3-15% speedup to HardLight / Overlay xfermodes.

tests/SkNxTest.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Sk4px.h"
 #include "SkNx.h"
 #include "SkRandom.h"
@@ skipping 174 matching lines @@
 
         // We're a bit more flexible on this method: correct for 0 or 255, otherwise off by <=1.
         int fast = av.approxMulDiv255(bv).kth<0>();
         REPORTER_ASSERT(r, fast-exact >= -1 && fast-exact <= 1);
         if (a == 0 || a == 255 || b == 0 || b == 255) {
             REPORTER_ASSERT(r, fast == exact);
         }
     }
     }
 }
+
+DEF_TEST(Sk4px_widening, r) {
+    SkPMColor colors[] = {
+        SkPreMultiplyColor(0xff00ff00),
+        SkPreMultiplyColor(0x40008000),
+        SkPreMultiplyColor(0x7f020406),
+        SkPreMultiplyColor(0x00000000),
+    };
+    auto packed = Sk4px::Load4(colors);
+
+    auto wideLo = packed.widenLo(),
+         wideHi = packed.widenHi(),
+         wideLoHi    = packed.widenLoHi(),
+         wideLoHiAlt = wideLo + wideHi;
+    REPORTER_ASSERT(r, 0 == memcmp(&wideLoHi, &wideLoHiAlt, sizeof(wideLoHi)));
+}