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diff --git a/doc/lzip.info b/doc/lzip.info index 7c6d812..5c397d3 100644 --- a/doc/lzip.info +++ b/doc/lzip.info @@ -11,13 +11,13 @@ File: lzip.info, Node: Top, Next: Introduction, Up: (dir) Lzip Manual *********** -This manual is for Lzip (version 1.23, 24 January 2022). +This manual is for Lzip (version 1.24-rc2, 19 January 2024). * Menu: * Introduction:: Purpose and features of lzip * Output:: Meaning of lzip's output -* Invoking lzip:: Command line interface +* Invoking lzip:: Command-line interface * Quality assurance:: Design, development, and testing of lzip * Algorithm:: How lzip compresses the data * File format:: Detailed format of the compressed file @@ -29,7 +29,7 @@ This manual is for Lzip (version 1.23, 24 January 2022). * Concept index:: Index of concepts - Copyright (C) 2008-2022 Antonio Diaz Diaz. + Copyright (C) 2008-2024 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute, and modify it. @@ -42,14 +42,15 @@ File: lzip.info, Node: Introduction, Next: Output, Prev: Top, Up: Top 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 and provides a 3 factor integrity -checking to maximize interoperability and optimize safety. 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. +chain-Algorithm' (LZMA) stream format to maximize interoperability. The +maximum dictionary size is 512 MiB so that any lzip file can be decompressed +on 32-bit machines. Lzip provides accurate and robust 3-factor integrity +checking. 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 @@ -87,22 +88,22 @@ byte near the beginning is a thing of the past. 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 "End Of Stream" marker, provide a 3 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 lzip (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. +with the "End Of Stream" marker, provide a 3-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 lzip (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. 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 automatically uses 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 @@ -121,22 +122,22 @@ filename.tlz becomes filename.tar anyothername becomes anyothername.out (De)compressing a file is much like copying or moving it. Therefore lzip -preserves the access and modification dates, permissions, and, when -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). +preserves the access and modification dates, permissions, and, if you have +appropriate privileges, 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 either the option '-c' or the option '-o' is specified. - 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 refuses 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 correctly decompresses 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 @@ -208,7 +209,8 @@ The format for running lzip is: If no file names are specified, lzip compresses (or decompresses) from standard input to standard output. A hyphen '-' used as a FILE argument means standard input. It can be mixed with other FILES and is read just -once, the first time it appears in the command line. +once, the first time it appears in the command line. Remember to prepend +'./' to any file name beginning with a hyphen, or use '--'. lzip supports the following options: *Note Argument syntax: (arg_parser)Argument syntax. @@ -248,13 +250,14 @@ once, the first time it appears in the command line. '-d' '--decompress' - Decompress the files specified. If a file does not exist, can't be - opened, or the destination file already exists and '--force' has not - been specified, lzip continues decompressing the rest of the files and - exits with error status 1. If a file fails to decompress, or is a - terminal, lzip exits immediately with error status 2 without - decompressing the rest of the files. A terminal is considered an - uncompressed file, and therefore invalid. + Decompress the files specified. The integrity of the files specified is + checked. If a file does not exist, can't be opened, or the destination + file already exists and '--force' has not been specified, lzip + continues decompressing the rest of the files and exits with error + status 1. If a file fails to decompress, or is a terminal, lzip exits + immediately with error status 2 without decompressing the rest of the + files. A terminal is considered an uncompressed file, and therefore + invalid. '-f' '--force' @@ -281,26 +284,27 @@ once, the first time it appears in the command line. printed. If any file is damaged, does not exist, can't be opened, or is not - regular, the final exit status will be > 0. '-lq' can be used to verify + regular, the final exit status is > 0. '-lq' can be used to check quickly (without decompressing) the structural integrity of the files - specified. (Use '--test' to verify the data integrity). '-alq' - additionally verifies that none of the files specified contain - trailing data. + specified. (Use '--test' to check the data integrity). '-alq' + additionally checks that none of the files specified contain trailing + data. '-m BYTES' '--match-length=BYTES' When compressing, 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. + to 273. Larger values usually give better compression ratios but + longer compression times. '-o FILE' '--output=FILE' - If '-c' has not been also specified, write the (de)compressed output to - FILE; keep input files unchanged. If compressing several files, each - file is compressed independently. (The output consists of a sequence of - independently compressed members). This option (or '-c') is needed when - reading from a named pipe (fifo) or from a device. '-o -' is + If '-c' has not been also specified, write the (de)compressed output + to FILE, automatically creating any missing parent directories; keep + input files unchanged. If compressing several files, each file is + compressed independently. (The output consists of a sequence of + independently compressed members). This option (or '-c') is needed + when reading from a named pipe (fifo) or from a device. '-o -' is equivalent to '-c'. '-o' has no effect when testing or listing. In order to keep backward compatibility with lzip versions prior to @@ -321,14 +325,14 @@ once, the first time it appears in the command line. '-s BYTES' '--dictionary-size=BYTES' - When compressing, set the dictionary size limit in bytes. Lzip will use - for each file the largest dictionary size that does not exceed neither - the file size nor this limit. Valid values range from 4 KiB to - 512 MiB. Values 12 to 29 are interpreted as powers of two, meaning - 2^12 to 2^29 bytes. Dictionary sizes are quantized so that they can be - coded in just one byte (*note coded-dict-size::). If the size specified - does not match one of the valid sizes, it will be rounded upwards by - adding up to (BYTES / 8) to it. + When compressing, set the dictionary size limit in bytes. Lzip uses for + each file the largest dictionary size that does not exceed neither the + file size nor this limit. Valid values range from 4 KiB to 512 MiB. + Values 12 to 29 are interpreted as powers of two, meaning 2^12 to 2^29 + bytes. Dictionary sizes are quantized so that they can be coded in + just one byte (*note coded-dict-size::). If the size specified does + not match one of the valid sizes, it is rounded upwards by adding up + to (BYTES / 8) 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 @@ -350,8 +354,8 @@ once, the first time it appears in the command line. really performs a trial decompression and throws away the result. Use it together with '-v' to see information about the files. If a file fails the test, does not exist, can't be opened, or is a terminal, lzip - continues checking the rest of the files. A final diagnostic is shown - at verbosity level 1 or higher if any file fails the test when testing + continues testing the rest of the files. A final diagnostic is shown at + verbosity level 1 or higher if any file fails the test when testing multiple files. '-v' @@ -398,6 +402,16 @@ once, the first time it appears in the command line. '--best' Aliases for GNU gzip compatibility. +'--empty-error' + Exit with error status 2 if any empty member is found in the input + files. + +'--marking-error' + Exit with error status 2 if the first LZMA byte is non-zero in any + member of the input files. This may be caused by data corruption or by + deliberate insertion of tracking information in the file. Use + 'lziprecover --clear-marking' to clear any such non-zero bytes. + '--loose-trailing' When decompressing, testing, or listing, allow trailing data whose first bytes are so similar to the magic bytes of a lzip header that @@ -406,26 +420,29 @@ once, the first time it appears in the command line. corrupt header. - Numbers given as arguments to options may be followed by a multiplier -and an optional 'B' for "byte". + Numbers given as arguments to options may be expressed in decimal, +hexadecimal, or octal (using the same syntax as integer constants in C++), +and may be followed by a multiplier and an optional 'B' for "byte". Table of SI and binary prefixes (unit multipliers): -Prefix Value | Prefix Value -k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024) -M megabyte (10^6) | Mi mebibyte (2^20) -G gigabyte (10^9) | Gi gibibyte (2^30) -T terabyte (10^12) | Ti tebibyte (2^40) -P petabyte (10^15) | Pi pebibyte (2^50) -E exabyte (10^18) | Ei exbibyte (2^60) -Z zettabyte (10^21) | Zi zebibyte (2^70) -Y yottabyte (10^24) | Yi yobibyte (2^80) +Prefix Value | Prefix Value +k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024) +M