The Android Open Source Project | cfb3b27 | 2009-03-03 19:29:20 -0800 | [diff] [blame] | 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 | |
Elliott Hughes | 8645cf6 | 2021-12-08 15:07:46 -0800 | [diff] [blame] | 11 | bzip2/libbzip2 version 1.0.8 of 13 July 2019 |
| 12 | Copyright (C) 1996-2019 Julian Seward <jseward@acm.org> |
The Android Open Source Project | cfb3b27 | 2009-03-03 19:29:20 -0800 | [diff] [blame] | 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 | /*-------------------------------------------------------------*/ |