Port convolve functions to SkOpts

src/opts/SkBitmapFilter_opts.h

Index: src/opts/SkBitmapFilter_opts.h
diff --git a/src/opts/SkBitmapFilter_opts.h b/src/opts/SkBitmapFilter_opts.h
new file mode 100644
index 0000000000000000000000000000000000000000..ccf2e942796775114d78e4d4c954c57c52dd23a0
--- /dev/null
+++ b/src/opts/SkBitmapFilter_opts.h
@@ -0,0 +1,938 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkBitmapFilter_opts_DEFINED
+#define SkBitmapFilter_opts_DEFINED
+
+#include "SkConvolver.h"
+
+namespace SK_OPTS_NS {
+
+#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
+
+#include <emmintrin.h>

[mtklein_C, 2016/11/16 14:24:47]

This will #include the SSE intrinsics into the SK_OPTS_NS namespace (sse2, etc).
 This is somewhat unusual.  It probably will work, but it sort of looks like
we're doing it because we _have_ to.

We usually put this at the top before opening the SK_OPTS_NS namespace.

#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
    #include <immintrin.h>
#endif

[xiangze.zhang, 2016/11/17 02:33:07]

Done.

+
+    static SK_ALWAYS_INLINE void AccumRemainder(const unsigned char* pixelsLeft,
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues, __m128i& accum, int r) {
+        int remainder[4] = {0};
+        for (int i = 0; i < r; i++) {
+            SkConvolutionFilter1D::ConvolutionFixed coeff = filterValues[i];
+            remainder[0] += coeff * pixelsLeft[i * 4 + 0];
+            remainder[1] += coeff * pixelsLeft[i * 4 + 1];
+            remainder[2] += coeff * pixelsLeft[i * 4 + 2];
+            remainder[3] += coeff * pixelsLeft[i * 4 + 3];
+        }
+        __m128i t = _mm_setr_epi32(remainder[0], remainder[1], remainder[2], remainder[3]);
+        accum = _mm_add_epi32(accum, t);
+    }
+
+    // Convolves horizontally along a single row. The row data is given in
+    // |srcData| and continues for the numValues() of the filter.
+    void convolve_horizontally(const unsigned char* srcData,
+                               const SkConvolutionFilter1D& filter,
+                               unsigned char* outRow,
+                               bool /*hasAlpha*/) {
+        // Output one pixel each iteration, calculating all channels (RGBA) together.
+        int numValues = filter.numValues();
+        for (int outX = 0; outX < numValues; outX++) {
+            // Get the filter that determines the current output pixel.
+            int filterOffset, filterLength;
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues =
+                filter.FilterForValue(outX, &filterOffset, &filterLength);
+
+            // Compute the first pixel in this row that the filter affects. It will
+            // touch |filterLength| pixels (4 bytes each) after this.
+            const unsigned char* rowToFilter = &srcData[filterOffset * 4];
+
+            __m128i zero = _mm_setzero_si128();
+            __m128i accum = _mm_setzero_si128();
+
+            // We will load and accumulate with four coefficients per iteration.
+            for (int filterX = 0; filterX < filterLength >> 2; filterX++) {
+                // Load 4 coefficients => duplicate 1st and 2nd of them for all channels.
+                __m128i coeff, coeff16;
+                // [16] xx xx xx xx c3 c2 c1 c0
+                coeff = _mm_loadl_epi64(reinterpret_cast<const __m128i*>(filterValues));
+                // [16] xx xx xx xx c1 c1 c0 c0
+                coeff16 = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(1, 1, 0, 0));
+                // [16] c1 c1 c1 c1 c0 c0 c0 c0
+                coeff16 = _mm_unpacklo_epi16(coeff16, coeff16);
+
+                // Load four pixels => unpack the first two pixels to 16 bits =>
+                // multiply with coefficients => accumulate the convolution result.
+                // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+                __m128i src8 = _mm_loadu_si128(reinterpret_cast<const __m128i*>(rowToFilter));
+                // [16] a1 b1 g1 r1 a0 b0 g0 r0
+                __m128i src16 = _mm_unpacklo_epi8(src8, zero);
+                __m128i mul_hi = _mm_mulhi_epi16(src16, coeff16);
+                __m128i mul_lo = _mm_mullo_epi16(src16, coeff16);
+                // [32]  a0*c0 b0*c0 g0*c0 r0*c0
+                __m128i t = _mm_unpacklo_epi16(mul_lo, mul_hi);
+                accum = _mm_add_epi32(accum, t);
+                // [32]  a1*c1 b1*c1 g1*c1 r1*c1
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);
+                accum = _mm_add_epi32(accum, t);
+
+                // Duplicate 3rd and 4th coefficients for all channels =>
+                // unpack the 3rd and 4th pixels to 16 bits => multiply with coefficients
+                // => accumulate the convolution results.
+                // [16] xx xx xx xx c3 c3 c2 c2
+                coeff16 = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(3, 3, 2, 2));
+                // [16] c3 c3 c3 c3 c2 c2 c2 c2
+                coeff16 = _mm_unpacklo_epi16(coeff16, coeff16);
+                // [16] a3 g3 b3 r3 a2 g2 b2 r2
+                src16 = _mm_unpackhi_epi8(src8, zero);
+                mul_hi = _mm_mulhi_epi16(src16, coeff16);
+                mul_lo = _mm_mullo_epi16(src16, coeff16);
+                // [32]  a2*c2 b2*c2 g2*c2 r2*c2
+                t = _mm_unpacklo_epi16(mul_lo, mul_hi);
