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authorDaniel Baumann <mail@daniel-baumann.ch>2015-11-07 09:56:46 +0000
committerDaniel Baumann <mail@daniel-baumann.ch>2015-11-07 09:56:46 +0000
commit55197b06a813dd7f90e70b0af7928c375f31f625 (patch)
tree8edc055ee8db674f5357e522269233f85fe813db /doc/lzip.texinfo
parentAdding upstream version 1.14. (diff)
downloadlzip-55197b06a813dd7f90e70b0af7928c375f31f625.tar.xz
lzip-55197b06a813dd7f90e70b0af7928c375f31f625.zip
Adding upstream version 1.15~pre1.upstream/1.15_pre1
Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>
Diffstat (limited to 'doc/lzip.texinfo')
-rw-r--r--doc/lzip.texinfo676
1 files changed, 667 insertions, 9 deletions
diff --git a/doc/lzip.texinfo b/doc/lzip.texinfo
index 76ccfc9..632abc5 100644
--- a/doc/lzip.texinfo
+++ b/doc/lzip.texinfo
@@ -6,8 +6,8 @@
@finalout
@c %**end of header
-@set UPDATED 17 February 2013
-@set VERSION 1.14
+@set UPDATED 21 March 2013
+@set VERSION 1.15-pre1
@dircategory Data Compression
@direntry
@@ -35,13 +35,15 @@
This manual is for Lzip (version @value{VERSION}, @value{UPDATED}).
@menu
-* Introduction:: Purpose and features of lzip
-* Algorithm:: How lzip compresses the data
-* Invoking Lzip:: Command line interface
-* File Format:: Detailed format of the compressed file
-* Examples:: A small tutorial with examples
-* Problems:: Reporting bugs
-* Concept Index:: Index of concepts
+* Introduction:: Purpose and features of lzip
+* Algorithm:: How lzip compresses the data
+* Invoking Lzip:: Command line interface
+* File Format:: Detailed format of the compressed file
+* Stream Format:: Format of the LZMA stream in lzip files
+* Examples:: A small tutorial with examples
+* Problems:: Reporting bugs
+* Reference source code:: Source code illustrating stream format
+* Concept Index:: Index of concepts
@end menu
@sp 1
@@ -403,6 +405,7 @@ wedges between 0 and 7. The size of a wedge is (base_size / 16).@*
Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).@*
Bits 7-5 contain the number of wedges (0 to 7) to substract from the
base size to obtain the dictionary size.@*
+Example: 0xD3 = (2^19 - 6 * 2^15) = (512KiB - 6 * 32KiB) = 320KiB@*
Valid values for dictionary size range from 4KiB to 512MiB.
@item Lzma stream
@@ -423,6 +426,206 @@ members from multi-member files.
@end table
+@node Stream Format
+@chapter Format of the LZMA stream in lzip files
+@cindex format of the LZMA stream
+
+The LZMA algorithm has three parameters, called "special LZMA
+properties", to adjust it for some kinds of binary data. These
+parameters are; @samp{literal_context_bits} (with a default value of 3),
+@samp{literal_pos_state_bits} (with a default value of 0), and
+@samp{pos_state_bits} (with a default value of 2). As a general purpose
+compressor, lzip only uses the default values for these parameters.
+
+Lzip also finishes the LZMA stream with an "End Of Stream" 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 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 or LZMA-lzip.
+
+The second stage of LZMA is a range encoder that uses a different
+probability model for each type of symbol; distances, lengths, literal
+bytes, etc. Range encoding conceptually encodes all the symbols of the
+message into one number. Unlike Huffman coding, which assigns to each
+symbol a bit-pattern and concatenates all the bit-patterns together,
+range encoding can compress one symbol to less than one bit. Therefore
+the compressed data produced by a range encoder can't be split in pieces
+that could be individually described.
+
+It seems that the only way of describing the LZMA-302eos stream is
+describing the algorithm that decodes it. And given the many details
+about the range decoder that need to be described accurately, the source
+code of a real decoder seems the only appropiate 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. The source code of lzd is included in appendix A.