megabyte (10^6) | Mi mebibyte (2^20) +G gigabyte (10^9) | Gi gibibyte (2^30) +T terabyte (10^12) | Ti tebibyte (2^40) +P petabyte (10^15) | Pi pebibyte (2^50) +E exabyte (10^18) | Ei exbibyte (2^60) +Z zettabyte (10^21) | Zi zebibyte (2^70) +Y yottabyte (10^24) | Yi yobibyte (2^80) +R ronnabyte (10^27) | Ri robibyte (2^90) +Q quettabyte (10^30) | Qi quebibyte (2^100) 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 (e.g., bug) which caused -lzip to panic. +found, invalid command-line options, I/O errors, etc), 2 to indicate a +corrupt or invalid input file, 3 for an internal consistency error (e.g., +bug) which caused lzip to panic. File: lzip.info, Node: Quality assurance, Next: Algorithm, Prev: Invoking lzip, Up: Top @@ -439,17 +456,12 @@ make it so complicated that there are no obvious deficiencies. The first method is far more difficult. -- C.A.R. Hoare - Lzip is developed by volunteers who lack the resources required for -extensive testing in all circumstances. It is up to you to test lzip before -using it in mission-critical applications. However, a compressor like lzip -is not a toy, and maintaining it is not a hobby. Many people's data depend -on it. Therefore the lzip file format has been reviewed carefully and is -believed to be free from negligent design errors. - 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. This chapter describes the lessons learned from these -previous formats, and their application to the design of lzip. +Unix-like systems. This chapter describes the lessons learned from these +previous formats, and their application to the design of lzip. The lzip +format specification has been reviewed carefully and is believed to be free +from design errors. 4.1 Format design @@ -532,10 +544,10 @@ extraction of the decompressed data. Using an optional CRC for the header is not only a bad idea, it is an error; it circumvents the Hamming distance (HD) of the CRC and may prevent the extraction of perfectly good data. For example, if the CRC - is used and the bit enabling it is reset by a bit flip, the header - will appear to be intact (in spite of being corrupt) while the - compressed blocks will appear to be totally unrecoverable (in spite of - being intact). Very misleading indeed. + is used and the bit enabling it is reset by a bit flip, then the + header seems to be intact (in spite of being corrupt) while the + compressed blocks seem to be totally unrecoverable (in spite of being + intact). Very misleading indeed. 'Metadata' The gzip format stores some metadata, like the modification time of the @@ -550,8 +562,8 @@ extraction of the decompressed data. '64-bit size field' Probably the most frequently reported shortcoming of the gzip format is that it only stores the least significant 32 bits of the - uncompressed size. The size of any file larger than 4 GiB gets - truncated. + uncompressed size. The size of any file larger or equal than 4 GiB + gets truncated. Bzip2 does not store the uncompressed size of the file. @@ -575,8 +587,12 @@ extraction of the decompressed data. 4.2 Quality of implementation ============================= +Our civilization depends critically on software; it had better be quality +software. +-- Bjarne Stroustrup + 'Accurate and robust error detection' - The lzip format provides 3 factor integrity checking, and the + The lzip format provides 3-factor integrity checking, and the decompressors report mismatches in each factor separately. This method detects most false positives for corruption. If just one byte in one factor fails but the other two factors match the data, it probably @@ -585,15 +601,15 @@ extraction of the decompressed data. trailer. 'Multiple implementations' - Just like the lzip format provides 3 factor protection against + Just like the lzip format provides 3-factor protection against undetected data corruption, the development methodology of the lzip - family of compressors provides 3 factor protection against undetected + family of compressors provides 3-factor protection against undetected programming errors. Three related but independent compressor implementations, lzip, clzip, and minilzip/lzlib, are developed concurrently. Every stable release - of any of them is tested to verify that it produces identical output - to the other two. This guarantees that all three implement the same + of any of them is tested to check that it produces identical output to + the other two. This guarantees that all three implement the same algorithm, and makes it unlikely that any of them may contain serious undiscovered errors. In fact, no errors have been discovered in lzip since 2009. @@ -637,10 +653,10 @@ using the LZMA coding scheme. by option '-0') 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 -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. +compression ideas: sliding dictionaries (LZ77) 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. Lzip is a two stage compressor. The first stage is a Lempel-Ziv coder, which reduces redundancy by translating chunks of data to their @@ -685,7 +701,7 @@ get longer with higher compression levels because dictionary size increases (and compression speed decreases) with compression level. 