+                accum = _mm_add_epi32(accum, t);
+                // [32]  a3*c3 b3*c3 g3*c3 r3*c3
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);
+                accum = _mm_add_epi32(accum, t);
+
+                // Advance the pixel and coefficients pointers.
+                rowToFilter += 16;
+                filterValues += 4;
+            }
+
+            // When |filterLength| is not divisible by 4, we accumulate the last 1 - 3
+            // coefficients one at a time.
+            int r = filterLength & 3;
+            if (r) {
+                int remainderOffset = (filterOffset + filterLength - r) * 4;
+                AccumRemainder(srcData + remainderOffset, filterValues, accum, r);
+            }
+
+            // Shift right for fixed point implementation.
+            accum = _mm_srai_epi32(accum, SkConvolutionFilter1D::kShiftBits);
+
+            // Packing 32 bits |accum| to 16 bits per channel (signed saturation).
+            accum = _mm_packs_epi32(accum, zero);
+            // Packing 16 bits |accum| to 8 bits per channel (unsigned saturation).
+            accum = _mm_packus_epi16(accum, zero);
+
+            // Store the pixel value of 32 bits.
+            *(reinterpret_cast<int*>(outRow)) = _mm_cvtsi128_si32(accum);
+            outRow += 4;
+        }
+    }
+
+    // Convolves horizontally along four rows. The row data is given in
+    // |srcData| and continues for the numValues() of the filter.
+    // The algorithm is almost same as |convolve_horizontally|. Please
+    // refer to that function for detailed comments.
+    void convolve_4_rows_horizontally(const unsigned char* srcData[4],
+                                      const SkConvolutionFilter1D& filter,
+                                      unsigned char* outRow[4],
+                                      size_t outRowBytes) {
+        SkDEBUGCODE(const unsigned char* out_row_0_start = outRow[0];)
+
+        // Output one pixel each iteration, calculating all channels (RGBA) together.
+        int numValues = filter.numValues();
+        for (int outX = 0; outX < numValues; outX++) {
+            int filterOffset, filterLength;
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues =
+                filter.FilterForValue(outX, &filterOffset, &filterLength);
+
+            __m128i zero = _mm_setzero_si128();
+
+            // four pixels in a column per iteration.
+            __m128i accum0 = _mm_setzero_si128();
+            __m128i accum1 = _mm_setzero_si128();
+            __m128i accum2 = _mm_setzero_si128();
+            __m128i accum3 = _mm_setzero_si128();
+
+            int start = filterOffset * 4;
+            // We will load and accumulate with four coefficients per iteration.
+            for (int filterX = 0; filterX < (filterLength >> 2); filterX++) {
+                __m128i coeff, coeff16lo, coeff16hi;
+                // [16] xx xx xx xx c3 c2 c1 c0
+                coeff = _mm_loadl_epi64(reinterpret_cast<const __m128i*>(filterValues));
+                // [16] xx xx xx xx c1 c1 c0 c0
+                coeff16lo = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(1, 1, 0, 0));
+                // [16] c1 c1 c1 c1 c0 c0 c0 c0
+                coeff16lo = _mm_unpacklo_epi16(coeff16lo, coeff16lo);
+                // [16] xx xx xx xx c3 c3 c2 c2
+                coeff16hi = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(3, 3, 2, 2));
+                // [16] c3 c3 c3 c3 c2 c2 c2 c2
+                coeff16hi = _mm_unpacklo_epi16(coeff16hi, coeff16hi);
+
+                __m128i src8, src16, mul_hi, mul_lo, t;
+
+#define ITERATION(src, accum)                                                    \
+                src8 = _mm_loadu_si128(reinterpret_cast<const __m128i*>(src));   \
+                src16 = _mm_unpacklo_epi8(src8, zero);                           \
+                mul_hi = _mm_mulhi_epi16(src16, coeff16lo);                      \
+                mul_lo = _mm_mullo_epi16(src16, coeff16lo);                      \
+                t = _mm_unpacklo_epi16(mul_lo, mul_hi);                          \
+                accum = _mm_add_epi32(accum, t);                                 \
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);                          \
+                accum = _mm_add_epi32(accum, t);                                 \
+                src16 = _mm_unpackhi_epi8(src8, zero);                           \
+                mul_hi = _mm_mulhi_epi16(src16, coeff16hi);                      \
+                mul_lo = _mm_mullo_epi16(src16, coeff16hi);                      \
+                t = _mm_unpacklo_epi16(mul_lo, mul_hi);                          \
+                accum = _mm_add_epi32(accum, t);                                 \
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);                          \
+                accum = _mm_add_epi32(accum, t)
+
+                ITERATION(srcData[0] + start, accum0);
+                ITERATION(srcData[1] + start, accum1);
+                ITERATION(srcData[2] + start, accum2);
+                ITERATION(srcData[3] + start, accum3);
+
+                start += 16;
+                filterValues += 4;
+            }
+
+            int r = filterLength & 3;
+            if (r) {
