Sk4px: Difference and Exclusion

src/opts/Sk4px_SSE2.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.
  */
 
 inline Sk4px::Sk4px(SkPMColor px) : INHERITED(_mm_set1_epi32(px)) {}
 
 inline Sk4px Sk4px::Load4(const SkPMColor px[4]) {
@@ skipping 58 matching lines @@
         as = _mm_or_si128(as, _mm_slli_si128(as, 1));         // __33 __22 __11 __00
         as = _mm_or_si128(as, _mm_slli_si128(as, 2));         // 3333 2222 1111 0000
         return Sk16b(as);
     }
 #endif
 
 inline Sk4px Sk4px::Load2Alphas(const SkAlpha a[2]) {
     uint32_t as = *(const uint16_t*)a;   // Aa -> Aa00
     return Load4Alphas((const SkAlpha*)&as);
 }
+
+inline Sk4px Sk4px::zeroColors() const {
+    return Sk16b(_mm_and_si128(_mm_set1_epi32(0xFF << SK_A32_SHIFT), this->fVec));
+}
+
+inline Sk4px Sk4px::zeroAlphas() const {
+    // andnot(a,b) == ~a & b
+    return Sk16b(_mm_andnot_si128(_mm_set1_epi32(0xFF << SK_A32_SHIFT), this->fVec));
+}