diff -r 000000000000 -r 6474c204b198 gfx/layers/LayerUtils.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/layers/LayerUtils.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,101 @@
+/* -*- Mode: c++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "LayerUtils.h"
+#include "PremultiplyTables.h"
+#include "mozilla/Endian.h"
+
+namespace mozilla {
+namespace layers {
+
+using namespace mozilla::gfx;
+
+static inline const uint8_t PremultiplyValue(uint8_t a, uint8_t v) {
+  return PremultiplyTable[a*256+v];
+}
+
+static inline const uint8_t UnpremultiplyValue(uint8_t a, uint8_t v) {
+  return UnpremultiplyTable[a*256+v];
+}
+
+#ifdef DEBUG
+static bool IsLittleEndian()
+{
+    // Violate strict aliasing, because violating strict aliasing is how
+    // we always pack and unpack between uint32_t and uint8_t[].
+    uint16_t testShort;
+    static const uint8_t testBytes[2] = { 0xAA, 0xBB };
+    memcpy(&testShort, testBytes, sizeof(testBytes));
+    return testShort == 0xBBAA;
+}
+#endif // DEBUG
+
+#ifdef MOZ_LITTLE_ENDIAN
+#define ASSERT_ENDIAN() MOZ_ASSERT(IsLittleEndian(), "Defined as little endian, but actually big!")
+#else
+#define ASSERT_ENDIAN() MOZ_ASSERT(!IsLittleEndian(), "Defined as big endian, but actually little!")
+#endif
+
+void
+PremultiplySurface(DataSourceSurface* srcSurface,
+                   DataSourceSurface* destSurface)
+{
+  if (!destSurface)
+    destSurface = srcSurface;
+
+  IntSize srcSize = srcSurface->GetSize();
+  MOZ_ASSERT(srcSurface->GetFormat() == destSurface->GetFormat() &&
+             srcSize.width  == destSurface->GetSize().width &&
+             srcSize.height  == destSurface->GetSize().height &&
+             srcSurface->Stride() == destSurface->Stride(),
+             "Source and destination surfaces don't have identical characteristics");
+
+  MOZ_ASSERT(srcSurface->Stride() == srcSize.width * 4,
+             "Source surface stride isn't tightly packed");
+
+  // Only premultiply ARGB32
+  if (srcSurface->GetFormat() != SurfaceFormat::B8G8R8A8) {
+    if (destSurface != srcSurface) {
+      memcpy(destSurface->GetData(), srcSurface->GetData(),
+             srcSurface->Stride() * srcSize.height);
+    }
+    return;
+  }
+
+  uint8_t *src = srcSurface->GetData();
+  uint8_t *dst = destSurface->GetData();
+
+  // Assert that our endian define is correct.
+  ASSERT_ENDIAN();
+
+  uint32_t dim = srcSize.width * srcSize.height;
+  for (uint32_t i = 0; i < dim; ++i) {
+#ifdef MOZ_LITTLE_ENDIAN
+    uint8_t b = *src++;
+    uint8_t g = *src++;
+    uint8_t r = *src++;
+    uint8_t a = *src++;
+
+    *dst++ = PremultiplyValue(a, b);
+    *dst++ = PremultiplyValue(a, g);
+    *dst++ = PremultiplyValue(a, r);
+    *dst++ = a;
+#else
+    uint8_t a = *src++;
+    uint8_t r = *src++;
+    uint8_t g = *src++;
+    uint8_t b = *src++;
+
+    *dst++ = a;
+    *dst++ = PremultiplyValue(a, r);
+    *dst++ = PremultiplyValue(a, g);
+    *dst++ = PremultiplyValue(a, b);
+#endif
+  }
+}
+
+
+}
+}