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diff --git a/winsup/bz2lib/bzip2.1 b/winsup/bz2lib/bzip2.1 deleted file mode 100644 index 7de54a011..000000000 --- a/winsup/bz2lib/bzip2.1 +++ /dev/null @@ -1,439 +0,0 @@ -.PU -.TH bzip2 1 -.SH NAME -bzip2, bunzip2 \- a block-sorting file compressor, v1.0 -.br -bzcat \- decompresses files to stdout -.br -bzip2recover \- recovers data from damaged bzip2 files - -.SH SYNOPSIS -.ll +8 -.B bzip2 -.RB [ " \-cdfkqstvzVL123456789 " ] -[ -.I "filenames \&..." -] -.ll -8 -.br -.B bunzip2 -.RB [ " \-fkvsVL " ] -[ -.I "filenames \&..." -] -.br -.B bzcat -.RB [ " \-s " ] -[ -.I "filenames \&..." -] -.br -.B bzip2recover -.I "filename" - -.SH DESCRIPTION -.I 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. - -The command-line options are deliberately very similar to -those of -.I GNU gzip, -but they are not identical. - -.I 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. - -.I bzip2 -and -.I bunzip2 -will by default not overwrite existing -files. If you want this to happen, specify the \-f flag. - -If no file names are specified, -.I bzip2 -compresses from standard -input to standard output. In this case, -.I bzip2 -will decline to -write compressed output to a terminal, as this would be entirely -incomprehensible and therefore pointless. - -.I bunzip2 -(or -.I bzip2 \-d) -decompresses all -specified files. Files which were not created by -.I bzip2 -will be detected and ignored, and a warning issued. -.I bzip2 -attempts to guess the filename for the decompressed file -from that of the compressed file as follows: - - filename.bz2 becomes filename - filename.bz becomes filename - filename.tbz2 becomes filename.tar - filename.tbz becomes filename.tar - anyothername becomes anyothername.out - -If the file does not end in one of the recognised endings, -.I .bz2, -.I .bz, -.I .tbz2 -or -.I .tbz, -.I bzip2 -complains that it cannot -guess the name of the original file, and uses the original name -with -.I .out -appended. - -As with compression, supplying no -filenames causes decompression from -standard input to standard output. - -.I bunzip2 -will correctly decompress a file which is the -concatenation of two or more compressed files. The result is the -concatenation of the corresponding uncompressed files. Integrity -testing (\-t) -of concatenated -compressed files is also supported. - -You can also compress or decompress files to the standard output by -giving the \-c flag. Multiple files may be compressed and -decompressed like this. The resulting outputs are fed sequentially to -stdout. Compression of multiple files -in this manner generates a stream -containing multiple compressed file representations. Such a stream -can be decompressed correctly only by -.I bzip2 -version 0.9.0 or -later. Earlier versions of -.I bzip2 -will stop after decompressing -the first file in the stream. - -.I bzcat -(or -.I bzip2 -dc) -decompresses all specified files to -the standard output. - -.I bzip2 -will read arguments from the environment variables -.I BZIP2 -and -.I BZIP, -in that order, and will process them -before any arguments read from the command line. This gives a -convenient way to supply default arguments. - -Compression is always performed, even if the compressed -file is slightly -larger than the original. Files of less than about one hundred bytes -tend to get larger, since the compression mechanism has a constant -overhead in the region of 50 bytes. Random data (including the output -of most file compressors) is coded at about 8.05 bits per byte, giving -an expansion of around 0.5%. - -As a self-check for your protection, -.I -bzip2 -uses 32-bit CRCs to -make sure that the decompressed version of a file is identical to the -original. This guards against corruption of the compressed data, and -against undetected bugs in -.I bzip2 -(hopefully very unlikely). The -chances of data corruption going undetected is microscopic, about one -chance in four billion for each file processed. Be aware, though, that -the check occurs upon decompression, so it can only tell you that -something is wrong. It can't help you -recover the original uncompressed -data. You can use -.I bzip2recover -to try to recover data from -damaged files. - -Return values: 0 for a normal exit, 1 for environmental problems (file -not found, invalid flags, I/O errors, &c), 2 to indicate a corrupt -compressed file, 3 for an internal consistency error (eg, bug) which -caused -.I bzip2 -to panic. - -.SH OPTIONS -.TP -.B \-c --stdout -Compress or decompress to standard output. -.TP -.B \-d --decompress -Force decompression. -.I bzip2, -.I bunzip2 -and -.I bzcat -are -really the same program, and the decision about what actions to take is -done on the basis of which name is used. This flag overrides that -mechanism, and forces -.I bzip2 -to decompress. -.TP -.B \-z --compress -The complement to \-d: forces