huffman.c (8571B)
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 /*-------------------------------------------------------------*/