src/opts/SkBitmapProcState_opts.h

/*
 * Copyright 2018 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkBitmapProcState_opts_DEFINED
#define SkBitmapProcState_opts_DEFINED

#include "include/private/SkVx.h"
#include "src/core/SkBitmapProcState.h"
#include "src/core/SkMSAN.h"

// SkBitmapProcState optimized Shader, Sample, or Matrix procs.
//
// Only S32_alpha_D32_filter_DX exploits instructions beyond
// our common baseline SSE2/NEON instruction sets, so that's
// all that lives here.
//
// The rest are scattershot at the moment but I want to get them
// all migrated to be normal code inside SkBitmapProcState.cpp.

#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
    #include <immintrin.h>
#elif defined(SK_ARM_HAS_NEON)
    #include <arm_neon.h>
#endif

namespace SK_OPTS_NS {

// This same basic packing scheme is used throughout the file.
template <typename U32, typename Out>
static void decode_packed_coordinates_and_weight(U32 packed, Out* v0, Out* v1, Out* w) {
    *v0 = (packed >> 18);       // Integer coordinate x0 or y0.
    *v1 = (packed & 0x3fff);    // Integer coordinate x1 or y1.
    *w  = (packed >> 14) & 0xf; // Lerp weight for v1; weight for v0 is 16-w.
}

#if 1 && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_AVX2
    /*not static*/ inline
    void S32_alpha_D32_filter_DX(const SkBitmapProcState& s,
                                 const uint32_t* xy, int count, uint32_t* colors) {
        SkASSERT(count > 0 && colors != nullptr);
        SkASSERT(s.fBilerp);
        SkASSERT(kN32_SkColorType == s.fPixmap.colorType());
        SkASSERT(s.fAlphaScale <= 256);

        // In a _DX variant only X varies; all samples share y0/y1 coordinates and wy weight.
        int y0, y1, wy;
        decode_packed_coordinates_and_weight(*xy++, &y0, &y1, &wy);

        const uint32_t* row0 = s.fPixmap.addr32(0,y0);
        const uint32_t* row1 = s.fPixmap.addr32(0,y1);

        auto bilerp = [&](skvx::Vec<8,uint32_t> packed_x_coordinates) -> skvx::Vec<8,uint32_t> {
            // Decode up to 8 output pixels' x-coordinates and weights.
            skvx::Vec<8,uint32_t> x0,x1,wx;
            decode_packed_coordinates_and_weight(packed_x_coordinates, &x0, &x1, &wx);

            // Splat wx to each color channel.
            wx = (wx <<  0)
               | (wx <<  8)
               | (wx << 16)
               | (wx << 24);

            auto gather = [](const uint32_t* ptr, skvx::Vec<8,uint32_t> ix) {
            #if 1
                // Drop into AVX2 intrinsics for vpgatherdd.
                return skvx::bit_pun<skvx::Vec<8,uint32_t>>(
                        _mm256_i32gather_epi32((const int*)ptr, skvx::bit_pun<__m256i>(ix), 4));
            #else
                // Portable version... sometimes I don't trust vpgatherdd.
                return skvx::Vec<8,uint32_t>{
                    ptr[ix[0]], ptr[ix[1]], ptr[ix[2]], ptr[ix[3]],
                    ptr[ix[4]], ptr[ix[5]], ptr[ix[6]], ptr[ix[7]],
                };
            #endif
            };

            // Gather the 32 32-bit pixels that we'll bilerp into our 8 output pixels.
            skvx::Vec<8,uint32_t> tl = gather(row0, x0), tr = gather(row0, x1),
                                  bl = gather(row1, x0), br = gather(row1, x1);

        #if 1
            // We'll use _mm256_maddubs_epi16() to lerp much like in the SSSE3 code.
            auto lerp_x = [&](skvx::Vec<8,uint32_t> L, skvx::Vec<8,uint32_t> R) {
                __m256i l = skvx::bit_pun<__m256i>(L),
                        r = skvx::bit_pun<__m256i>(R),
                       wr = skvx::bit_pun<__m256i>(wx),
                       wl = _mm256_sub_epi8(_mm256_set1_epi8(16), wr);

