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@@ -1,65 +1,64 @@ Description -Lzlib is a data compression library providing in-memory LZMA compression -and decompression functions, including integrity checking of the -decompressed data. The compressed data format used by the library is the -lzip format. Lzlib is written in C. +Lzlib is a data compression library providing in-memory LZMA compression and +decompression functions, including integrity checking of the decompressed +data. The compressed data format used by the library is the lzip format. +Lzlib is written in C. 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. -The functions and variables forming the interface of the compression -library are declared in the file 'lzlib.h'. Usage examples of the -library are given in the files 'main.c' and 'bbexample.c' from the -source distribution. +The functions and variables forming the interface of the compression library +are declared in the file 'lzlib.h'. Usage examples of the library are given +in the files 'bbexample.c', 'ffexample.c', and 'main.c' from the source +distribution. Compression/decompression is done by repeatedly calling a couple of -read/write functions until all the data have been processed by the -library. This interface is safer and less error prone than the -traditional zlib interface. +read/write functions until all the data have been processed by the library. +This interface is safer and less error prone than the traditional zlib +interface. Compression/decompression is done when the read function is called. This -means the value returned by the position functions will not be updated -until a read call, even if a lot of data are written. If you want the -data to be compressed in advance, just call the read function with a -size equal to 0. +means the value returned by the position functions will not be updated until +a read call, even if a lot of data are written. If you want the data to be +compressed in advance, just call the read function with a size equal to 0. If all the data to be compressed are written in advance, lzlib will -automatically adjust the header of the compressed data to use the -largest dictionary size that does not exceed neither the data size nor -the limit given to LZ_compress_open. This feature reduces the amount of -memory needed for decompression and allows minilzip to produce identical -compressed output as lzip. +automatically adjust the header of the compressed data to use the largest +dictionary size that does not exceed neither the data size nor the limit +given to 'LZ_compress_open'. This feature reduces the amount of memory +needed for decompression and allows minilzip to produce identical compressed +output as lzip. -Lzlib will correctly decompress a data stream which is the concatenation -of two or more compressed data streams. The result is the concatenation -of the corresponding decompressed data streams. Integrity testing of -concatenated compressed data streams is also supported. +Lzlib will correctly decompress a data stream which is the concatenation of +two or more compressed data streams. The result is the concatenation of the +corresponding decompressed data streams. Integrity testing of concatenated +compressed data streams is also supported. Lzlib 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. All the library functions are thread safe. The library does not install any signal handler. The decoder checks the consistency of the compressed @@ -67,16 +66,15 @@ data, so the library should never crash even in case of corrupted input. 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. -Lzlib currently implements two variants of the LZMA algorithm; fast -(used by option '-0' of minilzip) and normal (used by all other -compression levels). +Lzlib currently implements two variants of the LZMA algorithm; fast (used by +option '-0' of minilzip) and normal (used by all other compression levels). The high compression of LZMA comes from combining two basic, well-proven compression ideas: sliding dictionaries (LZ77/78) and markov models (the @@ -85,20 +83,20 @@ 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 lzlib 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) 2009-2019 Antonio Diaz Diaz. +Copyright (C) 2009-2021 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 |