compression, regardless of the -invokation name. -.TP -.B \-t --test -Check integrity of the specified file(s), but don't decompress them. -This really performs a trial decompression and throws away the result. -.TP -.B \-f --force -Force overwrite of output files. Normally, -.I bzip2 -will not overwrite -existing output files. Also forces -.I bzip2 -to break hard links -to files, which it otherwise wouldn't do. -.TP -.B \-k --keep -Keep (don't delete) input files during compression -or decompression. -.TP -.B \-s --small -Reduce memory usage, for compression, decompression and testing. Files -are decompressed and tested using a modified algorithm which only -requires 2.5 bytes per block byte. This means any file can be -decompressed in 2300k of memory, albeit at about half the normal speed. - -During compression, \-s selects a block size of 200k, which limits -memory use to around the same figure, at the expense of your compression -ratio. In short, if your machine is low on memory (8 megabytes or -less), use \-s for everything. See MEMORY MANAGEMENT below. -.TP -.B \-q --quiet -Suppress non-essential warning messages. Messages pertaining to -I/O errors and other critical events will not be suppressed. -.TP -.B \-v --verbose -Verbose mode -- show the compression ratio for each file processed. -Further \-v's increase the verbosity level, spewing out lots of -information which is primarily of interest for diagnostic purposes. -.TP -.B \-L --license -V --version -Display the software version, license terms and conditions. -.TP -.B \-1 to \-9 -Set the block size to 100 k, 200 k .. 900 k when compressing. Has no -effect when decompressing. See MEMORY MANAGEMENT below. -.TP -.B \-- -Treats all subsequent arguments as file names, even if they start -with a dash. This is so you can handle files with names beginning -with a dash, for example: bzip2 \-- \-myfilename. -.TP -.B \--repetitive-fast --repetitive-best -These flags are redundant in versions 0.9.5 and above. They provided -some coarse control over the behaviour of the sorting algorithm in -earlier versions, which was sometimes useful. 0.9.5 and above have an -improved algorithm which renders these flags irrelevant. - -.SH MEMORY MANAGEMENT -.I bzip2 -compresses large files in blocks. The block size affects -both the compression ratio achieved, and the amount of memory needed for -compression and decompression. The flags \-1 through \-9 -specify the block size to be 100,000 bytes through 900,000 bytes (the -default) respectively. At decompression time, the block size used for -compression is read from the header of the compressed file, and -.I bunzip2 -then allocates itself just enough memory to decompress -the file. Since block sizes are stored in compressed files, it follows -that the flags \-1 to \-9 are irrelevant to and so ignored -during decompression. - -Compression and decompression requirements, -in bytes, can be estimated as: - - Compression: 400k + ( 8 x block size ) - - Decompression: 100k + ( 4 x block size ), or - 100k + ( 2.5 x block size ) - -Larger block sizes give rapidly diminishing marginal returns. Most of -the compression comes from the first two or three hundred k of block -size, a fact worth bearing in mind when using -.I bzip2 -on small machines. -It is also important to appreciate that the decompression memory -requirement is set at compression time by the choice of block size. - -For files compressed with the default 900k block size, -.I bunzip2 -will require about 3700 kbytes to decompress. To support decompression -of any file on a 4 megabyte machine, -.I bunzip2 -has an option to -decompress using approximately half this amount of memory, about 2300 -kbytes. Decompression speed is also halved, so you should use this -option only where necessary. The relevant flag is -s. - -In general, try and use the largest block size memory constraints allow, -since that maximises the compression achieved. Compression and -decompression speed are virtually unaffected by block size. - -Another significant point applies to files which fit in a single block --- that means most files you'd encounter using a large block size. The -amount of real memory touched is proportional to the size of the file, -since the file is smaller than a block. For example, compressing a file -20,000 bytes long with the flag -9 will cause the compressor to -allocate around 7600k of memory, but only touch 400k + 20000 * 8 = 560 -kbytes of it. Similarly, the decompressor will allocate 3700k but only -touch 100k + 20000 * 4 = 180 kbytes. - -Here is a table which summarises the maximum memory usage for different -block sizes. Also recorded is the total compressed size for 14 files of -the Calgary Text Compression Corpus totalling 3,141,622 bytes. This -column gives some feel for how compression varies with block size. -These figures tend to understate the advantage of larger block sizes for -larger files, since the Corpus is dominated by smaller files. - - Compress Decompress Decompress Corpus - Flag usage usage -s usage Size - - -1 1200k 500k 350k 914704 - -2 2000k 900k 600k 877703 - -3 2800k 1300k 850k 860338 - -4 3600k 1700k 1100k 846899 - -5 4400k 2100k 1350k 845160 - -6 5200k 2500k 1600k 838626 - -7 6100k 2900k 1850k 834096 - -8 6800k 3300k 2100k 828642 - -9 7600k 3700k 2350k 828642 - -.SH RECOVERING DATA FROM DAMAGED FILES -.I bzip2 -compresses files in blocks, usually 900kbytes long. Each -block is handled independently. If a media or transmission error causes -a multi-block .bz2 -file to become damaged, it may be possible to -recover data from the undamaged blocks in the file. - -The compressed representation of each block is delimited by a 48-bit -pattern, which makes it possible to find the block boundaries with -reasonable certainty. Each block also carries its own 32-bit CRC, so -damaged blocks can be distinguished from undamaged ones. - -.I bzip2recover -is a simple program whose purpose is to search for -blocks in .bz2 files, and write each block out into its own .bz2 -file. You can then use -.I bzip2 -\-t -to test the -integrity of the resulting files, and decompress those which are -undamaged. - -.I bzip2recover -takes a single argument, the name of the damaged file, -and writes a number of files "rec0001file.bz2", -"rec0002file.bz2", etc, containing the extracted blocks. -The output filenames are designed so that the use of -wildcards in subsequent processing -- for example, -"bzip2 -dc rec*file.bz2 > recovered_data" -- lists the files in -the correct order. - -.I bzip2recover -should be of most use dealing with large .bz2 -files, as these will contain many blocks. It is clearly -futile to use it on damaged single-block files, since a -damaged block cannot be recovered. If you wish to minimise -any potential data loss through media or transmission errors, -you might consider compressing with a smaller -block size. - -.SH PERFORMANCE NOTES -The sorting phase of compression gathers together similar strings in the -file. Because of this, files containing very long runs of repeated -symbols, like "aabaabaabaab ..." (repeated several hundred times) may -compress more slowly than normal. Versions 0.9.5 and above fare much -better than previous versions in this respect. The ratio between -worst-case and average-case compression time is in the region of 10:1. -For previous versions, this figure was more like 100:1. You can use the -\-vvvv option to monitor progress in great detail, if you want. - -Decompression speed is unaffected by these phenomena. - -.I bzip2 -usually allocates several megabytes of memory to operate -in, and then charges all over it in a fairly random fashion. This means -that performance, both for compressing and decompressing, is largely -determined by the speed at which your machine can service cache misses. -Because of this, small changes to the code to reduce the miss rate have -been observed to give disproportionately large performance improvements. -I imagine -.I bzip2 -will perform best on machines with very large caches. - -.SH CAVEATS -I/O error messages are not as helpful as they could be. -.I bzip2 -tries hard to detect I/O errors and exit cleanly, but the details of -what the problem is sometimes seem rather misleading. - -This manual page pertains to version 1.0 of -.I bzip2. -Compressed -data created by this version is entirely forwards and backwards -compatible with the previous public releases, versions 0.1pl2, 0.9.0 -and 0.9.5, -but with the following exception: 0.9.0 and above can correctly -decompress multiple concatenated compressed files. 0.1pl2 cannot do -this; it will stop after decompressing just the first file in the -stream. - -.I bzip2recover -uses 32-bit integers to represent bit positions in -compressed files, so it cannot handle compressed files more than 512 -megabytes long. This could easily be fixed. - -.SH AUTHOR -Julian Seward, jseward@acm.org. - -http://sourceware.cygnus.com/bzip2 -http://www.muraroa.demon.co.uk - -The ideas embodied in -.I bzip2 -are due to (at least) the following -people: Michael Burrows and David Wheeler (for the block sorting -transformation), David Wheeler (again, for the Huffman coder), Peter -Fenwick (for the structured coding model in the original -.I bzip, -and many refinements), and Alistair Moffat, Radford Neal and Ian Witten -(for the arithmetic coder in the original -.I bzip). -I am much -indebted for their help, support and advice. See the manual in the -source distribution for pointers to sources of documentation. Christian -von Roques encouraged me to look for faster sorting algorithms, so as to -speed up compression. Bela Lubkin encouraged me to improve the -worst-case compression performance. Many people sent patches, helped -with portability problems, lent machines, gave advice and were generally -helpful. |