136 lines
3.7 KiB
C
136 lines
3.7 KiB
C
/*
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Copyright 2011 Google Inc. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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Author: lode.vandevenne@gmail.com (Lode Vandevenne)
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Author: jyrki.alakuijala@gmail.com (Jyrki Alakuijala)
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*/
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#include "hash.h"
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#include <assert.h>
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#include <stdio.h>
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#include <stdlib.h>
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#define HASH_SHIFT 5
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#define HASH_MASK 32767
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void ZopfliInitHash(size_t window_size, ZopfliHash* h) {
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size_t i;
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h->val = 0;
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h->head = (int*)malloc(sizeof(*h->head) * 65536);
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h->prev = (unsigned short*)malloc(sizeof(*h->prev) * window_size);
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h->hashval = (int*)malloc(sizeof(*h->hashval) * window_size);
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for (i = 0; i < 65536; i++) {
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h->head[i] = -1; /* -1 indicates no head so far. */
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}
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for (i = 0; i < window_size; i++) {
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h->prev[i] = i; /* If prev[j] == j, then prev[j] is uninitialized. */
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h->hashval[i] = -1;
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}
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#ifdef ZOPFLI_HASH_SAME
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h->same = (unsigned short*)malloc(sizeof(*h->same) * window_size);
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for (i = 0; i < window_size; i++) {
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h->same[i] = 0;
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}
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#endif
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#ifdef ZOPFLI_HASH_SAME_HASH
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h->val2 = 0;
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h->head2 = (int*)malloc(sizeof(*h->head2) * 65536);
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h->prev2 = (unsigned short*)malloc(sizeof(*h->prev2) * window_size);
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h->hashval2 = (int*)malloc(sizeof(*h->hashval2) * window_size);
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for (i = 0; i < 65536; i++) {
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h->head2[i] = -1;
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}
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for (i = 0; i < window_size; i++) {
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h->prev2[i] = i;
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h->hashval2[i] = -1;
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}
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#endif
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}
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void ZopfliCleanHash(ZopfliHash* h) {
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free(h->head);
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free(h->prev);
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free(h->hashval);
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#ifdef ZOPFLI_HASH_SAME_HASH
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free(h->head2);
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free(h->prev2);
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free(h->hashval2);
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#endif
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#ifdef ZOPFLI_HASH_SAME
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free(h->same);
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#endif
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}
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/*
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Update the sliding hash value with the given byte. All calls to this function
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must be made on consecutive input characters. Since the hash value exists out
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of multiple input bytes, a few warmups with this function are needed initially.
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*/
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static void UpdateHashValue(ZopfliHash* h, unsigned char c) {
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h->val = (((h->val) << HASH_SHIFT) ^ (c)) & HASH_MASK;
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}
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void ZopfliUpdateHash(const unsigned char* array, size_t pos, size_t end,
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ZopfliHash* h) {
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unsigned short hpos = pos & ZOPFLI_WINDOW_MASK;
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#ifdef ZOPFLI_HASH_SAME
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size_t amount = 0;
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#endif
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UpdateHashValue(h, pos + ZOPFLI_MIN_MATCH <= end ?
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array[pos + ZOPFLI_MIN_MATCH - 1] : 0);
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h->hashval[hpos] = h->val;
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if (h->head[h->val] != -1 && h->hashval[h->head[h->val]] == h->val) {
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h->prev[hpos] = h->head[h->val];
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}
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else h->prev[hpos] = hpos;
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h->head[h->val] = hpos;
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#ifdef ZOPFLI_HASH_SAME
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/* Update "same". */
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if (h->same[(pos - 1) & ZOPFLI_WINDOW_MASK] > 1) {
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amount = h->same[(pos - 1) & ZOPFLI_WINDOW_MASK] - 1;
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}
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while (pos + amount + 1 < end &&
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array[pos] == array[pos + amount + 1] && amount < (unsigned short)(-1)) {
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amount++;
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}
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h->same[hpos] = amount;
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#endif
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#ifdef ZOPFLI_HASH_SAME_HASH
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h->val2 = ((h->same[hpos] - ZOPFLI_MIN_MATCH) & 255) ^ h->val;
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h->hashval2[hpos] = h->val2;
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if (h->head2[h->val2] != -1 && h->hashval2[h->head2[h->val2]] == h->val2) {
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h->prev2[hpos] = h->head2[h->val2];
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}
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else h->prev2[hpos] = hpos;
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h->head2[h->val2] = hpos;
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#endif
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}
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void ZopfliWarmupHash(const unsigned char* array, size_t pos, size_t end,
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ZopfliHash* h) {
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(void)end;
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UpdateHashValue(h, array[pos + 0]);
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UpdateHashValue(h, array[pos + 1]);
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}
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