Adding upstream version 1.0~rc2.
Signed-off-by: Daniel Baumann <daniel@debian.org>
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doc/clzip.info
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doc/clzip.info
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This is clzip.info, produced by makeinfo version 4.13 from
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clzip.texinfo.
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INFO-DIR-SECTION Data Compression
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START-INFO-DIR-ENTRY
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* Clzip: (clzip). Data compressor based on the LZMA algorithm
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END-INFO-DIR-ENTRY
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File: clzip.info, Node: Top, Next: Introduction, Up: (dir)
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Clzip Manual
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************
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This manual is for Clzip (version 1.0-rc2, 21 February 2010).
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* Menu:
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* Introduction:: Purpose and features of clzip
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* Algorithm:: How clzip compresses the data
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* Invoking Clzip:: Command line interface
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* File Format:: Detailed format of the compressed file
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* Examples:: A small tutorial with examples
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* Problems:: Reporting bugs
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* Concept Index:: Index of concepts
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Copyright (C) 2010 Antonio Diaz Diaz.
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This manual is free documentation: you have unlimited permission to
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copy, distribute and modify it.
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File: clzip.info, Node: Introduction, Next: Algorithm, Prev: Top, Up: Top
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1 Introduction
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**************
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Clzip is a lossless data compressor based on the LZMA algorithm, with
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very safe integrity checking and a user interface similar to the one of
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gzip or bzip2. Clzip decompresses almost as fast as gzip and compresses
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better than bzip2, which makes it well suited for software distribution
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and data archiving.
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Clzip replaces every file given in the command line with a compressed
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version of itself, with the name "original_name.lz". Each compressed
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file has the same modification date, permissions, and, when possible,
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ownership as the corresponding original, so that these properties can be
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correctly restored at decompression time. Clzip is able to read from
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some types of non regular files if the `--stdout' option is specified.
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If no file names are specified, clzip compresses (or decompresses)
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from standard input to standard output. In this case, clzip will
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decline to write compressed output to a terminal, as this would be
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entirely incomprehensible and therefore pointless.
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Clzip will correctly decompress a file which is the concatenation of
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two 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 multimember 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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The amount of memory required for compression is about 5 MiB plus 1
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or 2 times the dictionary size limit (1 if input file size is less than
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dictionary size limit, else 2) plus 8 times the dictionary size really
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used. For decompression is a little more than the dictionary size really
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used. Clzip will automatically use the smallest possible dictionary size
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without exceeding the given limit. It is important to appreciate that
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the decompression memory requirement is affected at compression time by
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the choice of dictionary size limit.
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When decompressing, clzip attempts to guess the name for the
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decompressed 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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As a self-check for your protection, clzip stores in the member
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trailer the 32-bit CRC of the original data and the size of the
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original data, to make sure that the decompressed version of the data
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is identical to the original. This guards against corruption of the
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compressed data, and against undetected bugs in clzip (hopefully very
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unlikely). The chances of data corruption going undetected are
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microscopic, less than one chance in 4000 million for each member
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processed. Be aware, though, that the check occurs upon decompression,
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so it can only tell you that something is wrong. It can't help you
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recover the original uncompressed data.
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Return values: 0 for a normal exit, 1 for environmental problems
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(file not found, invalid flags, I/O errors, etc), 2 to indicate a
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corrupt or invalid input file, 3 for an internal consistency error (eg,
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bug) which caused clzip to panic.
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File: clzip.info, Node: Algorithm, Next: Invoking Clzip, Prev: Introduction, Up: Top
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2 Algorithm
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***********
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Clzip implements a simplified version of the LZMA (Lempel-Ziv-Markov
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chain-Algorithm) algorithm. The original LZMA algorithm was designed by
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Igor Pavlov.
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The high compression of LZMA comes from combining two basic,
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well-proven compression ideas: sliding dictionaries (LZ77/78) and
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markov models (the thing used by every compression algorithm that uses
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a range encoder or similar order-0 entropy coder as its last stage)
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with segregation of contexts according to what the bits are used for.
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Clzip is a two stage compressor. The first stage is a Lempel-Ziv
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coder, which reduces redundancy by translating chunks of data to their
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corresponding distance-length pairs. The second stage is a range encoder
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that uses a different probability model for each type of data;
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distances, lengths, literal bytes, etc.
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The match finder, part of the LZ coder, is the most important piece
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of the LZMA algorithm, as it is in many Lempel-Ziv based algorithms.
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Most of clzip's execution time is spent in the match finder, and it has
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the greatest influence on the compression ratio.
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Here is how it works, step by step:
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1) The member header is written to the output stream.
