From 19fcc7494e68843cb9f2de819a7287ee216e3c5e Mon Sep 17 00:00:00 2001
From: mtklein <mtklein@chromium.org>
Date: Fri, 11 Jul 2014 08:42:17 -0700
Subject: [PATCH] Slim Skia down to just one murmur3 implementation.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/6ac0037b70410ff7d5ce5788bc89314223e1a587

Committed: https://skia.googlesource.com/skia/+/67a3271f0de9ccc32d559b042b862528272047cc

Committed: https://skia.googlesource.com/skia/+/53d435990bdb4d14df78013da45a9364d0287ebe

CQ_EXTRA_TRYBOTS=tryserver.skia:Perf-Mac10.6-MacMini4.1-GeForce320M-x86_64-Release-Trybot
R=reed@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/376183004
---
 src/core/SkChecksum.h      | 23 +++++++++++++++++------
 src/core/SkImageFilter.cpp | 28 ++--------------------------
 2 files changed, 19 insertions(+), 32 deletions(-)

diff --git a/src/core/SkChecksum.h b/src/core/SkChecksum.h
index fe1e958..9f2ebf4 100644
--- a/src/core/SkChecksum.h
+++ b/src/core/SkChecksum.h
@@ -62,12 +62,18 @@ public:
      *  @return hash result
      */
     static uint32_t Murmur3(const uint32_t* data, size_t bytes, uint32_t seed=0) {
+        // Use may_alias to remind the compiler we're intentionally violating strict aliasing,
+        // and so not to apply strict-aliasing-based optimizations.
+        typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t;
+        const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data;
+
         SkASSERTF(SkIsAlign4(bytes), "Expected 4-byte multiple, got %zu", bytes);
         const size_t words = bytes/4;
 
+
         uint32_t hash = seed;
         for (size_t i = 0; i < words; i++) {
-            uint32_t k = data[i];
+            uint32_t k = safe_data[i];
             k *= 0xcc9e2d51;
             k = (k << 15) | (k >> 17);
             k *= 0x1b873593;
@@ -95,6 +101,11 @@ public:
      *  @return checksum result
      */
     static uint32_t Compute(const uint32_t* data, size_t size) {
+        // Use may_alias to remind the compiler we're intentionally violating strict aliasing,
+        // and so not to apply strict-aliasing-based optimizations.
+        typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t;
+        const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data;
+
         SkASSERT(SkIsAlign4(size));
 
         /*
@@ -104,7 +115,7 @@ public:
          *  sizeof()).
          */
         uintptr_t result = 0;
-        const uintptr_t* ptr = reinterpret_cast<const uintptr_t*>(data);
+        const uintptr_t* ptr = reinterpret_cast<const uintptr_t*>(safe_data);
 
         /*
          *  count the number of quad element chunks. This takes into account
@@ -120,10 +131,10 @@ public:
         }
         size &= ((sizeof(uintptr_t) << 2) - 1);
 
-        data = reinterpret_cast<const uint32_t*>(ptr);
-        const uint32_t* stop = data + (size >> 2);
-        while (data < stop) {
-            result = Mash(result, *data++);
+        safe_data = reinterpret_cast<const aliased_uint32_t*>(ptr);
+        const aliased_uint32_t* stop = safe_data + (size >> 2);
+        while (safe_data < stop) {
+            result = Mash(result, *safe_data++);
         }
 
         /*
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index 64603b4..8a0e734 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -8,6 +8,7 @@
 #include "SkImageFilter.h"
 
 #include "SkBitmap.h"
+#include "SkChecksum.h"
 #include "SkDevice.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
@@ -334,31 +335,6 @@ bool SkImageFilter::getInputResultGPU(SkImageFilter::Proxy* proxy,
 }
 #endif
 
-static uint32_t compute_hash(const uint32_t* data, int count) {
-    uint32_t hash = 0;
-
-    for (int i = 0; i < count; ++i) {
-        uint32_t k = data[i];
-        k *= 0xcc9e2d51;
-        k = (k << 15) | (k >> 17);
-        k *= 0x1b873593;
-
-        hash ^= k;
-        hash = (hash << 13) | (hash >> 19);
-        hash *= 5;
-        hash += 0xe6546b64;
-    }
-
-    //    hash ^= size;
-    hash ^= hash >> 16;
-    hash *= 0x85ebca6b;
-    hash ^= hash >> 13;
-    hash *= 0xc2b2ae35;
-    hash ^= hash >> 16;
-
-    return hash;
-}
-
 class CacheImpl : public SkImageFilter::Cache {
 public:
     explicit CacheImpl(int minChildren) : fMinChildren(minChildren) {
@@ -381,7 +357,7 @@ private:
             return v.fKey;
         }
         static uint32_t Hash(Key key) {
-            return compute_hash(reinterpret_cast<const uint32_t*>(&key), sizeof(Key) / sizeof(uint32_t));
+            return SkChecksum::Murmur3(reinterpret_cast<const uint32_t*>(&key), sizeof(Key));
         }
     };
     SkTDynamicHash<Value, Key> fData;
-- 
2.7.4