+@ref{Reference source code}
+
+@sp 1
+@section What is coded
+
+The LZMA stream includes literals, matches and repeated matches (matches
+reusing a recently used distance). There are 7 different coding sequences:
+
+@multitable @columnfractions .35 .14 .51
+@headitem Bit sequence @tab Name @tab Description
+@item 0 + byte @tab literal @tab literal byte
+@item 1 + 0 + len + dis @tab match @tab distance-length pair
+@item 1 + 1 + 0 + 0 @tab shortrep @tab 1 byte match at latest used
+distance
+@item 1 + 1 + 0 + 1 + len @tab rep0 @tab len bytes match at latest used
+distance
+@item 1 + 1 + 1 + 0 + len @tab rep1 @tab len bytes match at second
+latest used distance
+@item 1 + 1 + 1 + 1 + 0 + len @tab rep2 @tab len bytes match at third
+latest used distance
+@item 1 + 1 + 1 + 1 + 1 + len @tab rep3 @tab len bytes match at fourth
+latest used distance
+@end multitable
+
+@sp 1
+In the following tables, multi-bit sequences are coded in normal order,
+from MSB to LSB, except where noted otherwise.
+
+Lengths (the @samp{len} in the table above) are coded as follows:
+
+@multitable @columnfractions .5 .5
+@headitem Bit sequence @tab Description
+@item 0 + 3 bits @tab lengths from 2 to 9
+@item 1 + 0 + 3 bits @tab lengths from 10 to 17
+@item 1 + 1 + 8 bits @tab lengths from 18 to 273
+@end multitable
+
+@sp 1
+The coding of distances is a little more complicated. LZMA divides the
+interval between any two powers of 2 into 2 halves, named slots. As
+possible distances range from 0 to (2^32 - 1), there are 64 slots (0 to
+63). The slot number is context-coded in 6 bits. @samp{direct_bits} are
+the remaining bits (from 0 to 30) needed to form a complete distance,
+and are calculated as (slot >> 1) - 1. If a distance needs 6 or more
+direct_bits, the last 4 bits are coded separately. The last piece
+(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.
+
+@multitable @columnfractions .5 .5
+@headitem Bit sequence @tab Description
+@item slot @tab distances from 0 to 3
+@item slot + direct_bits @tab distances from 4 to 127
+@item slot + (direct_bits - 4) + 4 bits @tab distances from 128 to
+2^32 - 1
+@end multitable
+
+@sp 1
+@section The coding contexts
+
+These contexts (@samp{Bit_model} in the source), are integers or arrays
+of integers representing the probability of the corresponding bit being 0.
+
+The indices used in these arrays are:
+
+@table @samp
+@item state
+
+A state machine (@samp{State} in the source) coding the latest 2 to 4
+types of sequences processed. The initial state is 0.
+
+@item pos_state
+Value of the 2 least significant bits of the current position in the
+decoded data.
+
+@item literal_state
+Value of the 3 most significant bits of the latest byte decoded.
+
+@item dis_state
+Coded value of length (real length - 2), with a maximum of 3. The
+resulting value is in the range 0 to 3.