+                int remainderOffset = (filterOffset + filterLength - r) * 4;
+                AccumRemainder(srcData[0] + remainderOffset, filterValues, accum0, r);
+                AccumRemainder(srcData[1] + remainderOffset, filterValues, accum1, r);
+                AccumRemainder(srcData[2] + remainderOffset, filterValues, accum2, r);
+                AccumRemainder(srcData[3] + remainderOffset, filterValues, accum3, r);
+            }
+
+            accum0 = _mm_srai_epi32(accum0, SkConvolutionFilter1D::kShiftBits);
+            accum0 = _mm_packs_epi32(accum0, zero);
+            accum0 = _mm_packus_epi16(accum0, zero);
+            accum1 = _mm_srai_epi32(accum1, SkConvolutionFilter1D::kShiftBits);
+            accum1 = _mm_packs_epi32(accum1, zero);
+            accum1 = _mm_packus_epi16(accum1, zero);
+            accum2 = _mm_srai_epi32(accum2, SkConvolutionFilter1D::kShiftBits);
+            accum2 = _mm_packs_epi32(accum2, zero);
+            accum2 = _mm_packus_epi16(accum2, zero);
+            accum3 = _mm_srai_epi32(accum3, SkConvolutionFilter1D::kShiftBits);
+            accum3 = _mm_packs_epi32(accum3, zero);
+            accum3 = _mm_packus_epi16(accum3, zero);
+
+            // We seem to be running off the edge here (chromium:491660).
+            SkASSERT(((size_t)outRow[0] - (size_t)out_row_0_start) < outRowBytes);
+
+            *(reinterpret_cast<int*>(outRow[0])) = _mm_cvtsi128_si32(accum0);
+            *(reinterpret_cast<int*>(outRow[1])) = _mm_cvtsi128_si32(accum1);
+            *(reinterpret_cast<int*>(outRow[2])) = _mm_cvtsi128_si32(accum2);
+            *(reinterpret_cast<int*>(outRow[3])) = _mm_cvtsi128_si32(accum3);
+
+            outRow[0] += 4;
+            outRow[1] += 4;
+            outRow[2] += 4;
+            outRow[3] += 4;
+        }
+    }
+
+    // Does vertical convolution to produce one output row. The filter values and
+    // length are given in the first two parameters. These are applied to each
+    // of the rows pointed to in the |sourceDataRows| array, with each row
+    // being |pixelWidth| wide.
+    //
+    // The output must have room for |pixelWidth * 4| bytes.
+    template<bool hasAlpha>
+    void convolveVertically(const SkConvolutionFilter1D::ConvolutionFixed* filterValues,
+                            int filterLength,
+                            unsigned char* const* sourceDataRows,
+                            int pixelWidth,
+                            unsigned char* outRow) {
+        // Output four pixels per iteration (16 bytes).
+        int width = pixelWidth & ~3;
+        __m128i zero = _mm_setzero_si128();
+        for (int outX = 0; outX < width; outX += 4) {
+            // Accumulated result for each pixel. 32 bits per RGBA channel.
+            __m128i accum0 = _mm_setzero_si128();
+            __m128i accum1 = _mm_setzero_si128();
+            __m128i accum2 = _mm_setzero_si128();
+            __m128i accum3 = _mm_setzero_si128();
+
+            // Convolve with one filter coefficient per iteration.
+            for (int filterY = 0; filterY < filterLength; filterY++) {
+
+                // Duplicate the filter coefficient 8 times.
+                // [16] cj cj cj cj cj cj cj cj
+                __m128i coeff16 = _mm_set1_epi16(filterValues[filterY]);
+
+                // Load four pixels (16 bytes) together.
+                // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+                const __m128i* src = reinterpret_cast<const __m128i*>(
+                    &sourceDataRows[filterY][outX << 2]);
+                __m128i src8 = _mm_loadu_si128(src);
+
+                // Unpack 1st and 2nd pixels from 8 bits to 16 bits for each channels =>
+                // multiply with current coefficient => accumulate the result.
+                // [16] a1 b1 g1 r1 a0 b0 g0 r0
+                __m128i src16 = _mm_unpacklo_epi8(src8, zero);
+                __m128i mul_hi = _mm_mulhi_epi16(src16, coeff16);
+                __m128i mul_lo = _mm_mullo_epi16(src16, coeff16);
+                // [32] a0 b0 g0 r0
+                __m128i t = _mm_unpacklo_epi16(mul_lo, mul_hi);
+                accum0 = _mm_add_epi32(accum0, t);
+                // [32] a1 b1 g1 r1
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);
+                accum1 = _mm_add_epi32(accum1, t);
+
+                // Unpack 3rd and 4th pixels from 8 bits to 16 bits for each channels =>
+                // multiply with current coefficient => accumulate the result.
+                // [16] a3 b3 g3 r3 a2 b2 g2 r2
+                src16 = _mm_unpackhi_epi8(src8, zero);
+                mul_hi = _mm_mulhi_epi16(src16, coeff16);
+                mul_lo = _mm_mullo_epi16(src16, coeff16);
+                // [32] a2 b2 g2 r2
+                t = _mm_unpacklo_epi16(mul_lo, mul_hi);
+                accum2 = _mm_add_epi32(accum2, t);
+                // [32] a3 b3 g3 r3
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);
+                accum3 = _mm_add_epi32(accum3, t);
+            }
+
+            // Shift right for fixed point implementation.
+            accum0 = _mm_srai_epi32(accum0, SkConvolutionFilter1D::kShiftBits);
+            accum1 = _mm_srai_epi32(accum1, SkConvolutionFilter1D::kShiftBits);
+            accum2 = _mm_srai_epi32(accum2, SkConvolutionFilter1D::kShiftBits);
