lossless_neon.c

// Copyright 2014 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// NEON variant of methods for lossless decoder
//
// Author: Skal ([email protected])

#include "src/dsp/dsp.h"

#if defined(WEBP_USE_NEON)

#include <arm_neon.h>

#include "src/dsp/lossless.h"
#include "src/dsp/neon.h"

//------------------------------------------------------------------------------
// Colorspace conversion functions

#if !defined(WORK_AROUND_GCC)
// gcc 4.6.0 had some trouble (NDK-r9) with this code. We only use it for
// gcc-4.8.x at least.
static void ConvertBGRAToRGBA_NEON(const uint32_t* WEBP_RESTRICT src,
                                   int num_pixels, uint8_t* WEBP_RESTRICT dst) {
  const uint32_t* const end = src + (num_pixels & ~15);
  for (; src < end; src += 16) {
    uint8x16x4_t pixel = vld4q_u8((uint8_t*)src);
    // swap B and R. (VSWP d0,d2 has no intrinsics equivalent!)
    const uint8x16_t tmp = pixel.val[0];
    pixel.val[0] = pixel.val[2];
    pixel.val[2] = tmp;
    vst4q_u8(dst, pixel);
    dst += 64;
  }
  VP8LConvertBGRAToRGBA_C(src, num_pixels & 15, dst);  // left-overs
}

static void ConvertBGRAToBGR_NEON(const uint32_t* WEBP_RESTRICT src,
                                  int num_pixels, uint8_t* WEBP_RESTRICT dst) {
  const uint32_t* const end = src + (num_pixels & ~15);
  for (; src < end; src += 16) {
    const uint8x16x4_t pixel = vld4q_u8((uint8_t*)src);
    const uint8x16x3_t tmp = { { pixel.val[0], pixel.val[1], pixel.val[2] } };
    vst3q_u8(dst, tmp);
    dst += 48;
  }
  VP8LConvertBGRAToBGR_C(src, num_pixels & 15, dst);  // left-overs
}

static void ConvertBGRAToRGB_NEON(const uint32_t* WEBP_RESTRICT src,
                                  int num_pixels, uint8_t* WEBP_RESTRICT dst) {
  const uint32_t* const end = src + (num_pixels & ~15);
  for (; src < end; src += 16) {
    const uint8x16x4_t pixel = vld4q_u8((uint8_t*)src);
    const uint8x16x3_t tmp = { { pixel.val[2], pixel.val[1], pixel.val[0] } };
    vst3q_u8(dst, tmp);
    dst += 48;
  }
  VP8LConvertBGRAToRGB_C(src, num_pixels & 15, dst);  // left-overs
}

#else  // WORK_AROUND_GCC

// gcc-4.6.0 fallback

static const uint8_t kRGBAShuffle[8] = { 2, 1, 0, 3, 6, 5, 4, 7 };

static void ConvertBGRAToRGBA_NEON(const uint32_t* WEBP_RESTRICT src,
                                   int num_pixels, uint8_t* WEBP_RESTRICT dst) {
  const uint32_t* const end = src + (num_pixels & ~1);
  const uint8x8_t shuffle = vld1_u8(kRGBAShuffle);
  for (; src < end; src += 2) {
    const uint8x8_t pixels = vld1_u8((uint8_t*)src);
    vst1_u8(dst, vtbl1_u8(pixels, shuffle));
    dst += 8;
  }
  VP8LConvertBGRAToRGBA_C(src, num_pixels & 1, dst);  // left-overs
}

static const uint8_t kBGRShuffle[3][8] = {
  {  0,  1,  2,  4,  5,  6,  8,  9 },
  { 10, 12, 13, 14, 16, 17, 18, 20 },
  { 21, 22, 24, 25, 26, 28, 29, 30 }
};

