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/*-------------------------------------------------------------*/
/*--- Compression machinery (not incl block sorting)        ---*/
/*---                                            compress.c ---*/
/*-------------------------------------------------------------*/

/* ------------------------------------------------------------------
   This file is part of bzip2/libbzip2, a program and library for
   lossless, block-sorting data compression.

   bzip2/libbzip2 version 1.0.5 of 10 December 2007
   Copyright (C) 1996-2007 Julian Seward <jseward@bzip.org>

   Please read the WARNING, DISCLAIMER and PATENTS sections in the 
   README file.

   This program is released under the terms of the license contained
   in the file LICENSE.
   ------------------------------------------------------------------ */


/* CHANGES
    0.9.0    -- original version.
    0.9.0a/b -- no changes in this file.
    0.9.0c   -- changed setting of nGroups in sendMTFValues() 
                so as to do a bit better on small files
*/

#include "bzlib_private.h"

ABC_NAMESPACE_IMPL_START



/*---------------------------------------------------*/
/*--- Bit stream I/O                              ---*/
/*---------------------------------------------------*/

/*---------------------------------------------------*/
void BZ2_bsInitWrite ( EState* s )
{
   s->bsLive = 0;
   s->bsBuff = 0;
}


/*---------------------------------------------------*/
static
void bsFinishWrite ( EState* s )
{
   while (s->bsLive > 0) {
      s->zbits[s->numZ] = (UChar)(s->bsBuff >> 24);
      s->numZ++;
      s->bsBuff <<= 8;
      s->bsLive -= 8;
   }
}


/*---------------------------------------------------*/
#define bsNEEDW(nz)                           \
{                                             \
   while (s->bsLive >= 8) {                   \
      s->zbits[s->numZ]                       \
         = (UChar)(s->bsBuff >> 24);          \
      s->numZ++;                              \
      s->bsBuff <<= 8;                        \
      s->bsLive -= 8;                         \
   }                                          \
}


/*---------------------------------------------------*/
static
__inline__
void bsW ( EState* s, Int32 n, UInt32 v )
{
   bsNEEDW ( n );
   s->bsBuff |= (v << (32 - s->bsLive - n));
   s->bsLive += n;
}


/*---------------------------------------------------*/
static
void bsPutUInt32 ( EState* s, UInt32 u )
{
   bsW ( s, 8, (u >> 24) & 0xffL );
   bsW ( s, 8, (u >> 16) & 0xffL );
   bsW ( s, 8, (u >>  8) & 0xffL );
   bsW ( s, 8,  u        & 0xffL );
}


/*---------------------------------------------------*/
static
void bsPutUChar ( EState* s, UChar c )
{
   bsW( s, 8, (UInt32)c );
}


/*---------------------------------------------------*/
/*--- The back end proper                         ---*/
/*---------------------------------------------------*/

/*---------------------------------------------------*/
static
void makeMaps_e ( EState* s )
{
   Int32 i;
   s->nInUse = 0;
   for (i = 0; i < 256; i++)
      if (s->inUse[i]) {
         s->unseqToSeq[i] = s->nInUse;
         s->nInUse++;
      }
}


/*---------------------------------------------------*/
static
void generateMTFValues ( EState* s )
{
   UChar   yy[256];
   Int32   i, j;
   Int32   zPend;
   Int32   wr;
   Int32   EOB;

   /* 
      After sorting (eg, here),
         s->arr1 [ 0 .. s->nblock-1 ] holds sorted order,
         and
         ((UChar*)s->arr2) [ 0 .. s->nblock-1 ] 
         holds the original block data.

      The first thing to do is generate the MTF values,
      and put them in
         ((UInt16*)s->arr1) [ 0 .. s->nblock-1 ].
      Because there are strictly fewer or equal MTF values
      than block values, ptr values in this area are overwritten
      with MTF values only when they are no longer needed.