+            accum3 = _mm_srai_epi32(accum3, SkConvolutionFilter1D::kShiftBits);
+
+            // Packing 32 bits |accum| to 16 bits per channel (signed saturation).
+            // [16] a1 b1 g1 r1 a0 b0 g0 r0
+            accum0 = _mm_packs_epi32(accum0, accum1);
+            // [16] a3 b3 g3 r3 a2 b2 g2 r2
+            accum2 = _mm_packs_epi32(accum2, accum3);
+
+            // Packing 16 bits |accum| to 8 bits per channel (unsigned saturation).
+            // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+            accum0 = _mm_packus_epi16(accum0, accum2);
+
+            if (hasAlpha) {
+                // Compute the max(ri, gi, bi) for each pixel.
+                // [8] xx a3 b3 g3 xx a2 b2 g2 xx a1 b1 g1 xx a0 b0 g0
+                __m128i a = _mm_srli_epi32(accum0, 8);
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                __m128i b = _mm_max_epu8(a, accum0);  // Max of r and g.
+                // [8] xx xx a3 b3 xx xx a2 b2 xx xx a1 b1 xx xx a0 b0
+                a = _mm_srli_epi32(accum0, 16);
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                b = _mm_max_epu8(a, b);  // Max of r and g and b.
+                // [8] max3 00 00 00 max2 00 00 00 max1 00 00 00 max0 00 00 00
+                b = _mm_slli_epi32(b, 24);
+
+                // Make sure the value of alpha channel is always larger than maximum
+                // value of color channels.
+                accum0 = _mm_max_epu8(b, accum0);
+            } else {
+                // Set value of alpha channels to 0xFF.
+                __m128i mask = _mm_set1_epi32(0xff000000);
+                accum0 = _mm_or_si128(accum0, mask);
+            }
+
+            // Store the convolution result (16 bytes) and advance the pixel pointers.
+            _mm_storeu_si128(reinterpret_cast<__m128i*>(outRow), accum0);
+            outRow += 16;
+        }
+
+        // When the width of the output is not divisible by 4, We need to save one
+        // pixel (4 bytes) each time. And also the fourth pixel is always absent.
+        int r = pixelWidth & 3;
+        if (r) {
+            __m128i accum0 = _mm_setzero_si128();
+            __m128i accum1 = _mm_setzero_si128();
+            __m128i accum2 = _mm_setzero_si128();
+            for (int filterY = 0; filterY < filterLength; ++filterY) {
+                __m128i coeff16 = _mm_set1_epi16(filterValues[filterY]);
+                // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+                const __m128i* src = reinterpret_cast<const __m128i*>(
+                    &sourceDataRows[filterY][width << 2]);
+                __m128i src8 = _mm_loadu_si128(src);
+                // [16] a1 b1 g1 r1 a0 b0 g0 r0
+                __m128i src16 = _mm_unpacklo_epi8(src8, zero);
+                __m128i mul_hi = _mm_mulhi_epi16(src16, coeff16);
+                __m128i mul_lo = _mm_mullo_epi16(src16, coeff16);
+                // [32] a0 b0 g0 r0
+                __m128i t = _mm_unpacklo_epi16(mul_lo, mul_hi);
+                accum0 = _mm_add_epi32(accum0, t);
+                // [32] a1 b1 g1 r1
+                t = _mm_unpackhi_epi16(mul_lo, mul_hi);
+                accum1 = _mm_add_epi32(accum1, t);
+                // [16] a3 b3 g3 r3 a2 b2 g2 r2
+                src16 = _mm_unpackhi_epi8(src8, zero);
+                mul_hi = _mm_mulhi_epi16(src16, coeff16);
+                mul_lo = _mm_mullo_epi16(src16, coeff16);
+                // [32] a2 b2 g2 r2
+                t = _mm_unpacklo_epi16(mul_lo, mul_hi);
+                accum2 = _mm_add_epi32(accum2, t);
+            }
+
+            accum0 = _mm_srai_epi32(accum0, SkConvolutionFilter1D::kShiftBits);
+            accum1 = _mm_srai_epi32(accum1, SkConvolutionFilter1D::kShiftBits);
+            accum2 = _mm_srai_epi32(accum2, SkConvolutionFilter1D::kShiftBits);
+            // [16] a1 b1 g1 r1 a0 b0 g0 r0
+            accum0 = _mm_packs_epi32(accum0, accum1);
+            // [16] a3 b3 g3 r3 a2 b2 g2 r2
+            accum2 = _mm_packs_epi32(accum2, zero);
+            // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+            accum0 = _mm_packus_epi16(accum0, accum2);
+            if (hasAlpha) {
+                // [8] xx a3 b3 g3 xx a2 b2 g2 xx a1 b1 g1 xx a0 b0 g0
+                __m128i a = _mm_srli_epi32(accum0, 8);
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                __m128i b = _mm_max_epu8(a, accum0);  // Max of r and g.
+                // [8] xx xx a3 b3 xx xx a2 b2 xx xx a1 b1 xx xx a0 b0
+                a = _mm_srli_epi32(accum0, 16);
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                b = _mm_max_epu8(a, b);  // Max of r and g and b.
+                // [8] max3 00 00 00 max2 00 00 00 max1 00 00 00 max0 00 00 00
+                b = _mm_slli_epi32(b, 24);
+                accum0 = _mm_max_epu8(b, accum0);
+            } else {
+                __m128i mask = _mm_set1_epi32(0xff000000);
+                accum0 = _mm_or_si128(accum0, mask);
+            }
+
+            for (int i = 0; i < r; i++) {
+                *(reinterpret_cast<int*>(outRow)) = _mm_cvtsi128_si32(accum0);
+                accum0 = _mm_srli_si128(accum0, 4);
+                outRow += 4;
+            }
+        }
+    }
+
+#elif defined(SK_ARM_HAS_NEON)
+
+#include <arm_neon.h>

