add utils/color_cache.[hc] from experimental

Pulled from the current HEAD (218c32e).
The history of this and related files is a bit entangled so rather
trying to split the changes and introduce some noise in master's history
we'll start with a fresh snapshot.
The file progression is still available in the experimental branch.

Change-Id: Id879be453a94d9f44ec8d47747823ca7297ae008

src/utils/color_cache.c

@@ -0,0 +1,45 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Color Cache for WebP Lossless
+//
+// Author: jyrki@google.com (Jyrki Alakuijala)
+
+#include <assert.h>
+#include <stdlib.h>
+#include "./color_cache.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+//------------------------------------------------------------------------------
+// VP8LColorCache.
+
+int VP8LColorCacheInit(VP8LColorCache* const cc, int hash_bits) {
+  int hash_size;
+  assert(cc != NULL);
+
+  if (hash_bits == 0) hash_bits = 1;
+  hash_size = 1 << hash_bits;
+  cc->colors_ = (uint32_t*)calloc(hash_size, sizeof(*cc->colors_));
+  if (cc->colors_ == NULL) return 0;
+  cc->hash_shift_ = 32 - hash_bits;
+  return 1;
+}
+
+void VP8LColorCacheDelete(VP8LColorCache* const cc) {
+  if (cc != NULL) {
+    free(cc->colors_);
+    free(cc);
+  }
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}
+#endif
+

src/utils/color_cache.h

@@ -0,0 +1,68 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Color Cache for WebP Lossless
+//
+// Authors: jyrki@google.com (Jyrki Alakuijala)
+//          urvang@google.com (Urvang Joshi)
+
+#ifndef WEBP_UTILS_COLOR_CACHE_H_
+#define WEBP_UTILS_COLOR_CACHE_H_
+
+#include "../webp/types.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+// Main color cache struct.
+typedef struct {
+  uint32_t *colors_;  // color entries
+  int hash_shift_;    // Hash shift: 32 - hash_bits.
+} VP8LColorCache;
+
+static const uint32_t kHashMul = 0x1e35a7bd;
+
+static WEBP_INLINE uint32_t VP8LColorCacheLookup(
+    const VP8LColorCache* const cc, uint32_t key) {
+  assert(key <= (~0U >> cc->hash_shift_));
+  return cc->colors_[key];
+}
+
+static WEBP_INLINE void VP8LColorCacheInsert(const VP8LColorCache* const cc,
+                                             uint32_t argb) {
+  const uint32_t key = (kHashMul * argb) >> cc->hash_shift_;
+  cc->colors_[key] = argb;
+}
+
+static WEBP_INLINE int VP8LColorCacheGetIndex(const VP8LColorCache* const cc,
+                                              uint32_t argb) {
+  return (kHashMul * argb) >> cc->hash_shift_;
+}
+
+static WEBP_INLINE int VP8LColorCacheContains(const VP8LColorCache* const cc,
+                                              uint32_t argb) {
+  const uint32_t key = (kHashMul * argb) >> cc->hash_shift_;
+  return cc->colors_[key] == argb;
+}
+
+//------------------------------------------------------------------------------
+
+// Initializes the color cache with 'hash_bits' bits for the keys.
+// Returns false in case of memory error.
+int VP8LColorCacheInit(VP8LColorCache* const color_cache, int hash_bits);
+
+// Delete the color cache.
+void VP8LColorCacheDelete(VP8LColorCache* const color_cache);
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}
+#endif
+
+#endif  // WEBP_UTILS_COLOR_CACHE_H_