compress.c

高效率的一种通用压缩/解压程序

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

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

  Copyright (C) 1996-1998 Julian R Seward.  All rights reserved.

  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. The origin of this software must not be misrepresented; you must 
     not claim that you wrote the original software.  If you use this 
     software in a product, an acknowledgment in the product 
     documentation would be appreciated but is not required.

  3. Altered source versions must be plainly marked as such, and must
     not be misrepresented as being the original software.

  4. The name of the author may not be used to endorse or promote 
     products derived from this software without specific prior written 
     permission.

  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
  OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  Julian Seward, Guildford, Surrey, UK.
  [e-mail]
  bzip2/libbzip2 version 0.9.0 of 28 June 1998

  This program is based on (at least) the work of:
     Mike Burrows
     David Wheeler
     Peter Fenwick
     Alistair Moffat
     Radford Neal
     Ian H. Witten
     Robert Sedgewick
     Jon L. Bentley

  For more information on these sources, see the manual.
--*/

/*--
   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"


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

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


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


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


/*---------------------------------------------------*/
static
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;
   UChar  tmp;
   UChar  tmp2;
   Int32  zPend;
   Int32  wr;
   Int32  EOB;

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

      j = 0;
      tmp = yy[j];
      while ( ll_i != tmp ) {
         j++;
         tmp2 = tmp;
         tmp = yy[j];
         yy[j] = tmp2;
      };
      yy[0] = tmp;

      if (j == 0) {
         zPend++;
      } else {
         if (zPend > 0) {
            zPend--;
            while (True) {
               switch (zPend % 2) {
                  case 0: s->szptr[wr] = BZ_RUNA; wr++; s->mtfFreq[BZ_RUNA]++; break;
                  case 1: s->szptr[wr] = BZ_RUNB; wr++; s->mtfFreq[BZ_RUNB]++; break;
               };
               if (zPend < 2) break;
               zPend = (zPend - 2) / 2;
            };
            zPend = 0;
         }
         s->szptr[wr] = j+1; wr++; s->mtfFreq[j+1]++;
      }
   }

   if (zPend > 0) {
      zPend--;
      while (True) {
         switch (zPend % 2) {
            case 0:  s->szptr[wr] = BZ_RUNA; wr++; s->mtfFreq[BZ_RUNA]++; break;
            case 1:  s->szptr[wr] = BZ_RUNB; wr++; s->mtfFreq[BZ_RUNB]++; break;
         };
         if (zPend < 2) break;
         zPend = (zPend - 2) / 2;
      };
   }

   s->szptr[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];

   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];
         }