[mtklein_C, 2016/11/16 14:24:47]

Same deal with emmintrin.  It's probably best to put the include outside the
namespace.

[xiangze.zhang, 2016/11/17 02:33:07]

Done.

+
+    static SK_ALWAYS_INLINE void AccumRemainder(const unsigned char* pixelsLeft,
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues, int32x4_t& accum, int r) {
+        int remainder[4] = {0};
+        for (int i = 0; i < r; i++) {
+            SkConvolutionFilter1D::ConvolutionFixed coeff = filterValues[i];
+            remainder[0] += coeff * pixelsLeft[i * 4 + 0];
+            remainder[1] += coeff * pixelsLeft[i * 4 + 1];
+            remainder[2] += coeff * pixelsLeft[i * 4 + 2];
+            remainder[3] += coeff * pixelsLeft[i * 4 + 3];
+        }
+        int32x4_t t = {remainder[0], remainder[1], remainder[2], remainder[3]};
+        accum += t;
+    }
+
+    // Convolves horizontally along a single row. The row data is given in
+    // |srcData| and continues for the numValues() of the filter.
+    void convolve_horizontally(const unsigned char* srcData,
+                               const SkConvolutionFilter1D& filter,
+                               unsigned char* outRow,
+                               bool /*hasAlpha*/) {
+        // Loop over each pixel on this row in the output image.
+        int numValues = filter.numValues();
+        for (int outX = 0; outX < numValues; outX++) {
+            uint8x8_t coeff_mask0 = vcreate_u8(0x0100010001000100);
+            uint8x8_t coeff_mask1 = vcreate_u8(0x0302030203020302);
+            uint8x8_t coeff_mask2 = vcreate_u8(0x0504050405040504);
+            uint8x8_t coeff_mask3 = vcreate_u8(0x0706070607060706);
+            // Get the filter that determines the current output pixel.
+            int filterOffset, filterLength;
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues =
+                filter.FilterForValue(outX, &filterOffset, &filterLength);
+
+            // Compute the first pixel in this row that the filter affects. It will
+            // touch |filterLength| pixels (4 bytes each) after this.
+            const unsigned char* rowToFilter = &srcData[filterOffset * 4];
+
+            // Apply the filter to the row to get the destination pixel in |accum|.
+            int32x4_t accum = vdupq_n_s32(0);
+            for (int filterX = 0; filterX < filterLength >> 2; filterX++) {
+                // Load 4 coefficients
+                int16x4_t coeffs, coeff0, coeff1, coeff2, coeff3;
+                coeffs = vld1_s16(filterValues);
+                coeff0 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask0));
+                coeff1 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask1));
+                coeff2 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask2));
+                coeff3 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask3));
+
+                // Load pixels and calc
+                uint8x16_t pixels = vld1q_u8(rowToFilter);
+                int16x8_t p01_16 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(pixels)));
+                int16x8_t p23_16 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(pixels)));
+
+                int16x4_t p0_src = vget_low_s16(p01_16);
+                int16x4_t p1_src = vget_high_s16(p01_16);
+                int16x4_t p2_src = vget_low_s16(p23_16);
+                int16x4_t p3_src = vget_high_s16(p23_16);
+
+                int32x4_t p0 = vmull_s16(p0_src, coeff0);
+                int32x4_t p1 = vmull_s16(p1_src, coeff1);
+                int32x4_t p2 = vmull_s16(p2_src, coeff2);
+                int32x4_t p3 = vmull_s16(p3_src, coeff3);
+
+                accum += p0;
+                accum += p1;
+                accum += p2;
+                accum += p3;
+
+                // Advance the pointers
+                rowToFilter += 16;
+                filterValues += 4;
+            }
+
+            int r = filterLength & 3;
+            if (r) {
+                int remainder_offset = (filterOffset + filterLength - r) * 4;
+                AccumRemainder(srcData + remainder_offset, filterValues, accum, r);
+            }
+
+            // Bring this value back in range. All of the filter scaling factors
+            // are in fixed point with kShiftBits bits of fractional part.
+            accum = vshrq_n_s32(accum, SkConvolutionFilter1D::kShiftBits);
+
+            // Pack and store the new pixel.
+            int16x4_t accum16 = vqmovn_s32(accum);
+            uint8x8_t accum8 = vqmovun_s16(vcombine_s16(accum16, accum16));
+            vst1_lane_u32(reinterpret_cast<uint32_t*>(outRow), vreinterpret_u32_u8(accum8), 0);
+            outRow += 4;
+        }
+    }
+
+    // Convolves horizontally along four rows. The row data is given in
+    // |srcData| and continues for the numValues() of the filter.
+    // The algorithm is almost same as |convolve_horizontally|. Please
+    // refer to that function for detailed comments.
+    void convolve_4_rows_horizontally(const unsigned char* srcData[4],
+                                      const SkConvolutionFilter1D& filter,
+                                      unsigned char* outRow[4],
+                                      size_t outRowBytes) {
+        // Output one pixel each iteration, calculating all channels (RGBA) together.
+        int numValues = filter.numValues();
+        for (int outX = 0; outX < numValues; outX++) {
+
+            int filterOffset, filterLength;
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues =
+            filter.FilterForValue(outX, &filterOffset, &filterLength);
+
+            // four pixels in a column per iteration.
+            int32x4_t accum0 = vdupq_n_s32(0);
+            int32x4_t accum1 = vdupq_n_s32(0);
+            int32x4_t accum2 = vdupq_n_s32(0);
+            int32x4_t accum3 = vdupq_n_s32(0);
+
+            uint8x8_t coeff_mask0 = vcreate_u8(0x0100010001000100);
+            uint8x8_t coeff_mask1 = vcreate_u8(0x0302030203020302);
+            uint8x8_t coeff_mask2 = vcreate_u8(0x0504050405040504);
+            uint8x8_t coeff_mask3 = vcreate_u8(0x0706070607060706);
+
+            int start = filterOffset * 4;
+
+            // We will load and accumulate with four coefficients per iteration.
+            for (int filterX = 0; filterX < (filterLength >> 2); filterX++) {
+                int16x4_t coeffs, coeff0, coeff1, coeff2, coeff3;
+
+                coeffs = vld1_s16(filterValues);
+                coeff0 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask0));
+                coeff1 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask1));
+                coeff2 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask2));
