Color dodge and burn with SkPMFloat.

src/opts/SkPMFloat_sse.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.
  */
 
 namespace {  // See SkPMFloat.h
 
 inline SkPMFloat::SkPMFloat(SkPMColor c) {
@@ skipping 15 matching lines @@
     // We don't use _mm_cvtps_epi32, because we want precise control over how 0.5 rounds (up).
     __m128 scaled = _mm_mul_ps(_mm_set1_ps(255), fVec);
     __m128i fix8_32 = _mm_cvttps_epi32(_mm_add_ps(_mm_set1_ps(0.5f), scaled)),
             fix8_16 = _mm_packus_epi16(fix8_32, fix8_32),
             fix8    = _mm_packus_epi16(fix8_16, fix8_16);
     SkPMColor c = _mm_cvtsi128_si32(fix8);
     SkPMColorAssert(c);
     return c;
 }
 
+inline Sk4f SkPMFloat::alphas() const {
+    static_assert(SK_A32_SHIFT == 24, "");
+    return _mm_shuffle_ps(fVec, fVec, 0xff);  // Read as 11 11 11 11, copying lane 3 to all lanes.
+}
+
 }  // namespace