      The final compressed bitstream is generated into the
      area starting at
         (UChar*) (&((UChar*)s->arr2)[s->nblock])

      These storage aliases are set up in bzCompressInit(),
      except for the last one, which is arranged in 
      compressBlock().
   */
   UInt32* ptr   = s->ptr;
   UChar* block  = s->block;
   UInt16* mtfv  = s->mtfv;

   makeMaps_e ( s );
   EOB = s->nInUse+1;

   for (i = 0; i <= EOB; i++) s->mtfFreq[i] = 0;

   wr = 0;
   zPend = 0;
   for (i = 0; i < s->nInUse; i++) yy[i] = (UChar) i;

   for (i = 0; i < s->nblock; i++) {
      UChar ll_i;
      AssertD ( wr <= i, "generateMTFValues(1)" );
      j = ptr[i]-1; if (j < 0) j += s->nblock;
      ll_i = s->unseqToSeq[block[j]];
      AssertD ( ll_i < s->nInUse, "generateMTFValues(2a)" );

      if (yy[0] == ll_i) { 
         zPend++;
      } else {

         if (zPend > 0) {
            zPend--;
            while (True) {
               if (zPend & 1) {
                  mtfv[wr] = BZ_RUNB; wr++; 
                  s->mtfFreq[BZ_RUNB]++; 
               } else {
                  mtfv[wr] = BZ_RUNA; wr++; 
                  s->mtfFreq[BZ_RUNA]++; 
               }
               if (zPend < 2) break;
               zPend = (zPend - 2) / 2;
            };
            zPend = 0;
         }
         {
            register UChar  rtmp;
            register UChar* ryy_j;
            register UChar  rll_i;
            rtmp  = yy[1];
            yy[1] = yy[0];
            ryy_j = &(yy[1]);
            rll_i = ll_i;
            while ( rll_i != rtmp ) {
               register UChar rtmp2;
               ryy_j++;
               rtmp2  = rtmp;
               rtmp   = *ryy_j;
               *ryy_j = rtmp2;
            };
            yy[0] = rtmp;
            j = ryy_j - &(yy[0]);
            mtfv[wr] = j+1; wr++; s->mtfFreq[j+1]++;
         }

      }
   }

   if (zPend > 0) {
      zPend--;
      while (True) {
         if (zPend & 1) {
            mtfv[wr] = BZ_RUNB; wr++; 
            s->mtfFreq[BZ_RUNB]++; 
         } else {
            mtfv[wr] = BZ_RUNA; wr++; 
            s->mtfFreq[BZ_RUNA]++; 
         }
         if (zPend < 2) break;
         zPend = (zPend - 2) / 2;
      };
      zPend = 0;
   }

   mtfv[wr] = EOB; wr++; s->mtfFreq[EOB]++;

   s->nMTF = wr;
}


/*---------------------------------------------------*/
#define BZ_LESSER_ICOST  0
#define BZ_GREATER_ICOST 15

static
void sendMTFValues ( EState* s )
{
   Int32 v, t, i, j, gs, ge, totc, bt, bc, iter;
   Int32 nSelectors, alphaSize, minLen, maxLen, selCtr;
   Int32 nGroups, nBytes;

   /*--
   UChar  len [BZ_N_GROUPS][BZ_MAX_ALPHA_SIZE];
   is a global since the decoder also needs it.

   Int32  code[BZ_N_GROUPS][BZ_MAX_ALPHA_SIZE];
   Int32  rfreq[BZ_N_GROUPS][BZ_MAX_ALPHA_SIZE];
   are also globals only used in this proc.
   Made global to keep stack frame size small.
   --*/


   UInt16 cost[BZ_N_GROUPS];
   Int32  fave[BZ_N_GROUPS];

