```
/* Lzd - Educational decompressor for the lzip format
Copyright (C) 2013-2020 Antonio Diaz Diaz.
This program is free software. Redistribution and use in source and
binary forms, with or without modification, are permitted provided
that the following conditions are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions, and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions, and the following disclaimer in the
documentation and/or other materials provided with the distribution.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*/
/*
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.
*/
Diaz Informational [Page 13]
draft-diaz-lzip-02 application/lzip October 2020
#include
```
#include
#include
#include
#include
#include
#include
#if defined(__MSVCRT__) || defined(__OS2__) || defined(__DJGPP__)
#include
#include
#endif
#define PROGVERSION "1.2"
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()
{
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 {
min_dictionary_size = 1 << 12,
max_dictionary_size = 1 << 29,
literal_context_bits = 3,
literal_pos_state_bits = 0, // not used
pos_state_bits = 2,
pos_states = 1 << pos_state_bits,
pos_state_mask = pos_states - 1,
len_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,
Diaz Informational [Page 14]
draft-diaz-lzip-02 application/lzip October 2020
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 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_buf( uint32_t & crc, const uint8_t * const buffer,
const int size ) const
{
for( int i = 0; i < size; ++i )
crc = data[(crc^buffer[i])&0xFF] ^ ( crc >> 8 );
Diaz Informational [Page 15]
draft-diaz-lzip-02 application/lzip October 2020
}
};
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];
// 0-3 CRC32 of the uncompressed data
// 4-11 size of the uncompressed data
// 12-19 member size including header and trailer
class Range_decoder
{
unsigned long long member_pos;
uint32_t code;
uint32_t range;
public:
Range_decoder() : member_pos( 6 ), code( 0 ), range( 0xFFFFFFFFU )
{
for( int i = 0; i < 5; ++i ) code = ( code << 8 ) | get_byte();
}
uint8_t get_byte() { ++member_pos; return std::getc( stdin ); }
unsigned long long member_position() const { return member_pos; }
unsigned decode( const int num_bits )
{
unsigned symbol = 0;
for( int i = num_bits; i > 0; --i )
{
range >>= 1;
symbol <<= 1;
if( code >= range ) { code -= range; symbol |= 1; }
if( range <= 0x00FFFFFFU ) // normalize
{ range <<= 8; code = ( code << 8 ) | get_byte(); }
}
return symbol;
}
unsigned decode_bit( Bit_model & bm )
{
unsigned symbol;
const uint32_t bound =
( range >> bit_model_total_bits ) * bm.probability;
if( code < bound )
{
range = bound;
Diaz Informational [Page 16]
draft-diaz-lzip-02 application/lzip October 2020
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 ) | get_byte(); }
return symbol;
}
unsigned decode_tree( Bit_model bm[], const int num_bits )
{
unsigned symbol = 1;
for( int i = 0; i < num_bits; ++i )
symbol = ( symbol << 1 ) | decode_bit( bm[symbol] );
return symbol - ( 1 << num_bits );
}
unsigned decode_tree_reversed( Bit_model bm[], const int num_bits )
{
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 );
symbol >>= 1;
}
return reversed_symbol;
}
unsigned decode_matched( Bit_model bm[], const unsigned match_byte )
{
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]);
symbol = ( symbol << 1 ) | bit;
if( match_bit != bit )
{
while( symbol < 0x100 )
symbol = ( symbol << 1 ) | decode_bit( bm[symbol] );
break;
}
}
Diaz Informational [Page 17]
draft-diaz-lzip-02 application/lzip October 2020
return symbol & 0xFF;
}
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 );
if( decode_bit( lm.choice2 ) == 0 )
return len_low_symbols +
decode_tree( lm.bm_mid[pos_state], len_mid_bits );
return 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_;
bool pos_wrapped;
void flush_data();
uint8_t peek( const unsigned distance ) const
{
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 )
{
buffer[pos] = b;
if( ++pos >= dictionary_size ) flush_data();
}
public:
explicit 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 ),
Diaz Informational [Page 18]