+                coeff3 = vreinterpret_s16_u8(vtbl1_u8(vreinterpret_u8_s16(coeffs), coeff_mask3));
+
+                uint8x16_t pixels;
+                int16x8_t p01_16, p23_16;
+                int32x4_t p0, p1, p2, p3;
+
+#define ITERATION(src, accum)                                                   \
+                pixels = vld1q_u8(src);                                         \
+                p01_16 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(pixels)));  \
+                p23_16 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(pixels))); \
+                p0 = vmull_s16(vget_low_s16(p01_16), coeff0);                   \
+                p1 = vmull_s16(vget_high_s16(p01_16), coeff1);                  \
+                p2 = vmull_s16(vget_low_s16(p23_16), coeff2);                   \
+                p3 = vmull_s16(vget_high_s16(p23_16), coeff3);                  \
+                accum += p0;                                                    \
+                accum += p1;                                                    \
+                accum += p2;                                                    \
+                accum += p3
+
+                ITERATION(srcData[0] + start, accum0);
+                ITERATION(srcData[1] + start, accum1);
+                ITERATION(srcData[2] + start, accum2);
+                ITERATION(srcData[3] + start, accum3);
+
+                start += 16;
+                filterValues += 4;
+            }
+
+            int r = filterLength & 3;
+            if (r) {
+                int remainder_offset = (filterOffset + filterLength - r) * 4;
+                AccumRemainder(srcData[0] + remainder_offset, filterValues, accum0, r);
+                AccumRemainder(srcData[1] + remainder_offset, filterValues, accum1, r);
+                AccumRemainder(srcData[2] + remainder_offset, filterValues, accum2, r);
+                AccumRemainder(srcData[3] + remainder_offset, filterValues, accum3, r);
+            }
+
+            int16x4_t accum16;
+            uint8x8_t res0, res1, res2, res3;
+
+#define PACK_RESULT(accum, res)                                             \
+            accum = vshrq_n_s32(accum, SkConvolutionFilter1D::kShiftBits);  \
+            accum16 = vqmovn_s32(accum);                                    \
+            res = vqmovun_s16(vcombine_s16(accum16, accum16));
+
+            PACK_RESULT(accum0, res0);
+            PACK_RESULT(accum1, res1);
+            PACK_RESULT(accum2, res2);
+            PACK_RESULT(accum3, res3);
+
+            vst1_lane_u32(reinterpret_cast<uint32_t*>(outRow[0]), vreinterpret_u32_u8(res0), 0);
+            vst1_lane_u32(reinterpret_cast<uint32_t*>(outRow[1]), vreinterpret_u32_u8(res1), 0);
+            vst1_lane_u32(reinterpret_cast<uint32_t*>(outRow[2]), vreinterpret_u32_u8(res2), 0);
+            vst1_lane_u32(reinterpret_cast<uint32_t*>(outRow[3]), vreinterpret_u32_u8(res3), 0);
+            outRow[0] += 4;
+            outRow[1] += 4;
+            outRow[2] += 4;
+            outRow[3] += 4;
+        }
+    }
+
+
+    // Does vertical convolution to produce one output row. The filter values and
+    // length are given in the first two parameters. These are applied to each
+    // of the rows pointed to in the |sourceDataRows| array, with each row
+    // being |pixelWidth| wide.
+    //
+    // The output must have room for |pixelWidth * 4| bytes.
+    template<bool hasAlpha>
+    void convolveVertically(const SkConvolutionFilter1D::ConvolutionFixed* filterValues,
+                            int filterLength,
+                            unsigned char* const* sourceDataRows,
+                            int pixelWidth,
+                            unsigned char* outRow) {
+        int width = pixelWidth & ~3;
+
+        // Output four pixels per iteration (16 bytes).
+        for (int outX = 0; outX < width; outX += 4) {
+
+            // Accumulated result for each pixel. 32 bits per RGBA channel.
+            int32x4_t accum0 = vdupq_n_s32(0);
+            int32x4_t accum1 = vdupq_n_s32(0);
+            int32x4_t accum2 = vdupq_n_s32(0);
+            int32x4_t accum3 = vdupq_n_s32(0);
+
+            // Convolve with one filter coefficient per iteration.
+            for (int filterY = 0; filterY < filterLength; filterY++) {
+
+                // Duplicate the filter coefficient 4 times.
+                // [16] cj cj cj cj
+                int16x4_t coeff16 = vdup_n_s16(filterValues[filterY]);
+
+                // Load four pixels (16 bytes) together.
+                // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+                uint8x16_t src8 = vld1q_u8(&sourceDataRows[filterY][outX << 2]);
+
+                int16x8_t src16_01 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(src8)));
+                int16x8_t src16_23 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(src8)));
+                int16x4_t src16_0 = vget_low_s16(src16_01);
+                int16x4_t src16_1 = vget_high_s16(src16_01);
+                int16x4_t src16_2 = vget_low_s16(src16_23);
+                int16x4_t src16_3 = vget_high_s16(src16_23);
+
+                accum0 += vmull_s16(src16_0, coeff16);
+                accum1 += vmull_s16(src16_1, coeff16);
+                accum2 += vmull_s16(src16_2, coeff16);
+                accum3 += vmull_s16(src16_3, coeff16);
+            }
+
+            // Shift right for fixed point implementation.
+            accum0 = vshrq_n_s32(accum0, SkConvolutionFilter1D::kShiftBits);
+            accum1 = vshrq_n_s32(accum1, SkConvolutionFilter1D::kShiftBits);
+            accum2 = vshrq_n_s32(accum2, SkConvolutionFilter1D::kShiftBits);
+            accum3 = vshrq_n_s32(accum3, SkConvolutionFilter1D::kShiftBits);
+
+            // Packing 32 bits |accum| to 16 bits per channel (signed saturation).
+            // [16] a1 b1 g1 r1 a0 b0 g0 r0
+            int16x8_t accum16_0 = vcombine_s16(vqmovn_s32(accum0), vqmovn_s32(accum1));
+            // [16] a3 b3 g3 r3 a2 b2 g2 r2
+            int16x8_t accum16_1 = vcombine_s16(vqmovn_s32(accum2), vqmovn_s32(accum3));
+
+            // Packing 16 bits |accum| to 8 bits per channel (unsigned saturation).
+            // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+            uint8x16_t accum8 = vcombine_u8(vqmovun_s16(accum16_0), vqmovun_s16(accum16_1));
+
+            if (hasAlpha) {
+                // Compute the max(ri, gi, bi) for each pixel.
+                // [8] xx a3 b3 g3 xx a2 b2 g2 xx a1 b1 g1 xx a0 b0 g0
+                uint8x16_t a = vreinterpretq_u8_u32(vshrq_n_u32(vreinterpretq_u32_u8(accum8), 8));
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                uint8x16_t b = vmaxq_u8(a, accum8); // Max of r and g
+                // [8] xx xx a3 b3 xx xx a2 b2 xx xx a1 b1 xx xx a0 b0
