Revert of De-proc Color32

src/opts/SkBlitRow_opts_arm_neon.cpp

Index: src/opts/SkBlitRow_opts_arm_neon.cpp
diff --git a/src/opts/SkBlitRow_opts_arm_neon.cpp b/src/opts/SkBlitRow_opts_arm_neon.cpp
index 4a6514af7f0d431f0c152b7a85c06f41c6479d61..bd0c45f4c0b84c837877d99ef60779abd4ee39ef 100644
--- a/src/opts/SkBlitRow_opts_arm_neon.cpp
+++ b/src/opts/SkBlitRow_opts_arm_neon.cpp
@@ -1679,6 +1679,69 @@
     }
 }
 
+#define SK_SUPPORT_LEGACY_COLOR32_MATHx
+
+// Color32 and its SIMD specializations use the blend_256_round_alt algorithm
+// from tests/BlendTest.cpp.  It's not quite perfect, but it's never wrong in the
+// interesting edge cases, and it's quite a bit faster than blend_perfect.
+//
+// blend_256_round_alt is our currently blessed algorithm.  Please use it or an analogous one.
+void Color32_arm_neon(SkPMColor* dst, const SkPMColor* src, int count, SkPMColor color) {
+    switch (SkGetPackedA32(color)) {
+        case   0: memmove(dst, src, count * sizeof(SkPMColor)); return;
+        case 255: sk_memset32(dst, color, count);               return;
+    }
+
+    uint16x8_t colorHigh = vshll_n_u8((uint8x8_t)vdup_n_u32(color), 8);
+#ifdef SK_SUPPORT_LEGACY_COLOR32_MATH  // blend_256_plus1_trunc, busted
+    uint16x8_t colorAndRound = colorHigh;
+#else                          // blend_256_round_alt, good
+    uint16x8_t colorAndRound = vaddq_u16(colorHigh, vdupq_n_u16(128));
+#endif
+
+    unsigned invA = 255 - SkGetPackedA32(color);
+#ifdef SK_SUPPORT_LEGACY_COLOR32_MATH  // blend_256_plus1_trunc, busted
+    uint8x8_t invA8 = vdup_n_u8(invA);
+#else                          // blend_256_round_alt, good
+    SkASSERT(invA + (invA >> 7) < 256);  // This next part only works if alpha is not 0.
+    uint8x8_t invA8 = vdup_n_u8(invA + (invA >> 7));
+#endif
+
+    // Does the core work of blending color onto 4 pixels, returning the resulting 4 pixels.
+    auto kernel = [&](const uint32x4_t& src4) -> uint32x4_t {
+        uint16x8_t lo = vmull_u8(vget_low_u8( (uint8x16_t)src4), invA8),
+                   hi = vmull_u8(vget_high_u8((uint8x16_t)src4), invA8);
+        return (uint32x4_t)
+            vcombine_u8(vaddhn_u16(colorAndRound, lo), vaddhn_u16(colorAndRound, hi));
+    };
+
+    while (count >= 8) {
+        uint32x4_t dst0 = kernel(vld1q_u32(src+0)),
+                   dst4 = kernel(vld1q_u32(src+4));
+        vst1q_u32(dst+0, dst0);
+        vst1q_u32(dst+4, dst4);
+        src   += 8;
+        dst   += 8;
+        count -= 8;
+    }
+    if (count >= 4) {
+        vst1q_u32(dst, kernel(vld1q_u32(src)));
+        src   += 4;
+        dst   += 4;
+        count -= 4;
+    }
+    if (count >= 2) {
+        uint32x2_t src2 = vld1_u32(src);
+        vst1_u32(dst, vget_low_u32(kernel(vcombine_u32(src2, src2))));
+        src   += 2;
+        dst   += 2;
+        count -= 2;
+    }
+    if (count >= 1) {
+        vst1q_lane_u32(dst, kernel(vdupq_n_u32(*src)), 0);
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 const SkBlitRow::Proc16 sk_blitrow_platform_565_procs_arm_neon[] = {