1 2 /*-------------------------------------------------------------*/ 3 /*--- Huffman coding low-level stuff ---*/ 4 /*--- huffman.c ---*/ 5 /*-------------------------------------------------------------*/ 6 7 /* ------------------------------------------------------------------ 8 This file is part of bzip2/libbzip2, a program and library for 9 lossless, block-sorting data compression. 10 11 bzip2/libbzip2 version 1.0.5 of 10 December 2007 12 Copyright (C) 1996-2007 Julian Seward <jseward@bzip.org> 13 14 Please read the WARNING, DISCLAIMER and PATENTS sections in the 15 README file. 16 17 This program is released under the terms of the license contained 18 in the file LICENSE. 19 ------------------------------------------------------------------ */ 20 21 22 #include "bzlib_private.h" 23 24 /*---------------------------------------------------*/ 25 #define WEIGHTOF(zz0) ((zz0) & 0xffffff00) 26 #define DEPTHOF(zz1) ((zz1) & 0x000000ff) 27 #define MYMAX(zz2,zz3) ((zz2) > (zz3) ? (zz2) : (zz3)) 28 29 #define ADDWEIGHTS(zw1,zw2) \ 30 (WEIGHTOF(zw1)+WEIGHTOF(zw2)) | \ 31 (1 + MYMAX(DEPTHOF(zw1),DEPTHOF(zw2))) 32 33 #define UPHEAP(z) \ 34 { \ 35 Int32 zz, tmp; \ 36 zz = z; tmp = heap[zz]; \ 37 while (weight[tmp] < weight[heap[zz >> 1]]) { \ 38 heap[zz] = heap[zz >> 1]; \ 39 zz >>= 1; \ 40 } \ 41 heap[zz] = tmp; \ 42 } 43 44 #define DOWNHEAP(z) \ 45 { \ 46 Int32 zz, yy, tmp; \ 47 zz = z; tmp = heap[zz]; \ 48 while (True) { \ 49 yy = zz << 1; \ 50 if (yy > nHeap) break; \ 51 if (yy < nHeap && \ 52 weight[heap[yy+1]] < weight[heap[yy]]) \ 53 yy++; \ 54 if (weight[tmp] < weight[heap[yy]]) break; \ 55 heap[zz] = heap[yy]; \ 56 zz = yy; \ 57 } \ 58 heap[zz] = tmp; \ 59 } 60 61 62 /*---------------------------------------------------*/ 63 void BZ2_hbMakeCodeLengths ( UChar *len, 64 Int32 *freq, 65 Int32 alphaSize, 66 Int32 maxLen ) 67 { 68 /*-- 69 Nodes and heap entries run from 1. Entry 0 70 for both the heap and nodes is a sentinel. 71 --*/ 72 Int32 nNodes, nHeap, n1, n2, i, j, k; 73 Bool tooLong; 74 75 Int32 heap [ BZ_MAX_ALPHA_SIZE + 2 ]; 76 Int32 weight [ BZ_MAX_ALPHA_SIZE * 2 ]; 77 Int32 parent [ BZ_MAX_ALPHA_SIZE * 2 ]; 78 79 for (i = 0; i < alphaSize; i++) 80 weight[i+1] = (freq[i] == 0 ? 1 : freq[i]) << 8; 81 82 while (True) { 83 84 nNodes = alphaSize; 85 nHeap = 0; 86 87 heap[0] = 0; 88 weight[0] = 0; 89 parent[0] = -2; 90 91 for (i = 1; i <= alphaSize; i++) { 92 parent[i] = -1; 93 nHeap++; 94 heap[nHeap] = i; 95 UPHEAP(nHeap); 96 } 97 98 AssertH( nHeap < (BZ_MAX_ALPHA_SIZE+2), 2001 ); 99 100 while (nHeap > 1) { 101 n1 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1); 102 n2 = heap[1]; heap[1] = heap[nHeap]; nHeap--; DOWNHEAP(1); 103 nNodes++; 104 parent[n1] = parent[n2] = nNodes; 105 weight[nNodes] = ADDWEIGHTS(weight[n1], weight[n2]); 106 parent[nNodes] = -1; 107 nHeap++; 108 heap[nHeap] = nNodes; 109 UPHEAP(nHeap); 110 } 111 112 AssertH( nNodes < (BZ_MAX_ALPHA_SIZE * 2), 2002 ); 113 114 tooLong = False; 115 for (i = 1; i <= alphaSize; i++) { 116 j = 0; 117 k = i; 118 while (parent[k] >= 0) { k = parent[k]; j++; } 119 len[i-1] = j; 120 if (j > maxLen) tooLong = True; 121 } 122 123 if (! tooLong) break; 124 125 /* 17 Oct 04: keep-going condition for the following loop used 126 to be 'i < alphaSize', which missed the last element, 127 theoretically leading to the possibility of the compressor 128 looping. However, this count-scaling step is only needed if 129 one of the generated Huffman code words is longer than 130 maxLen, which up to and including version 1.0.2 was 20 bits, 131 which is extremely unlikely. In version 1.0.3 maxLen was 132 changed to 17 bits, which has minimal effect on compression 133 ratio, but does mean this scaling step is used from time to 134 time, enough to verify that it works. 135 136 This means that bzip2-1.0.3 and later will only produce 137 Huffman codes with a maximum length of 17 bits. However, in 138 order to preserve backwards compatibility with bitstreams 139 produced by versions pre-1.0.3, the decompressor must still 140 handle lengths of up to 20. */ 141 142 for (i = 1; i <= alphaSize; i++) { 143 j = weight[i] >> 8; 144 j = 1 + (j / 2); 145 weight[i] = j << 8; 146 } 147 } 148 } 149 150 151 /*---------------------------------------------------*/ 152 void BZ2_hbAssignCodes ( Int32 *code, 153 UChar *length, 154 Int32 minLen, 155 Int32 maxLen, 156 Int32 alphaSize ) 157 { 158 Int32 n, vec, i; 159 160 vec = 0; 161 for (n = minLen; n <= maxLen; n++) { 162 for (i = 0; i < alphaSize; i++) 163 if (length[i] == n) { code[i] = vec; vec++; }; 164 vec <<= 1; 165 } 166 } 167 168 169 /*---------------------------------------------------*/ 170 void BZ2_hbCreateDecodeTables ( Int32 *limit, 171 Int32 *base, 172 Int32 *perm, 173 UChar *length, 174 Int32 minLen, 175 Int32 maxLen, 176 Int32 alphaSize ) 177 { 178 Int32 pp, i, j, vec; 179 180 pp = 0; 181 for (i = minLen; i <= maxLen; i++) 182 for (j = 0; j < alphaSize; j++) 183 if (length[j] == i) { perm[pp] = j; pp++; }; 184 185 for (i = 0; i < BZ_MAX_CODE_LEN; i++) base[i] = 0; 186 for (i = 0; i < alphaSize; i++) base[length[i]+1]++; 187 188 for (i = 1; i < BZ_MAX_CODE_LEN; i++) base[i] += base[i-1]; 189 190 for (i = 0; i < BZ_MAX_CODE_LEN; i++) limit[i] = 0; 191 vec = 0; 192 193 for (i = minLen; i <= maxLen; i++) { 194 vec += (base[i+1] - base[i]); 195 limit[i] = vec-1; 196 vec <<= 1; 197 } 198 for (i = minLen + 1; i <= maxLen; i++) 199 base[i] = ((limit[i-1] + 1) << 1) - base[i]; 200 } 201 202 203 /*-------------------------------------------------------------*/ 204 /*--- end huffman.c ---*/ 205 /*-------------------------------------------------------------*/ 206