path: root/src/opts/SkBitmapFilter_opts_SSE2.cpp

/*
 * Copyright 2013 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include <emmintrin.h>
#include "SkBitmap.h"
#include "SkBitmapFilter_opts_SSE2.h"
#include "SkBitmapProcState.h"
#include "SkColor.h"
#include "SkColorPriv.h"
#include "SkConvolver.h"
#include "SkShader.h"
#include "SkUnPreMultiply.h"

#if 0
static inline void print128i(__m128i value) {
    int *v = (int*) &value;
    printf("% .11d % .11d % .11d % .11d\n", v[0], v[1], v[2], v[3]);
}

static inline void print128i_16(__m128i value) {
    short *v = (short*) &value;
    printf("% .5d % .5d % .5d % .5d % .5d % .5d % .5d % .5d\n", v[0], v[1], v[2], v[3], v[4], v[5], v[6], v[7]);
}

static inline void print128i_8(__m128i value) {
    unsigned char *v = (unsigned char*) &value;
    printf("%.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u %.3u\n",
           v[0], v[1], v[2], v[3], v[4], v[5], v[6], v[7],
           v[8], v[9], v[10], v[11], v[12], v[13], v[14], v[15]
           );
}

static inline void print128f(__m128 value) {
    float *f = (float*) &value;
    printf("%3.4f %3.4f %3.4f %3.4f\n", f[0], f[1], f[2], f[3]);
}
#endif

// because the border is handled specially, this is guaranteed to have all 16 pixels
// available to it without running off the bitmap's edge.

void highQualityFilter_SSE2(const SkBitmapProcState& s, int x, int y,
                            SkPMColor* SK_RESTRICT colors, int count) {

    const int maxX = s.fBitmap->width();
    const int maxY = s.fBitmap->height();
    SkAutoTMalloc<SkScalar> xWeights(maxX);

    while (count-- > 0) {
        SkPoint srcPt;
        s.fInvProc(s.fInvMatrix, x + 0.5f, y + 0.5f, &srcPt);
        srcPt.fX -= SK_ScalarHalf;
        srcPt.fY -= SK_ScalarHalf;

        __m128 weight = _mm_setzero_ps();
        __m128 accum = _mm_setzero_ps();

        int y0 = SkClampMax(SkScalarCeilToInt(srcPt.fY-s.getBitmapFilter()->width()), maxY);
        int y1 = SkClampMax(SkScalarFloorToInt(srcPt.fY+s.getBitmapFilter()->width()+1), maxY);
        int x0 = SkClampMax(SkScalarCeilToInt(srcPt.fX-s.getBitmapFilter()->width()), maxX);
        int x1 = SkClampMax(SkScalarFloorToInt(srcPt.fX+s.getBitmapFilter()->width())+1, maxX);

        for (int srcX = x0; srcX < x1 ; srcX++) {
            // Looking these up once instead of each loop is a ~15% speedup.
            xWeights[srcX - x0] = s.getBitmapFilter()->lookupScalar((srcPt.fX - srcX));
        }

        for (int srcY = y0; srcY < y1; srcY++) {
            SkScalar yWeight = s.getBitmapFilter()->lookupScalar((srcPt.fY - srcY));

            for (int srcX = x0; srcX < x1 ; srcX++) {
                SkScalar xWeight = xWeights[srcX - x0];

                SkScalar combined_weight = SkScalarMul(xWeight, yWeight);

                SkPMColor color = *s.fBitmap->getAddr32(srcX, srcY);

                __m128i c = _mm_cvtsi32_si128(color);
                c = _mm_unpacklo_epi8(c, _mm_setzero_si128());
                c = _mm_unpacklo_epi16(c, _mm_setzero_si128());
                __m128 cfloat = _mm_cvtepi32_ps(c);

                __m128 weightVector = _mm_set1_ps(combined_weight);
                accum = _mm_add_ps(accum, _mm_mul_ps(cfloat, weightVector));
                weight = _mm_add_ps( weight, weightVector );
            }
        }

        accum = _mm_div_ps(accum, weight);
        accum = _mm_add_ps(accum, _mm_set1_ps(0.5f));
        __m128i accumInt = _mm_cvttps_epi32(accum);
        accumInt = _mm_packs_epi32(accumInt, _mm_setzero_si128());
        accumInt = _mm_packus_epi16(accumInt, _mm_setzero_si128());
        SkPMColor c = _mm_cvtsi128_si32(accumInt);

        int a = SkClampMax(SkGetPackedA32(c), 255);
        int r = SkClampMax(SkGetPackedR32(c), a);
        int g = SkClampMax(SkGetPackedG32(c), a);
        int b = SkClampMax(SkGetPackedB32(c), a);

