1 files changed, 70 insertions, 0 deletions
diff --git a/gfx/skia/skia/include/private/SkChecksum.h b/gfx/skia/skia/include/private/SkChecksum.h
new file mode 100644
index 000000000..8a04c89ae
--- /dev/null
+++ b/gfx/skia/skia/include/private/SkChecksum.h
@@ -0,0 +1,70 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkChecksum_DEFINED
+#define SkChecksum_DEFINED
+
+#include "SkString.h"
+#include "SkTLogic.h"
+#include "SkTypes.h"
+
+// #include "SkOpts.h"
+// It's sort of pesky to be able to include SkOpts.h here, so we'll just re-declare what we need.
+namespace SkOpts {
+    extern uint32_t (*hash_fn)(const void*, size_t, uint32_t);
+}
+
+class SkChecksum : SkNoncopyable {
+public:
+    /**
+     * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
+     * suspect its low bits aren't well mixed.
+     *
+     * This is the Murmur3 finalizer.
+     */
+    static uint32_t Mix(uint32_t hash) {
+        hash ^= hash >> 16;
+        hash *= 0x85ebca6b;
+        hash ^= hash >> 13;
+        hash *= 0xc2b2ae35;
+        hash ^= hash >> 16;
+        return hash;
+    }
+
+    /**
+     * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
+     * suspect its low bits aren't well mixed.
+     *
+     *  This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache.
+     */
+    static uint32_t CheapMix(uint32_t hash) {
+        hash ^= hash >> 16;
+        hash *= 0x85ebca6b;
+        hash ^= hash >> 16;
+        return hash;
+    }
+};
+
+// SkGoodHash should usually be your first choice in hashing data.
+// It should be both reasonably fast and high quality.
+struct SkGoodHash {
+    template <typename K>
+    SK_WHEN(sizeof(K) == 4, uint32_t) operator()(const K& k) const {
+        return SkChecksum::Mix(*(const uint32_t*)&k);
+    }
+
+    template <typename K>
+    SK_WHEN(sizeof(K) != 4, uint32_t) operator()(const K& k) const {
+        return SkOpts::hash_fn(&k, sizeof(K), 0);
+    }
+
+    uint32_t operator()(const SkString& k) const {
+        return SkOpts::hash_fn(k.c_str(), k.size(), 0);
+    }
+};
+
+#endif