                // Interlace l,r bytewise and line them up with their weights, then lerp.
                __m256i lo = _mm256_maddubs_epi16(_mm256_unpacklo_epi8( l, r),
                                                  _mm256_unpacklo_epi8(wl,wr));
                __m256i hi = _mm256_maddubs_epi16(_mm256_unpackhi_epi8( l, r),
                                                  _mm256_unpackhi_epi8(wl,wr));

                // Those _mm256_unpack??_epi8() calls left us in a bit of an odd order:
                //
                //    if   l = a b c d | e f g h
                //   and   r = A B C D | E F G H
                //
                // then   lo = a A b B | e E f F   (low  half of each input)
                //  and   hi = c C d D | g G h H   (high half of each input)
                //
                // To get everything back in original order we need to transpose that.
                __m256i abcd = _mm256_permute2x128_si256(lo, hi, 0x20),
                        efgh = _mm256_permute2x128_si256(lo, hi, 0x31);

                return skvx::join(skvx::bit_pun<skvx::Vec<16,uint16_t>>(abcd),
                                  skvx::bit_pun<skvx::Vec<16,uint16_t>>(efgh));
            };

            skvx::Vec<32, uint16_t> top = lerp_x(tl, tr),
                                    bot = lerp_x(bl, br),
                                    sum = 16*top + (bot-top)*wy;
        #else
            // Treat 32-bit pixels as 4 8-bit values, and expand to 16-bit for room to multiply.
            auto to_16x4 = [](auto v) -> skvx::Vec<32, uint16_t> {
                return skvx::cast<uint16_t>(skvx::bit_pun<skvx::Vec<32, uint8_t>>(v));
            };

            // Sum up weighted sample pixels.  The naive, redundant math would be,
            //
            //   sum = tl * (16-wy) * (16-wx)
            //       + bl * (   wy) * (16-wx)
            //       + tr * (16-wy) * (   wx)
            //       + br * (   wy) * (   wx)
            //
            // But we refactor to eliminate a bunch of those common factors.
            auto lerp = [](auto lo, auto hi, auto w) {
                return 16*lo + (hi-lo)*w;
            };
            skvx::Vec<32, uint16_t> sum = lerp(lerp(to_16x4(tl), to_16x4(bl), wy),
                                               lerp(to_16x4(tr), to_16x4(br), wy), to_16x4(wx));
        #endif

            // Get back to [0,255] by dividing by maximum weight 16x16 = 256.
            sum >>= 8;

            // Scale by alpha if needed.
            if(s.fAlphaScale < 256) {
                sum *= s.fAlphaScale;
                sum >>= 8;
            }

            // Pack back to 8-bit channels, undoing to_16x4().
            return skvx::bit_pun<skvx::Vec<8,uint32_t>>(skvx::cast<uint8_t>(sum));
        };

        while (count >= 8) {
            bilerp(skvx::Vec<8,uint32_t>::Load(xy)).store(colors);
            xy     += 8;
            colors += 8;
            count  -= 8;
        }
        if (count > 0) {
            __m256i active = skvx::bit_pun<__m256i>( count > skvx::Vec<8,int>{0,1,2,3, 4,5,6,7} ),
                    coords = _mm256_maskload_epi32((const int*)xy, active),
                    pixels;

            bilerp(skvx::bit_pun<skvx::Vec<8,uint32_t>>(coords)).store(&pixels);
            _mm256_maskstore_epi32((int*)colors, active, pixels);

            sk_msan_mark_initialized(colors, colors+count,
                                     "MSAN still doesn't understand AVX2 mask loads and stores.");
        }
    }

#elif 1 && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSSE3

    /*not static*/ inline
    void S32_alpha_D32_filter_DX(const SkBitmapProcState& s,
                                 const uint32_t* xy, int count, uint32_t* colors) {
        SkASSERT(count > 0 && colors != nullptr);
        SkASSERT(s.fBilerp);
        SkASSERT(kN32_SkColorType == s.fPixmap.colorType());
        SkASSERT(s.fAlphaScale <= 256);

        // interpolate_in_x() is the crux of the SSSE3 implementation,
        // interpolating in X for up to two output pixels (A and B) using _mm_maddubs_epi16().
        auto interpolate_in_x = [](uint32_t A0, uint32_t A1,
                                   uint32_t B0, uint32_t B1,
                                   __m128i interlaced_x_weights) {
            // _mm_maddubs_epi16() is a little idiosyncratic, but great as the core of a lerp.
            //
            // It takes two arguments interlaced byte-wise:
            //    - first  arg: [ l,r, ... 7 more pairs of unsigned 8-bit values ...]
            //    - second arg: [ w,W, ... 7 more pairs of   signed 8-bit values ...]
            // and returns 8 signed 16-bit values: [ l*w + r*W, ... 7 more ... ].
            //
            // That's why we go to all this trouble to make interlaced_x_weights,
            // and here we're about to interlace A0 with A1 and B0 with B1 to match.
            //
            // Our interlaced_x_weights are all in [0,16], and so we need not worry about
            // the signedness of that input nor about the signedness of the output.

