1 files changed, 135 insertions, 0 deletions
diff --git a/src/zopfli/hash.c b/src/zopfli/hash.c
new file mode 100644
index 0000000..a3b294f
--- /dev/null
+++ b/src/zopfli/hash.c
@@ -0,0 +1,135 @@
+/*
+Copyright 2011 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+Author: lode.vandevenne@gmail.com (Lode Vandevenne)
+Author: jyrki.alakuijala@gmail.com (Jyrki Alakuijala)
+*/
+
+#include "hash.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define HASH_SHIFT 5
+#define HASH_MASK 32767
+
+void ZopfliInitHash(size_t window_size, ZopfliHash* h) {
+  size_t i;
+
+  h->val = 0;
+  h->head = (int*)malloc(sizeof(*h->head) * 65536);
+  h->prev = (unsigned short*)malloc(sizeof(*h->prev) * window_size);
+  h->hashval = (int*)malloc(sizeof(*h->hashval) * window_size);
+  for (i = 0; i < 65536; i++) {
+    h->head[i] = -1;  /* -1 indicates no head so far. */
+  }
+  for (i = 0; i < window_size; i++) {
+    h->prev[i] = i;  /* If prev[j] == j, then prev[j] is uninitialized. */
+    h->hashval[i] = -1;
+  }
+
+#ifdef ZOPFLI_HASH_SAME
+  h->same = (unsigned short*)malloc(sizeof(*h->same) * window_size);
+  for (i = 0; i < window_size; i++) {
+    h->same[i] = 0;
+  }
+#endif
+
+#ifdef ZOPFLI_HASH_SAME_HASH
+  h->val2 = 0;
+  h->head2 = (int*)malloc(sizeof(*h->head2) * 65536);
+  h->prev2 = (unsigned short*)malloc(sizeof(*h->prev2) * window_size);
+  h->hashval2 = (int*)malloc(sizeof(*h->hashval2) * window_size);
+  for (i = 0; i < 65536; i++) {
+    h->head2[i] = -1;
+  }
+  for (i = 0; i < window_size; i++) {
+    h->prev2[i] = i;
+    h->hashval2[i] = -1;
+  }
+#endif
+}
+
+void ZopfliCleanHash(ZopfliHash* h) {
+  free(h->head);
+  free(h->prev);
+  free(h->hashval);
+
+#ifdef ZOPFLI_HASH_SAME_HASH
+  free(h->head2);
+  free(h->prev2);
+  free(h->hashval2);
+#endif
+
+#ifdef ZOPFLI_HASH_SAME
+  free(h->same);
+#endif
+}
+
+/*
+Update the sliding hash value with the given byte. All calls to this function
+must be made on consecutive input characters. Since the hash value exists out
+of multiple input bytes, a few warmups with this function are needed initially.
+*/
+static void UpdateHashValue(ZopfliHash* h, unsigned char c) {
+  h->val = (((h->val) << HASH_SHIFT) ^ (c)) & HASH_MASK;
+}
+
+void ZopfliUpdateHash(const unsigned char* array, size_t pos, size_t end,
+                ZopfliHash* h) {
+  unsigned short hpos = pos & ZOPFLI_WINDOW_MASK;
+#ifdef ZOPFLI_HASH_SAME
+  size_t amount = 0;
+#endif
+
+  UpdateHashValue(h, pos + ZOPFLI_MIN_MATCH <= end ?
+      array[pos + ZOPFLI_MIN_MATCH - 1] : 0);
+  h->hashval[hpos] = h->val;
+  if (h->head[h->val] != -1 && h->hashval[h->head[h->val]] == h->val) {
+    h->prev[hpos] = h->head[h->val];
+  }
+  else h->prev[hpos] = hpos;
+  h->head[h->val] = hpos;
+
+#ifdef ZOPFLI_HASH_SAME
+  /* Update "same". */
+  if (h->same[(pos - 1) & ZOPFLI_WINDOW_MASK] > 1) {
+    amount = h->same[(pos - 1) & ZOPFLI_WINDOW_MASK] - 1;
+  }
+  while (pos + amount + 1 < end &&
+      array[pos] == array[pos + amount + 1] && amount < (unsigned short)(-1)) {
+    amount++;
+  }
+  h->same[hpos] = amount;
+#endif
+
+#ifdef ZOPFLI_HASH_SAME_HASH
+  h->val2 = ((h->same[hpos] - ZOPFLI_MIN_MATCH) & 255) ^ h->val;
+  h->hashval2[hpos] = h->val2;
+  if (h->head2[h->val2] != -1 && h->hashval2[h->head2[h->val2]] == h->val2) {
+    h->prev2[hpos] = h->head2[h->val2];
+  }
+  else h->prev2[hpos] = hpos;
+  h->head2[h->val2] = hpos;
+#endif
+}
+
+void ZopfliWarmupHash(const unsigned char* array, size_t pos, size_t end,
+                ZopfliHash* h) {
+  (void)end;
+  UpdateHashValue(h, array[pos + 0]);
+  UpdateHashValue(h, array[pos + 1]);
+}