static void ConvertBGRAToBGR_NEON(const uint32_t* WEBP_RESTRICT src,
                                  int num_pixels, uint8_t* WEBP_RESTRICT dst) {
  const uint32_t* const end = src + (num_pixels & ~7);
  const uint8x8_t shuffle0 = vld1_u8(kBGRShuffle[0]);
  const uint8x8_t shuffle1 = vld1_u8(kBGRShuffle[1]);
  const uint8x8_t shuffle2 = vld1_u8(kBGRShuffle[2]);
  for (; src < end; src += 8) {
    uint8x8x4_t pixels;
    INIT_VECTOR4(pixels,
                 vld1_u8((const uint8_t*)(src + 0)),
                 vld1_u8((const uint8_t*)(src + 2)),
                 vld1_u8((const uint8_t*)(src + 4)),
                 vld1_u8((const uint8_t*)(src + 6)));
    vst1_u8(dst +  0, vtbl4_u8(pixels, shuffle0));
    vst1_u8(dst +  8, vtbl4_u8(pixels, shuffle1));
    vst1_u8(dst + 16, vtbl4_u8(pixels, shuffle2));
    dst += 8 * 3;
  }
  VP8LConvertBGRAToBGR_C(src, num_pixels & 7, dst);  // left-overs
}

static const uint8_t kRGBShuffle[3][8] = {
  {  2,  1,  0,  6,  5,  4, 10,  9 },
  {  8, 14, 13, 12, 18, 17, 16, 22 },
  { 21, 20, 26, 25, 24, 30, 29, 28 }
};

static void ConvertBGRAToRGB_NEON(const uint32_t* WEBP_RESTRICT src,
                                  int num_pixels, uint8_t* WEBP_RESTRICT dst) {
  const uint32_t* const end = src + (num_pixels & ~7);
  const uint8x8_t shuffle0 = vld1_u8(kRGBShuffle[0]);
  const uint8x8_t shuffle1 = vld1_u8(kRGBShuffle[1]);
  const uint8x8_t shuffle2 = vld1_u8(kRGBShuffle[2]);
  for (; src < end; src += 8) {
    uint8x8x4_t pixels;
    INIT_VECTOR4(pixels,
                 vld1_u8((const uint8_t*)(src + 0)),
                 vld1_u8((const uint8_t*)(src + 2)),
                 vld1_u8((const uint8_t*)(src + 4)),
                 vld1_u8((const uint8_t*)(src + 6)));
    vst1_u8(dst +  0, vtbl4_u8(pixels, shuffle0));
    vst1_u8(dst +  8, vtbl4_u8(pixels, shuffle1));
    vst1_u8(dst + 16, vtbl4_u8(pixels, shuffle2));
    dst += 8 * 3;
  }
  VP8LConvertBGRAToRGB_C(src, num_pixels & 7, dst);  // left-overs
}

#endif   // !WORK_AROUND_GCC

//------------------------------------------------------------------------------
// Predictor Transform

#define LOAD_U32_AS_U8(IN) vreinterpret_u8_u32(vdup_n_u32((IN)))
#define LOAD_U32P_AS_U8(IN) vreinterpret_u8_u32(vld1_u32((IN)))
#define LOADQ_U32_AS_U8(IN) vreinterpretq_u8_u32(vdupq_n_u32((IN)))
#define LOADQ_U32P_AS_U8(IN) vreinterpretq_u8_u32(vld1q_u32((IN)))
#define GET_U8_AS_U32(IN) vget_lane_u32(vreinterpret_u32_u8((IN)), 0)
#define GETQ_U8_AS_U32(IN) vgetq_lane_u32(vreinterpretq_u32_u8((IN)), 0)
#define STOREQ_U8_AS_U32P(OUT, IN) vst1q_u32((OUT), vreinterpretq_u32_u8((IN)))
#define ROTATE32_LEFT(L) vextq_u8((L), (L), 12)    // D|C|B|A -> C|B|A|D