            __m128i interlaced_A = _mm_unpacklo_epi8(_mm_cvtsi32_si128(A0), _mm_cvtsi32_si128(A1)),
                    interlaced_B = _mm_unpacklo_epi8(_mm_cvtsi32_si128(B0), _mm_cvtsi32_si128(B1));

            return _mm_maddubs_epi16(_mm_unpacklo_epi64(interlaced_A, interlaced_B),
                                     interlaced_x_weights);
        };

        // Interpolate {A0..A3} --> output pixel A, and {B0..B3} --> output pixel B.
        // Returns two pixels, with each color channel in a 16-bit lane of the __m128i.
        auto interpolate_in_x_and_y = [&](uint32_t A0, uint32_t A1,
                                          uint32_t A2, uint32_t A3,
                                          uint32_t B0, uint32_t B1,
                                          uint32_t B2, uint32_t B3,
                                          __m128i interlaced_x_weights,
                                          int wy) {
            // Interpolate each row in X, leaving 16-bit lanes scaled by interlaced_x_weights.
            __m128i top = interpolate_in_x(A0,A1, B0,B1, interlaced_x_weights),
                    bot = interpolate_in_x(A2,A3, B2,B3, interlaced_x_weights);

            // Interpolate in Y.  As in the SSE2 code, we calculate top*(16-wy) + bot*wy
            // as 16*top + (bot-top)*wy to save a multiply.
            __m128i px = _mm_add_epi16(_mm_slli_epi16(top, 4),
                                       _mm_mullo_epi16(_mm_sub_epi16(bot, top),
                                                       _mm_set1_epi16(wy)));

            // Scale down by total max weight 16x16 = 256.
            px = _mm_srli_epi16(px, 8);

            // Scale by alpha if needed.
            if (s.fAlphaScale < 256) {
                px = _mm_srli_epi16(_mm_mullo_epi16(px, _mm_set1_epi16(s.fAlphaScale)), 8);
            }
            return px;
        };

        // We're in _DX mode here, so we're only varying in X.
        // That means the first entry of xy is our constant pair of Y coordinates and weight in Y.
        // All the other entries in xy will be pairs of X coordinates and the X weight.
        int y0, y1, wy;
        decode_packed_coordinates_and_weight(*xy++, &y0, &y1, &wy);

        auto row0 = (const uint32_t*)((const uint8_t*)s.fPixmap.addr() + y0 * s.fPixmap.rowBytes()),
             row1 = (const uint32_t*)((const uint8_t*)s.fPixmap.addr() + y1 * s.fPixmap.rowBytes());

        while (count >= 4) {
            // We can really get going, loading 4 X-pairs at a time to produce 4 output pixels.
            int x0[4],
                x1[4];
            __m128i wx;

            // decode_packed_coordinates_and_weight(), 4x.
            __m128i packed = _mm_loadu_si128((const __m128i*)xy);
            _mm_storeu_si128((__m128i*)x0, _mm_srli_epi32(packed, 18));
            _mm_storeu_si128((__m128i*)x1, _mm_and_si128 (packed, _mm_set1_epi32(0x3fff)));
            wx = _mm_and_si128(_mm_srli_epi32(packed, 14), _mm_set1_epi32(0xf));  // [0,15]

            // Splat each x weight 4x (for each color channel) as wr for pixels on the right at x1,
            // and sixteen minus that as wl for pixels on the left at x0.
            __m128i wr = _mm_shuffle_epi8(wx, _mm_setr_epi8(0,0,0,0,4,4,4,4,8,8,8,8,12,12,12,12)),
                    wl = _mm_sub_epi8(_mm_set1_epi8(16), wr);