+
+@end table
+
+
+The contexts for decoding the type of coding sequence are:
+
+@multitable @columnfractions .2 .4 .4
+@headitem Name @tab Indices @tab Used when
+@item bm_match @tab state, pos_state @tab sequence start
+@item bm_rep @tab state @tab after sequence 1
+@item bm_rep0 @tab state @tab after sequence 11
+@item bm_rep1 @tab state @tab after sequence 111
+@item bm_rep2 @tab state @tab after sequence 1111
+@item bm_len @tab state, pos_state @tab after sequence 110
+@end multitable
+
+@sp 1
+The contexts for decoding distances are:
+
+@multitable @columnfractions .2 .4 .4
+@headitem Name @tab Indices @tab Used when
+@item bm_dis_slot @tab dis_state, bit tree @tab distance start
+@item bm_dis @tab reverse bit tree @tab after slots 4 to 13
+@item bm_align @tab reverse bit tree @tab for distances >= 128, after
+fixed probability bits
+@end multitable
+
+@sp 1
+There are two separated sets of length contexts (@samp{Len_model} in the
+source). One for normal matches, the other for repeated matches. The
+contexts in each Len_model are (see @samp{decode_len} in the source):
+
+@multitable @columnfractions .2 .4 .4
+@headitem Name @tab Indices @tab Used when
+@item choice1 @tab none @tab length start
+@item choice2 @tab none @tab after sequence 1
+@item bm_low @tab pos_state, bit tree @tab after sequence 0
+@item bm_mid @tab pos_state, bit tree @tab after sequence 10
+@item bm_high @tab bit tree @tab after sequence 11
+@end multitable
+
+@sp 1
+The context array @samp{bm_literal} is special. In principle it acts as
+a normal bit tree context, the one selected by @samp{literal_state}. But
+if the previous decoded byte was not a literal, two other bit tree
+contexts are used depending on the value of each bit in
+@samp{match_byte} (the byte at the latest used distance), until a bit is
+decoded that is different from its corresponding bit in
+@samp{match_byte}. After the first difference is found, the rest of the
+byte is decoded using the normal bit tree context. (See
+@samp{decode_matched} in the source).
+
+@sp 1
+@section The range decoder
+
+The LZMA stream is consumed one byte at a time by the range decoder.
+(See @samp{normalize} in the source). Every byte consumed produces a
+variable number of decoded bits, depending on how well these bits agree
+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{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{code} instead of 4. (See the @samp{Range_decoder} constructor in
+the source).
+
+@sp 1
+@section Decoding 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 @samp{decode_member} in the source) where it invokes the range
+decoder with the appropiate contexts to decode the different coding
+sequences (matches, repeated matches, and literal bytes), until the "End
+Of Stream" marker is decoded.
+
+
@node Examples
@chapter A small tutorial with examples
@cindex examples
@@ -541,6 +744,461 @@ If you find a bug in lzip, please send electronic mail to
find by running @w{@samp{lzip --version}}.
+@node Reference source code
+@appendix Reference source code
+@cindex reference source code
+
+@verbatim
+#include <algorithm>
+#include <cerrno>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <stdint.h>
+#include <unistd.h>
+
+
+class State
+ {
+ int st;
+
+public:
+ enum { states = 12 };
+ State() : st( 0 ) {}
+ int operator()() const { return st; }
+ bool is_char() const { return st < 7; }
+
+ void set_char()
+ {
+ static const int next[states] = { 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 4, 5 };
+ st = next[st];
+ }
+
+ void set_match() { st = ( ( st < 7 ) ? 7 : 10 ); }
+ void set_rep() { st = ( ( st < 7 ) ? 8 : 11 ); }
+ void set_short_rep() { st = ( ( st < 7 ) ? 9 : 11 ); }
+ };
+
+
+enum {
+ literal_context_bits = 3,
+ pos_state_bits = 2,
+ pos_states = 1 << pos_state_bits,
+ pos_state_mask = pos_states - 1,
+
+ max_dis_states = 4,
+ dis_slot_bits = 6,
+ start_dis_model = 4,
+ end_dis_model = 14,
+ modeled_distances = 1 << (end_dis_model / 2), // 128
+ dis_align_bits = 4,
+ dis_align_size = 1 << dis_align_bits,