   UInt16* mtfv = s->mtfv;

   if (s->verbosity >= 3)
      VPrintf3( "      %d in block, %d after MTF & 1-2 coding, "
                "%d+2 syms in use\n", 
                s->nblock, s->nMTF, s->nInUse );

   alphaSize = s->nInUse+2;
   for (t = 0; t < BZ_N_GROUPS; t++)
      for (v = 0; v < alphaSize; v++)
         s->len[t][v] = BZ_GREATER_ICOST;

   /*--- Decide how many coding tables to use ---*/
   AssertH ( s->nMTF > 0, 3001 );
   if (s->nMTF < 200)  nGroups = 2; else
   if (s->nMTF < 600)  nGroups = 3; else
   if (s->nMTF < 1200) nGroups = 4; else
   if (s->nMTF < 2400) nGroups = 5; else
                       nGroups = 6;

   /*--- Generate an initial set of coding tables ---*/
   { 
      Int32 nPart, remF, tFreq, aFreq;

      nPart = nGroups;
      remF  = s->nMTF;
      gs = 0;
      while (nPart > 0) {
         tFreq = remF / nPart;
         ge = gs-1;
         aFreq = 0;
         while (aFreq < tFreq && ge < alphaSize-1) {
            ge++;
            aFreq += s->mtfFreq[ge];
         }

         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;

      /*---
        Set up an auxiliary length table which is used to fast-track
    the common case (nGroups == 6). 
      ---*/
      if (nGroups == 6) {
         for (v = 0; v < alphaSize; v++) {
            s->len_pack[v][0] = (s->len[1][v] << 16) | s->len[0][v];
            s->len_pack[v][1] = (s->len[3][v] << 16) | s->len[2][v];
            s->len_pack[v][2] = (s->len[5][v] << 16) | s->len[4][v];
     }
      }

      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 && 50 == ge-gs+1) {
            /*--- fast track the common case ---*/
            register UInt32 cost01, cost23, cost45;
            register UInt16 icv;
            cost01 = cost23 = cost45 = 0;

#           define BZ_ITER(nn)                \
               icv = mtfv[gs+(nn)];           \
               cost01 += s->len_pack[icv][0]; \
               cost23 += s->len_pack[icv][1]; \
               cost45 += s->len_pack[icv][2]; \

            BZ_ITER(0);  BZ_ITER(1);  BZ_ITER(2);  BZ_ITER(3);  BZ_ITER(4);
            BZ_ITER(5);  BZ_ITER(6);  BZ_ITER(7);  BZ_ITER(8);  BZ_ITER(9);
            BZ_ITER(10); BZ_ITER(11); BZ_ITER(12); BZ_ITER(13); BZ_ITER(14);
            BZ_ITER(15); BZ_ITER(16); BZ_ITER(17); BZ_ITER(18); BZ_ITER(19);
            BZ_ITER(20); BZ_ITER(21); BZ_ITER(22); BZ_ITER(23); BZ_ITER(24);
            BZ_ITER(25); BZ_ITER(26); BZ_ITER(27); BZ_ITER(28); BZ_ITER(29);
            BZ_ITER(30); BZ_ITER(31); BZ_ITER(32); BZ_ITER(33); BZ_ITER(34);
            BZ_ITER(35); BZ_ITER(36); BZ_ITER(37); BZ_ITER(38); BZ_ITER(39);
            BZ_ITER(40); BZ_ITER(41); BZ_ITER(42); BZ_ITER(43); BZ_ITER(44);
            BZ_ITER(45); BZ_ITER(46); BZ_ITER(47); BZ_ITER(48); BZ_ITER(49);

#           undef BZ_ITER

            cost[0] = cost01 & 0xffff; cost[1] = cost01 >> 16;
            cost[2] = cost23 & 0xffff; cost[3] = cost23 >> 16;
            cost[4] = cost45 & 0xffff; cost[5] = cost45 >> 16;

         } else {
        /*--- slow version which correctly handles all situations ---*/
            for (i = gs; i <= ge; i++) { 
               UInt16 icv = mtfv[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.
          --*/
         if (nGroups == 6 && 50 == ge-gs+1) {
            /*--- fast track the common case ---*/