            // We need to interlace wl and wr for _mm_maddubs_epi16().
            __m128i interlaced_x_weights_AB = _mm_unpacklo_epi8(wl,wr),
                    interlaced_x_weights_CD = _mm_unpackhi_epi8(wl,wr);

            enum { A,B,C,D };

            // interpolate_in_x_and_y() can produce two output pixels (A and B) at a time
            // from eight input pixels {A0..A3} and {B0..B3}, arranged in a 2x2 grid for each.
            __m128i AB = interpolate_in_x_and_y(row0[x0[A]], row0[x1[A]],
                                                row1[x0[A]], row1[x1[A]],
                                                row0[x0[B]], row0[x1[B]],
                                                row1[x0[B]], row1[x1[B]],
                                                interlaced_x_weights_AB, wy);

            // Once more with the other half of the x-weights for two more pixels C,D.
            __m128i CD = interpolate_in_x_and_y(row0[x0[C]], row0[x1[C]],
                                                row1[x0[C]], row1[x1[C]],
                                                row0[x0[D]], row0[x1[D]],
                                                row1[x0[D]], row1[x1[D]],
                                                interlaced_x_weights_CD, wy);

            // Scale by alpha, pack back together to 8-bit lanes, and write out four pixels!
            _mm_storeu_si128((__m128i*)colors, _mm_packus_epi16(AB, CD));
            xy     += 4;
            colors += 4;
            count  -= 4;
        }

        while (count --> 0) {
            // This is exactly the same flow as the count >= 4 loop above, but writing one pixel.
            int x0, x1, wx;
            decode_packed_coordinates_and_weight(*xy++, &x0, &x1, &wx);

            // As above, splat out wx four times as wr, and sixteen minus that as wl.
            __m128i wr = _mm_set1_epi8(wx),     // This splats it out 16 times, but that's fine.
                    wl = _mm_sub_epi8(_mm_set1_epi8(16), wr);

            __m128i interlaced_x_weights = _mm_unpacklo_epi8(wl, wr);

            __m128i A = interpolate_in_x_and_y(row0[x0], row0[x1],
                                               row1[x0], row1[x1],
                                                      0,        0,
                                                      0,        0,
                                               interlaced_x_weights, wy);

            *colors++ = _mm_cvtsi128_si32(_mm_packus_epi16(A, _mm_setzero_si128()));
        }
    }


#elif 1 && SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2

    /*not static*/ inline
    void S32_alpha_D32_filter_DX(const SkBitmapProcState& s,
                                 const uint32_t* xy, int count, uint32_t* colors) {
        SkASSERT(count > 0 && colors != nullptr);
        SkASSERT(s.fBilerp);
        SkASSERT(kN32_SkColorType == s.fPixmap.colorType());
        SkASSERT(s.fAlphaScale <= 256);

        int y0, y1, wy;
        decode_packed_coordinates_and_weight(*xy++, &y0, &y1, &wy);

        auto row0 = (const uint32_t*)( (const char*)s.fPixmap.addr() + y0 * s.fPixmap.rowBytes() ),
             row1 = (const uint32_t*)( (const char*)s.fPixmap.addr() + y1 * s.fPixmap.rowBytes() );

        // We'll put one pixel in the low 4 16-bit lanes to line up with wy,
        // and another in the upper 4 16-bit lanes to line up with 16 - wy.
        const __m128i allY = _mm_unpacklo_epi64(_mm_set1_epi16(   wy),   // Bottom pixel goes here.
                                                _mm_set1_epi16(16-wy));  // Top pixel goes here.

        while (count --> 0) {
            int x0, x1, wx;
            decode_packed_coordinates_and_weight(*xy++, &x0, &x1, &wx);

            // Load the 4 pixels we're interpolating, in this grid:
            //    | tl  tr |
            //    | bl  br |
            const __m128i tl = _mm_cvtsi32_si128(row0[x0]), tr = _mm_cvtsi32_si128(row0[x1]),
                          bl = _mm_cvtsi32_si128(row1[x0]), br = _mm_cvtsi32_si128(row1[x1]);