+                a = vreinterpretq_u8_u32(vshrq_n_u32(vreinterpretq_u32_u8(accum8), 16));
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                b = vmaxq_u8(a, b); // Max of r and g and b.
+                // [8] max3 00 00 00 max2 00 00 00 max1 00 00 00 max0 00 00 00
+                b = vreinterpretq_u8_u32(vshlq_n_u32(vreinterpretq_u32_u8(b), 24));
+
+                // Make sure the value of alpha channel is always larger than maximum
+                // value of color channels.
+                accum8 = vmaxq_u8(b, accum8);
+            } else {
+                // Set value of alpha channels to 0xFF.
+                accum8 = vreinterpretq_u8_u32(vreinterpretq_u32_u8(accum8) | vdupq_n_u32(0xFF000000));
+            }
+
+            // Store the convolution result (16 bytes) and advance the pixel pointers.
+            vst1q_u8(outRow, accum8);
+            outRow += 16;
+        }
+
+        // Process the leftovers when the width of the output is not divisible
+        // by 4, that is at most 3 pixels.
+        int r = pixelWidth & 3;
+        if (r) {
+
+            int32x4_t accum0 = vdupq_n_s32(0);
+            int32x4_t accum1 = vdupq_n_s32(0);
+            int32x4_t accum2 = vdupq_n_s32(0);
+
+            for (int filterY = 0; filterY < filterLength; ++filterY) {
+                int16x4_t coeff16 = vdup_n_s16(filterValues[filterY]);
+
+                // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+                uint8x16_t src8 = vld1q_u8(&sourceDataRows[filterY][width << 2]);
+
+                int16x8_t src16_01 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(src8)));
+                int16x8_t src16_23 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(src8)));
+                int16x4_t src16_0 = vget_low_s16(src16_01);
+                int16x4_t src16_1 = vget_high_s16(src16_01);
+                int16x4_t src16_2 = vget_low_s16(src16_23);
+
+                accum0 += vmull_s16(src16_0, coeff16);
+                accum1 += vmull_s16(src16_1, coeff16);
+                accum2 += vmull_s16(src16_2, coeff16);
+            }
+
+            accum0 = vshrq_n_s32(accum0, SkConvolutionFilter1D::kShiftBits);
+            accum1 = vshrq_n_s32(accum1, SkConvolutionFilter1D::kShiftBits);
+            accum2 = vshrq_n_s32(accum2, SkConvolutionFilter1D::kShiftBits);
+
+            int16x8_t accum16_0 = vcombine_s16(vqmovn_s32(accum0), vqmovn_s32(accum1));
+            int16x8_t accum16_1 = vcombine_s16(vqmovn_s32(accum2), vqmovn_s32(accum2));
+
+            uint8x16_t accum8 = vcombine_u8(vqmovun_s16(accum16_0), vqmovun_s16(accum16_1));
+
+            if (hasAlpha) {
+                // Compute the max(ri, gi, bi) for each pixel.
+                // [8] xx a3 b3 g3 xx a2 b2 g2 xx a1 b1 g1 xx a0 b0 g0
+                uint8x16_t a = vreinterpretq_u8_u32(vshrq_n_u32(vreinterpretq_u32_u8(accum8), 8));
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                uint8x16_t b = vmaxq_u8(a, accum8); // Max of r and g
+                // [8] xx xx a3 b3 xx xx a2 b2 xx xx a1 b1 xx xx a0 b0
+                a = vreinterpretq_u8_u32(vshrq_n_u32(vreinterpretq_u32_u8(accum8), 16));
+                // [8] xx xx xx max3 xx xx xx max2 xx xx xx max1 xx xx xx max0
+                b = vmaxq_u8(a, b); // Max of r and g and b.
+                // [8] max3 00 00 00 max2 00 00 00 max1 00 00 00 max0 00 00 00
+                b = vreinterpretq_u8_u32(vshlq_n_u32(vreinterpretq_u32_u8(b), 24));
+
+                // Make sure the value of alpha channel is always larger than maximum
+                // value of color channels.
+                accum8 = vmaxq_u8(b, accum8);
+            } else {
+                // Set value of alpha channels to 0xFF.
+                accum8 = vreinterpretq_u8_u32(vreinterpretq_u32_u8(accum8) | vdupq_n_u32(0xFF000000));
+            }
+
+            switch(r) {
+            case 1:
+                vst1q_lane_u32(reinterpret_cast<uint32_t*>(outRow), vreinterpretq_u32_u8(accum8), 0);
+                break;
+            case 2:
+                vst1_u32(reinterpret_cast<uint32_t*>(outRow),
+                         vreinterpret_u32_u8(vget_low_u8(accum8)));
+                break;
+            case 3:
+                vst1_u32(reinterpret_cast<uint32_t*>(outRow),
+                         vreinterpret_u32_u8(vget_low_u8(accum8)));
+                vst1q_lane_u32(reinterpret_cast<uint32_t*>(outRow+8), vreinterpretq_u32_u8(accum8), 2);
+                break;
+            }
+        }
+    }
+
+#else
+
+    // Converts the argument to an 8-bit unsigned value by clamping to the range
+    // 0-255.
+    inline unsigned char ClampTo8(int a) {
+        if (static_cast<unsigned>(a) < 256) {
+            return a;  // Avoid the extra check in the common case.
+        }
+        if (a < 0) {
+            return 0;
+        }
+        return 255;
+    }
+
+    // Convolves horizontally along a single row. The row data is given in
+    // |srcData| and continues for the numValues() of the filter.
+    template<bool hasAlpha>
+    void ConvolveHorizontally(const unsigned char* srcData,
+                              const SkConvolutionFilter1D& filter,
+                              unsigned char* outRow) {
+        // Loop over each pixel on this row in the output image.
+        int numValues = filter.numValues();
+        for (int outX = 0; outX < numValues; outX++) {
+            // Get the filter that determines the current output pixel.
+            int filterOffset, filterLength;
+            const SkConvolutionFilter1D::ConvolutionFixed* filterValues =
+                filter.FilterForValue(outX, &filterOffset, &filterLength);
+
+            // Compute the first pixel in this row that the filter affects. It will
+            // touch |filterLength| pixels (4 bytes each) after this.
+            const unsigned char* rowToFilter = &srcData[filterOffset * 4];
+
+            // Apply the filter to the row to get the destination pixel in |accum|.
+            int accum[4] = {0};
+            for (int filterX = 0; filterX < filterLength; filterX++) {
+                SkConvolutionFilter1D::ConvolutionFixed curFilter = filterValues[filterX];
+                accum[0] += curFilter * rowToFilter[filterX * 4 + 0];
+                accum[1] += curFilter * rowToFilter[filterX * 4 + 1];
+                accum[2] += curFilter * rowToFilter[filterX * 4 + 2];
+                if (hasAlpha) {
+                    accum[3] += curFilter * rowToFilter[filterX * 4 + 3];
+                }
+            }
+
+            // Bring this value back in range. All of the filter scaling factors
+            // are in fixed point with kShiftBits bits of fractional part.
