contrib/bzip2-1.0/huffman.c

   1
   2 /*-------------------------------------------------------------*/
   3 /*--- Huffman coding low-level stuff                        ---*/
   4 /*---                                             huffman.c ---*/
   5 /*-------------------------------------------------------------*/
   6
   7 /*--
   8   This file is a part of bzip2 and/or libbzip2, a program and
   9   library for lossless, block-sorting data compression.
  10
  11   Copyright (C) 1996-2005 Julian R Seward.  All rights reserved.
  12
  13   Redistribution and use in source and binary forms, with or without
  14   modification, are permitted provided that the following conditions
  15   are met:
  16
  17   1. Redistributions of source code must retain the above copyright
  18      notice, this list of conditions and the following disclaimer.
  19
  20   2. The origin of this software must not be misrepresented; you must
  21      not claim that you wrote the original software.  If you use this
  22      software in a product, an acknowledgment in the product
  23      documentation would be appreciated but is not required.
  24
  25   3. Altered source versions must be plainly marked as such, and must
  26      not be misrepresented as being the original software.
  27
  28   4. The name of the author may not be used to endorse or promote
  29      products derived from this software without specific prior written
  30      permission.
  31
  32   THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
  33   OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  34   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  35   ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  36   DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  37   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  38   GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  39   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  40   WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  41   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  42   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  43
  44   Julian Seward, Cambridge, UK.
  45   jseward@bzip.org
  46   bzip2/libbzip2 version 1.0 of 21 March 2000
  47
  48   This program is based on (at least) the work of:
  49      Mike Burrows
  50      David Wheeler
  51      Peter Fenwick
  52      Alistair Moffat
  53      Radford Neal
  54      Ian H. Witten
  55      Robert Sedgewick
  56      Jon L. Bentley
  57
  58   For more information on these sources, see the manual.
  59 --*/
  60
  61
  62 #include "bzlib_private.h"
  63
  64 /*---------------------------------------------------*/
  65 #define WEIGHTOF(zz0)  ((zz0) & 0xffffff00)
  66 #define DEPTHOF(zz1)   ((zz1) & 0x000000ff)
  67 #define MYMAX(zz2,zz3) ((zz2) > (zz3) ? (zz2) : (zz3))
  68
  69 #define ADDWEIGHTS(zw1,zw2)                           \
  70    (WEIGHTOF(zw1)+WEIGHTOF(zw2)) |                    \
  71    (1 + MYMAX(DEPTHOF(zw1),DEPTHOF(zw2)))
  72
  73 #define UPHEAP(z)                                     \
  74 {                                                     \
  75    Int32 zz, tmp;                                     \
  76    zz = z; tmp = heap[zz];                            \
  77    while (weight[tmp] < weight[heap[zz >> 1]]) {      \
  78       heap[zz] = heap[zz >> 1];                       \
  79       zz >>= 1;                                       \
  80    }                                                  \
  81    heap[zz] = tmp;                                    \
  82 }
  83
  84 #define DOWNHEAP(z)                                   \
  85 {                                                     \
  86    Int32 zz, yy, tmp;                                 \
  87    zz = z; tmp = heap[zz];                            \
  88    while (True) {                                     \
  89       yy = zz << 1;                                   \
  90       if (yy > nHeap) break;                          \
  91       if (yy < nHeap &&                               \
  92           weight[heap[yy+1]] < weight[heap[yy]])      \
  93          yy++;                                        \
  94       if (weight[tmp] < weight[heap[yy]]) break;      \
  95       heap[zz] = heap[yy];                            \
  96       zz = yy;                                        \
  97    }                                                  \
  98    heap[zz] = tmp;                                    \
  99 }
 100
 101
 102 /*---------------------------------------------------*/
 103 void BZ2_hbMakeCodeLengths ( UChar *len,
 104                              Int32 *freq,
 105                              Int32 alphaSize,
 106                              Int32 maxLen )
 107 {
 108    /*--
 109       Nodes and heap entries run from 1.  Entry 0
 110       for both the heap and nodes is a sentinel.