            // We want to calculate a sum of 4 pixels weighted in two directions:
            //
            //  sum = tl * (16-wy) * (16-wx)
            //      + bl * (   wy) * (16-wx)
            //      + tr * (16-wy) * (   wx)
            //      + br * (   wy) * (   wx)
            //
            // (Notice top --> 16-wy, bottom --> wy, left --> 16-wx, right --> wx.)
            //
            // We've already prepared allY as a vector containing [wy, 16-wy] as a way
            // to apply those y-direction weights.  So we'll start on the x-direction
            // first, grouping into left and right halves, lined up with allY:
            //
            //     L = [bl, tl]
            //     R = [br, tr]
            //
            //   sum = horizontalSum( allY * (L*(16-wx) + R*wx) )
            //
            // Rewriting that one more step, we can replace a multiply with a shift:
            //
            //   sum = horizontalSum( allY * (16*L + (R-L)*wx) )
            //
            // That's how we'll actually do this math.

            __m128i L = _mm_unpacklo_epi8(_mm_unpacklo_epi32(bl, tl), _mm_setzero_si128()),
                    R = _mm_unpacklo_epi8(_mm_unpacklo_epi32(br, tr), _mm_setzero_si128());

            __m128i inner = _mm_add_epi16(_mm_slli_epi16(L, 4),
                                          _mm_mullo_epi16(_mm_sub_epi16(R,L), _mm_set1_epi16(wx)));

            __m128i sum_in_x = _mm_mullo_epi16(inner, allY);

            // sum = horizontalSum( ... )
            __m128i sum = _mm_add_epi16(sum_in_x, _mm_srli_si128(sum_in_x, 8));

            // Get back to [0,255] by dividing by maximum weight 16x16 = 256.
            sum = _mm_srli_epi16(sum, 8);

            if (s.fAlphaScale < 256) {
                // Scale by alpha, which is in [0,256].
                sum = _mm_mullo_epi16(sum, _mm_set1_epi16(s.fAlphaScale));
                sum = _mm_srli_epi16(sum, 8);
            }

            // Pack back into 8-bit values and store.
            *colors++ = _mm_cvtsi128_si32(_mm_packus_epi16(sum, _mm_setzero_si128()));
        }
    }

#else

    // The NEON code only actually differs from the portable code in the
    // filtering step after we've loaded all four pixels we want to bilerp.

    #if defined(SK_ARM_HAS_NEON)
        static void filter_and_scale_by_alpha(unsigned x, unsigned y,
                                              SkPMColor a00, SkPMColor a01,
                                              SkPMColor a10, SkPMColor a11,
                                              SkPMColor *dst,
                                              uint16_t scale) {
            uint8x8_t vy, vconst16_8, v16_y, vres;
            uint16x4_t vx, vconst16_16, v16_x, tmp, vscale;
            uint32x2_t va0, va1;
            uint16x8_t tmp1, tmp2;

            vy = vdup_n_u8(y);                // duplicate y into vy
            vconst16_8 = vmov_n_u8(16);       // set up constant in vconst16_8
            v16_y = vsub_u8(vconst16_8, vy);  // v16_y = 16-y

            va0 = vdup_n_u32(a00);            // duplicate a00
            va1 = vdup_n_u32(a10);            // duplicate a10
            va0 = vset_lane_u32(a01, va0, 1); // set top to a01
            va1 = vset_lane_u32(a11, va1, 1); // set top to a11

            tmp1 = vmull_u8(vreinterpret_u8_u32(va0), v16_y); // tmp1 = [a01|a00] * (16-y)
            tmp2 = vmull_u8(vreinterpret_u8_u32(va1), vy);    // tmp2 = [a11|a10] * y

            vx = vdup_n_u16(x);                // duplicate x into vx
            vconst16_16 = vmov_n_u16(16);      // set up constant in vconst16_16
            v16_x = vsub_u16(vconst16_16, vx); // v16_x = 16-x

            tmp = vmul_u16(vget_high_u16(tmp1), vx);        // tmp  = a01 * x
            tmp = vmla_u16(tmp, vget_high_u16(tmp2), vx);   // tmp += a11 * x
            tmp = vmla_u16(tmp, vget_low_u16(tmp1), v16_x); // tmp += a00 * (16-x)
            tmp = vmla_u16(tmp, vget_low_u16(tmp2), v16_x); // tmp += a10 * (16-x)

            if (scale < 256) {
                vscale = vdup_n_u16(scale);        // duplicate scale
                tmp = vshr_n_u16(tmp, 8);          // shift down result by 8
                tmp = vmul_u16(tmp, vscale);       // multiply result by scale
            }

