1 /* 2 Copyright 2011 Google Inc. All Rights Reserved. 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15 16 Author: lode.vandevenne (at) gmail.com (Lode Vandevenne) 17 Author: jyrki.alakuijala (at) gmail.com (Jyrki Alakuijala) 18 */ 19 20 #include "hash.h" 21 22 #include <assert.h> 23 #include <stdio.h> 24 #include <stdlib.h> 25 26 #define HASH_SHIFT 5 27 #define HASH_MASK 32767 28 29 void ZopfliInitHash(size_t window_size, ZopfliHash* h) { 30 size_t i; 31 32 h->val = 0; 33 h->head = (int*)malloc(sizeof(*h->head) * 65536); 34 h->prev = (unsigned short*)malloc(sizeof(*h->prev) * window_size); 35 h->hashval = (int*)malloc(sizeof(*h->hashval) * window_size); 36 for (i = 0; i < 65536; i++) { 37 h->head[i] = -1; /* -1 indicates no head so far. */ 38 } 39 for (i = 0; i < window_size; i++) { 40 h->prev[i] = i; /* If prev[j] == j, then prev[j] is uninitialized. */ 41 h->hashval[i] = -1; 42 } 43 44 #ifdef ZOPFLI_HASH_SAME 45 h->same = (unsigned short*)malloc(sizeof(*h->same) * window_size); 46 for (i = 0; i < window_size; i++) { 47 h->same[i] = 0; 48 } 49 #endif 50 51 #ifdef ZOPFLI_HASH_SAME_HASH 52 h->val2 = 0; 53 h->head2 = (int*)malloc(sizeof(*h->head2) * 65536); 54 h->prev2 = (unsigned short*)malloc(sizeof(*h->prev2) * window_size); 55 h->hashval2 = (int*)malloc(sizeof(*h->hashval2) * window_size); 56 for (i = 0; i < 65536; i++) { 57 h->head2[i] = -1; 58 } 59 for (i = 0; i < window_size; i++) { 60 h->prev2[i] = i; 61 h->hashval2[i] = -1; 62 } 63 #endif 64 } 65 66 void ZopfliCleanHash(ZopfliHash* h) { 67 free(h->head); 68 free(h->prev); 69 free(h->hashval); 70 71 #ifdef ZOPFLI_HASH_SAME_HASH 72 free(h->head2); 73 free(h->prev2); 74 free(h->hashval2); 75 #endif 76 77 #ifdef ZOPFLI_HASH_SAME 78 free(h->same); 79 #endif 80 } 81 82 /* 83 Update the sliding hash value with the given byte. All calls to this function 84 must be made on consecutive input characters. Since the hash value exists out 85 of multiple input bytes, a few warmups with this function are needed initially. 86 */ 87 static void UpdateHashValue(ZopfliHash* h, unsigned char c) { 88 h->val = (((h->val) << HASH_SHIFT) ^ (c)) & HASH_MASK; 89 } 90 91 void ZopfliUpdateHash(const unsigned char* array, size_t pos, size_t end, 92 ZopfliHash* h) { 93 unsigned short hpos = pos & ZOPFLI_WINDOW_MASK; 94 #ifdef ZOPFLI_HASH_SAME 95 size_t amount = 0; 96 #endif 97 98 UpdateHashValue(h, pos + ZOPFLI_MIN_MATCH <= end ? 99 array[pos + ZOPFLI_MIN_MATCH - 1] : 0); 100 h->hashval[hpos] = h->val; 101 if (h->head[h->val] != -1 && h->hashval[h->head[h->val]] == h->val) { 102 h->prev[hpos] = h->head[h->val]; 103 } 104 else h->prev[hpos] = hpos; 105 h->head[h->val] = hpos; 106 107 #ifdef ZOPFLI_HASH_SAME 108 /* Update "same". */ 109 if (h->same[(pos - 1) & ZOPFLI_WINDOW_MASK] > 1) { 110 amount = h->same[(pos - 1) & ZOPFLI_WINDOW_MASK] - 1; 111 } 112 while (pos + amount + 1 < end && 113 array[pos] == array[pos + amount + 1] && amount < (unsigned short)(-1)) { 114 amount++; 115 } 116 h->same[hpos] = amount; 117 #endif 118 119 #ifdef ZOPFLI_HASH_SAME_HASH 120 h->val2 = ((h->same[hpos] - ZOPFLI_MIN_MATCH) & 255) ^ h->val; 121 h->hashval2[hpos] = h->val2; 122 if (h->head2[h->val2] != -1 && h->hashval2[h->head2[h->val2]] == h->val2) { 123 h->prev2[hpos] = h->head2[h->val2]; 124 } 125 else h->prev2[hpos] = hpos; 126 h->head2[h->val2] = hpos; 127 #endif 128 } 129 130 void ZopfliWarmupHash(const unsigned char* array, size_t pos, size_t end, 131 ZopfliHash* h) { 132 (void)end; 133 UpdateHashValue(h, array[pos + 0]); 134 UpdateHashValue(h, array[pos + 1]); 135 } 136