static WEBP_INLINE uint8x8_t Average2_u8_NEON(uint32_t a0, uint32_t a1) {
  const uint8x8_t A0 = LOAD_U32_AS_U8(a0);
  const uint8x8_t A1 = LOAD_U32_AS_U8(a1);
  return vhadd_u8(A0, A1);
}

static WEBP_INLINE uint32_t ClampedAddSubtractHalf_NEON(uint32_t c0,
                                                        uint32_t c1,
                                                        uint32_t c2) {
  const uint8x8_t avg = Average2_u8_NEON(c0, c1);
  // Remove one to c2 when bigger than avg.
  const uint8x8_t C2 = LOAD_U32_AS_U8(c2);
  const uint8x8_t cmp = vcgt_u8(C2, avg);
  const uint8x8_t C2_1 = vadd_u8(C2, cmp);
  // Compute half of the difference between avg and c2.
  const int8x8_t diff_avg = vreinterpret_s8_u8(vhsub_u8(avg, C2_1));
  // Compute the sum with avg and saturate.
  const int16x8_t avg_16 = vreinterpretq_s16_u16(vmovl_u8(avg));
  const uint8x8_t res = vqmovun_s16(vaddw_s8(avg_16, diff_avg));
  const uint32_t output = GET_U8_AS_U32(res);
  return output;
}

static WEBP_INLINE uint32_t Average2_NEON(uint32_t a0, uint32_t a1) {
  const uint8x8_t avg_u8x8 = Average2_u8_NEON(a0, a1);
  const uint32_t avg = GET_U8_AS_U32(avg_u8x8);
  return avg;
}

static WEBP_INLINE uint32_t Average3_NEON(uint32_t a0, uint32_t a1,
                                          uint32_t a2) {
  const uint8x8_t avg0 = Average2_u8_NEON(a0, a2);
  const uint8x8_t A1 = LOAD_U32_AS_U8(a1);
  const uint32_t avg = GET_U8_AS_U32(vhadd_u8(avg0, A1));
  return avg;
}

static uint32_t Predictor5_NEON(const uint32_t* const left,
                                const uint32_t* const top) {
  return Average3_NEON(*left, top[0], top[1]);
}
static uint32_t Predictor6_NEON(const uint32_t* const left,
                                const uint32_t* const top) {
  return Average2_NEON(*left, top[-1]);
}
static uint32_t Predictor7_NEON(const uint32_t* const left,
                                const uint32_t* const top) {
  return Average2_NEON(*left, top[0]);
}
static uint32_t Predictor13_NEON(const uint32_t* const left,
                                 const uint32_t* const top) {
  return ClampedAddSubtractHalf_NEON(*left, top[0], top[-1]);
}

// Batch versions of those functions.

// Predictor0: ARGB_BLACK.
static void PredictorAdd0_NEON(const uint32_t* in, const uint32_t* upper,
                               int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  const uint8x16_t black = vreinterpretq_u8_u32(vdupq_n_u32(ARGB_BLACK));
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t res = vaddq_u8(src, black);
    STOREQ_U8_AS_U32P(&out[i], res);
  }
  VP8LPredictorsAdd_C[0](in + i, upper + i, num_pixels - i, out + i);
}

// Predictor1: left.
static void PredictorAdd1_NEON(const uint32_t* in, const uint32_t* upper,
                               int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  const uint8x16_t zero = LOADQ_U32_AS_U8(0);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    // a | b | c | d
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    // 0 | a | b | c
    const uint8x16_t shift0 = vextq_u8(zero, src, 12);
    // a | a + b | b + c | c + d
    const uint8x16_t sum0 = vaddq_u8(src, shift0);
    // 0 | 0 | a | a + b
    const uint8x16_t shift1 = vextq_u8(zero, sum0, 8);
    // a | a + b | a + b + c | a + b + c + d
    const uint8x16_t sum1 = vaddq_u8(sum0, shift1);
    const uint8x16_t prev = LOADQ_U32_AS_U8(out[i - 1]);
    const uint8x16_t res = vaddq_u8(sum1, prev);
    STOREQ_U8_AS_U32P(&out[i], res);
  }
  VP8LPredictorsAdd_C[1](in + i, upper + i, num_pixels - i, out + i);
}