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 +Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrei 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). @@ -716,7 +732,7 @@ when there is no longer anything to take away. represents a variable number of bytes. - A lzip file consists of a series of independent "members" (compressed + A lzip file consists of one or more independent "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 can encode in compressed form up to 16 EiB - 1 byte of uncompressed data. The @@ -760,10 +776,10 @@ size of a multimember file is unlimited. '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 the safe recovery of undamaged members from - multimember files. Member size should be limited to 2 PiB to prevent - the data size field from overflowing. + as a distributed index, improves the checking of stream integrity, and + facilitates the safe recovery of undamaged members from multimember + files. Lzip limits the member size to 2 PiB to prevent the data size + field from overflowing. @@ -783,12 +799,12 @@ in the code. Lzip finishes the LZMA stream with an "End Of Stream" (EOS) marker (the distance-length pair 0xFFFFFFFFU, 2), which in conjunction with the 'member -size' field in the member trailer allows the verification of stream -integrity. The EOS marker is the only marker allowed in lzip files. The -LZMA stream in lzip files always has these two features (default properties -and EOS marker) and is referred to in this document as LZMA-302eos. This -simplified form of the LZMA stream format has been chosen to maximize -interoperability and safety. +size' field in the member trailer allows the checking of stream integrity. +The EOS marker is the only LZMA marker allowed in lzip files. The LZMA +stream in lzip files always has these two features (default properties and +EOS marker) and is referred to in this document as LZMA-302eos. This +simplified and marker-terminated form of the LZMA stream format has been +chosen to maximize interoperability and safety. The second stage of LZMA is a range encoder that uses a different probability model for each type of symbol: distances, lengths, literal @@ -806,9 +822,9 @@ a real decompressor seems the only appropriate reference to use. What follows is a description of the decoding algorithm for LZMA-302eos streams using as reference the source code of "lzd", an educational -decompressor for lzip files which can be downloaded from the lzip download -directory. Lzd is written in C++11 and its source code is included in -appendix A. *Note Reference source code::. +decompressor for lzip files, included in appendix A. *Note Reference source +code::. Lzd is written in C++11 and can be downloaded from the lzip download +directory. 7.1 What is coded @@ -873,10 +889,10 @@ the distance is >= 4, the remaining bits are encoded as follows. 'direct_bits' is the amount of remaining bits (from 1 to 30) needed to form a complete distance, and is calculated as (slot >> 1) - 1. If a distance needs 6 or more direct_bits, the last 4 bits are encoded separately. The -last piece (all the direct_bits for distances 4 to 127, or the last 4 bits -for distances >= 128) is context-coded in reverse order (from LSB to MSB). -For distances >= 128, the 'direct_bits - 4' part is encoded with fixed 0.5 -probability. +last piece (all the direct_bits for distances 4 to 127 (slots 4 to 13), or +the last 4 bits for distances >= 128 (slot >= 14)) is context-coded in +reverse order (from LSB to MSB). For distances >= 128, the +'direct_bits - 4' part is encoded with fixed 0.5 probability. Bit sequence Description ---------------------------------------------------------------------------- @@ -990,12 +1006,11 @@ decoded) and 'code' (representing the current point within 'range'). 