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| -rw-r--r-- | doc/lzip.1 | 7 | ||||
| -rw-r--r-- | doc/lzip.info | 202 | ||||
| -rw-r--r-- | doc/lzip.texi | 186 |
3 files changed, 228 insertions, 167 deletions
@@ -1,5 +1,5 @@ .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.46.1. -.TH LZIP "1" "May 2016" "lzip 1.18" "User Commands" +.TH LZIP "1" "April 2017" "lzip 1.19" "User Commands" .SH NAME lzip \- reduces the size of files .SH SYNOPSIS @@ -36,6 +36,9 @@ force re\-compression of compressed files \fB\-k\fR, \fB\-\-keep\fR keep (don't delete) input files .TP +\fB\-l\fR, \fB\-\-list\fR +print (un)compressed file sizes +.TP \fB\-m\fR, \fB\-\-match\-length=\fR<bytes> set match length limit in bytes [36] .TP @@ -87,7 +90,7 @@ Report bugs to lzip\-bug@nongnu.org .br Lzip home page: http://www.nongnu.org/lzip/lzip.html .SH COPYRIGHT -Copyright \(co 2016 Antonio Diaz Diaz. +Copyright \(co 2017 Antonio Diaz Diaz. License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html> .br This is free software: you are free to change and redistribute it. diff --git a/doc/lzip.info b/doc/lzip.info index 0210f9e..cac370c 100644 --- a/doc/lzip.info +++ b/doc/lzip.info @@ -11,7 +11,7 @@ File: lzip.info, Node: Top, Next: Introduction, Up: (dir) Lzip Manual *********** -This manual is for Lzip (version 1.18, 14 May 2016). +This manual is for Lzip (version 1.19, 13 April 2017). * Menu: @@ -28,7 +28,7 @@ This manual is for Lzip (version 1.18, 14 May 2016). * Concept index:: Index of concepts - Copyright (C) 2008-2016 Antonio Diaz Diaz. + Copyright (C) 2008-2017 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it. @@ -40,9 +40,10 @@ File: lzip.info, Node: Introduction, Next: Invoking lzip, Prev: Top, Up: Top ************** Lzip is a lossless data compressor with a user interface similar to the -one of gzip or bzip2. Lzip is about as fast as gzip, compresses most -files more than bzip2, and is better than both from a data recovery -perspective. +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. The lzip file format is designed for data sharing and long-term archiving, taking into account both data integrity and decoder @@ -56,11 +57,11 @@ availability: (lziprecover)Data safety. * The lzip format is as simple as possible (but not simpler). The - lzip manual provides the 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. + 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. @@ -126,9 +127,9 @@ two or more compressed files. The result is the concatenation of the corresponding uncompressed files. Integrity testing of concatenated compressed files is also supported. - Lzip can produce multimember files and safely recover, with -lziprecover, the undamaged members in case of file damage. Lzip can -also split the compressed output in volumes of a given size, even when + 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. @@ -136,6 +137,10 @@ multivolume compressed tar archives. automatically creating multimember output. The members so created are large, about 2 PiB each. + 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. + File: lzip.info, Node: Invoking lzip, Next: Quality assurance, Prev: Introduction, Up: Top @@ -203,6 +208,21 @@ command line. Keep (don't delete) input files during compression or decompression. +'-l' +'--list' + Print the uncompressed size, compressed size and percentage saved + of the specified file(s). Trailing data are ignored. The values + produced are correct even for multimember files. If more than one + file is given, a final line containing the cumulative sizes is + printed. With '-v', the dictionary size, the number of members in + the file, and the amount of trailing data (if any) are also + printed. With '-vv', the positions and sizes of each member in + multimember files are also printed. '-lq' can be used to verify + quickly (without decompressing) the structural integrity of the + specified files. (Use '--test' to verify the data integrity). + '-alq' additionally verifies that none of the specified files + contain trailing data. + '-m BYTES' '--match-length=BYTES' Set the match length limit in bytes. After a match this long is @@ -252,8 +272,9 @@ command line. 