lzlib/fast_encoder.c

/* Lzlib - Compression library for the lzip format
   Copyright (C) 2009-2025 Antonio Diaz Diaz.

   This library 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 library 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.
*/

static int FLZe_longest_match_len( FLZ_encoder * const fe, int * const distance )
  {
  enum { len_limit = 16 };
  int32_t * ptr0 = fe->eb.mb.pos_array + fe->eb.mb.cyclic_pos;
  const int available = min( Mb_available_bytes( &fe->eb.mb ), max_match_len );
  if( available < len_limit ) { *ptr0 = 0; return 0; }

  const uint8_t * const data = Mb_ptr_to_current_pos( &fe->eb.mb );
  fe->key4 = ( ( fe->key4 << 4 ) ^ data[3] ) & fe->eb.mb.key4_mask;
  const int pos1 = fe->eb.mb.pos + 1;
  int newpos1 = fe->eb.mb.prev_positions[fe->key4];
  fe->eb.mb.prev_positions[fe->key4] = pos1;
  int maxlen = 0, count;

  for( count = 4; ; )
    {
    int delta;
    if( newpos1 <= 0 || --count < 0 ||
        ( delta = pos1 - newpos1 ) > fe->eb.mb.dictionary_size )
      { *ptr0 = 0; break; }
    int32_t * const newptr = fe->eb.mb.pos_array +
      ( fe->eb.mb.cyclic_pos - delta +
        ( ( fe->eb.mb.cyclic_pos >= delta ) ? 0 : fe->eb.mb.dictionary_size + 1 ) );

    if( data[maxlen-delta] == data[maxlen] )
      {
      int len = 0;
      while( len < available && data[len-delta] == data[len] ) ++len;
      if( maxlen < len )
        { maxlen = len; *distance = delta - 1;
          if( maxlen >= len_limit ) { *ptr0 = *newptr; break; } }
      }

    *ptr0 = newpos1;
    ptr0 = newptr;
    newpos1 = *ptr0;
    }
  return maxlen;
  }


static bool FLZe_encode_member( FLZ_encoder * const fe )
  {
  int rep = 0, i;
  State * const state = &fe->eb.state;

  if( fe->eb.member_finished ) return true;
  if( Re_member_position( &fe->eb.renc ) >= fe->eb.member_size_limit )
    { LZeb_try_full_flush( &fe->eb ); return true; }

  if( Mb_data_position( &fe->eb.mb ) == 0 &&
      !Mb_data_finished( &fe->eb.mb ) )		/* encode first byte */
    {
    if( !Mb_enough_available_bytes( &fe->eb.mb ) ||
        !Re_enough_free_bytes( &fe->eb.renc ) ) return true;
    const uint8_t prev_byte = 0;
    const uint8_t cur_byte = Mb_peek( &fe->eb.mb, 0 );
    Re_encode_bit( &fe->eb.renc, &fe->eb.bm_match[*state][0], 0 );
    LZeb_encode_literal( &fe->eb, prev_byte, cur_byte );
    CRC32_update_byte( &fe->eb.crc, cur_byte );
    FLZe_reset_key4( fe );
    if( !FLZe_update_and_move( fe, 1 ) ) return false;
    }

  while( !Mb_data_finished( &fe->eb.mb ) &&
         Re_member_position( &fe->eb.renc ) < fe->eb.member_size_limit )
    {
    if( !Mb_enough_available_bytes( &fe->eb.mb ) ||
        !Re_enough_free_bytes( &fe->eb.renc ) ) return true;
    int match_distance = 0;		/* avoid warning from gcc 6.1.0 */
    const int main_len = FLZe_longest_match_len( fe, &match_distance );
    const int pos_state = Mb_data_position( &fe->eb.mb ) & pos_state_mask;
    int len = 0;

