Use sse4.2 CRC32 instructions to hash when available.

include/private/SkChecksum.h

 /*
  * 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;
     }
-
-    /**
-     * Calculate 32-bit Murmur hash (murmur3).
-     * See en.wikipedia.org/wiki/MurmurHash.
-     *
-     *  @param data Memory address of the data block to be processed.
-     *  @param size Size of the data block in bytes.
-     *  @param seed Initial hash seed. (optional)
-     *  @return hash result
-     */
-    static uint32_t Murmur3(const void* data, size_t bytes, uint32_t seed=0);
 };
 
 // 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 SkChecksum::Murmur3(&k, sizeof(K));
+        return SkOpts::hash_fn(&k, sizeof(K), 0);
     }
 
     uint32_t operator()(const SkString& k) const {
-        return SkChecksum::Murmur3(k.c_str(), k.size());
+        return SkOpts::hash_fn(k.c_str(), k.size(), 0);
     }
 };
 
 #endif