compress.c

高效率的一种通用压缩/解压程序

         if (ge > gs 
             && nPart != nGroups && nPart != 1 
             && ((nGroups-nPart) % 2 == 1)) {
            aFreq -= s->mtfFreq[ge];
            ge--;
         }

         if (s->verbosity >= 3)
            VPrintf5( "      initial group %d, [%d .. %d], "
                      "has %d syms (%4.1f%%)\n",
                      nPart, gs, ge, aFreq, 
                      (100.0 * (float)aFreq) / (float)(s->nMTF) );
 
         for (v = 0; v < alphaSize; v++)
            if (v >= gs && v <= ge) 
               s->len[nPart-1][v] = BZ_LESSER_ICOST; else
               s->len[nPart-1][v] = BZ_GREATER_ICOST;
 
         nPart--;
         gs = ge+1;
         remF -= aFreq;
      }
   }

   /*--- 
      Iterate up to BZ_N_ITERS times to improve the tables.
   ---*/
   for (iter = 0; iter < BZ_N_ITERS; iter++) {

      for (t = 0; t < nGroups; t++) fave[t] = 0;

      for (t = 0; t < nGroups; t++)
         for (v = 0; v < alphaSize; v++)
            s->rfreq[t][v] = 0;

      nSelectors = 0;
      totc = 0;
      gs = 0;
      while (True) {

         /*--- Set group start & end marks. --*/
         if (gs >= s->nMTF) break;
         ge = gs + BZ_G_SIZE - 1; 
         if (ge >= s->nMTF) ge = s->nMTF-1;

         /*-- 
            Calculate the cost of this group as coded
            by each of the coding tables.
         --*/
         for (t = 0; t < nGroups; t++) cost[t] = 0;

         if (nGroups == 6) {
            register UInt16 cost0, cost1, cost2, cost3, cost4, cost5;
            cost0 = cost1 = cost2 = cost3 = cost4 = cost5 = 0;
            for (i = gs; i <= ge; i++) { 
               UInt16 icv = s->szptr[i];
               cost0 += s->len[0][icv];
               cost1 += s->len[1][icv];
               cost2 += s->len[2][icv];
               cost3 += s->len[3][icv];
               cost4 += s->len[4][icv];
               cost5 += s->len[5][icv];
            }
            cost[0] = cost0; cost[1] = cost1; cost[2] = cost2;
            cost[3] = cost3; cost[4] = cost4; cost[5] = cost5;
         } else {
            for (i = gs; i <= ge; i++) { 
               UInt16 icv = s->szptr[i];
               for (t = 0; t < nGroups; t++) cost[t] += s->len[t][icv];
            }
         }
 
         /*-- 
            Find the coding table which is best for this group,
            and record its identity in the selector table.
         --*/
         bc = 999999999; bt = -1;
         for (t = 0; t < nGroups; t++)
            if (cost[t] < bc) { bc = cost[t]; bt = t; };
         totc += bc;
         fave[bt]++;
         s->selector[nSelectors] = bt;
         nSelectors++;

         /*-- 
            Increment the symbol frequencies for the selected table.
          --*/
         for (i = gs; i <= ge; i++)
            s->rfreq[bt][ s->szptr[i] ]++;

         gs = ge+1;
      }
      if (s->verbosity >= 3) {
         VPrintf2 ( "      pass %d: size is %d, grp uses are ", 
                   iter+1, totc/8 );
         for (t = 0; t < nGroups; t++)
            VPrintf1 ( "%d ", fave[t] );
         VPrintf0 ( "\n" );
      }

      /*--
        Recompute the tables based on the accumulated frequencies.
      --*/
      for (t = 0; t < nGroups; t++)
         hbMakeCodeLengths ( &(s->len[t][0]), &(s->rfreq[t][0]), 
                             alphaSize, 20 );
   }


   AssertH( nGroups < 8, 3002 );
   AssertH( nSelectors < 32768 &&
            nSelectors <= (2 + (900000 / BZ_G_SIZE)),
            3003 );


   /*--- Compute MTF values for the selectors. ---*/
   {
      UChar pos[BZ_N_GROUPS], ll_i, tmp2, tmp;
      for (i = 0; i < nGroups; i++) pos[i] = i;
      for (i = 0; i < nSelectors; i++) {
         ll_i = s->selector[i];
         j = 0;
         tmp = pos[j];
         while ( ll_i != tmp ) {
            j++;
            tmp2 = tmp;
            tmp = pos[j];
            pos[j] = tmp2;
         };
         pos[0] = tmp;
         s->selectorMtf[i] = j;
      }
   };

   /*--- Assign actual codes for the tables. --*/
   for (t = 0; t < nGroups; t++) {
      minLen = 32;
      maxLen = 0;
      for (i = 0; i < alphaSize; i++) {
         if (s->len[t][i] > maxLen) maxLen = s->len[t][i];
         if (s->len[t][i] < minLen) minLen = s->len[t][i];
      }
      AssertH ( !(maxLen > 20), 3004 );
      AssertH ( !(minLen < 1),  3005 );
      hbAssignCodes ( &(s->code[t][0]), &(s->len[t][0]), 
                      minLen, maxLen, alphaSize );
   }

