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diff --git a/doc/clzip.texinfo b/doc/clzip.texinfo new file mode 100644 index 0000000..e9e6339 --- /dev/null +++ b/doc/clzip.texinfo @@ -0,0 +1,462 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename clzip.info +@settitle Clzip Manual +@finalout +@c %**end of header + +@set UPDATED 21 February 2010 +@set VERSION 1.0-rc2 + +@dircategory Data Compression +@direntry +* Clzip: (clzip). Data compressor based on the LZMA algorithm +@end direntry + + +@titlepage +@title Clzip +@subtitle A data compressor based on the LZMA algorithm +@subtitle for Clzip version @value{VERSION}, @value{UPDATED} +@author by Antonio Diaz Diaz + +@page +@vskip 0pt plus 1filll +@end titlepage + +@contents + +@node Top +@top + +This manual is for Clzip (version @value{VERSION}, @value{UPDATED}). + +@menu +* Introduction:: Purpose and features of clzip +* Algorithm:: How clzip compresses the data +* Invoking Clzip:: Command line interface +* File Format:: Detailed format of the compressed file +* Examples:: A small tutorial with examples +* Problems:: Reporting bugs +* Concept Index:: Index of concepts +@end menu + +@sp 1 +Copyright @copyright{} 2010 Antonio Diaz Diaz. + +This manual is free documentation: you have unlimited permission +to copy, distribute and modify it. + + +@node Introduction +@chapter Introduction +@cindex introduction + +Clzip is a lossless data compressor based on the LZMA algorithm, with +very safe integrity checking and a user interface similar to the one of +gzip or bzip2. Clzip decompresses almost as fast as gzip and compresses +better than bzip2, which makes it well suited for software distribution +and data archiving. + +Clzip replaces every file given in the command line with a compressed +version of itself, with the name "original_name.lz". 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. Clzip is able to read from some +types of non regular files if the @samp{--stdout} option is specified. + +If no file names are specified, clzip compresses (or decompresses) from +standard input to standard output. In this case, clzip will decline to +write compressed output to a terminal, as this would be entirely +incomprehensible and therefore pointless. + +Clzip 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 of concatenated +compressed files is also supported. + +Clzip can produce multimember files and safely recover, with lziprecover, +the undamaged members in case of file damage. Clzip can also split the +compressed output in volumes of a given size, even when reading from +standard input. This allows the direct creation of multivolume +compressed tar archives. + +The amount of memory required for compression is about 5 MiB plus 1 or 2 +times the dictionary size limit (1 if input file size is less than +dictionary size limit, else 2) plus 8 times the dictionary size really +used. For decompression is a little more than the dictionary size really +used. Clzip will automatically use the smallest possible dictionary size +without exceeding the given limit. It is important to appreciate that +the decompression memory requirement is affected at compression time by +the choice of dictionary size limit. + +When decompressing, clzip attempts to guess the name for the decompressed +file from that of the compressed file as follows: + +@multitable {anyothername} {becomes} {anyothername.out} +@item filename.lz @tab becomes @tab filename +@item filename.tlz @tab becomes @tab filename.tar +@item anyothername @tab becomes @tab anyothername.out +@end multitable + +As a self-check for your protection, clzip stores in the member trailer +the 32-bit CRC of the original data and the size of the original data, +to make sure that the decompressed version of the data is identical to +the original. This guards against corruption of the compressed data, and +against undetected bugs in clzip (hopefully very unlikely). The chances +of data corruption going undetected are microscopic, less than one +chance in 4000 million for each member 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. + +Return values: 0 for a normal exit, 1 for environmental problems (file +not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or +invalid input file, 3 for an internal consistency error (eg, bug) which +caused clzip to panic. + + +@node Algorithm +@chapter Algorithm +@cindex algorithm + +Clzip implements a simplified version of the LZMA (Lempel-Ziv-Markov +chain-Algorithm) algorithm. The original LZMA algorithm was designed by +Igor Pavlov. + +The high compression of LZMA comes from combining two basic, well-proven +compression ideas: sliding dictionaries (LZ77/78) and markov models (the +thing used by every compression algorithm that uses a range encoder or +similar order-0 entropy coder as its last stage) with segregation of +contexts according to what the bits are used for. + +Clzip is a two stage compressor. The first stage is a Lempel-Ziv coder, +which reduces redundancy by translating chunks of data to their +corresponding