+
+ len_low_bits = 3,
+ len_mid_bits = 3,
+ len_high_bits = 8,
+ len_low_symbols = 1 << len_low_bits,
+ len_mid_symbols = 1 << len_mid_bits,
+ len_high_symbols = 1 << len_high_bits,
+ max_len_symbols = len_low_symbols + len_mid_symbols + len_high_symbols,
+ min_match_len = 2, // must be 2
+
+ bit_model_move_bits = 5,
+ bit_model_total_bits = 11,
+ bit_model_total = 1 << bit_model_total_bits };
+
+
+struct Bit_model
+ {
+ int probability;
+ Bit_model() : probability( bit_model_total / 2 ) {}
+ };
+
+
+struct Len_model
+ {
+ Bit_model choice1;
+ Bit_model choice2;
+ Bit_model bm_low[pos_states][len_low_symbols];
+ Bit_model bm_mid[pos_states][len_mid_symbols];
+ Bit_model bm_high[len_high_symbols];
+ };
+
+
+class Range_decoder
+ {
+ uint32_t code;
+ uint32_t range;
+
+public:
+ Range_decoder() : code( 0 ), range( 0xFFFFFFFFU )
+ {
+ for( int i = 0; i < 5; ++i ) code = (code << 8) | std::getc( stdin );
+ }
+
+ int decode( const int num_bits )
+ {
+ int symbol = 0;
+ for( int i = 0; i < num_bits; ++i )
+ {
+ range >>= 1;
+ symbol <<= 1;
+ if( code >= range ) { code -= range; symbol |= 1; }
+ if( range <= 0x00FFFFFFU ) // normalize
+ { range <<= 8; code = (code << 8) | std::getc( stdin ); }
+ }
+ return symbol;
+ }
+
+ int decode_bit( Bit_model & bm )
+ {
+ int symbol;
+ const uint32_t bound = ( range >> bit_model_total_bits ) * bm.probability;
+ if( code < bound )
+ {
+ range = bound;
+ bm.probability += (bit_model_total - bm.probability) >> bit_model_move_bits;
+ symbol = 0;
+ }
+ else
+ {
+ range -= bound;
+ code -= bound;
+ bm.probability -= bm.probability >> bit_model_move_bits;
+ symbol = 1;
+ }
+ if( range <= 0x00FFFFFFU ) // normalize
+ { range <<= 8; code = (code << 8) | std::getc( stdin ); }
+ return symbol;
+ }
+
+ int decode_tree( Bit_model bm[], const int num_bits )
+ {
+ int 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 )
+ {
+ int symbol = decode_tree( bm, num_bits );
+ int reversed_symbol = 0;
+ for( int i = 0; i < num_bits; ++i )
+ {
+ reversed_symbol = ( reversed_symbol << 1 ) | ( symbol & 1 );
+ symbol >>= 1;
+ }
+ return reversed_symbol;
+ }
+
+ int decode_matched( Bit_model bm[], const int match_byte )
+ {
+ Bit_model * const bm1 = bm + 0x100;
+ int 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] );
+ symbol = ( symbol << 1 ) | bit;
+ if( match_bit != bit )
+ {
+ while( symbol < 0x100 )
+ symbol = ( symbol << 1 ) | decode_bit( bm[symbol] );
+ break;
+ }
+ }
+ return symbol - 0x100;
+ }
+
+ int decode_len( Len_model & lm, const int pos_state )
+ {
+ if( decode_bit( lm.choice1 ) == 0 )
+ return min_match_len +
+ decode_tree( lm.bm_low[pos_state], len_low_bits );
+ if( decode_bit( lm.choice2 ) == 0 )
+ return min_match_len + len_low_symbols +
+ decode_tree( lm.bm_mid[pos_state], len_mid_bits );
+ return min_match_len + len_low_symbols + len_mid_symbols +
+ decode_tree( lm.bm_high, len_high_bits );
+ }
+ };
+
+
+class LZ_decoder
+ {
+ unsigned long long partial_data_pos;
+ Range_decoder rdec;
+ const unsigned dictionary_size;
+ uint8_t * const buffer; // output buffer
+ unsigned pos; // current pos in buffer
+ unsigned stream_pos; // first byte not yet written to stdout
+ uint32_t crc_;
+
+ void flush_data();
+
+ uint8_t get_byte( const unsigned distance ) const
+ {
+ int i = pos - distance - 1;
+ if( i < 0 ) i += dictionary_size;
+ return buffer[i];
+ }
+
+ void put_byte( const uint8_t b )
+ {
+ buffer[pos] = b;
+ if( ++pos >= dictionary_size ) flush_data();
+ }
+
+public:
+ LZ_decoder( const unsigned dict_size )
+ :
+ partial_data_pos( 0 ),
+ dictionary_size( dict_size ),
+ buffer( new uint8_t[dictionary_size] ),
+ pos( 0 ),
+ stream_pos( 0 ),
+ crc_( 0xFFFFFFFFU )
+ { buffer[dictionary_size-1] = 0; } // prev_byte of first_byte
+
+ ~LZ_decoder() { delete[] buffer; }
+
+ unsigned crc() const { return crc_ ^ 0xFFFFFFFFU; }
+ unsigned long long data_position() const { return partial_data_pos + pos; }
+
+ bool decode_member();
+ };
+
+
+class CRC32
+ {
+ uint32_t data[256]; // Table of CRCs of all 8-bit messages.
