Color dodge and burn with SkPMFloat.

src/opts/SkPMFloat_neon.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) {
     SkPMColorAssert(c);
     uint8x8_t   fix8    = (uint8x8_t)vdup_n_u32(c);
     uint16x8_t  fix8_16 = vmovl_u8(fix8);
     uint32x4_t  fix8_32 = vmovl_u16(vget_low_u16(fix8_16));
     fVec = vmulq_f32(vcvtq_f32_u32(fix8_32), vdupq_n_f32(1.0f/255));
     SkASSERT(this->isValid());
 }
 
 inline SkPMColor SkPMFloat::round() const {
     // vcvt_u32_f32 truncates, so we round manually by adding a half before converting.
     float32x4_t rounded = vmlaq_f32(vdupq_n_f32(0.5f), fVec, vdupq_n_f32(255));
     uint32x4_t  fix8_32 = vcvtq_u32_f32(rounded);
     uint16x4_t  fix8_16 = vqmovn_u32(fix8_32);
     uint8x8_t   fix8    = vqmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
     SkPMColor c = vget_lane_u32((uint32x2_t)fix8, 0);
     SkPMColorAssert(c);
     return c;
 }
 
+inline Sk4f SkPMFloat::alphas() const {
+    static_assert(SK_A32_SHIFT == 24, "Assuming little-endian.");
+    return vdupq_lane_f32(vget_high_f32(fVec), 1);  // Duplicate high lane of high half i.e. lane 3.
+}
+
 }  // namespace