#           define BZ_ITUR(nn) s->rfreq[bt][ mtfv[gs+(nn)] ]++

            BZ_ITUR(0);  BZ_ITUR(1);  BZ_ITUR(2);  BZ_ITUR(3);  BZ_ITUR(4);
            BZ_ITUR(5);  BZ_ITUR(6);  BZ_ITUR(7);  BZ_ITUR(8);  BZ_ITUR(9);
            BZ_ITUR(10); BZ_ITUR(11); BZ_ITUR(12); BZ_ITUR(13); BZ_ITUR(14);
            BZ_ITUR(15); BZ_ITUR(16); BZ_ITUR(17); BZ_ITUR(18); BZ_ITUR(19);
            BZ_ITUR(20); BZ_ITUR(21); BZ_ITUR(22); BZ_ITUR(23); BZ_ITUR(24);
            BZ_ITUR(25); BZ_ITUR(26); BZ_ITUR(27); BZ_ITUR(28); BZ_ITUR(29);
            BZ_ITUR(30); BZ_ITUR(31); BZ_ITUR(32); BZ_ITUR(33); BZ_ITUR(34);
            BZ_ITUR(35); BZ_ITUR(36); BZ_ITUR(37); BZ_ITUR(38); BZ_ITUR(39);
            BZ_ITUR(40); BZ_ITUR(41); BZ_ITUR(42); BZ_ITUR(43); BZ_ITUR(44);
            BZ_ITUR(45); BZ_ITUR(46); BZ_ITUR(47); BZ_ITUR(48); BZ_ITUR(49);

#           undef BZ_ITUR

         } else {
        /*--- slow version which correctly handles all situations ---*/
            for (i = gs; i <= ge; i++)
               s->rfreq[bt][ mtfv[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.
      --*/
      /* maxLen was changed from 20 to 17 in bzip2-1.0.3.  See 
         comment in huffman.c for details. */
      for (t = 0; t < nGroups; t++)
         BZ2_hbMakeCodeLengths ( &(s->len[t][0]), &(s->rfreq[t][0]), 
                                 alphaSize, 17 /*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 > 17 /*20*/ ), 3004 );
      AssertH ( !(minLen < 1),  3005 );
      BZ2_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;
      AssertH ( s->selector[selCtr] < nGroups, 3006 );

      if (nGroups == 6 && 50 == ge-gs+1) {
            /*--- fast track the common case ---*/
            UInt16 mtfv_i;
            UChar* s_len_sel_selCtr 
               = &(s->len[s->selector[selCtr]][0]);
            Int32* s_code_sel_selCtr
               = &(s->code[s->selector[selCtr]][0]);

#           define BZ_ITAH(nn)                      \
               mtfv_i = mtfv[gs+(nn)];              \
               bsW ( s,                             \
                     s_len_sel_selCtr[mtfv_i],      \
                     s_code_sel_selCtr[mtfv_i] )

            BZ_ITAH(0);  BZ_ITAH(1);  BZ_ITAH(2);  BZ_ITAH(3);  BZ_ITAH(4);
            BZ_ITAH(5);  BZ_ITAH(6);  BZ_ITAH(7);  BZ_ITAH(8);  BZ_ITAH(9);
            BZ_ITAH(10); BZ_ITAH(11); BZ_ITAH(12); BZ_ITAH(13); BZ_ITAH(14);
            BZ_ITAH(15); BZ_ITAH(16); BZ_ITAH(17); BZ_ITAH(18); BZ_ITAH(19);
            BZ_ITAH(20); BZ_ITAH(21); BZ_ITAH(22); BZ_ITAH(23); BZ_ITAH(24);
            BZ_ITAH(25); BZ_ITAH(26); BZ_ITAH(27); BZ_ITAH(28); BZ_ITAH(29);
            BZ_ITAH(30); BZ_ITAH(31); BZ_ITAH(32); BZ_ITAH(33); BZ_ITAH(34);
            BZ_ITAH(35); BZ_ITAH(36); BZ_ITAH(37); BZ_ITAH(38); BZ_ITAH(39);
            BZ_ITAH(40); BZ_ITAH(41); BZ_ITAH(42); BZ_ITAH(43); BZ_ITAH(44);
            BZ_ITAH(45); BZ_ITAH(46); BZ_ITAH(47); BZ_ITAH(48); BZ_ITAH(49);