'range' is initialized to 2^32 - 1, and 'code' is initialized to 0. The range encoder produces a first 0 byte that must be ignored by the -range decoder. This is done by shifting 5 bytes in the initialization of -'code' instead of 4. (See the 'Range_decoder' constructor in the source). +range decoder. (See the 'Range_decoder' constructor in the source). -7.4 Decoding and verifying the LZMA stream -========================================== +7.4 Decoding and checking the LZMA stream +========================================= After decoding the member header and obtaining the dictionary size, the range decoder is initialized and then the LZMA decoder enters a loop (see @@ -1005,9 +1020,9 @@ repeated matches, and literal bytes), until the "End Of Stream" marker is decoded. Once the "End Of Stream" marker has been decoded, the decompressor reads -and decodes the member trailer, and verifies that the three integrity -factors stored there (CRC, data size, and member size) match those computed -from the data. +and decodes the member trailer, and checks that the three integrity factors +stored there (CRC, data size, and member size) match those computed from the +data. File: lzip.info, Node: Trailing data, Next: Examples, Prev: Stream format, Up: Top @@ -1022,12 +1037,13 @@ member. Such trailing data may be: example when writing to a tape. It is safe to append any amount of padding zero bytes to a lzip file. - * Useful data added by the user; a cryptographically secure hash, a + * Useful data added by the user; an "End Of File" string (to check that + the file has not been truncated), a cryptographically secure hash, a description of file contents, etc. It is safe to append any amount of - text to a lzip file as long as none of the first four bytes of the text - match the corresponding byte in the string "LZIP", and the text does - not contain any zero bytes (null characters). Nonzero bytes and zero - bytes can't be safely mixed in trailing data. + text to a lzip file as long as none of the first four bytes of the + text matches the corresponding byte in the string "LZIP", and the text + does not contain any zero bytes (null characters). Nonzero bytes and + zero bytes can't be safely mixed in trailing data. * Garbage added by some not totally successful copy operation. @@ -1043,7 +1059,7 @@ member. Such trailing data may be: discriminate trailing data from a corrupt header has a Hamming distance (HD) of 3, and the 3 bit flips must happen in different magic bytes for the test to fail. In any case, the option '--trailing-error' - guarantees that any corrupt header will be detected. + guarantees that any corrupt header is detected. Trailing data are in no way part of the lzip file format, but tools reading lzip files are expected to behave as correctly and usefully as @@ -1063,7 +1079,7 @@ File: lzip.info, Node: Examples, Next: Problems, Prev: Trailing data, Up: To WARNING! Even if lzip 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 are important, give the -option '--keep' to lzip and don't remove the original file until you verify +option '--keep' to lzip and don't remove the original file until you check the compressed file with a command like 'lzip -cd file.lz | cmp file -'. Most RAM errors happening during compression can only be detected by comparing the compressed file with the original because the corruption @@ -1096,7 +1112,7 @@ the operation is successful, 'file.lz' is removed. lzip -d file.lz -Example 5: Verify the integrity of the compressed file 'file.lz' and show +Example 5: Check the integrity of the compressed file 'file.lz' and show status. lzip -tv file.lz @@ -1170,7 +1186,7 @@ Appendix A Reference source code ******************************** /* Lzd - Educational decompressor for the lzip format - Copyright (C) 2013-2022 Antonio Diaz Diaz. + Copyright (C) 2013-2024 Antonio Diaz Diaz. This program is free software. Redistribution and use in source and binary forms, with or without modification, are permitted provided @@ -1189,8 +1205,8 @@ Appendix A Reference source code */ /* 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. + (file not found, invalid command-line options, I/O errors, etc), 2 to + indicate a corrupt or invalid input file. */ #include <algorithm> @@ -1301,10 +1317,11 @@ public: const CRC32 crc32; -typedef uint8_t Lzip_header[6]; // 0-3 magic bytes - // 4 version - // 5 coded dictionary size -typedef uint8_t Lzip_trailer[20]; +enum { header_size = 6, trailer_size = 20 }; +typedef uint8_t Lzip_header[header_size]; // 0-3 magic bytes + // 4 version + // 5 coded dictionary size +typedef uint8_t Lzip_trailer[trailer_size]; // 0-3 CRC32 of the uncompressed data // 4-11 size of the uncompressed data // 12-19 member size including header and trailer @@ -1316,9 +1333,11 @@ class Range_decoder uint32_t range; public: - Range_decoder() : member_pos( 6 ), code( 0 ), range( 0xFFFFFFFFU ) + Range_decoder() + : member_pos( header_size ), code( 0 ), range( 0xFFFFFFFFU ) { - for( int i = 0; i < 5; ++i ) code = ( code << 8 ) | get_byte(); + get_byte(); // discard first byte of the LZMA stream + for( int i = 0; i < 4; ++i ) code = ( code << 8 ) | get_byte(); } uint8_t get_byte() { ++member_pos; return std::getc( stdin ); } @@ -1338,9 +1357,9 @@ public: return symbol; } - unsigned decode_bit( Bit_model & bm ) + bool decode_bit( Bit_model & bm ) { - unsigned symbol; + bool symbol; const uint32_t