diff options
Diffstat (limited to 'README')
| -rw-r--r-- | README | 123 |
1 files changed, 66 insertions, 57 deletions
@@ -1,52 +1,62 @@ Description -Lzip is a lossless data compressor with a user interface similar to the -one of gzip or bzip2. Lzip can compress about as fast as gzip (lzip -0) -or compress most files more than bzip2 (lzip -9). Decompression speed is -intermediate between gzip and bzip2. Lzip is better than gzip and bzip2 -from a data recovery perspective. Lzip has been designed, written and -tested with great care to replace gzip and bzip2 as the standard -general-purpose compressed format for unix-like systems. +Lzip is a lossless data compressor with a user interface similar to the one +of gzip or bzip2. Lzip uses a simplified form of the 'Lempel-Ziv-Markov +chain-Algorithm' (LZMA) stream format, chosen to maximize safety and +interoperability. Lzip can compress about as fast as gzip (lzip -0) or +compress most files more than bzip2 (lzip -9). Decompression speed is +intermediate between gzip and bzip2. Lzip is better than gzip and bzip2 from +a data recovery perspective. Lzip has been designed, written, and tested +with great care to replace gzip and bzip2 as the standard general-purpose +compressed format for unix-like systems. + +For compressing/decompressing large files on multiprocessor machines plzip +can be much faster than lzip at the cost of a slightly reduced compression +ratio. + +For creation and manipulation of compressed tar archives tarlz can be more +efficient than using tar and plzip because tarlz is able to keep the +alignment between tar members and lzip members. The lzip file format is designed for data sharing and long-term archiving, taking into account both data integrity and decoder availability: * The lzip format provides very safe integrity checking and some data - recovery means. The lziprecover program can repair bit flip errors - (one of the most common forms of data corruption) in lzip files, - and provides data recovery capabilities, including error-checked - merging of damaged copies of a file. - - * The lzip format is as simple as possible (but not simpler). The - lzip manual provides the source code of a simple decompressor - along with a detailed explanation of how it works, so that with - the only help of the lzip manual it would be possible for a - digital archaeologist to extract the data from a lzip file long - after quantum computers eventually render LZMA obsolete. + recovery means. The program lziprecover can repair bit flip errors + (one of the most common forms of data corruption) in lzip files, and + provides data recovery capabilities, including error-checked merging + of damaged copies of a file. + + * The lzip format is as simple as possible (but not simpler). The lzip + manual provides the source code of a simple decompressor along with a + detailed explanation of how it works, so that with the only help of the + lzip manual it would be possible for a digital archaeologist to extract + the data from a lzip file long after quantum computers eventually + render LZMA obsolete. * Additionally the lzip reference implementation is copylefted, which guarantees that it will remain free forever. -A nice feature of the lzip format is that a corrupt byte is easier to -repair the nearer it is from the beginning of the file. Therefore, with -the help of lziprecover, losing an entire archive just because of a -corrupt byte near the beginning is a thing of the past. +A nice feature of the lzip format is that a corrupt byte is easier to repair +the nearer it is from the beginning of the file. Therefore, with the help of +lziprecover, losing an entire archive just because of a corrupt byte near +the beginning is a thing of the past. Lzip uses the same well-defined exit status values used by bzip2, which makes it safer than compressors returning ambiguous warning values (like gzip) when it is used as a back end for other programs like tar or zutils. -Lzip will automatically use for each file the largest dictionary size -that does not exceed neither the file size nor the limit given. Keep in -mind that the decompression memory requirement is affected at -compression time by the choice of dictionary size limit. +Lzip will automatically use for each file the largest dictionary size that +does not exceed neither the file size nor the limit given. Keep in mind that +the decompression memory requirement is affected at compression time by the +choice of dictionary size limit. 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 option -'-0' is special and only requires about 1.5 MiB at most. The amount of -memory required for decompression is about 46 kB larger than the -dictionary size really used. +limit, else 2) plus 9 times the dictionary size really used. The option '-0' +is special and only requires about 1.5 MiB at most. The amount of memory +required for decompression is about 46 kB larger than the dictionary size +really used. When compressing, lzip replaces every file given in the command line with a compressed version of itself, with the name "original_name.lz". @@ -63,37 +73,36 @@ possible, ownership of the file just as 'cp -p' does. (If the user ID or the group ID can't be duplicated, the file permission bits S_ISUID and S_ISGID are cleared). -Lzip is able to read from some types of non regular files if the -'--stdout' option is specified. +Lzip is able to read from some types of non-regular files if either the +option '-c' or the option '-o' is specified. If no file names are specified, lzip compresses (or decompresses) from -standard input to standard output. In this case, lzip will decline to -write compressed output to a terminal, as this would be entirely -incomprehensible and therefore pointless. +standard input to standard output. Lzip will refuse to read compressed data +from a terminal or write compressed data to a terminal, as this would be +entirely incomprehensible and might leave the terminal in an abnormal state. Lzip will correctly decompress a file which is the concatenation of two or more compressed files. The result is the concatenation of the corresponding decompressed files. Integrity testing of concatenated compressed files is also supported. -Lzip can produce multimember files, and lziprecover can safely recover -the undamaged members in case of file damage. Lzip 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. +Lzip can produce multimember files, and lziprecover can safely recover the +undamaged members in case of file damage. Lzip 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. Lzip is able to compress and decompress streams of unlimited size by -automatically creating multimember output. The members so created are -large, about 2 PiB each. +automatically creating multimember output. The members so created are large, +about 2 PiB each. In spite of its name (Lempel-Ziv-Markov chain-Algorithm), LZMA is not a concrete algorithm; it is more like "any algorithm using the LZMA coding -scheme". For example, the option '-0' of lzip uses the scheme in almost -the simplest way possible; issuing the longest match it can find, or a -literal byte if it can't find a match. Inversely, a much more elaborated -way of finding coding sequences of minimum size than the one currently -used by lzip could be developed, and the resulting sequence could also -be coded using the LZMA coding scheme. +scheme". For example, the option '-0' of lzip uses the scheme in almost the +simplest way possible; issuing the longest match it can find, or a literal +byte if it can't find a match. Inversely, a much more elaborated way of +finding coding sequences of minimum size than the one currently used by lzip +could be developed, and the resulting sequence could also be coded using the +LZMA coding scheme. Lzip currently implements two variants of the LZMA algorithm; fast (used by option '-0') and normal (used by all other compression levels). @@ -105,20 +114,20 @@ 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 lzip 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). +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). -LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never -have been compressed. Decompressed is used to refer to data which have -undergone the process of decompression. +LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never have +been compressed. Decompressed is used to refer to data which have undergone +the process of decompression. -Copyright (C) 2008-2019 Antonio Diaz Diaz. +Copyright (C) 2008-2021 Antonio Diaz Diaz. This file is free documentation: you have unlimited permission to copy, -distribute and modify it. +distribute, and modify it. The file Makefile.in is a data file used by configure to produce the Makefile. It has the same copyright owner and permissions that configure |