#           undef BZ_ITAH

      } else {
     /*--- slow version which correctly handles all situations ---*/
         for (i = gs; i <= ge; i++) {
            bsW ( s, 
                  s->len  [s->selector[selCtr]] [mtfv[i]],
                  s->code [s->selector[selCtr]] [mtfv[i]] );
         }
      }


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

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


/*---------------------------------------------------*/
void BZ2_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%08x, "
                   "combined CRC = 0x%08x, size = %d\n",
                   s->blockNo, s->blockCRC, s->combinedCRC, s->nblock );

      BZ2_blockSort ( s );
   }

   s->zbits = (UChar*) (&((UChar*)s->arr2)[s->nblock]);

   /*-- If this is the first block, create the stream header. --*/
   if (s->blockNo == 1) {
      BZ2_bsInitWrite ( s );
      bsPutUChar ( s, BZ_HDR_B );
      bsPutUChar ( s, BZ_HDR_Z );
      bsPutUChar ( s, BZ_HDR_h );
      bsPutUChar ( s, (UChar)(BZ_HDR_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 (non-)randomisation. 
         As of version 0.9.5, we use a better sorting algorithm
         which makes randomisation unnecessary.  So always set
         the randomised bit to 'no'.  Of course, the decoder
         still needs to be able to handle randomised blocks
         so as to maintain backwards compatibility with
         older versions of bzip2.
      --*/
      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) {

      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%08x\n   ", s->combinedCRC );
      bsFinishWrite ( s );
   }
}


