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authorDaniel Baumann <mail@daniel-baumann.ch>2015-11-06 12:43:36 +0000
committerDaniel Baumann <mail@daniel-baumann.ch>2015-11-06 12:43:36 +0000
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-\input texinfo @c -*-texinfo-*-
-@c %**start of header
-@setfilename clzip.info
-@documentencoding ISO-8859-15
-@settitle Clzip Manual
-@finalout
-@c %**end of header
-
-@set UPDATED 17 September 2013
-@set VERSION 1.5
-
-@dircategory Data Compression
-@direntry
-* Clzip: (clzip). LZMA lossless data compressor
-@end direntry
-
-
-@ifnothtml
-@titlepage
-@title Clzip
-@subtitle LZMA lossless data compressor
-@subtitle for Clzip version @value{VERSION}, @value{UPDATED}
-@author by Antonio Diaz Diaz
-
-@page
-@vskip 0pt plus 1filll
-@end titlepage
-
-@contents
-@end ifnothtml
-
-@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, 2011, 2012, 2013 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 with a user interface similar to the
-one of gzip or bzip2. Clzip decompresses almost as fast as gzip and
-compresses more than bzip2, which makes it well suited for software
-distribution and data archiving. Clzip is a clean implementation of the
-LZMA algorithm.
-
-Clzip uses the lzip file format; the files produced by clzip are fully
-compatible with lzip-1.4 or newer, and can be rescued with lziprecover.
-Clzip is in fact a C language version of lzip, intended for embedded
-devices or systems lacking a C++ compiler.
-
-The lzip file format is designed for long-term data archiving and
-provides very safe integrity checking. The member trailer stores the
-32-bit CRC of the original data, the size of the original data and the
-size of the member. These values, together with the value remaining in
-the range decoder and the end-of-stream marker, provide a 4 factor
-integrity checking which guarantees 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. 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.
-
-If you ever need to recover data from a damaged lzip file, try the
-lziprecover program. Lziprecover makes lzip files resistant to bit-flip
-(one of the most common forms of data corruption), and provides data
-recovery capabilities, including error-checked merging of damaged copies
-of a file.
-
-Clzip uses the same well-defined exit status values used by lzip and
-bzip2, which makes it safer when used in pipes or scripts than
-compressors returning ambiguous warning values, like gzip.
-
-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 multi-member 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 is able to compress and decompress streams of unlimited size by
-automatically creating multi-member output. The members so created are
-large, about 64 PiB each.
-
-The amount of memory required for compression is about 1 or 2 times the
-dictionary size limit (1 if input file size is less than dictionary size
-limit, else 2) plus 9 times the dictionary size really used. The amount
-of memory required for decompression is only a few tens of KiB larger
-than the dictionary size really used.
-
-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.
-
-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
-
-
-@node Algorithm
-@chapter Algorithm
-@cindex algorithm
-
-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.
-
-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.
-
-@sp 1
-@noindent
-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).
-
-
-@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 -h
-@itemx --help
-Print an informative help message describing the options and exit.
-
-@item -V
-@itemx --version
-Print the version number of clzip on the standard output and exit.
-
-@item -b @var{bytes}
-@itemx --member-size=@var{bytes}
-Set the member size limit to @var{bytes}. A small member size may
-degrade compression ratio, so use it only when needed. Valid values
-range from 100 kB to 64 PiB. Defaults to 64 PiB.
-
-@item -c
-@itemx --stdout
-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 -d
-@itemx --decompress
-Decompress.
-
-@item -f
-@itemx --force
-Force overwrite of output files.
-
-@item -F
-@itemx --recompress
-Force recompression of files whose name already has the @samp{.lz} or
-@samp{.tlz} suffix.
-
-@item -k
-@itemx --keep
-Keep (don't delete) input files during compression or decompression.
-
-@item -m @var{bytes}
-@itemx --match-length=@var{bytes}
-Set the match length limit in bytes. After a match this long is found,
-the search is finished. Valid values range from 5 to 273. Larger values
-usually give better compression ratios but longer compression times.
-
-@item -o @var{file}
-@itemx --output=@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 -q
-@itemx --quiet
-Quiet operation. Suppress all messages.
-
-@item -s @var{bytes}
-@itemx --dictionary-size=@var{bytes}
-Set the dictionary size limit in bytes. Valid values range from 4 KiB to
-512 MiB. 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 by adding up to (@var{bytes} / 16) to it.
-
-For maximum compression you should use a dictionary size limit as large
-as possible, but keep in mind that the decompression memory requirement
-is affected at compression time by the choice of dictionary size limit.
-
-@item -S @var{bytes}
-@itemx --volume-size=@var{bytes}
-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{bytes}. Each volume is a complete, maybe
-multi-member, lzip file. A small volume size may degrade compression
-ratio, so use it only when needed. Valid values range from 100 kB to 4
-EiB.
-
-@item -t
-@itemx --test
-Check integrity of the specified file(s), but don't decompress them.
-This really performs a trial decompression and throws away the result.
-Use it together with @samp{-v} to see information about the file.
-
-@item -v
-@itemx --verbose
-Verbose mode.@*
-When compressing, show the compression ratio for each file processed. A
-second @samp{-v} shows the progress of compression.@*
-When decompressing or testing, further -v's (up to 4) increase the
-verbosity level, showing status, compression ratio, dictionary size,
-and trailer contents (CRC, data size, member size).