+            accum[0] >>= SkConvolutionFilter1D::kShiftBits;
+            accum[1] >>= SkConvolutionFilter1D::kShiftBits;
+            accum[2] >>= SkConvolutionFilter1D::kShiftBits;
+            if (hasAlpha) {
+                accum[3] >>= SkConvolutionFilter1D::kShiftBits;
+            }
+
+            // Store the new pixel.
+            outRow[outX * 4 + 0] = ClampTo8(accum[0]);
+            outRow[outX * 4 + 1] = ClampTo8(accum[1]);
+            outRow[outX * 4 + 2] = ClampTo8(accum[2]);
+            if (hasAlpha) {
+                outRow[outX * 4 + 3] = ClampTo8(accum[3]);
+            }
+        }
+    }
+
+    // Does vertical convolution to produce one output row. The filter values and
+    // length are given in the first two parameters. These are applied to each
+    // of the rows pointed to in the |sourceDataRows| array, with each row
+    // being |pixelWidth| wide.
+    //
+    // The output must have room for |pixelWidth * 4| bytes.
+    template<bool hasAlpha>
+    void ConvolveVertically(const SkConvolutionFilter1D::ConvolutionFixed* filterValues,
+                            int filterLength,
+                            unsigned char* const* sourceDataRows,
+                            int pixelWidth,
+                            unsigned char* outRow) {
+        // We go through each column in the output and do a vertical convolution,
+        // generating one output pixel each time.
+        for (int outX = 0; outX < pixelWidth; outX++) {
+            // Compute the number of bytes over in each row that the current column
+            // we're convolving starts at. The pixel will cover the next 4 bytes.
+            int byteOffset = outX * 4;
+
+            // Apply the filter to one column of pixels.
+            int accum[4] = {0};
+            for (int filterY = 0; filterY < filterLength; filterY++) {
+                SkConvolutionFilter1D::ConvolutionFixed curFilter = filterValues[filterY];
+                accum[0] += curFilter * sourceDataRows[filterY][byteOffset + 0];
+                accum[1] += curFilter * sourceDataRows[filterY][byteOffset + 1];
+                accum[2] += curFilter * sourceDataRows[filterY][byteOffset + 2];
+                if (hasAlpha) {
+                    accum[3] += curFilter * sourceDataRows[filterY][byteOffset + 3];
+                }
+            }
+
+            // Bring this value back in range. All of the filter scaling factors
+            // are in fixed point with kShiftBits bits of precision.
+            accum[0] >>= SkConvolutionFilter1D::kShiftBits;
+            accum[1] >>= SkConvolutionFilter1D::kShiftBits;
+            accum[2] >>= SkConvolutionFilter1D::kShiftBits;
+            if (hasAlpha) {
+                accum[3] >>= SkConvolutionFilter1D::kShiftBits;
+            }
+
+            // Store the new pixel.
+            outRow[byteOffset + 0] = ClampTo8(accum[0]);
+            outRow[byteOffset + 1] = ClampTo8(accum[1]);
+            outRow[byteOffset + 2] = ClampTo8(accum[2]);
+            if (hasAlpha) {
+                unsigned char alpha = ClampTo8(accum[3]);
+
+                // Make sure the alpha channel doesn't come out smaller than any of the
+                // color channels. We use premultipled alpha channels, so this should
+                // never happen, but rounding errors will cause this from time to time.
+                // These "impossible" colors will cause overflows (and hence random pixel
+                // values) when the resulting bitmap is drawn to the screen.
+                //
+                // We only need to do this when generating the final output row (here).
+                int maxColorChannel = SkTMax(outRow[byteOffset + 0],
+                                               SkTMax(outRow[byteOffset + 1],
+                                                      outRow[byteOffset + 2]));
+                if (alpha < maxColorChannel) {
+                    outRow[byteOffset + 3] = maxColorChannel;
+                } else {
+                    outRow[byteOffset + 3] = alpha;
+                }
+            } else {
+                // No alpha channel, the image is opaque.
+                outRow[byteOffset + 3] = 0xff;
+            }
+        }
+    }
+
+    // There's a bug somewhere here with GCC autovectorization (-ftree-vectorize).  We originally
+    // thought this was 32 bit only, but subsequent tests show that some 64 bit gcc compiles
+    // suffer here too.
+    //
+    // Dropping to -O2 disables -ftree-vectorize.  GCC 4.6 needs noinline.  https://bug.skia.org/2575
+#if SK_HAS_ATTRIBUTE(optimize) && defined(SK_RELEASE)
+        #define SK_MAYBE_DISABLE_VECTORIZATION __attribute__((optimize("O2"), noinline))
+#else
+        #define SK_MAYBE_DISABLE_VECTORIZATION
+#endif
+
+    SK_MAYBE_DISABLE_VECTORIZATION
+    void convolve_horizontally(const unsigned char* srcData,
+                               const SkConvolutionFilter1D& filter,
+                               unsigned char* outRow,
+                               bool has_alpha) {
+        if (has_alpha) {
+            ConvolveHorizontally<true>(srcData, filter, outRow);
+        } else {
+            ConvolveHorizontally<false>(srcData, filter, outRow);
+        }
+    }
+#undef SK_MAYBE_DISABLE_VECTORIZATION
+
+    void (*convolve_4_rows_horizontally)(const unsigned char* src_data[4],

[mtklein_C, 2016/11/16 14:24:47]

Do you think it'd make the calling code clearer to just implement this in terms
of convolve_horizontally?  (Maybe that's best left as a follow up.)

[xiangze.zhang, 2016/11/17 02:33:07]

The calling code can check and allocate a smaller row buffer when
convolve_4_rows_horizontally is nullptr. So I'd like to not change it for now.

+                                         const SkConvolutionFilter1D& filter,
+                                         unsigned char* out_row[4],
+                                         size_t out_row_bytes)
+        = nullptr;
+
+
+#endif
+
+    void convolve_vertically(const SkConvolutionFilter1D::ConvolutionFixed* filter_values,
+                             int filter_length,
+                             unsigned char* const* source_data_rows,
+                             int pixel_width,
+                             unsigned char* out_row,
+                             bool has_alpha) {
+        if (has_alpha) {
+            convolveVertically<true>(filter_values, filter_length, source_data_rows,
+                                     pixel_width, out_row);
+        } else {
+            convolveVertically<false>(filter_values, filter_length, source_data_rows,
+                                      pixel_width, out_row);
+        }
+    }
+
+}  // namespace SK_OPTS_NS
+
+#endif//SkBitmapFilter_opts_DEFINED