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 '-v' to see information about - the file(s). If a file fails the test, lzip continues checking the - rest of the files. + the file(s). 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. '-v' '--verbose' @@ -263,7 +284,8 @@ command line. When decompressing or testing, further -v's (up to 4) increase the verbosity level, showing status, compression ratio, dictionary size, trailer contents (CRC, data size, member size), and up to 6 - bytes of trailing data (if any). + bytes of trailing data (if any) both in hexadecimal and as a + string of printable ASCII characters. '-0 .. -9' Set the compression parameters (dictionary size and match length @@ -714,10 +736,10 @@ You may first send the position of the most significant bit that is set to 1, which you may find by making a bit scan from the left (from the MSB). A position of 0 means that the number is 0 (no bit is set), 1 means the LSB is the first bit set (the number is 1), and 32 means the -MSB is set (i.e., the number is >= 0x80000000). Lets call this bit -position a "slot". Then, if slot is > 1, you send the remaining slot - -1 bits. Lets call these bits "direct_bits" because they are coded -directly by value instead of indirectly by position. +MSB is set (i.e., the number is >= 0x80000000). Let's call this bit +position a "slot". Then, if slot is > 1, you send the remaining +slot - 1 bits. Let's call these bits "direct_bits" because they are +coded directly by value instead of indirectly by position. The inconvenient of this simple method is that it needs 6 bits to code the slot, but it just uses 33 of the 64 possible values, wasting @@ -729,14 +751,15 @@ same 6 bits that would take to encode the position alone. This seems to need 66 slots (2 * position + next_bit), but for slots 0 and 1 there is no next bit, so the number of needed slots is 64 (0 to 63). - The slot number is context-coded in 6 bits. 'direct_bits' is the -amount of remaining bits (from 0 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 coded 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 coded with fixed -0.5 probability. + The 6 bits representing this "slot number" are then context-coded. If +the distance is >= 4, the remaining bits are coded as follows. +'direct_bits' is the amount of remaining bits (from 0 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 coded +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 coded with fixed 0.5 probability. Bit sequence Description -------------------------------------------------------------------------- @@ -871,16 +894,21 @@ File: lzip.info, Node: Trailing data, Next: Examples, Prev: Stream format, U 7 Extra data appended to the file ********************************* -Sometimes extra data is found appended to a lzip file after the last +Sometimes extra data are found appended to a lzip file after the last member. Such trailing data may be: * Padding added to make the file size a multiple of some block size, - for example when writing to a tape. - - * Garbage added by some not totally successful copy operation. + for 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 - description of file contents, etc. + description of file contents, etc. It is safe to append any amount + of text to a lzip file as long as the text does not begin with the + string "LZIP", and 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. * Malicious data added to the file in order to make its total size and hash value (for a chosen hash) coincide with those of another @@ -893,8 +921,12 @@ member. Such trailing data may be: the corruption of the integrity information itself. Therefore it can be considered to be below the noise level. + 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 +possible in the presence of trailing data. + Trailing data can be safely ignored in most cases. In some cases, -like that of user-added data, it is expected to be ignored. In those +like that of user-added data, they are expected to be ignored. In those cases where a file containing trailing data must be rejected, the option '--trailing-error' can be used. *Note --trailing-error::. @@ -942,8 +974,8 @@ Example 5: Compress a whole device in /dev/sdc and send the output to lzip -c /dev/sdc > file.lz -Example 6: The right way of concatenating compressed files. *Note -Trailing data::. +Example 6: The right way of concatenating the decompressed output of two +or more compressed files. *Note Trailing data::. Don't do this cat file1.lz file2.lz file3.lz | lzip -d @@ -1002,7 +1034,7 @@ Appendix A Reference source code ******************************** /* Lzd - Educational decompressor for the lzip format - Copyright (C) 2013-2016 Antonio Diaz Diaz. + Copyright (C) 2013-2017 Antonio Diaz Diaz. This program is free software. Redistribution and use in source and binary forms, with or without modification, are permitted provided @@ -1153,10 +1185,10 @@ public: uint8_t get_byte() { return std::getc( stdin ); } - int decode( const int num_bits ) + unsigned decode( const int num_bits ) { - int symbol = 0; - for( int i = 0; i < num_bits; ++i ) + unsigned symbol = 0; + for( int i = num_bits; i > 0; --i ) { range >>= 1; symbol <<= 1; @@ -1167,9 +1199,9 @@ public: return symbol; } - int decode_bit( Bit_model & bm ) + unsigned decode_bit( Bit_model & bm ) { - int symbol; + unsigned symbol; const uint32_t bound = ( range >> bit_model_total_bits ) * bm.probability; if( code < bound ) { @@ -1189,18 +1221,18 @@ public: return symbol; } - int decode_tree( Bit_model bm[], const int num_bits ) + unsigned decode_tree( Bit_model bm[], const int num_bits ) { - int symbol = 1; + unsigned symbol = 1; for( int i = 0; i < num_bits; ++i ) symbol = ( symbol << 1 ) | decode_bit( bm[symbol] ); return symbol - (1 << num_bits); } - int decode_tree_reversed( Bit_model bm[], const int num_bits ) + unsigned decode_tree_reversed( Bit_model bm[], const int num_bits ) { - int symbol = decode_tree( bm, num_bits ); - int reversed_symbol = 0; + unsigned symbol = decode_tree( bm, num_bits ); + unsigned reversed_symbol = 0; for( int i = 0; i < num_bits; ++i ) { reversed_symbol = ( reversed_symbol << 1 ) | ( symbol & 1 ); @@ -1209,14 +1241,13 @@ public: return reversed_symbol; } - int decode_matched( Bit_model bm[], const int match_byte ) + unsigned decode_matched( Bit_model bm[], const unsigned match_byte ) { - Bit_model * const bm1 = bm + 0x100; - int symbol = 1; + unsigned symbol = 1; for( int i = 7; i >= 0; --i ) { - const int match_bit = ( match_byte >> i ) & 1; - const int bit = decode_bit( bm1[(match_bit<<8)+symbol] ); + const unsigned match_bit = ( match_byte >> i ) & 1; + const unsigned bit = decode_bit( bm[symbol+(match_bit<<8)+0x100] ); symbol = ( symbol << 1 ) | bit; if( match_bit != bit ) { @@ -1228,7 +1259,7 @@ public: return symbol & 0xFF; } - int decode_len( Len_model & lm, const int pos_state ) + 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 ); @@ -1256,9 +1287,9 @@ class LZ_decoder uint8_t peek( const unsigned distance ) const { - unsigned i = pos - distance - 1; - if( pos <= distance ) i += dictionary_size; - return buffer[i]; + if( pos > distance ) return buffer[pos - distance - 1]; + if( pos_wrapped ) return buffer[dictionary_size + pos - distance - 1]; + return 0; // prev_byte of first byte } void put_byte( const uint8_t b ) @@ -1277,7 +1308,7 @@ public: stream_pos( 0 ), crc_( 0xFFFFFFFFU ), pos_wrapped( false ) - { buffer[dictionary_size-1] = 0; } // prev_byte of first byte + {} ~LZ_decoder() { delete[] buffer; } @@ -1315,7 +1346,7 @@ bool LZ_decoder::decode_member() // Returns false if error Bit_model bm_rep2[State::states]; Bit_model bm_len[State::states][pos_states]; Bit_model