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2) The first byte is coded literally, because there are no previous
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bytes to which the match finder can refer to.
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3) The main encoder advances to the next byte in the input data and
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calls the match finder.
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4) The match finder fills an array with the minimum distances before
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the current byte where a match of a given length can be found.
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5) Go back to step 3 until a sequence (formed of pairs, repeated
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distances and literal bytes) of minimum price has been formed. Where the
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price represents the number of output bits produced.
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6) The range encoder encodes the sequence produced by the main
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encoder and sends the produced bytes to the output stream.
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7) Go back to step 3 until the input data is finished or until the
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member or volume size limits are reached.
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8) The range encoder is flushed.
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9) The member trailer is written to the output stream.
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10) If there are more data to compress, go back to step 1.
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File: clzip.info, Node: Invoking Clzip, Next: File Format, Prev: Algorithm, Up: Top
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3 Invoking Clzip
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****************
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The format for running clzip is:
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clzip [OPTIONS] [FILES]
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Clzip supports the following options:
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`--help'
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`-h'
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Print an informative help message describing the options and exit.
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`--version'
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`-V'
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Print the version number of clzip on the standard output and exit.
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`--member-size=SIZE'
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`-b SIZE'
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Produce a multimember file and set the member size limit to SIZE
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bytes. Minimum member size limit is 100kB. Small member size may
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degrade compression ratio, so use it only when needed. The default
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is to produce single member files.
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`--stdout'
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`-c'
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Compress or decompress to standard output. Needed when reading
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from a named pipe (fifo) or from a device. Use it to recover as
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much of the uncompressed data as possible when decompressing a
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corrupt file.
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`--decompress'
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`-d'
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Decompress.
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`--force'
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`-f'
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Force overwrite of output file.
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`--keep'
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`-k'
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Keep (don't delete) input files during compression or
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decompression.
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`--match-length=LENGTH'
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`-m LENGTH'
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Set the match length limit in bytes. Valid values range from 5 to
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273. Larger values usually give better compression ratios but
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longer compression times.
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`--output=FILE'
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`-o FILE'
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When reading from standard input and `--stdout' has not been
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specified, use `FILE' as the virtual name of the uncompressed
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file. This produces a file named `FILE' when decompressing, a file
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named `FILE.lz' when compressing, and several files named
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`FILE00001.lz', `FILE00002.lz', etc, when compressing and
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splitting the output in volumes.
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`--quiet'
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`-q'
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Quiet operation. Suppress all messages.
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`--dictionary-size=SIZE'
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`-s SIZE'
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Set the dictionary size limit in bytes. Valid values range from
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4KiB to 512MiB. Clzip will use the smallest possible dictionary
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size for each member without exceeding this limit. Note that
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dictionary sizes are quantized. If the specified size does not
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match one of the valid sizes, it will be rounded upwards.
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`--volume-size=SIZE'
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`-S SIZE'
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Split the compressed output into several volume files with names
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`original_name00001.lz', `original_name00002.lz', etc, and set the
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volume size limit to SIZE bytes. Each volume is a complete, maybe
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multimember, lzip file. Minimum volume size limit is 100kB. Small
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volume size may degrade compression ratio, so use it only when
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needed.
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`--test'
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`-t'
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Check integrity of the specified file(s), but don't decompress
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them. This really performs a trial decompression and throws away
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the result. Use `-tvv' or `-tvvv' to see information about the
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file.
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`--verbose'
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`-v'
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Verbose mode. Show the compression ratio for each file processed.
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Further -v's increase the verbosity level.
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`-1 .. -9'
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Set the compression parameters (dictionary size and match length
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limit) as shown in the table below. Note that `-9' can be much
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slower than `-1'. These options have no effect when decompressing.
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Level Dictionary size Match length limit
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-1 1 MiB 10 bytes
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-2 1.5 MiB 12 bytes
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-3 2 MiB 17 bytes
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-4 3 MiB 26 bytes
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-5 4 MiB 44 bytes
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-6 8 MiB 80 bytes
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-7 16 MiB 108 bytes
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-8 24 MiB 163 bytes
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-9 32 MiB 273 bytes
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`--fast'
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`--best'
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Aliases for GNU gzip compatibility.
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Numbers given as arguments to options may be followed by a multiplier
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and an optional `B' for "byte".