distance-length pairs. The second stage is a range encoder +that uses a different probability model for each type of data; +distances, lengths, literal bytes, etc. + +The match finder, part of the LZ coder, is the most important piece of +the LZMA algorithm, as it is in many Lempel-Ziv based algorithms. Most +of clzip's execution time is spent in the match finder, and it has the +greatest influence on the compression ratio. + +Here is how it works, step by step: + +1) The member header is written to the output stream. + +2) The first byte is coded literally, because there are no previous +bytes to which the match finder can refer to. + +3) The main encoder advances to the next byte in the input data and +calls the match finder. + +4) The match finder fills an array with the minimum distances before the +current byte where a match of a given length can be found. + +5) Go back to step 3 until a sequence (formed of pairs, repeated +distances and literal bytes) of minimum price has been formed. Where the +price represents the number of output bits produced. + +6) The range encoder encodes the sequence produced by the main encoder +and sends the produced bytes to the output stream. + +7) Go back to step 3 until the input data is finished or until the +member or volume size limits are reached. + +8) The range encoder is flushed. + +9) The member trailer is written to the output stream. + +10) If there are more data to compress, go back to step 1. + + +@node Invoking Clzip +@chapter Invoking Clzip +@cindex invoking +@cindex options +@cindex usage +@cindex version + +The format for running clzip is: + +@example +clzip [@var{options}] [@var{files}] +@end example + +Clzip supports the following options: + +@table @samp +@item --help +@itemx -h +Print an informative help message describing the options and exit. + +@item --version +@itemx -V +Print the version number of clzip on the standard output and exit. + +@item --member-size=@var{size} +@itemx -b @var{size} +Produce a multimember file and set the member size limit to @var{size} +bytes. Minimum member size limit is 100kB. Small member size may degrade +compression ratio, so use it only when needed. The default is to produce +single member files. + +@item --stdout +@itemx -c +Compress or decompress to standard output. Needed when reading from a +named pipe (fifo) or from a device. Use it to recover as much of the +uncompressed data as possible when decompressing a corrupt file. + +@item --decompress +@itemx -d +Decompress. + +@item --force +@itemx -f +Force overwrite of output file. + +@item --keep +@itemx -k +Keep (don't delete) input files during compression or decompression. + +@item --match-length=@var{length} +@itemx -m @var{length} +Set the match length limit in bytes. Valid values range from 5 to 273. +Larger values usually give better compression ratios but longer +compression times. + +@item --output=@var{file} +@itemx -o @var{file} +When reading from standard input and @samp{--stdout} has not been +specified, use @samp{@var{file}} as the virtual name of the uncompressed +file. This produces a file named @samp{@var{file}} when decompressing, a +file named @samp{@var{file}.lz} when compressing, and several files +named @samp{@var{file}00001.lz}, @samp{@var{file}00002.lz}, etc, when +compressing and splitting the output in volumes. + +@item --quiet +@itemx -q +Quiet operation. Suppress all messages. + +@item --dictionary-size=@var{size} +@itemx -s @var{size} +Set the dictionary size limit in bytes. Valid values range from 4KiB to +512MiB. Clzip will use the smallest possible dictionary size for each +member without exceeding this limit. Note that dictionary sizes are +quantized. If the specified size does not match one of the valid sizes, +it will be rounded upwards. + +@item --volume-size=@var{size} +@itemx -S @var{size} +Split the compressed output into several volume files with names +@samp{original_name00001.lz}, @samp{original_name00002.lz}, etc, and set +the volume size limit to @var{size} bytes. Each volume is a complete, +maybe multimember, lzip file. Minimum volume size limit is 100kB. Small +volume size may degrade compression ratio, so use it only when needed. + +@item --test +@itemx -t +Check integrity of the specified file(s), but don't decompress them. +This really performs a trial decompression and throws away the result. +Use @samp{-tvv} or @samp{-tvvv} to see information about the file. + +@item --verbose +@itemx -v +Verbose mode. Show the compression ratio for each file processed. +Further -v's increase the verbosity level. + +@item -1 .. -9 +Set the compression parameters (dictionary size and match length limit) +as shown in the table below. Note that @samp{-9} can be much slower than +@samp{-1}. These options have no effect when decompressing. + +@multitable {Level} {Dictionary size} {Match length limit} +@item Level @tab Dictionary size @tab Match length limit +@item -1 @tab 1 MiB @tab 10 bytes +@item -2 @tab 1.5 MiB @tab 12 bytes +@item -3 @tab 2 MiB @tab 17 bytes +@item -4 @tab 3 MiB @tab 26 