A UNIX Command
$wget http://www.kernel.org/pub/linux/kernel/v3.0/patch-3.0.4.bz2 --2011-09-03 19:22:43-- http://www.kernel.org/pub/linux/kernel/v3.0/patch-3.0.4.bz2 Resolving www.kernel.org... 130.239.17.5, 149.20.4.69, 199.6.1.165, ... Connecting to www.kernel.org|130.239.17.5|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 96120 (94K) [application/x-bzip2] Saving to: `patch-3.0.4.bz2' 100%[===================================================================================>] 96,120 85.3K/s in 1.1s 2011-09-03 19:22:45 (85.3 KB/s) - `patch-3.0.4.bz2' saved [96120/96120] $bunzip2 patch-3.0.4.bz2 $ls patch-3.0.4 patch-3.0.4 $
UNIX Explanation
bzip2 compresses files using the Burrows-Wheeler block sorting text compression algorithm, and Huffman coding. Compression is generally considerably better than that achieved by more conventional LZ77/LZ78-based compressors, and approaches the performance of the PPM family of statistical compressors.
Related Source Code Exposition
for (t = 0; t < nGroups; t++) {
minLen = 32;
maxLen = 0;
for (i = 0; i len[t][i] > maxLen) maxLen = s->len[t][i];
if (s->len[t][i] len[t][i];
}
BZ2_hbCreateDecodeTables (
&(s->limit[t][0]),
&(s->base[t][0]),
&(s->perm[t][0]),
&(s->len[t][0]),
minLen, maxLen, alphaSize
);
s->minLens[t] = minLen;
}
Source Code Highlight
Create the Huffman decoding tables
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Related Knowledge
bzip2 expects a list of file names to accompany the command-line flags. Each file is replaced by a compressed version of itself, with the name "original_name.bz2". Each compressed file has the same modification date, permissions, and, when possible, ownership as the corresponding original, so that these properties can be correctly restored at decompression time. File name handling is naive in the sense that there is no mechanism for preserving original file names, permissions, ownerships or dates in filesystems which lack these concepts, or have serious file name length restrictions, such as MS-DOS. source : debian manual pages for bzip2