+
+public:
+ CRC32()
+ {
+ for( unsigned n = 0; n < 256; ++n )
+ {
+ unsigned c = n;
+ for( int k = 0; k < 8; ++k )
+ { if( c & 1 ) c = 0xEDB88320U ^ ( c >> 1 ); else c >>= 1; }
+ data[n] = c;
+ }
+ }
+
+ void update( uint32_t & crc, const uint8_t * buffer, const int size ) const
+ {
+ for( int i = 0; i < size; ++i )
+ crc = data[(crc^buffer[i])&0xFF] ^ ( crc >> 8 );
+ }
+ };
+
+const CRC32 crc32;
+
+
+void LZ_decoder::flush_data()
+ {
+ if( pos > stream_pos )
+ {
+ const unsigned size = pos - stream_pos;
+ crc32.update( crc_, buffer + stream_pos, size );
+ errno = 0;
+ if( std::fwrite( buffer + stream_pos, 1, size, stdout ) != size )
+ { std::fprintf( stderr, "Write error: %s\n", std::strerror( errno ) );
+ std::exit( 1 ); }
+ if( pos >= dictionary_size ) { partial_data_pos += pos; pos = 0; }
+ stream_pos = pos;
+ }
+ }
+
+
+bool LZ_decoder::decode_member() // Returns false if error
+ {
+ Bit_model bm_literal[1<<literal_context_bits][0x300];
+ Bit_model bm_match[State::states][pos_states];
+ Bit_model bm_rep[State::states];
+ Bit_model bm_rep0[State::states];
+ Bit_model bm_rep1[State::states];
+ Bit_model bm_rep2[State::states];
+ Bit_model bm_len[State::states][pos_states];
+ Bit_model bm_dis_slot[max_dis_states][1<<dis_slot_bits];
+ Bit_model bm_dis[modeled_distances-end_dis_model];
+ Bit_model bm_align[dis_align_size];
+ Len_model match_len_model;
+ Len_model rep_len_model;
+ unsigned rep0 = 0; // rep[0-3] latest four distances
+ unsigned rep1 = 0; // used for efficient coding of
+ unsigned rep2 = 0; // repeated distances
+ unsigned rep3 = 0;
+ State state;
+
+ while( !std::feof( stdin ) && !std::ferror( stdin ) )
+ {
+ const int pos_state = data_position() & pos_state_mask;
+ if( rdec.decode_bit( bm_match[state()][pos_state] ) == 0 ) // 1st bit
+ {
+ const uint8_t prev_byte = get_byte( 0 );
+ const int literal_state = prev_byte >> ( 8 - literal_context_bits );
+ Bit_model * const bm = bm_literal[literal_state];
+ if( state.is_char() )
+ put_byte( rdec.decode_tree( bm, 8 ) );
+ else
+ put_byte( rdec.decode_matched( bm, get_byte( rep0 ) ) );
+ state.set_char();
+ }
+ else
+ {
+ int len;
+ if( rdec.decode_bit( bm_rep[state()] ) == 1 ) // 2nd 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( get_byte( rep0 ) ); continue; }
+ }
+ else
+ {
+ unsigned distance;
+ if( rdec.decode_bit( bm_rep1[state()] ) == 0 ) // 4th bit
+ distance = rep1;
+ else
+ {
+ if( rdec.decode_bit( bm_rep2[state()] ) == 0 ) // 5th bit
+ distance = rep2;
+ else
+ { distance = rep3; rep3 = rep2; }
+ rep2 = rep1;
+ }
+ rep1 = rep0;
+ rep0 = distance;
+ }
+ len = rdec.decode_len( rep_len_model, pos_state );
+ state.set_rep();
+ }
+ else
+ {
+ rep3 = rep2; rep2 = rep1; rep1 = rep0;
+ len = rdec.decode_len( match_len_model, pos_state );
+ const int dis_state = std::min( len - min_match_len, max_dis_states - 1 );
+ const int dis_slot =
+ rdec.decode_tree( bm_dis_slot[dis_state], dis_slot_bits );
+ if( dis_slot < start_dis_model ) rep0 = dis_slot;
+ else
+ {