/*-------------------------------------------------------------*/
/*--- end                                        compress.c ---*/
/*-------------------------------------------------------------*/
ABC_NAMESPACE_IMPL_END
` family of macros **directly** in the `MockFoo` class. If a mock method is defined in a **base class** of `MockFoo`, the "nice" or "strict" modifier may not affect it, depending on the compiler. In particular, nesting `NiceMock` and `StrictMock` (e.g. `NiceMock<StrictMock<MockFoo> >`) is **not** supported. 1. The constructors of the base mock (`MockFoo`) cannot have arguments passed by non-const reference, which happens to be banned by the [Google C++ style guide](http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml). 1. During the constructor or destructor of `MockFoo`, the mock object is _not_ nice or strict. This may cause surprises if the constructor or destructor calls a mock method on `this` object. (This behavior, however, is consistent with C++'s general rule: if a constructor or destructor calls a virtual method of `this` object, that method is treated as non-virtual. In other words, to the base class's constructor or destructor, `this` object behaves like an instance of the base class, not the derived class. This rule is required for safety. Otherwise a base constructor may use members of a derived class before they are initialized, or a base destructor may use members of a derived class after they have been destroyed.) Finally, you should be **very cautious** when using this feature, as the decision you make applies to **all** future changes to the mock class. If an important change is made in the interface you are mocking (and thus in the mock class), it could break your tests (if you use `StrictMock`) or let bugs pass through without a warning (if you use `NiceMock`). Therefore, try to specify the mock's behavior using explicit `EXPECT_CALL` first, and only turn to `NiceMock` or `StrictMock` as the last resort. ## Simplifying the Interface without Breaking Existing Code ## Sometimes a method has a long list of arguments that is mostly uninteresting. For example, ``` class LogSink { public: ... virtual void send(LogSeverity severity, const char* full_filename, const char* base_filename, int line, const struct tm* tm_time, const char* message, size_t message_len) = 0; }; ``` This method's argument list is lengthy and hard to work with (let's say that the `message` argument is not even 0-terminated). If we mock it as is, using the mock will be awkward. If, however, we try to simplify this interface, we'll need to fix all clients depending on it, which is often infeasible. The trick is to re-dispatch the method in the mock class: ``` class ScopedMockLog : public LogSink { public: ... virtual void send(LogSeverity severity, const char* full_filename, const char* base_filename, int line, const tm* tm_time, const char* message, size_t message_len) { // We are only interested in the log severity, full file name, and // log message. Log(severity, full_filename, std::string(message, message_len)); } // Implements the mock method: // // void Log(LogSeverity severity, // const string& file_path, // const string& message); MOCK_METHOD3(Log, void(LogSeverity severity, const string& file_path, const string& message)); }; ``` By defining a new mock method with a trimmed argument list, we make the mock class much more user-friendly. ## Alternative to Mocking Concrete Classes ## Often you may find yourself using classes that don't implement interfaces. In order to test your code that uses such a class (let's call it `Concrete`), you may be tempted to make the methods of `Concrete` virtual and then mock it. Try not to do that. Making a non-virtual function virtual is a big decision. It creates an extension point where subclasses can tweak your class' behavior. This weakens your control on the class because now it's harder to maintain the class' invariants. You should make a function virtual only when there is a valid reason for a subclass to override it. Mocking concrete classes directly is problematic as it creates a tight coupling between the class and the tests - any small change in the class may invalidate your tests and make test maintenance a pain. To avoid such problems, many programmers have been practicing "coding to interfaces": instead of talking to the `Concrete` class, your code would define an interface and talk to it. Then you implement that interface as an adaptor on top of `Concrete`. In tests, you can easily mock that interface to observe how your code is doing. This technique incurs some overhead: * You pay the cost of virtual function calls (usually not a problem). * There is more abstraction for the programmers to learn. However, it can also bring significant benefits in addition to better testability: * `Concrete`'s API may not fit your problem domain very well, as you may not be the only client it tries to serve. By designing your own interface, you have a chance to tailor it to your need - you may add higher-level functionalities, rename stuff, etc instead of just trimming the class. This allows you to write your code (user of the interface) in a more natural way, which means it will be more readable, more maintainable, and you'll be more productive. * If `Concrete`'s implementation ever has to change, you don't have to rewrite everywhere it is used. Instead, you can absorb the change in your implementation of the interface, and your other code and tests will be insulated from this change. Some people worry that if everyone is practicing this technique, they will end up writing lots of redundant code. This concern is totally understandable. However, there are two reasons why it may not be the case: * Different projects may need to use `Concrete` in different ways, so the best interfaces for them will be different. Therefore, each of them will have its own domain-specific interface on top of `Concrete`, and they will not be the same code. * If enough projects want to use the same interface, they can always share it, just like they have been sharing `Concrete`. You can check in the interface and the adaptor somewhere near `Concrete` (perhaps in a `contrib` sub-directory) and let many projects use it. You need to weigh the pros and cons carefully for your particular problem, but I'd like to assure you that the Java community has been practicing this for a long time and it's a proven effective technique applicable in a wide variety of situations. :-) ## Delegating Calls to a Fake ## Some times you have a non-trivial fake implementation of an interface. For example: ``` class Foo { public: virtual ~Foo() {} virtual char DoThis(int n) = 0; virtual void DoThat(const char* s, int* p) = 0; }; class FakeFoo : public Foo { public: virtual char DoThis(int n) { return (n > 0) ? '+' : (n < 0) ? '-' : '0'; } virtual void DoThat(const char* s, int* p) { *p = strlen(s); } }; ``` Now you want to mock this interface such that you can set expectations on it. However, you also want to use `FakeFoo` for the default behavior, as duplicating it in the mock object is, well, a lot of work. When you define the mock class using Google Mock, you can have it