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Table of SI and binary prefixes (unit multipliers):
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Prefix Value | Prefix Value
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k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024)
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M megabyte (10^6) | Mi mebibyte (2^20)
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G gigabyte (10^9) | Gi gibibyte (2^30)
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T terabyte (10^12) | Ti tebibyte (2^40)
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P petabyte (10^15) | Pi pebibyte (2^50)
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E exabyte (10^18) | Ei exbibyte (2^60)
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Z zettabyte (10^21) | Zi zebibyte (2^70)
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Y yottabyte (10^24) | Yi yobibyte (2^80)
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File: clzip.info, Node: File Format, Next: Examples, Prev: Invoking Clzip, Up: Top
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4 File Format
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*************
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In the diagram below, a box like this:
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+---+
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| | <-- the vertical bars might be missing
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+---+
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represents one byte; a box like this:
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+==============+
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| |
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+==============+
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represents a variable number of bytes.
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A lzip file consists of a series of "members" (compressed data sets).
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The members simply appear one after another in the file, with no
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additional information before, between, or after them.
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Each member has the following structure:
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+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| ID string | VN | DS | Lzma stream | CRC32 | Data size | Member size |
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+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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All multibyte values are stored in little endian order.
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`ID string'
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A four byte string, identifying the member type, with the value
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"LZIP".
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`VN (version number, 1 byte)'
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Just in case something needs to be modified in the future. Valid
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values are 0 and 1. Version 0 files have only one member and lack
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`Member size'.
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`DS (coded dictionary size, 1 byte)'
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Bits 4-0 contain the base 2 logarithm of the base dictionary size.
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Bits 7-5 contain the number of "wedges" to substract from the base
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dictionary size to obtain the dictionary size. The size of a wedge
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is (base dictionary size / 16).
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Valid values for dictionary size range from 4KiB to 512MiB.
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`Lzma stream'
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The lzma stream, finished by an end of stream marker. Uses default
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values for encoder properties.
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`CRC32 (4 bytes)'
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CRC of the uncompressed original data.
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`Data size (8 bytes)'
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Size of the uncompressed original data.
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`Member size (8 bytes)'
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Total size of the member, including header and trailer. This
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facilitates safe recovery of undamaged members from multimember
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files.
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File: clzip.info, Node: Examples, Next: Problems, Prev: File Format, Up: Top
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5 A small tutorial with examples
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********************************
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WARNING! If your data is important, give the `--keep' option to clzip
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and do not remove the original file until you verify the compressed
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file with a command like `clzip -cd file.lz | cmp file -'.
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Example 1: Replace a regular file with its compressed version file.lz
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and show the compression ratio.
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clzip -v file
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Example 2: Like example 1 but the created file.lz is multimember with a
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member size of 1MiB.
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clzip -b 1MiB file
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Example 3: Compress a whole floppy in /dev/fd0 and send the output to
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file.lz.
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clzip -c /dev/fd0 > file.lz
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Example 4: Create a multivolume compressed tar archive with a volume
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size of 1440KiB.
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tar -c some_directory | clzip -S 1440KiB -o volume_name
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Example 5: Extract a multivolume compressed tar archive.
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clzip -cd volume_name*.lz | tar -xf -
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Example 6: Create a multivolume compressed backup of a big database file
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with a volume size of 650MB, where each volume is a multimember file
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with a member size of 32MiB.
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clzip -b 32MiB -S 650MB big_database
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File: clzip.info, Node: Problems, Next: Concept Index, Prev: Examples, Up: Top
|
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6 Reporting Bugs
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****************
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There are probably bugs in clzip. There are certainly errors and
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omissions in this manual. If you report them, they will get fixed. If
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you don't, no one will ever know about them and they will remain unfixed
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for all eternity, if not longer.
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If you find a bug in clzip, please send electronic mail to
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<lzip-bug@nongnu.org>. Include the version number, which you can find
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by running `clzip --version'.
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File: clzip.info, Node: Concept Index, Prev: Problems, Up: Top
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||||
Concept Index
|
||||
*************
|
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[index ]
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* Menu:
|
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|
||||
* algorithm: Algorithm. (line 6)
|
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* bugs: Problems. (line 6)
|
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* examples: Examples. (line 6)
|
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* file format: File Format. (line 6)
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* getting help: Problems. (line 6)
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* introduction: Introduction. (line 6)
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* invoking: Invoking Clzip. (line 6)
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* options: Invoking Clzip. (line 6)
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* usage: Invoking Clzip. (line 6)
|
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* version: Invoking Clzip. (line 6)
|
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|
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|
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Tag Table:
|
||||
Node: Top226
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||||
Node: Introduction838
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Node: Algorithm4160
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Node: Invoking Clzip6391
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Node: File Format10747
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Node: Examples12703
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||||
Node: Problems13880
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Node: Concept Index14406
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||||
|
||||
End Tag Table
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