Revert of Slim Skia down to just one murmur3 implementation. (https://codereview.chromium.org/376183004/)

Reason for revert:
broke 10.6 compile

[17:13:56.863876] [4/336] CXX obj/src/core/core.SkBBoxHierarchyRecord.o
[17:13:56.863997] FAILED: c++ -MMD -MF obj/src/core/core.SkBBoxRecord.o.d -DSK_INTERNAL -DSK_GAMMA_SRGB -DSK_GAMMA_APPLY_TO_A8 -DSK_SCALAR_TO_FLOAT_EXCLUDED -DSK_ALLOW_STATIC_GLOBAL_INITIALIZERS=1 -DSK_SUPPORT_GPU=1 -DSK_SUPPORT_OPENCL=0 -DSK_FORCE_DISTANCEFIELD_FONTS=0 -DSK_SCALAR_IS_FLOAT -DSK_BUILD_FOR_MAC -DSK_USE_POSIX_THREADS -DSK_RELEASE -DNDEBUG -I../../include/config -I../../include/core -I../../include/pathops -I../../include/pipe -I../../include/ports -I../../include/utils -I../../include/xml -I../../src/core -I../../src/sfnt -I../../src/image -I../../src/opts -I../../src/utils -I../../include/utils/mac -I../../include/gpu -I../../src/gpu -fasm-blocks -mpascal-strings -O3 -gdwarf-2 -Wnewline-eof -mmacosx-version-min=10.6 -arch x86_64 -mssse3 -fvisibility=hidden -fvisibility-inlines-hidden  -c ../../src/core/SkBBoxRecord.cpp -o obj/src/core/core.SkBBoxRecord.o
[17:13:56.864085] In file included from ../../src/core/SkPictureFlat.h:14,
[17:13:56.864130]                  from ../../src/core/SkPictureData.h:14,
[17:13:56.864173]                  from ../../src/core/SkPictureRecord.h:18,
[17:13:56.864217]                  from ../../src/core/SkBBoxRecord.h:12,
[17:13:56.864261]                  from ../../src/core/SkBBoxRecord.cpp:9:
[17:13:56.864336] ../../src/core/SkChecksum.h: In static member function ‘static uint32_t SkChecksum::Compute(const uint32_t*, size_t)’:
[17:13:56.864397] ../../src/core/SkChecksum.h:127: error: invalid conversion from ‘const uint32_t*’ to ‘const uint32_t*’
[17:13:56.864462] ../../src/core/SkChecksum.h:128: error: invalid conversion from ‘const uint32_t*’ to ‘const uint32_t*’
[17:13:56.864510] ../../src/core/SkChecksum.h:129: error: comparison between distinct pointer types ‘const uint32_t*’ and ‘const uint32_t*’ lacks a cast

Original issue's description:
> 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

R=mtklein@google.com, mtklein@chromium.org
TBR=mtklein@chromium.org, mtklein@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Author: reed@google.com

Review URL: https://codereview.chromium.org/381253003

2 files changed, 28 insertions, 8 deletions

diff --git a/src/core/SkChecksum.h b/src/core/SkChecksum.h
index daf87cf62e..fe1e9584a2 100644
--- a/src/core/SkChecksum.h
+++ b/src/core/SkChecksum.h
@@ -51,10 +51,6 @@ public:
         return hash;
     }
 
-    // Remind compiler that our users will be intentionally violating strict aliasing by casting
-    // their data to const uint32_t*, so don't apply any strict-aliasing-based optimizations.
-    typedef uint32_t SK_ATTRIBUTE(may_alias) FourByteAligned;
-
     /**
      * Calculate 32-bit Murmur hash (murmur3).
      * This should take 2-3x longer than SkChecksum::Compute, but is a considerably better hash.
@@ -65,7 +61,7 @@ public:
      *  @param seed Initial hash seed. (optional)
      *  @return hash result
      */
-    static uint32_t Murmur3(const FourByteAligned* data, size_t bytes, uint32_t seed=0) {
+    static uint32_t Murmur3(const uint32_t* data, size_t bytes, uint32_t seed=0) {
         SkASSERTF(SkIsAlign4(bytes), "Expected 4-byte multiple, got %zu", bytes);
         const size_t words = bytes/4;
 
@@ -98,7 +94,7 @@ public:
      *  @param size Size of the data block in bytes. Must be a multiple of 4.
      *  @return checksum result
      */
-    static uint32_t Compute(const FourByteAligned* data, size_t size) {
+    static uint32_t Compute(const uint32_t* data, size_t size) {
         SkASSERT(SkIsAlign4(size));
 
         /*
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index 8a0e734b24..64603b4cb5 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -8,7 +8,6 @@
 #include "SkImageFilter.h"
 
 #include "SkBitmap.h"
-#include "SkChecksum.h"
 #include "SkDevice.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
@@ -335,6 +334,31 @@ 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) {
@@ -357,7 +381,7 @@ private:
             return v.fKey;
         }
         static uint32_t Hash(Key key) {
-            return SkChecksum::Murmur3(reinterpret_cast<const uint32_t*>(&key), sizeof(Key));
+            return compute_hash(reinterpret_cast<const uint32_t*>(&key), sizeof(Key) / sizeof(uint32_t));
         }
     };
     SkTDynamicHash<Value, Key> fData;