bytes +@item -5 @tab 4 MiB @tab 44 bytes +@item -6 @tab 8 MiB @tab 80 bytes +@item -7 @tab 16 MiB @tab 108 bytes +@item -8 @tab 24 MiB @tab 163 bytes +@item -9 @tab 32 MiB @tab 273 bytes +@end multitable + +@item --fast +@itemx --best +Aliases for GNU gzip compatibility. + +@end table + +@sp 1 +Numbers given as arguments to options may be followed by a multiplier +and an optional @samp{B} for "byte". + +Table of SI and binary prefixes (unit multipliers): + +@multitable {Prefix} {kilobyte (10^3 = 1000)} {|} {Prefix} {kibibyte (2^10 = 1024)} +@item Prefix @tab Value @tab | @tab Prefix @tab Value +@item k @tab kilobyte (10^3 = 1000) @tab | @tab Ki @tab kibibyte (2^10 = 1024) +@item M @tab megabyte (10^6) @tab | @tab Mi @tab mebibyte (2^20) +@item G @tab gigabyte (10^9) @tab | @tab Gi @tab gibibyte (2^30) +@item T @tab terabyte (10^12) @tab | @tab Ti @tab tebibyte (2^40) +@item P @tab petabyte (10^15) @tab | @tab Pi @tab pebibyte (2^50) +@item E @tab exabyte (10^18) @tab | @tab Ei @tab exbibyte (2^60) +@item Z @tab zettabyte (10^21) @tab | @tab Zi @tab zebibyte (2^70) +@item Y @tab yottabyte (10^24) @tab | @tab Yi @tab yobibyte (2^80) +@end multitable + + +@node File Format +@chapter File Format +@cindex file format + +In the diagram below, a box like this: +@verbatim ++---+ +| | <-- the vertical bars might be missing ++---+ +@end verbatim + +represents one byte; a box like this: +@verbatim ++==============+ +| | ++==============+ +@end verbatim + +represents a variable number of bytes. + +@sp 1 +A lzip file consists of a series of "members" (compressed data sets). +The members simply appear one after another in the file, with no +additional information before, between, or after them. + +Each member has the following structure: +@verbatim ++--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +| ID string | VN | DS | Lzma stream | CRC32 | Data size | Member size | ++--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +@end verbatim + +All multibyte values are stored in little endian order. + +@table @samp +@item ID string +A four byte string, identifying the member type, with the value "LZIP". + +@item VN (version number, 1 byte) +Just in case something needs to be modified in the future. Valid values +are 0 and 1. Version 0 files have only one member and lack @samp{Member +size}. + +@item DS (coded dictionary size, 1 byte) +Bits 4-0 contain the base 2 logarithm of the base dictionary size.@* +Bits 7-5 contain the number of "wedges" to substract from the base +dictionary size to obtain the dictionary size. The size of a wedge is +(base dictionary size / 16).@* +Valid values for dictionary size range from 4KiB to 512MiB. + +@item Lzma stream +The lzma stream, finished by an end of stream marker. Uses default values +for encoder properties. + +@item CRC32 (4 bytes) +CRC of the uncompressed original data. + +@item Data size (8 bytes) +Size of the uncompressed original data. + +@item Member size (8 bytes) +Total size of the member, including header and trailer. This facilitates +safe recovery of undamaged members from multimember files. + +@end table + + +@node Examples +@chapter A small tutorial with examples +@cindex examples + +WARNING! If your data is important, give the @samp{--keep} option to +clzip and do not remove the original file until you verify the compressed +file with a command like @samp{clzip -cd file.lz | cmp file -}. + +@sp 1 +@noindent +Example 1: Replace a regular file with its compressed version file.lz +and show the compression ratio. + +@example +clzip -v file +@end example + +@sp 1 +@noindent +Example 2: Like example 1 but the created file.lz is multimember with a +member size of 1MiB. + +@example +clzip -b 1MiB file +@end example + +@sp 1 +@noindent +Example 3: Compress a whole floppy in /dev/fd0 and send the output to +file.lz. + +@example +clzip -c /dev/fd0 > file.lz +@end example + +@sp 1 +@noindent +Example 4: Create a multivolume compressed tar archive with a volume +size of 1440KiB. + +@example +tar -c some_directory | clzip -S 1440KiB -o volume_name +@end example + +@sp 1 +@noindent +Example 5: Extract a multivolume compressed tar archive. + +@example +clzip -cd volume_name*.lz | tar -xf - +@end example + +@sp 1 +@noindent +Example 6: Create a multivolume compressed backup of a big database file +with a volume size of 650MB, where each volume is a multimember file +with a member size of 32MiB. + +@example +clzip -b 32MiB -S 650MB big_database +@end example + + +@node Problems +@chapter Reporting Bugs +@cindex bugs +@cindex getting help + +There are probably bugs in clzip. There are certainly errors and +omissions in this manual. If you report them, they will get fixed. If +you don't, no one will ever know about them and they will remain unfixed +for all eternity, if not longer. + +If you find a bug in clzip, please send electronic mail to +@email{lzip-bug@@nongnu.org}. Include the version number, which you can +find by running @w{@samp{clzip --version}}. + + +@node Concept Index +@unnumbered Concept Index + +@printindex cp + +@bye |