   /*--- Transmit the mapping table. ---*/
   { 
      Bool inUse16[16];
      for (i = 0; i < 16; i++) {
          inUse16[i] = False;
          for (j = 0; j < 16; j++)
             if (s->inUse[i * 16 + j]) inUse16[i] = True;
      }
     
      nBytes = s->numZ;
      for (i = 0; i < 16; i++)
         if (inUse16[i]) bsW(s,1,1); else bsW(s,1,0);

      for (i = 0; i < 16; i++)
         if (inUse16[i])
            for (j = 0; j < 16; j++) {
               if (s->inUse[i * 16 + j]) bsW(s,1,1); else bsW(s,1,0);
            }

      if (s->verbosity >= 3) 
         VPrintf1( "      bytes: mapping %d, ", s->numZ-nBytes );
   }

   /*--- Now the selectors. ---*/
   nBytes = s->numZ;
   bsW ( s, 3, nGroups );
   bsW ( s, 15, nSelectors );
   for (i = 0; i < nSelectors; i++) { 
      for (j = 0; j < s->selectorMtf[i]; j++) bsW(s,1,1);
      bsW(s,1,0);
   }
   if (s->verbosity >= 3)
      VPrintf1( "selectors %d, ", s->numZ-nBytes );

   /*--- Now the coding tables. ---*/
   nBytes = s->numZ;

   for (t = 0; t < nGroups; t++) {
      Int32 curr = s->len[t][0];
      bsW ( s, 5, curr );
      for (i = 0; i < alphaSize; i++) {
         while (curr < s->len[t][i]) { bsW(s,2,2); curr++; /* 10 */ };
         while (curr > s->len[t][i]) { bsW(s,2,3); curr--; /* 11 */ };
         bsW ( s, 1, 0 );
      }
   }

   if (s->verbosity >= 3)
      VPrintf1 ( "code lengths %d, ", s->numZ-nBytes );

   /*--- And finally, the block data proper ---*/
   nBytes = s->numZ;
   selCtr = 0;
   gs = 0;
   while (True) {
      if (gs >= s->nMTF) break;
      ge = gs + BZ_G_SIZE - 1; 
      if (ge >= s->nMTF) ge = s->nMTF-1;
      for (i = gs; i <= ge; i++) {
         AssertH ( s->selector[selCtr] < nGroups, 3006 );
         bsW ( s, 
               s->len  [s->selector[selCtr]] [s->szptr[i]],
               s->code [s->selector[selCtr]] [s->szptr[i]] );
      }

      gs = ge+1;
      selCtr++;
   }
   AssertH( selCtr == nSelectors, 3007 );

   if (s->verbosity >= 3)
      VPrintf1( "codes %d\n", s->numZ-nBytes );
}


/*---------------------------------------------------*/
void compressBlock ( EState* s, Bool is_last_block )
{
   if (s->nblock > 0) {

      BZ_FINALISE_CRC ( s->blockCRC );
      s->combinedCRC = (s->combinedCRC << 1) | (s->combinedCRC >> 31);
      s->combinedCRC ^= s->blockCRC;
      if (s->blockNo > 1) s->numZ = 0;

      if (s->verbosity >= 2)
         VPrintf4( "    block %d: crc = 0x%8x, "
                   "combined CRC = 0x%8x, size = %d\n",
                   s->blockNo, s->blockCRC, s->combinedCRC, s->nblock );

      blockSort ( s );
   }

   /*-- If this is the first block, create the stream header. --*/
   if (s->blockNo == 1) {
      bsInitWrite ( s );
      bsPutUChar ( s, 'B' );
      bsPutUChar ( s, 'Z' );
      bsPutUChar ( s, 'h' );
      bsPutUChar ( s, '0' + s->blockSize100k );
   }

   if (s->nblock > 0) {

      bsPutUChar ( s, 0x31 ); bsPutUChar ( s, 0x41 );
      bsPutUChar ( s, 0x59 ); bsPutUChar ( s, 0x26 );
      bsPutUChar ( s, 0x53 ); bsPutUChar ( s, 0x59 );

      /*-- Now the block's CRC, so it is in a known place. --*/
      bsPutUInt32 ( s, s->blockCRC );

      /*-- Now a single bit indicating randomisation. --*/
      if (s->blockRandomised) {
         bsW(s,1,1); s->nBlocksRandomised++;
      } else
         bsW(s,1,0);

      bsW ( s, 24, s->origPtr );
      generateMTFValues ( s );
      sendMTFValues ( s );
   }


   /*-- If this is the last block, add the stream trailer. --*/
   if (is_last_block) {

      if (s->verbosity >= 2 && s->nBlocksRandomised > 0)
         VPrintf2 ( "    %d block%s needed randomisation\n", 
                    s->nBlocksRandomised,
                    s->nBlocksRandomised == 1 ? "" : "s" );

      bsPutUChar ( s, 0x17 ); bsPutUChar ( s, 0x72 );
      bsPutUChar ( s, 0x45 ); bsPutUChar ( s, 0x38 );
      bsPutUChar ( s, 0x50 ); bsPutUChar ( s, 0x90 );
      bsPutUInt32 ( s, s->combinedCRC );
      if (s->verbosity >= 2)
         VPrintf1( "    final combined CRC = 0x%x\n   ", s->combinedCRC );
      bsFinishWrite ( s );
   }
}


/*-------------------------------------------------------------*/
/*--- end                                        compress.c ---*/
/*-------------------------------------------------------------*/