draft-diaz-lzip-02 application/lzip October 2020
pos_wrapped( false )
{}
~LZ_decoder() { delete[] buffer; }
unsigned crc() const { return crc_ ^ 0xFFFFFFFFU; }
unsigned long long data_position() const
{ return partial_data_pos + pos; }
uint8_t get_byte() { return rdec.get_byte(); }
unsigned long long member_position() const
{ return rdec.member_position(); }
bool decode_member();
};
void LZ_decoder::flush_data()
{
if( pos > stream_pos )
{
const unsigned size = pos - stream_pos;
crc32.update_buf( crc_, buffer + stream_pos, size );
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; pos_wrapped = true; }
stream_pos = pos;
}
}
bool LZ_decoder::decode_member() // Returns false if error
{
Bit_model bm_literal[1<> (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, peek( rep0 ) ) );
state.set_char();
continue;
}
// match or repeated match
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_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
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;
}
state.set_rep();
len = min_match_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);
const int len_state = std::min( len-min_match_len, len_states-1 );
Diaz Informational [Page 20]
draft-diaz-lzip-02 application/lzip October 2020
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),
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 && !pos_wrapped ) )
{ flush_data(); return false; }
}
for( int i = 0; i < len; ++i ) put_byte( peek( rep0 ) );
}
flush_data();
return false;
}
int main( const int argc, const char * const argv[] )
{
if( argc > 2 || ( argc == 2 && std::strcmp( argv[1], "-d" ) != 0 ) )
{
std::printf(
"Lzd %s - Educational decompressor for the lzip format.\n"
"Study the source 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) 2020 Antonio Diaz Diaz.\n"
"License 2-clause BSD.\n"
"This is free software: you are free to change and redistribute "
"it.\nThere is NO WARRANTY, to the extent permitted by law.\n"
"Report bugs to lzip-bug@nongnu.org\n"
"Lzd home page: http://www.nongnu.org/lzip/lzd.html\n",
PROGVERSION, argv[0] );
return 0;
}
Diaz Informational [Page 21]
draft-diaz-lzip-02 application/lzip October 2020
#if defined(__MSVCRT__) || defined(__OS2__) || defined(__DJGPP__)
setmode( STDIN_FILENO, O_BINARY );
setmode( STDOUT_FILENO, O_BINARY );
#endif
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 );
if( std::feof( stdin ) || std::memcmp( header, "LZIP\x01",5 ) != 0 )
{
if( first_member )
{ std::fputs( "Bad magic number (file not in lzip format).\n",
stderr ); return 2; }
break; // ignore trailing data
}
unsigned dict_size = 1 << ( header[5] & 0x1F );
dict_size -= ( dict_size / 16 ) * ( ( header[5] >> 5 ) & 7 );
if( dict_sizemax_dictionary_size )
{ std::fputs( "Invalid dictionary size in member header.\n",
stderr ); return 2; }
LZ_decoder decoder( dict_size ); // decode LZMA stream
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();
int retval = 0;
unsigned crc = 0;
for( int i = 3; i >= 0; --i ) crc = ( crc << 8 ) + trailer[i];
if( crc != decoder.crc() )
{ std::fputs( "CRC mismatch\n", stderr ); retval = 2; }
unsigned long long data_size = 0;
for( int i = 11; i >= 4; --i )
data_size = ( data_size << 8 ) + trailer[i];
if( data_size != decoder.data_position() )
{ std::fputs( "Data size mismatch\n", stderr ); retval = 2; }
unsigned long long member_size = 0;
for( int i = 19; i >= 12; --i )
member_size = ( member_size << 8 ) + trailer[i];
if( member_size != decoder.member_position() )
{ std::fputs( "Member size mismatch\n", stderr ); retval = 2; }
if( retval ) return retval;
}
if( std::fclose( stdout ) != 0 )
{ std::fprintf( stderr, "Error closing stdout: %s\n",
std::strerror( errno ) ); return 1; }
Diaz Informational [Page 22]
draft-diaz-lzip-02 application/lzip October 2020
return 0;
}
```
Acknowledgments
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 definition of Markov chains), G.N.N. Martin (for the
definition of range encoding), and Igor Pavlov (for putting all the
above together in LZMA).
Author's Address
Antonio Diaz Diaz
GNU Project
Email: antonio@gnu.org
Expiration date: 2021-04-26
Diaz Informational [Page 23]
```