        *colors++ = SkPackARGB32(a, r, g, b);

        x++;
    }
}

// Convolves horizontally along a single row. The row data is given in
// |src_data| and continues for the num_values() of the filter.
void convolveHorizontally_SSE2(const unsigned char* src_data,
                               const SkConvolutionFilter1D& filter,
                               unsigned char* out_row,
                               bool /*has_alpha*/) {
    int num_values = filter.numValues();

    int filter_offset, filter_length;
    __m128i zero = _mm_setzero_si128();
    __m128i mask[4];
    // |mask| will be used to decimate all extra filter coefficients that are
    // loaded by SIMD when |filter_length| is not divisible by 4.
    // mask[0] is not used in following algorithm.
    mask[1] = _mm_set_epi16(0, 0, 0, 0, 0, 0, 0, -1);
    mask[2] = _mm_set_epi16(0, 0, 0, 0, 0, 0, -1, -1);
    mask[3] = _mm_set_epi16(0, 0, 0, 0, 0, -1, -1, -1);

    // Output one pixel each iteration, calculating all channels (RGBA) together.
    for (int out_x = 0; out_x < num_values; out_x++) {
        const SkConvolutionFilter1D::ConvolutionFixed* filter_values =
            filter.FilterForValue(out_x, &filter_offset, &filter_length);

        __m128i accum = _mm_setzero_si128();

        // Compute the first pixel in this row that the filter affects. It will
        // touch |filter_length| pixels (4 bytes each) after this.
        const __m128i* row_to_filter =
            reinterpret_cast<const __m128i*>(&src_data[filter_offset << 2]);

        // We will load and accumulate with four coefficients per iteration.
        for (int filter_x = 0; filter_x < filter_length >> 2; filter_x++) {

            // 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*>(filter_values));
            // [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(row_to_filter);
            // [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.
            row_to_filter += 1;
            filter_values += 4;
        }

        // When |filter_length| is not divisible by 4, we need to decimate some of
        // the filter coefficient that was loaded incorrectly to zero; Other than
        // that the algorithm is same with above, exceot that the 4th pixel will be
        // always absent.
        int r = filter_length&3;
        if (r) {
            // Note: filter_values must be padded to align_up(filter_offset, 8).
            __m128i coeff, coeff16;
            coeff = _mm_loadl_epi64(reinterpret_cast<const __m128i*>(filter_values));
            // Mask out extra filter taps.
            coeff = _mm_and_si128(coeff, mask[r]);
            coeff16 = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(1, 1, 0, 0));
            coeff16 = _mm_unpacklo_epi16(coeff16, coeff16);

            // Note: line buffer must be padded to align_up(filter_offset, 16).
            // We resolve this by use C-version for the last horizontal line.
            __m128i src8 = _mm_loadu_si128(row_to_filter);
            __m128i src16 = _mm_unpacklo_epi8(src8, zero);
            __m128i mul_hi = _mm_mulhi_epi16(src16, coeff16);
            __m128i mul_lo = _mm_mullo_epi16(src16, coeff16);
            __m128i 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);
            coeff16 = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(3, 3, 2, 2));
            coeff16 = _mm_unpacklo_epi16(coeff16, coeff16);
            mul_hi = _mm_mulhi_epi16(src16, coeff16);
            mul_lo = _mm_mullo_epi16(src16, coeff16);
            t = _mm_unpacklo_epi16(mul_lo, mul_hi);
            accum = _mm_add_epi32(accum, t);
        }

        // 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*>(out_row)) = _mm_cvtsi128_si32(accum);
        out_row += 4;
    }
}

// Convolves horizontally along four rows. The row data is given in
// |src_data| and continues for the num_values() of the filter.
// The algorithm is almost same as |ConvolveHorizontally_SSE2|. Please
// refer to that function for detailed comments.
void convolve4RowsHorizontally_SSE2(const unsigned char* src_data[4],
                                    const SkConvolutionFilter1D& filter,
                                    unsigned char* out_row[4]) {
    int num_values = filter.numValues();

    int filter_offset, filter_length;
    __m128i zero = _mm_setzero_si128();
    __m128i mask[4];
    // |mask| will be used to decimate all extra filter coefficients that are
    // loaded by SIMD when |filter_length| is not divisible by 4.
    // mask[0] is not used in following algorithm.
    mask[1] = _mm_set_epi16(0, 0, 0, 0, 0, 0, 0, -1);
    mask[2] = _mm_set_epi16(0, 0, 0, 0, 0, 0, -1, -1);
    mask[3] = _mm_set_epi16(0, 0, 0, 0, 0, -1, -1, -1);

    // Output one pixel each iteration, calculating all channels (RGBA) together.
    for (int out_x = 0; out_x < num_values; out_x++) {
        const SkConvolutionFilter1D::ConvolutionFixed* filter_values =
            filter.FilterForValue(out_x, &filter_offset, &filter_length);