bm_dis_slot[len_states][1<<dis_slot_bits]; - Bit_model bm_dis[modeled_distances-end_dis_model]; + Bit_model bm_dis[modeled_distances-end_dis_model+1]; Bit_model bm_align[dis_align_size]; Len_model match_len_model; Len_model rep_len_model; @@ -1344,7 +1375,12 @@ bool LZ_decoder::decode_member() // Returns false if error int len; if( rdec.decode_bit( bm_rep[state()] ) != 0 ) // 2nd bit { - if( rdec.decode_bit( bm_rep0[state()] ) != 0 ) // 3rd bit + if( rdec.decode_bit( bm_rep0[state()] ) == 0 ) // 3rd bit + { + if( rdec.decode_bit( bm_len[state()][pos_state] ) == 0 ) // 4th bit + { state.set_short_rep(); put_byte( peek( rep0 ) ); continue; } + } + else { unsigned distance; if( rdec.decode_bit( bm_rep1[state()] ) == 0 ) // 4th bit @@ -1360,11 +1396,6 @@ bool LZ_decoder::decode_member() // Returns false if error rep1 = rep0; rep0 = distance; } - else - { - if( rdec.decode_bit( bm_len[state()][pos_state] ) == 0 ) // 4th bit - { state.set_short_rep(); put_byte( peek( rep0 ) ); continue; } - } state.set_rep(); len = min_match_len + rdec.decode_len( rep_len_model, pos_state ); } @@ -1373,15 +1404,14 @@ bool LZ_decoder::decode_member() // Returns false if error rep3 = rep2; rep2 = rep1; rep1 = rep0; len = min_match_len + rdec.decode_len( match_len_model, pos_state ); const int len_state = std::min( len - min_match_len, len_states - 1 ); - const int dis_slot = - rdec.decode_tree( bm_dis_slot[len_state], dis_slot_bits ); - if( dis_slot < start_dis_model ) rep0 = dis_slot; - else + rep0 = rdec.decode_tree( bm_dis_slot[len_state], dis_slot_bits ); + if( rep0 >= start_dis_model ) { + const unsigned dis_slot = rep0; const int direct_bits = ( dis_slot >> 1 ) - 1; rep0 = ( 2 | ( dis_slot & 1 ) ) << direct_bits; if( dis_slot < end_dis_model ) - rep0 += rdec.decode_tree_reversed( bm_dis + rep0 - dis_slot - 1, + rep0 += rdec.decode_tree_reversed( bm_dis + ( rep0 - dis_slot ), direct_bits ); else { @@ -1417,7 +1447,7 @@ int main( const int argc, const char * const argv[] ) "It is not safe to use lzd for any real work.\n" "\nUsage: %s < file.lz > file\n", argv[0] ); std::printf( "Lzd decompresses from standard input to standard output.\n" - "\nCopyright (C) 2016 Antonio Diaz Diaz.\n" + "\nCopyright (C) 2017 Antonio Diaz Diaz.\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" "Report bugs to lzip-bug@nongnu.org\n" @@ -1432,7 +1462,7 @@ int main( const int argc, const char * const argv[] ) for( bool first_member = true; ; first_member = false ) { - File_header header; + File_header header; // verify header for( int i = 0; i < 6; ++i ) header[i] = std::getc( stdin ); if( std::feof( stdin ) || std::memcmp( header, "LZIP\x01", 5 ) != 0 ) { @@ -1447,11 +1477,11 @@ int main( const int argc, const char * const argv[] ) { std::fputs( "Invalid dictionary size in member header.\n", stderr ); return 2; } - LZ_decoder decoder( dict_size ); + LZ_decoder decoder( dict_size ); // decode LZMA stream if( !decoder.decode_member() ) { std::fputs( "Data error\n", stderr ); return 2; } - File_trailer trailer; + File_trailer trailer; // verify trailer for( int i = 0; i < 20; ++i ) trailer[i] = std::getc( stdin ); unsigned crc = 0; for( int i = 3; i >= 0; --i ) { crc <<= 8; crc += trailer[i]; } @@ -1495,19 +1525,19 @@ Concept index Tag Table: Node: Top208 -Node: Introduction1145 -Node: Invoking lzip6071 -Ref: --trailing-error6635 -Node: Quality assurance12628 -Node: File format20782 -Node: Algorithm23186 -Node: Stream format26012 -Node: Trailing data36660 -Node: Examples38038 -Ref: concat-example39211 -Node: Problems40211 -Node: Reference source code40741 -Node: Concept index54957 +Node: Introduction1147 +Node: Invoking lzip6367 +Ref: --trailing-error6931 +Node: Quality assurance13849 +Node: File format22003 +Node: Algorithm24407 +Node: Stream format27233 +Node: Trailing data37973 +Node: Examples39874 +Ref: concat-example41047 +Node: Problems42085 +Node: Reference source code42615 +Node: Concept index56932 End Tag Table diff --git a/doc/lzip.texi b/doc/lzip.texi