-
-@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.
-
-The bidimensional parameter space of LZMA can't be mapped to a linear
-scale optimal for all files. If your files are large, very repetitive,
-etc, you may need to use the @samp{--match-length} and
-@samp{--dictionary-size} options directly to achieve optimal
-performance. For example, @samp{-9m64} usually compresses executables
-more (and faster) than @samp{-9}.
-
-@multitable {Level} {Dictionary size} {Match length limit}
-@item Level @tab Dictionary size @tab Match length limit
-@item -1 @tab 1 MiB @tab 5 bytes
-@item -2 @tab 1.5 MiB @tab 6 bytes
-@item -3 @tab 2 MiB @tab 8 bytes
-@item -4 @tab 3 MiB @tab 12 bytes
-@item -5 @tab 4 MiB @tab 20 bytes
-@item -6 @tab 8 MiB @tab 36 bytes
-@item -7 @tab 16 MiB @tab 68 bytes
-@item -8 @tab 24 MiB @tab 132 bytes
-@item -9 @tab 32 MiB @tab 273 bytes
-@end multitable
-
-@item --fast
-@itemx --best
-Aliases for GNU gzip compatibility.
-
-@end table
-
-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
-
-@sp 1
-Exit status: 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 File format
-@chapter File format
-@cindex file format
-
-Perfection is reached, not when there is no longer anything to add, but
-when there is no longer anything to take away.@*
---- Antoine de Saint-Exupery
-
-@sp 1
-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 lzip format, with the value "LZIP"
-(0x4C, 0x5A, 0x49, 0x50).
-
-@item VN (version number, 1 byte)
-Just in case something needs to be modified in the future. 1 for now.
-
-@item DS (coded dictionary size, 1 byte)
-Lzip divides the distance between any two powers of 2 into 8 equally
-spaced intervals, named "wedges". The dictionary size is calculated by
-taking a power of 2 (the base size) and substracting from it a number of
-wedges between 0 and 7. The size of a wedge is (base_size / 16).@*
-Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).@*
-Bits 7-5 contain the number of wedges (0 to 7) to substract from the
-base size to obtain the dictionary size.@*
-Example: 0xD3 = 2^19 - 6 * 2^15 = 512 KiB - 6 * 32 KiB = 320 KiB@*
-Valid values for dictionary size range from 4 KiB to 512 MiB.
-
-@item Lzma stream
-The lzma stream, finished by an end of stream marker. Uses default values
-for encoder properties. See the lzip manual for a full description.
-
-@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 field acts
-as a distributed index, allows the verification of stream integrity, and
-facilitates safe recovery of undamaged members from multi-member files.
-
-@end table
-
-
-@node Examples
-@chapter A small tutorial with examples
-@cindex examples
-
-WARNING! Even if clzip is bug-free, other causes may result in a corrupt
-compressed file (bugs in the system libraries, memory errors, etc).
-Therefore, if the data you are going to compress 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
-@w{@samp{clzip -cd file.lz | cmp file -}}.
-
-@sp 1
-@noindent
-Example 1: Replace a regular file with its compressed version
-@samp{file.lz} and show the compression ratio.
-
-@example
-clzip -v file
-@end example
-
-@sp 1
-@noindent
-Example 2: Like example 1 but the created @samp{file.lz} is multi-member
-with a member size of 1 MiB. The compression ratio is not shown.
-
-@example
-clzip -b 1MiB file
-@end example
-
-@sp 1
-@noindent
-Example 3: Restore a regular file from its compressed version
-@samp{file.lz}. If the operation is successful, @samp{file.lz} is
-removed.
-
-@example
-clzip -d file.lz
-@end example
-
-@sp 1
-@noindent
-Example 4: Verify the integrity of the compressed file @samp{file.lz}
-and show status.
-
-@example
-clzip -tv file.lz
-@end example
-
-@sp 1
-@noindent
-Example 5: Compress a whole floppy in /dev/fd0 and send the output to
-@samp{file.lz}.
-
-@example
-clzip -c /dev/fd0 > file.lz
-@end example
-
-@sp 1
-@noindent
-Example 6: Decompress @samp{file.lz} partially until 10 KiB of
-decompressed data are produced.
-
-@example
-clzip -cd file.lz | dd bs=1024 count=10
-@end example
-
-@sp 1
-@noindent
-Example 7: Decompress @samp{file.lz} partially from decompressed byte
-10000 to decompressed byte 15000 (5000 bytes are produced).
-
-@example
-clzip -cd file.lz | dd bs=1000 skip=10 count=5
-@end example
-
-@sp 1
-@noindent
-Example 8: Create a multivolume compressed tar archive with a volume
-size of 1440 KiB.
-
-@example
-tar -c some_directory | clzip -S 1440KiB -o volume_name
-@end example
-
-@sp 1
-@noindent
-Example 9: Extract a multivolume compressed tar archive.
-
-@example
-clzip -cd volume_name*.lz | tar -xf -
-@end example
-
-@sp 1
-@noindent
-Example 10: Create a multivolume compressed backup of a large database
-file with a volume size of 650 MB, where each volume is a multi-member
-file with a member size of 32 MiB.
-
-@example
-clzip -b 32MiB -S 650MB big_db
-@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