Color dodge and burn with SkPMFloat.

src/core/SkPMFloat.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPM_DEFINED
 #define SkPM_DEFINED
 
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "SkColorPriv.h"
 #include "SkNx.h"
 
 // This file may be included multiple times by .cpp files with different flags, leading
 // to different definitions.  Usually that doesn't matter because it's all inlined, but
 // in Debug modes the compilers may not inline everything.  So wrap everything in an
 // anonymous namespace to give each includer their own silo of this code (or the linker
 // will probably pick one randomly for us, which is rarely correct).
 namespace {
 
 // A pre-multiplied color storing each component in the same order as SkPMColor,
 // but as a float in the range [0, 1].
 class SkPMFloat : public Sk4f {
 public:
     static SkPMFloat FromPMColor(SkPMColor c) { return SkPMFloat(c); }
     static SkPMFloat FromARGB(float a, float r, float g, float b) { return SkPMFloat(a,r,g,b); }
 
+    Sk4f alphas() const;  // argb -> aaaa, generally faster than the equivalent Sk4f(this->a()).
+
     // Uninitialized.
     SkPMFloat() {}
     explicit SkPMFloat(SkPMColor);
     SkPMFloat(float a, float r, float g, float b)
     #ifdef SK_PMCOLOR_IS_RGBA
         : INHERITED(r,g,b,a) {}
     #else
         : INHERITED(b,g,r,a) {}
     #endif
 
@@ skipping 26 matching lines @@
     #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
         #include "../opts/SkPMFloat_sse.h"
     #elif defined(SK_ARM_HAS_NEON)
         #include "../opts/SkPMFloat_neon.h"
     #else
         #include "../opts/SkPMFloat_none.h"
     #endif
 #endif
 
 #endif//SkPM_DEFINED