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@@ -1,30 +1,36 @@ Description Plzip is a massively parallel (multi-threaded) implementation of lzip, fully -compatible with lzip 1.4 or newer. Plzip uses the lzlib compression library. - -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. - -Plzip can compress/decompress large files on multiprocessor machines -much faster than lzip, at the cost of a slightly reduced compression -ratio (0.4 to 2 percent larger compressed files). Note that the number -of usable threads is limited by file size; on files larger than a few GB -plzip can use hundreds of processors, but on files of only a few MB -plzip is no faster than lzip. - -When compressing, plzip divides the input file into chunks and -compresses as many chunks simultaneously as worker threads are chosen, -creating a multimember compressed file. +compatible with lzip 1.4 or newer. Plzip uses the compression library lzlib. + +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. + +Plzip can compress/decompress large files on multiprocessor machines much +faster than lzip, at the cost of a slightly reduced compression ratio (0.4 +to 2 percent larger compressed files). Note that the number of usable +threads is limited by file size; on files larger than a few GB plzip can use +hundreds of processors, but on files of only a few MB plzip is no faster +than lzip. + +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. + +When compressing, plzip divides the input file into chunks and compresses as +many chunks simultaneously as worker threads are chosen, creating a +multimember compressed file. When decompressing, plzip decompresses as many members simultaneously as worker threads are chosen. Files that were compressed with lzip will not -be decompressed faster than using lzip (unless the '-b' option was used) +be decompressed faster than using lzip (unless the option '-b' was used) because lzip usually produces single-member files, which can't be decompressed in parallel. @@ -32,34 +38,34 @@ 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. Plzip uses the same well-defined exit status values used by lzip, 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. -Plzip 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. +Plzip 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. When compressing, plzip replaces every file given in the command line with a compressed version of itself, with the name "original_name.lz". @@ -76,28 +82,28 @@ 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). -Plzip is able to read from some types of non regular files if the -'--stdout' option is specified. +Plzip 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, plzip compresses (or decompresses) from -standard input to standard output. In this case, plzip will decline to -write compressed output to a terminal, as this would be entirely -incomprehensible and therefore pointless. +standard input to standard output. Plzip 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. Plzip 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. -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 |