        // 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 = (filter_offset<<2);
        // We will load and accumulate with four coefficients per iteration.
        for (int filter_x = 0; filter_x < (filter_length >> 2); filter_x++) {
            __m128i coeff, coeff16lo, coeff16hi;
            // [16] xx xx xx xx c3 c2 c1 c0
            coeff = _mm_loadl_epi64(reinterpret_cast<const __m128i*>(filter_values));
            // [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(src_data[0] + start, accum0);
            ITERATION(src_data[1] + start, accum1);
            ITERATION(src_data[2] + start, accum2);
            ITERATION(src_data[3] + start, accum3);

            start += 16;
            filter_values += 4;
        }

        int r = filter_length & 3;
        if (r) {
            // Note: filter_values must be padded to align_up(filter_offset, 8);
            __m128i coeff;
            coeff = _mm_loadl_epi64(reinterpret_cast<const __m128i*>(filter_values));
            // Mask out extra filter taps.
            coeff = _mm_and_si128(coeff, mask[r]);

            __m128i coeff16lo = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(1, 1, 0, 0));
            /* c1 c1 c1 c1 c0 c0 c0 c0 */
            coeff16lo = _mm_unpacklo_epi16(coeff16lo, coeff16lo);
            __m128i coeff16hi = _mm_shufflelo_epi16(coeff, _MM_SHUFFLE(3, 3, 2, 2));
            coeff16hi = _mm_unpacklo_epi16(coeff16hi, coeff16hi);

            __m128i src8, src16, mul_hi, mul_lo, t;

            ITERATION(src_data[0] + start, accum0);
            ITERATION(src_data[1] + start, accum1);
            ITERATION(src_data[2] + start, accum2);
            ITERATION(src_data[3] + start, accum3);
        }

        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);

        *(reinterpret_cast<int*>(out_row[0])) = _mm_cvtsi128_si32(accum0);
        *(reinterpret_cast<int*>(out_row[1])) = _mm_cvtsi128_si32(accum1);
        *(reinterpret_cast<int*>(out_row[2])) = _mm_cvtsi128_si32(accum2);
        *(reinterpret_cast<int*>(out_row[3])) = _mm_cvtsi128_si32(accum3);

        out_row[0] += 4;
        out_row[1] += 4;
        out_row[2] += 4;
        out_row[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 |source_data_rows| array, with each row
// being |pixel_width| wide.
//
// The output must have room for |pixel_width * 4| bytes.
template<bool has_alpha>
void convolveVertically_SSE2(const SkConvolutionFilter1D::ConvolutionFixed* filter_values,
                             int filter_length,
                             unsigned char* const* source_data_rows,
                             int pixel_width,
                             unsigned char* out_row) {
    int width = pixel_width & ~3;

    __m128i zero = _mm_setzero_si128();
    __m128i accum0, accum1, accum2, accum3, coeff16;
    const __m128i* src;
    // Output four pixels per iteration (16 bytes).
    for (int out_x = 0; out_x < width; out_x += 4) {

        // Accumulated result for each pixel. 32 bits per RGBA channel.
        accum0 = _mm_setzero_si128();
        accum1 = _mm_setzero_si128();
        accum2 = _mm_setzero_si128();
        accum3 = _mm_setzero_si128();

        // Convolve with one filter coefficient per iteration.
        for (int filter_y = 0; filter_y < filter_length; filter_y++) {

            // Duplicate the filter coefficient 8 times.
            // [16] cj cj cj cj cj cj cj cj
            coeff16 = _mm_set1_epi16(filter_values[filter_y]);

            // Load four pixels (16 bytes) together.
            // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
            src = reinterpret_cast<const __m128i*>(
                &source_data_rows[filter_y][out_x << 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 (has_alpha) {
            // 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*>(out_row), accum0);
        out_row += 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.
    if (pixel_width & 3) {
        accum0 = _mm_setzero_si128();
        accum1 = _mm_setzero_si128();
        accum2 = _mm_setzero_si128();
        for (int filter_y = 0; filter_y < filter_length; ++filter_y) {
            coeff16 = _mm_set1_epi16(filter_values[filter_y]);
            // [8] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
            src = reinterpret_cast<const __m128i*>(
                &source_data_rows[filter_y][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 (has_alpha) {
            // [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 out_x = width; out_x < pixel_width; out_x++) {
            *(reinterpret_cast<int*>(out_row)) = _mm_cvtsi128_si32(accum0);
            accum0 = _mm_srli_si128(accum0, 4);
            out_row += 4;
        }
    }
}

void convolveVertically_SSE2(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_SSE2<true>(filter_values,
                                      filter_length,
                                      source_data_rows,
                                      pixel_width,
                                      out_row);
    } else {
        convolveVertically_SSE2<false>(filter_values,
                                       filter_length,
                                       source_data_rows,
                                       pixel_width,
                                       out_row);
    }
}

void applySIMDPadding_SSE2(SkConvolutionFilter1D *filter) {
    // Padding |paddingCount| of more dummy coefficients after the coefficients
    // of last filter to prevent SIMD instructions which load 8 or 16 bytes
    // together to access invalid memory areas. We are not trying to align the
    // coefficients right now due to the opaqueness of <vector> implementation.
    // This has to be done after all |AddFilter| calls.
    for (int i = 0; i < 8; ++i) {
        filter->addFilterValue(static_cast<SkConvolutionFilter1D::ConvolutionFixed>(0));
    }
}