. 

  2538. </div>
    2539. 

  2539. </div></body>
    2540. 

  2540. </html>
    2541. 

  2541.