Description

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 uses the lzip file format; the files produced by clzip are fully
compatible with lzip-1.4 or newer. Clzip is in fact a C language version
of lzip, intended for embedded devices or systems lacking a C++
compiler.

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 "--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.

Clzip will automatically use the smallest possible dictionary size
without exceeding the given limit. Keep in mind that the decompression
memory requirement is affected at compression time by the choice of
dictionary size limit.

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.

Clzip implements a simplified version of the LZMA (Lempel-Ziv-Markov
chain-Algorithm) algorithm. 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.

The ideas embodied in clzip are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for
the definition of Markov chains), G.N.N. Martin (for the definition of
range encoding), Igor Pavlov (for putting all the above together in
LZMA), and Julian Seward (for bzip2's CLI and the idea of unzcrash).


Copyright (C) 2010, 2011 Antonio Diaz Diaz.

This file is free documentation: you have unlimited permission to copy,
distribute and modify it.

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