index 27feeff..17a2b1e 100644 --- a/doc/lzip.texi +++ b/doc/lzip.texi @@ -6,8 +6,8 @@ @finalout @c %**end of header -@set UPDATED 14 May 2016 -@set VERSION 1.18 +@set UPDATED 13 April 2017 +@set VERSION 1.19 @dircategory Data Compression @direntry @@ -49,7 +49,7 @@ This manual is for Lzip (version @value{VERSION}, @value{UPDATED}). @end menu @sp 1 -Copyright @copyright{} 2008-2016 Antonio Diaz Diaz. +Copyright @copyright{} 2008-2017 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it. @@ -60,9 +60,10 @@ to copy, distribute and modify it. @cindex introduction Lzip is a lossless data compressor with a user interface similar to the -one of gzip or bzip2. Lzip is about as fast as gzip, compresses most -files more than bzip2, and is better than both from a data recovery -perspective. +one of gzip or bzip2. Lzip can compress about as fast as gzip +@w{(lzip -0)}, or compress most files more than bzip2 @w{(lzip -9)}. +Decompression speed is intermediate between gzip and bzip2. Lzip is +better than gzip and bzip2 from a data recovery perspective. The lzip file format is designed for data sharing and long-term archiving, taking into account both data integrity and decoder @@ -82,10 +83,10 @@ including error-checked merging of damaged copies of a file. @item The lzip format is as simple as possible (but not simpler). The lzip -manual provides the 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 +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. @item @@ -156,7 +157,7 @@ or more compressed files. The result is the concatenation of the corresponding uncompressed files. Integrity testing of concatenated compressed files is also supported. -Lzip can produce multimember files and safely recover, with lziprecover, +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 @@ -166,6 +167,10 @@ 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. +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. + @node Invoking lzip @chapter Invoking lzip @@ -237,6 +242,20 @@ Force re-compression of files whose name already has the @samp{.lz} or @itemx --keep Keep (don't delete) input files during compression or decompression. +@item -l +@itemx --list +Print the uncompressed size, compressed size and percentage saved of the +specified file(s). Trailing data are ignored. The values produced are +correct even for multimember files. If more than one file is given, a +final line containing the cumulative sizes is printed. With @samp{-v}, +the dictionary size, the number of members in the file, and the amount +of trailing data (if any) are also printed. With @samp{-vv}, the +positions and sizes of each member in multimember files are also +printed. @samp{-lq} can be used to verify quickly (without +decompressing) the structural integrity of the specified files. (Use +@samp{--test} to verify the data integrity). @samp{-alq} additionally +verifies that none of the specified files contain trailing data. + @item -m @var{bytes} @itemx --match-length=@var{bytes} Set the match length limit in bytes. After a match this long is found, @@ -284,7 +303,8 @@ EiB. 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(s). If -a file fails the test, lzip continues checking the rest of the files. +a file fails the test, does not exist, can't be opened, or is a +terminal, lzip continues checking the rest of the files. @item -v @itemx --verbose @@ -294,7 +314,8 @@ 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, trailer contents (CRC, data size, member size), and up to 6 bytes of -trailing data (if any). +trailing data (if any) both in hexadecimal and as a string of printable +ASCII characters. @item -0 .. -9 Set the compression parameters (dictionary size and match length limit) @@ -756,16 +777,16 @@ Lengths (the @samp{len} in the table above) are coded as follows: The coding of distances is a little more complicated, so I'll begin explaining a simpler version of the encoding. -Imagine you need to code a number from 0 to 2^32 - 1, and you want to do -it in a way that produces shorter codes for the smaller numbers. You may -first send the position of the most significant bit that is set to 1, -which you may find by making a bit scan from the left (from the MSB). A -position of 0 means that the number is 0 (no bit is set), 1 means the -LSB is the first bit set (the number is 1), and 32 means the MSB is set -(i.e., the number is >= 0x80000000). Lets call this bit position a -"slot". Then, if slot is > 1, you send the remaining slot - 1 bits. Lets -call these bits "direct_bits" because they are coded directly by value -instead of indirectly by position. +Imagine you need to code a number from 0 to @w{2^32 - 1}, and you want +to do it in a way that produces shorter codes for the smaller numbers. +You may first send the position of the most significant bit that is set +to 1, which you may find by making a bit scan from the left (from the +MSB). A position of 0 means that the number is 0 (no bit is set), 1 +means the LSB is the first bit set (the number is 1), and 32 means the +MSB is set (i.e., the number is @w{>= 0x80000000}). Let's call this bit +position a "slot". Then, if slot is @w{> 1}, you send the remaining +@w{slot - 1} bits. Let's call these bits "direct_bits" because they are +coded directly by value instead of indirectly by position. The inconvenient of this simple method is that it needs 6 bits to code the slot, but it just uses 33 of the 64 possible values, wasting almost @@ -777,14 +798,15 @@ same 6 bits that would take to encode the position alone. This seems to need 66 slots (2 * position + next_bit), but for slots 0 and 1 there is no next bit, so the number of needed slots is 64 (0 to 63). -The slot number is context-coded in 6 bits. @samp{direct_bits} is the -amount of remaining bits (from 0 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 coded 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 @samp{direct_bits - 4} part is coded with -fixed 0.5 probability. +The 6 bits representing this "slot number" are then context-coded. If +the distance is @w{>= 4}, the remaining bits are coded as follows. +@samp{direct_bits} is the amount of remaining bits (from 0 to 30) needed +to form a complete distance, and is calculated as @w{(slot >> 1) - 1}. +If a distance needs 6 or more direct_bits, the last 4 bits are coded +separately. The last piece (all the direct_bits for distances 4 to 127 +or the last 4 bits for distances @w{>= 128}) is context-coded in reverse +order (from LSB to MSB). For distances @w{>= 128}, the +@w{@samp{direct_bits - 4}} part is coded with fixed 0.5 probability. @multitable @columnfractions .5 .5 @headitem Bit sequence @tab Description @@ -816,8 +838,8 @@ decoded data. Value of the 3 most significant bits of the latest byte decoded. @item len_state -Coded value of length (length - 2), with a maximum of 3. The resulting -value is in the range 0 to 3. +Coded value of length @w{(length - 2)}, with a maximum of 3. The +resulting value is in the range 0 to 3. @end table @@ -903,7 +925,7 @@ with their context. (See @samp{decode_bit} in the source). The range decoder state consists of two unsigned 32-bit variables; @code{range} (representing the most significant part of the range size not yet decoded), and @code{code} (representing the current point within -@code{range}). @code{range} is initialized to (2^32 - 1), and +@code{range}). @code{range} is initialized to @w{(2^32 - 1)}, and @code{code} is initialized to 0. The range encoder produces a first 0 byte that must be ignored by the @@ -926,20 +948,24 @@ Of Stream" marker is decoded. @chapter Extra data appended to the file @cindex trailing data -Sometimes extra data is found appended to a lzip file after the last +Sometimes extra data are found appended to a lzip file after the last member. Such trailing data may be: @itemize @bullet @item Padding added to make the file size a multiple of some block size, for -example when writing to a