+ 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,
+ direct_bits );
+ else
+ {
+ rep0 += rdec.decode( direct_bits - dis_align_bits ) << dis_align_bits;
+ rep0 += rdec.decode_tree_reversed( bm_align, dis_align_bits );
+ if( rep0 == 0xFFFFFFFFU ) // Marker found
+ {
+ flush_data();
+ return ( len == min_match_len ); // End Of Stream marker
+ }
+ }
+ }
+ state.set_match();
+ if( rep0 >= dictionary_size || ( rep0 >= pos && !partial_data_pos ) )
+ return false;
+ }
+ for( int i = 0; i < len; ++i )
+ put_byte( get_byte( rep0 ) );
+ }
+ }
+ return false;
+ }
+
+
+enum { min_dictionary_size = 1 << 12,
+ max_dictionary_size = 1 << 29 };
+
+typedef uint8_t File_header[6]; // 0-3 magic, 4 version, 5 coded_dict_size
+
+typedef uint8_t File_trailer[20];
+ // 0-3 CRC32 of the uncompressed data
+ // 4-11 size of the uncompressed data
+ // 12-19 member size including header and trailer
+
+
+/* Return values: 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. */
+
+int main( const int argc, const char * const argv[] )
+ {
+ if( argc > 1 )
+ {
+ std::printf( "Lzd %s - Educational decompressor for lzip files.\n",
+ PROGVERSION );
+ std::printf( "Study the source to learn how a simple lzip decompressor works.\n"
+ "It is not safe to use it 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) 2013 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"
+ "Lzip home page: http://www.nongnu.org/lzip/lzip.html\n" );
+ return 0;
+ }
+
+ if( isatty( STDIN_FILENO ) )
+ {
+ std::fprintf( stderr, "I won't read compressed data from a terminal.\n"
+ "Try '%s --help' for more information.\n", argv[0] );
+ return 1;
+ }
+
+ for( bool first_member = true; ; first_member = false )
+ {
+ File_header header;
+ for( int i = 0; i < 6; ++i )
+ header[i] = std::getc( stdin );
+ if( std::feof( stdin ) || std::memcmp( header, "LZIP", 4 ) != 0 )
+ {
+ if( first_member )
+ { std::fprintf( stderr, "Bad magic number (file not in lzip format)\n" );
+ return 2; }
+ break;
+ }
+ if( header[4] != 1 )
+ {
+ std::fprintf( stderr, "Version %d member format not supported.\n",
+ header[4] );
+ return 2;
+ }
+ unsigned dict_size = 1 << ( header[5] & 0x1F );
+ dict_size -= ( dict_size / 16 ) * ( ( header[5] >> 5 ) & 7 );
+ if( dict_size < min_dictionary_size || dict_size > max_dictionary_size )
+ { std::fprintf( stderr, "Invalid dictionary size in member header\n" );
+ return 2; }
+
+ LZ_decoder decoder( dict_size );
+ if( !decoder.decode_member() )
+ { std::fprintf( stderr, "Data error\n" ); return 2; }
+
+ File_trailer 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]; }
+ unsigned long long data_size = 0;
+ for( int i = 11; i >= 4; --i ) { data_size <<= 8; data_size += trailer[i]; }
+ if( crc != decoder.crc() || data_size != decoder.data_position() )
+ { std::fprintf( stderr, "CRC error\n" ); return 2; }
+ }
+
+ if( std::fclose( stdout ) != 0 )
+ { std::fprintf( stderr, "Can't close stdout: %s\n", std::strerror( errno ) );
+ return 1; }
+ return 0;
+ }
+@end verbatim
+
+
@node Concept Index
@unnumbered Concept Index