bound = ( range >> bit_model_total_bits ) * bm.probability; if( code < bound ) { @@ -1351,8 +1370,8 @@ public: } else { - range -= bound; code -= bound; + range -= bound; bm.probability -= bm.probability >> bit_model_move_bits; symbol = 1; } @@ -1386,8 +1405,8 @@ public: unsigned symbol = 1; for( int i = 7; i >= 0; --i ) { - const unsigned match_bit = ( match_byte >> i ) & 1; - const unsigned bit = decode_bit( bm[symbol+(match_bit<<8)+0x100] ); + const bool match_bit = ( match_byte >> i ) & 1; + const bool bit = decode_bit( bm[symbol+(match_bit<<8)+0x100] ); symbol = ( symbol << 1 ) | bit; if( match_bit != bit ) { @@ -1402,11 +1421,12 @@ public: unsigned decode_len( Len_model & lm, const int pos_state ) { if( decode_bit( lm.choice1 ) == 0 ) - return decode_tree( lm.bm_low[pos_state], len_low_bits ); + return min_match_len + + decode_tree( lm.bm_low[pos_state], len_low_bits ); if( decode_bit( lm.choice2 ) == 0 ) - return len_low_symbols + + return min_match_len + len_low_symbols + decode_tree( lm.bm_mid[pos_state], len_mid_bits ); - return len_low_symbols + len_mid_symbols + + return min_match_len + len_low_symbols + len_mid_symbols + decode_tree( lm.bm_high, len_high_bits ); } }; @@ -1479,7 +1499,7 @@ void LZ_decoder::flush_data() } -bool LZ_decoder::decode_member() // Returns false if error +bool LZ_decoder::decode_member() // Return false if error { Bit_model bm_literal[1<<literal_context_bits][0x300]; Bit_model bm_match[State::states][pos_states]; @@ -1541,12 +1561,12 @@ bool LZ_decoder::decode_member() // Returns false if error rep0 = distance; } state.set_rep(); - len = min_match_len + rdec.decode_len( rep_len_model, pos_state ); + len = rdec.decode_len( rep_len_model, pos_state ); } else // match { rep3 = rep2; rep2 = rep1; rep1 = rep0; - len = min_match_len + rdec.decode_len( match_len_model, pos_state ); + len = rdec.decode_len( match_len_model, pos_state ); const int len_state = std::min( len - min_match_len, len_states - 1 ); rep0 = rdec.decode_tree( bm_dis_slot[len_state], dis_slot_bits ); if( rep0 >= start_dis_model ) @@ -1565,7 +1585,7 @@ bool LZ_decoder::decode_member() // Returns false if error if( rep0 == 0xFFFFFFFFU ) // marker found { flush_data(); - return ( len == min_match_len ); // End Of Stream marker + return len == min_match_len; // End Of Stream marker } } } @@ -1586,11 +1606,11 @@ int main( const int argc, const char * const argv[] ) { std::printf( "Lzd %s - Educational decompressor for the lzip format.\n" - "Study the source to learn how a lzip decompressor works.\n" + "Study the source code to learn how a lzip decompressor works.\n" "See the lzip manual for an explanation of the code.\n" "\nUsage: %s [-d] < file.lz > file\n" "Lzd decompresses from standard input to standard output.\n" - "\nCopyright (C) 2022 Antonio Diaz Diaz.\n" + "\nCopyright (C) 2024 Antonio Diaz Diaz.\n" "License 2-clause BSD.\n" "This is free software: you are free to change and redistribute it.\n" "There is NO WARRANTY, to the extent permitted by law.\n" @@ -1607,8 +1627,8 @@ int main( const int argc, const char * const argv[] ) for( bool first_member = true; ; first_member = false ) { - Lzip_header header; // verify header - for( int i = 0; i < 6; ++i ) header[i] = std::getc( stdin ); + Lzip_header header; // check header + for( int i = 0; i < header_size; ++i ) header[i] = std::getc( stdin ); if( std::feof( stdin ) || std::memcmp( header, "LZIP\x01", 5 ) != 0 ) { if( first_member ) @@ -1626,8 +1646,8 @@ int main( const int argc, const char * const argv[] ) if( !decoder.decode_member() ) { std::fputs( "Data error\n", stderr ); return 2; } - Lzip_trailer trailer; // verify trailer - for( int i = 0; i < 20; ++i ) trailer[i] = decoder.get_byte(); + Lzip_trailer trailer; // check trailer + for( int i = 0; i < trailer_size; ++i ) trailer[i] = decoder.get_byte(); int retval = 0; unsigned crc = 0; for( int i = 3; i >= 0; --i ) crc = ( crc << 8 ) + trailer[i]; @@ -1683,22 +1703,22 @@ Concept index Tag Table: Node: Top203 -Node: Introduction1198 -Node: Output6972 -Node: Invoking lzip8567 -Ref: --trailing-error9356 -Node: Quality assurance18682 -Node: Algorithm27705 -Node: File format31109 -Ref: coded-dict-size32538 -Node: Stream format33773 -Ref: what-is-coded36169 -Node: Trailing data45097 -Node: Examples47358 -Ref: concat-example48800 -Node: Problems50021 -Node: Reference source code50553 -Node: Concept index65411 +Node: Introduction1202 +Node: Output7087 +Node: Invoking lzip8682 +Ref: --trailing-error9551 +Node: Quality assurance19649 +Node: Algorithm28462 +Node: File format31863 +Ref: coded-dict-size33292 +Node: Stream format34523 +Ref: what-is-coded36918 +Node: Trailing data45792 +Node: Examples48128 +Ref: concat-example49568 +Node: Problems50789 +Node: Reference source code51321 +Node: Concept index66366 End Tag Table |