tape. +example when writing to a tape. It is safe to append any amount of +padding zero bytes to a lzip file. @item -Garbage added by some not totally successful copy operation. +Useful data added by the user; 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 the text does not begin with the string +"LZIP", and does not contain any zero bytes (null characters). Nonzero +bytes and zero bytes can't be safely mixed in trailing data. @item -Useful data added by the user; a cryptographically secure hash, a -description of file contents, etc. +Garbage added by some not totally successful copy operation. @item Malicious data added to the file in order to make its total size and @@ -954,8 +980,12 @@ integrity information itself. Therefore it can be considered to be below the noise level. @end itemize +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 +possible in the presence of trailing data. + Trailing data can be safely ignored in most cases. In some cases, like -that of user-added data, it is expected to be ignored. In those cases +that of user-added data, they are expected to be ignored. In those cases where a file containing trailing data must be rejected, the option @samp{--trailing-error} can be used. @xref{--trailing-error}. @@ -1020,8 +1050,8 @@ lzip -c /dev/sdc > file.lz @sp 1 @anchor{concat-example} @noindent -Example 6: The right way of concatenating compressed files. -@xref{Trailing data}. +Example 6: The right way of concatenating the decompressed output of two +or more compressed files. @xref{Trailing data}. @example Don't do this @@ -1097,7 +1127,7 @@ find by running @w{@code{lzip --version}}. @verbatim /* Lzd - Educational decompressor for the lzip format - Copyright (C) 2013-2016 Antonio Diaz Diaz. + Copyright (C) 2013-2017 Antonio Diaz Diaz. This program is free software. Redistribution and use in source and binary forms, with or without modification, are permitted provided @@ -1248,10 +1278,10 @@ public: uint8_t get_byte() { return std::getc( stdin ); } - int decode( const int num_bits ) + unsigned decode( const int num_bits ) { - int symbol = 0; - for( int i = 0; i < num_bits; ++i ) + unsigned symbol = 0; + for( int i = num_bits; i > 0; --i ) { range >>= 1; symbol <<= 1; @@ -1262,9 +1292,9 @@ public: return symbol; } - int decode_bit( Bit_model & bm ) + unsigned decode_bit( Bit_model & bm ) { - int symbol; + unsigned symbol; const uint32_t bound = ( range >> bit_model_total_bits ) * bm.probability; if( code < bound ) { @@ -1284,18 +1314,18 @@ public: return symbol; } - int decode_tree( Bit_model bm[], const int num_bits ) + unsigned decode_tree( Bit_model bm[], const int num_bits ) { - int symbol = 1; + unsigned symbol = 1; for( int i = 0; i < num_bits; ++i ) symbol = ( symbol << 1 ) | decode_bit( bm[symbol] ); return symbol - (1 << num_bits); } - int decode_tree_reversed( Bit_model bm[], const int num_bits ) + unsigned decode_tree_reversed( Bit_model bm[], const int num_bits ) { - int symbol = decode_tree( bm, num_bits ); - int reversed_symbol = 0; + unsigned symbol = decode_tree( bm, num_bits ); + unsigned reversed_symbol = 0; for( int i = 0; i < num_bits; ++i ) { reversed_symbol = ( reversed_symbol << 1 ) | ( symbol & 1 ); @@ -1304,14 +1334,13 @@ public: return reversed_symbol; } - int decode_matched( Bit_model bm[], const int match_byte ) + unsigned decode_matched( Bit_model bm[], const unsigned match_byte ) { - Bit_model * const bm1 = bm + 0x100; - int symbol = 1; + unsigned symbol = 1; for( int i = 7; i >= 0; --i ) { - const int match_bit = ( match_byte >> i ) & 1; - const int bit = decode_bit( bm1[(match_bit<<8)+symbol] ); + const unsigned match_bit = ( match_byte >> i ) & 1; + const unsigned bit = decode_bit( bm[symbol+(match_bit<<8)+0x100] ); symbol = ( symbol << 1 ) | bit; if( match_bit != bit ) { @@ -1323,7 +1352,7 @@ public: return symbol & 0xFF; } - int decode_len( Len_model & lm, const int pos_state ) + 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 ); @@ -1351,9 +1380,9 @@ class LZ_decoder uint8_t peek( const unsigned distance ) const { - unsigned i = pos - distance - 1; - if( pos <= distance ) i += dictionary_size; - return buffer[i]; + if( pos > distance ) return buffer[pos - distance - 1]; + if( pos_wrapped ) return buffer[dictionary_size + pos - distance - 1]; + return 0; // prev_byte of first byte } void put_byte( const uint8_t b ) @@ -1372,7 +1401,7 @@ public: stream_pos( 0 ), crc_( 0xFFFFFFFFU ), pos_wrapped( false ) - { buffer[dictionary_size-1] = 0; } // prev_byte of first byte + {} ~LZ_decoder() { delete[] buffer; } @@ -1410,7 +1439,7 @@ bool LZ_decoder::decode_member() // Returns false if error Bit_model bm_rep2[State::states]; Bit_model bm_len[State::states][pos_states]; Bit_model bm_dis_slot[len_states][1<<dis_slot_bits]; - Bit_model bm_dis[modeled_distances-end_dis_model]; + Bit_model bm_dis[modeled_distances-end_dis_model+1]; Bit_model bm_align[dis_align_size]; Len_model match_len_model; Len_model rep_len_model; @@ -1439,7 +1468,12 @@ bool LZ_decoder::decode_member() // Returns false if error int len; if( rdec.decode_bit( bm_rep[state()] ) != 0 ) // 2nd bit { - if( rdec.decode_bit( bm_rep0[state()] ) != 0 ) // 3rd bit + if( rdec.decode_bit( bm_rep0[state()] ) == 0 ) // 3rd bit + { + if( rdec.decode_bit( bm_len[state()][pos_state] ) == 0 ) // 4th bit + { state.set_short_rep(); put_byte( peek( rep0 ) ); continue; } + } + else { unsigned distance; if( rdec.decode_bit( bm_rep1[state()] ) == 0 ) // 4th bit @@ -1455,11 +1489,6 @@ bool LZ_decoder::decode_member() // Returns false if error rep1 = rep0; rep0 = distance; } - else - { - if( rdec.decode_bit( bm_len[state()][pos_state] ) == 0 ) // 4th bit - { state.set_short_rep(); put_byte( peek( rep0 ) ); continue; } - } state.set_rep(); len = min_match_len + rdec.decode_len( rep_len_model, pos_state ); } @@ -1468,15 +1497,14 @@ bool LZ_decoder::decode_member() // Returns false if error rep3 = rep2; rep2 = rep1; rep1 = rep0; len = min_match_len + rdec.decode_len( match_len_model, pos_state ); const int len_state = std::min( len - min_match_len, len_states - 1 ); - const int dis_slot = - rdec.decode_tree( bm_dis_slot[len_state], dis_slot_bits ); - if( dis_slot < start_dis_model ) rep0 = dis_slot; - else + rep0 = rdec.decode_tree( bm_dis_slot[len_state], dis_slot_bits ); + if( rep0 >= start_dis_model ) { + const unsigned dis_slot = rep0; const int direct_bits = ( dis_slot >> 1 ) - 1; rep0 = ( 2 | ( dis_slot & 1 ) ) << direct_bits; if( dis_slot < end_dis_model ) - rep0 += rdec.decode_tree_reversed( bm_dis + rep0 - dis_slot - 1, + rep0 += rdec.decode_tree_reversed( bm_dis + ( rep0 - dis_slot ), direct_bits ); else { @@ -1512,7 +1540,7 @@ int main( const int argc, const char * const argv[] ) "It is not safe to use lzd for any real work.\n" "\nUsage: %s < file.lz > file\n", argv[0] ); std::printf( "Lzd decompresses from standard input to standard output.\n" - "\nCopyright (C) 2016 Antonio Diaz Diaz.\n" + "\nCopyright (C) 2017 Antonio Diaz Diaz.\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" "Report bugs to lzip-bug@nongnu.org\n" @@ -1527,7 +1555,7 @@ int main( const int argc, const char * const argv[] ) for( bool first_member = true; ; first_member = false ) { - File_header header; + File_header header; // verify header for( int i = 0; i < 6; ++i ) header[i] = std::getc( stdin ); if( std::feof( stdin ) || std::memcmp( header, "LZIP\x01", 5 ) != 0 ) { @@ -1542,11 +1570,11 @@ int main( const int argc, const char * const argv[] ) { std::fputs( "Invalid dictionary size in member header.\n", stderr ); return 2; } - LZ_decoder decoder( dict_size ); + LZ_decoder decoder( dict_size ); // decode LZMA stream if( !decoder.decode_member() ) { std::fputs( "Data error\n", stderr ); return 2; } - File_trailer trailer; + File_trailer trailer; // verify trailer for( int i = 0; i < 20; ++i ) trailer[i] = std::getc( stdin ); unsigned crc = 0; for( int i = 3; i >= 0; --i ) { crc <<= 8; crc += trailer[i]; } |