            vres = vshrn_n_u16(vcombine_u16(tmp, vcreate_u16((uint64_t)0)), 8); // shift down result by 8
            vst1_lane_u32(dst, vreinterpret_u32_u8(vres), 0);         // store result
        }
    #else
        static void filter_and_scale_by_alpha(unsigned x, unsigned y,
                                              SkPMColor a00, SkPMColor a01,
                                              SkPMColor a10, SkPMColor a11,
                                              SkPMColor* dstColor,
                                              unsigned alphaScale) {
            SkASSERT((unsigned)x <= 0xF);
            SkASSERT((unsigned)y <= 0xF);
            SkASSERT(alphaScale <= 256);

            int xy = x * y;
            const uint32_t mask = 0xFF00FF;

            int scale = 256 - 16*y - 16*x + xy;
            uint32_t lo = (a00 & mask) * scale;
            uint32_t hi = ((a00 >> 8) & mask) * scale;

            scale = 16*x - xy;
            lo += (a01 & mask) * scale;
            hi += ((a01 >> 8) & mask) * scale;

            scale = 16*y - xy;
            lo += (a10 & mask) * scale;
            hi += ((a10 >> 8) & mask) * scale;

            lo += (a11 & mask) * xy;
            hi += ((a11 >> 8) & mask) * xy;

            if (alphaScale < 256) {
                lo = ((lo >> 8) & mask) * alphaScale;
                hi = ((hi >> 8) & mask) * alphaScale;
            }

            *dstColor = ((lo >> 8) & mask) | (hi & ~mask);
        }
    #endif


    /*not static*/ inline
    void S32_alpha_D32_filter_DX(const SkBitmapProcState& s,
                                 const uint32_t* xy, int count, SkPMColor* colors) {
        SkASSERT(count > 0 && colors != nullptr);
        SkASSERT(s.fBilerp);
        SkASSERT(4 == s.fPixmap.info().bytesPerPixel());
        SkASSERT(s.fAlphaScale <= 256);

        int y0, y1, wy;
        decode_packed_coordinates_and_weight(*xy++, &y0, &y1, &wy);

        auto row0 = (const uint32_t*)( (const char*)s.fPixmap.addr() + y0 * s.fPixmap.rowBytes() ),
             row1 = (const uint32_t*)( (const char*)s.fPixmap.addr() + y1 * s.fPixmap.rowBytes() );

        while (count --> 0) {
            int x0, x1, wx;
            decode_packed_coordinates_and_weight(*xy++, &x0, &x1, &wx);

            filter_and_scale_by_alpha(wx, wy,
                                      row0[x0], row0[x1],
                                      row1[x0], row1[x1],
                                      colors++,
                                      s.fAlphaScale);
        }
    }

#endif

#if defined(SK_ARM_HAS_NEON)
    /*not static*/ inline
    void S32_alpha_D32_filter_DXDY(const SkBitmapProcState& s,
                                   const uint32_t* xy, int count, SkPMColor* colors) {
        SkASSERT(count > 0 && colors != nullptr);
        SkASSERT(s.fBilerp);
        SkASSERT(4 == s.fPixmap.info().bytesPerPixel());
        SkASSERT(s.fAlphaScale <= 256);

        auto src = (const char*)s.fPixmap.addr();
        size_t rb = s.fPixmap.rowBytes();

        while (count --> 0) {
            int y0, y1, wy,
                x0, x1, wx;
            decode_packed_coordinates_and_weight(*xy++, &y0, &y1, &wy);
            decode_packed_coordinates_and_weight(*xy++, &x0, &x1, &wx);

            auto row0 = (const uint32_t*)(src + y0*rb),
                 row1 = (const uint32_t*)(src + y1*rb);

            filter_and_scale_by_alpha(wx, wy,
                                      row0[x0], row0[x1],
                                      row1[x0], row1[x1],
                                      colors++,
                                      s.fAlphaScale);
        }
    }
#else
    // It's not yet clear whether it's worthwhile specializing for SSE2/SSSE3/AVX2.
    constexpr static void (*S32_alpha_D32_filter_DXDY)(const SkBitmapProcState&,
                                                       const uint32_t*, int, SkPMColor*) = nullptr;
#endif

}  // namespace SK_OPTS_NS

#endif