    for( i = 0; i < num_rep_distances; ++i )
      {
      const int tlen = Mb_true_match_len( &fe->eb.mb, 0, fe->eb.reps[i] + 1 );
      if( tlen > len ) { len = tlen; rep = i; }
      }
    if( len > min_match_len && len + 3 > main_len )
      {
      CRC32_update_buf( &fe->eb.crc, Mb_ptr_to_current_pos( &fe->eb.mb ), len );
      Re_encode_bit( &fe->eb.renc, &fe->eb.bm_match[*state][pos_state], 1 );
      Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep[*state], 1 );
      Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep0[*state], rep != 0 );
      if( rep == 0 )
        Re_encode_bit( &fe->eb.renc, &fe->eb.bm_len[*state][pos_state], 1 );
      else
        {
        Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep1[*state], rep > 1 );
        if( rep > 1 )
          Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep2[*state], rep > 2 );
        const int distance = fe->eb.reps[rep];
        for( i = rep; i > 0; --i ) fe->eb.reps[i] = fe->eb.reps[i-1];
        fe->eb.reps[0] = distance;
        }
      *state = St_set_rep( *state );
      Re_encode_len( &fe->eb.renc, &fe->eb.rep_len_model, len, pos_state );
      if( !Mb_move_pos( &fe->eb.mb ) ) return false;
      if( !FLZe_update_and_move( fe, len - 1 ) ) return false;
      continue;
      }

    if( main_len > min_match_len )
      {
      CRC32_update_buf( &fe->eb.crc, Mb_ptr_to_current_pos( &fe->eb.mb ), main_len );
      Re_encode_bit( &fe->eb.renc, &fe->eb.bm_match[*state][pos_state], 1 );
      Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep[*state], 0 );
      *state = St_set_match( *state );
      for( i = num_rep_distances - 1; i > 0; --i ) fe->eb.reps[i] = fe->eb.reps[i-1];
      fe->eb.reps[0] = match_distance;
      LZeb_encode_pair( &fe->eb, match_distance, main_len, pos_state );
      if( !Mb_move_pos( &fe->eb.mb ) ) return false;
      if( !FLZe_update_and_move( fe, main_len - 1 ) ) return false;
      continue;
      }

    const uint8_t prev_byte = Mb_peek( &fe->eb.mb, 1 );
    const uint8_t cur_byte = Mb_peek( &fe->eb.mb, 0 );
    const uint8_t match_byte = Mb_peek( &fe->eb.mb, fe->eb.reps[0] + 1 );
    if( !Mb_move_pos( &fe->eb.mb ) ) return false;
    CRC32_update_byte( &fe->eb.crc, cur_byte );

    if( match_byte == cur_byte )
      {
      const int shortrep_price = price1( fe->eb.bm_match[*state][pos_state] ) +
                                 price1( fe->eb.bm_rep[*state] ) +
                                 price0( fe->eb.bm_rep0[*state] ) +
                                 price0( fe->eb.bm_len[*state][pos_state] );
      int price = price0( fe->eb.bm_match[*state][pos_state] );
      if( St_is_char( *state ) )
        price += LZeb_price_literal( &fe->eb, prev_byte, cur_byte );
      else
        price += LZeb_price_matched( &fe->eb, prev_byte, cur_byte, match_byte );
      if( shortrep_price < price )
        {
        Re_encode_bit( &fe->eb.renc, &fe->eb.bm_match[*state][pos_state], 1 );
        Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep[*state], 1 );
        Re_encode_bit( &fe->eb.renc, &fe->eb.bm_rep0[*state], 0 );
        Re_encode_bit( &fe->eb.renc, &fe->eb.bm_len[*state][pos_state], 0 );
        *state = St_set_shortrep( *state );
        continue;
        }
      }

    /* literal byte */
    Re_encode_bit( &fe->eb.renc, &fe->eb.bm_match[*state][pos_state], 0 );
    if( ( *state = St_set_char( *state ) ) < 4 )
      LZeb_encode_literal( &fe->eb, prev_byte, cur_byte );
    else
      LZeb_encode_matched( &fe->eb, prev_byte, cur_byte, match_byte );
    }

  LZeb_try_full_flush( &fe->eb );
  return true;
  }