path: root/gfx/2d/ConvolutionFilterNEON.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2011-2016 Google Inc.
// Use of this source code is governed by a BSD-style license that can be
// found in the gfx/skia/LICENSE file.

#include "SkConvolver.h"
#include "mozilla/Attributes.h"
#include <arm_neon.h>

namespace skia {

static MOZ_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_neon(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;
  }
}

// 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>
static 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;
    }
  }
}

void convolve_vertically_neon(
    const SkConvolutionFilter1D::ConvolutionFixed* filterValues,
    int filterLength, unsigned char* const* sourceDataRows, int pixelWidth,
    unsigned char* outRow, bool hasAlpha) {
  if (hasAlpha) {
    ConvolveVertically<true>(filterValues, filterLength, sourceDataRows,
                             pixelWidth, outRow);
  } else {
    ConvolveVertically<false>(filterValues, filterLength, sourceDataRows,
                              pixelWidth, outRow);
  }
}

}  // namespace skia