 111    --*/
 112    Int32 nNodes, nHeap, n1, n2, i, j, k;
 113    Bool  tooLong;
 114
 115    Int32 heap   [ BZ_MAX_ALPHA_SIZE + 2 ];
 116    Int32 weight [ BZ_MAX_ALPHA_SIZE * 2 ];
 117    Int32 parent [ BZ_MAX_ALPHA_SIZE * 2 ];
 118
 119    for (i = 0; i < alphaSize; i++)
 120       weight[i+1] = (freq[i] == 0 ? 1 : freq[i]) << 8;
 121
 122    while (True) {
 123
 124       nNodes = alphaSize;
 125       nHeap = 0;
 126
 127       heap[0] = 0;
 128       weight[0] = 0;
 129       parent[0] = -2;
 130
 131       for (i = 1; i <= alphaSize; i++) {
 132          parent[i] = -1;
 133          nHeap++;
 134          heap[nHeap] = i;
 135          UPHEAP(nHeap);
 136       }
 137
 138       AssertH( nHeap < (BZ_MAX_ALPHA_SIZE+2), 2001 );
 139
 140       while (nHeap > 1) {
 141          n1 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
 142          n2 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1);
 143          nNodes++;
 144          parent[n1] = parent[n2] = nNodes;
 145          weight[nNodes] = ADDWEIGHTS(weight[n1], weight[n2]);
 146          parent[nNodes] = -1;
 147          nHeap++;
 148          heap[nHeap] = nNodes;
 149          UPHEAP(nHeap);
 150       }
 151
 152       AssertH( nNodes < (BZ_MAX_ALPHA_SIZE * 2), 2002 );
 153
 154       tooLong = False;
 155       for (i = 1; i <= alphaSize; i++) {
 156          j = 0;
 157          k = i;
 158          while (parent[k] >= 0) { k = parent[k]; j++; }
 159          len[i-1] = j;
 160          if (j > maxLen) tooLong = True;
 161       }
 162
 163       if (! tooLong) break;
 164
 165       /* 17 Oct 04: keep-going condition for the following loop used
 166          to be 'i < alphaSize', which missed the last element,
 167          theoretically leading to the possibility of the compressor
 168          looping.  However, this count-scaling step is only needed if
 169          one of the generated Huffman code words is longer than
 170          maxLen, which up to and including version 1.0.2 was 20 bits,
 171          which is extremely unlikely.  In version 1.0.3 maxLen was
 172          changed to 17 bits, which has minimal effect on compression
 173          ratio, but does mean this scaling step is used from time to
 174          time, enough to verify that it works.
 175
 176          This means that bzip2-1.0.3 and later will only produce
 177          Huffman codes with a maximum length of 17 bits.  However, in
 178          order to preserve backwards compatibility with bitstreams
 179          produced by versions pre-1.0.3, the decompressor must still
 180          handle lengths of up to 20. */
 181
 182       for (i = 1; i <= alphaSize; i++) {
 183          j = weight[i] >> 8;
 184          j = 1 + (j / 2);
 185          weight[i] = j << 8;
 186       }
 187    }
 188 }
 189
 190
 191 /*---------------------------------------------------*/
 192 void BZ2_hbAssignCodes ( Int32 *code,
 193                          UChar *length,
 194                          Int32 minLen,
 195                          Int32 maxLen,
 196                          Int32 alphaSize )
 197 {
 198    Int32 n, vec, i;
 199
 200    vec = 0;
 201    for (n = minLen; n <= maxLen; n++) {
 202       for (i = 0; i < alphaSize; i++)
 203          if (length[i] == n) { code[i] = vec; vec++; };
 204       vec <<= 1;
 205    }
 206 }
 207
 208
 209 /*---------------------------------------------------*/
 210 void BZ2_hbCreateDecodeTables ( Int32 *limit,
 211                                 Int32 *base,
 212                                 Int32 *perm,
 213                                 UChar *length,
 214                                 Int32 minLen,
 215                                 Int32 maxLen,
 216                                 Int32 alphaSize )
 217 {
 218    Int32 pp, i, j, vec;
 219
 220    pp = 0;
 221    for (i = minLen; i <= maxLen; i++)
 222       for (j = 0; j < alphaSize; j++)
 223          if (length[j] == i) { perm[pp] = j; pp++; };
 224
 225    for (i = 0; i < BZ_MAX_CODE_LEN; i++) base[i] = 0;
 226    for (i = 0; i < alphaSize; i++) base[length[i]+1]++;
 227
 228    for (i = 1; i < BZ_MAX_CODE_LEN; i++) base[i] += base[i-1];
 229
 230    for (i = 0; i < BZ_MAX_CODE_LEN; i++) limit[i] = 0;
 231    vec = 0;
 232
 233    for (i = minLen; i <= maxLen; i++) {
 234       vec += (base[i+1] - base[i]);
 235       limit[i] = vec-1;
 236       vec <<= 1;
 237    }
 238    for (i = minLen + 1; i <= maxLen; i++)
 239       base[i] = ((limit[i-1] + 1) << 1) - base[i];
 240 }
 241
 242
 243 /*-------------------------------------------------------------*/
 244 /*--- end                                         huffman.c ---*/
 245 /*-------------------------------------------------------------*/