118 lines
5.5 KiB
Text
118 lines
5.5 KiB
Text
Description
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Clzip is a lossless data compressor with a user interface similar to the
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one of gzip or bzip2. Clzip decompresses almost as fast as gzip,
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compresses most files more than bzip2, and is better than both from a
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data recovery perspective. Clzip is a clean implementation of the LZMA
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"algorithm".
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Clzip uses the lzip file format; the files produced by clzip are fully
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compatible with lzip-1.4 or newer, and can be rescued with lziprecover.
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Clzip is in fact a C language version of lzip, intended for embedded
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devices or systems lacking a C++ compiler.
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The lzip file format is designed for long-term data archiving, taking
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into account both data integrity and decoder availability:
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* The lzip format provides very safe integrity checking and some data
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recovery means. The lziprecover program can repair bit-flip errors
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(one of the most common forms of data corruption) in lzip files,
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and provides data recovery capabilities, including error-checked
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merging of damaged copies of a file.
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* The lzip format is as simple as possible (but not simpler). The
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lzip manual provides the code of a simple decompressor along with a
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detailed explanation of how it works, so that with the only help of
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the lzip manual it would be possible for a digital archaeologist to
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extract the data from a lzip file long after quantum computers
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eventually render LZMA obsolete.
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* Additionally lzip is copylefted, which guarantees that it will
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remain free forever.
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A nice feature of the lzip format is that a corrupt byte is easier to
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repair the nearer it is from the beginning of the file. Therefore, with
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the help of lziprecover, losing an entire archive just because of a
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corrupt byte near the beginning is a thing of the past.
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Clzip uses the same well-defined exit status values used by lzip and
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bzip2, which makes it safer than compressors returning ambiguous warning
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values (like gzip) when it is used as a back end for other programs like
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tar or zutils.
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Clzip will automatically use the smallest possible dictionary size for
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each file without exceeding the given limit. Keep in mind that the
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decompression memory requirement is affected at compression time by the
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choice of dictionary size limit.
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When compressing, clzip replaces every file given in the command line
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with a compressed version of itself, with the name "original_name.lz".
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When decompressing, clzip attempts to guess the name for the decompressed
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file from that of the compressed file as follows:
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filename.lz becomes filename
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filename.tlz becomes filename.tar
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anyothername becomes anyothername.out
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(De)compressing a file is much like copying or moving it; therefore clzip
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preserves the access and modification dates, permissions, and, when
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possible, ownership of the file just as "cp -p" does. (If the user ID or
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the group ID can't be duplicated, the file permission bits S_ISUID and
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S_ISGID are cleared).
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Clzip is able to read from some types of non regular files if the
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"--stdout" option is specified.
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If no file names are specified, clzip compresses (or decompresses) from
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standard input to standard output. In this case, clzip will decline to
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write compressed output to a terminal, as this would be entirely
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incomprehensible and therefore pointless.
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Clzip will correctly decompress a file which is the concatenation of two
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or more compressed files. The result is the concatenation of the
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corresponding uncompressed files. Integrity testing of concatenated
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compressed files is also supported.
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Clzip can produce multi-member files and safely recover, with
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lziprecover, the undamaged members in case of file damage. Clzip can
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also split the compressed output in volumes of a given size, even when
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reading from standard input. This allows the direct creation of
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multivolume compressed tar archives.
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Clzip is able to compress and decompress streams of unlimited size by
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automatically creating multi-member output. The members so created are
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large, about 64 PiB each.
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There is no such thing as a "LZMA algorithm"; it is more like a "LZMA
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coding scheme". For example, the option '-0' of lzip uses the scheme in
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almost the simplest way possible; issuing the longest match it can find,
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or a literal byte if it can't find a match. Inversely, a much more
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elaborated way of finding coding sequences of minimum price than the one
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currently used by lzip could be developed, and the resulting sequence
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could also be coded using the LZMA coding scheme.
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Lzip currently implements two variants of the LZMA algorithm; fast (used
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by option -0) and normal (used by all other compression levels). Clzip
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just implements the "normal" variant.
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The high compression of LZMA comes from combining two basic, well-proven
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compression ideas: sliding dictionaries (LZ77/78) and markov models (the
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thing used by every compression algorithm that uses a range encoder or
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similar order-0 entropy coder as its last stage) with segregation of
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contexts according to what the bits are used for.
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The ideas embodied in clzip are due to (at least) the following people:
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Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for
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the definition of Markov chains), G.N.N. Martin (for the definition of
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range encoding), Igor Pavlov (for putting all the above together in
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LZMA), and Julian Seward (for bzip2's CLI).
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Copyright (C) 2010-2014 Antonio Diaz Diaz.
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This file is free documentation: you have unlimited permission to copy,
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distribute and modify it.
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The file Makefile.in is a data file used by configure to produce the
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Makefile. It has the same copyright owner and permissions that configure
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itself.
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