// Macro that adds 32-bit integers from IN using mod 256 arithmetic
// per 8 bit channel.
#define GENERATE_PREDICTOR_1(X, IN)                                       \
static void PredictorAdd##X##_NEON(const uint32_t* in,                    \
                                   const uint32_t* upper, int num_pixels, \
                                   uint32_t* WEBP_RESTRICT out) {         \
  int i;                                                                  \
  for (i = 0; i + 4 <= num_pixels; i += 4) {                              \
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);                      \
    const uint8x16_t other = LOADQ_U32P_AS_U8(&(IN));                     \
    const uint8x16_t res = vaddq_u8(src, other);                          \
    STOREQ_U8_AS_U32P(&out[i], res);                                      \
  }                                                                       \
  VP8LPredictorsAdd_C[(X)](in + i, upper + i, num_pixels - i, out + i);   \
}
// Predictor2: Top.
GENERATE_PREDICTOR_1(2, upper[i])
// Predictor3: Top-right.
GENERATE_PREDICTOR_1(3, upper[i + 1])
// Predictor4: Top-left.
GENERATE_PREDICTOR_1(4, upper[i - 1])
#undef GENERATE_PREDICTOR_1

// Predictor5: average(average(left, TR), T)
#define DO_PRED5(LANE) do {                                              \
  const uint8x16_t avgLTR = vhaddq_u8(L, TR);                            \
  const uint8x16_t avg = vhaddq_u8(avgLTR, T);                           \
  const uint8x16_t res = vaddq_u8(avg, src);                             \
  vst1q_lane_u32(&out[i + (LANE)], vreinterpretq_u32_u8(res), (LANE));   \
  L = ROTATE32_LEFT(res);                                                \
} while (0)

static void PredictorAdd5_NEON(const uint32_t* in, const uint32_t* upper,
                               int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint8x16_t L = LOADQ_U32_AS_U8(out[-1]);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t T = LOADQ_U32P_AS_U8(&upper[i + 0]);
    const uint8x16_t TR = LOADQ_U32P_AS_U8(&upper[i + 1]);
    DO_PRED5(0);
    DO_PRED5(1);
    DO_PRED5(2);
    DO_PRED5(3);
  }
  VP8LPredictorsAdd_C[5](in + i, upper + i, num_pixels - i, out + i);
}
#undef DO_PRED5

#define DO_PRED67(LANE) do {                                             \
  const uint8x16_t avg = vhaddq_u8(L, top);                              \
  const uint8x16_t res = vaddq_u8(avg, src);                             \
  vst1q_lane_u32(&out[i + (LANE)], vreinterpretq_u32_u8(res), (LANE));   \
  L = ROTATE32_LEFT(res);                                                \
} while (0)

// Predictor6: average(left, TL)
static void PredictorAdd6_NEON(const uint32_t* in, const uint32_t* upper,
                               int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint8x16_t L = LOADQ_U32_AS_U8(out[-1]);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t top = LOADQ_U32P_AS_U8(&upper[i - 1]);
    DO_PRED67(0);
    DO_PRED67(1);
    DO_PRED67(2);
    DO_PRED67(3);
  }
  VP8LPredictorsAdd_C[6](in + i, upper + i, num_pixels - i, out + i);
}

// Predictor7: average(left, T)
static void PredictorAdd7_NEON(const uint32_t* in, const uint32_t* upper,
                               int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint8x16_t L = LOADQ_U32_AS_U8(out[-1]);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t top = LOADQ_U32P_AS_U8(&upper[i]);
    DO_PRED67(0);
    DO_PRED67(1);
    DO_PRED67(2);
    DO_PRED67(3);
  }
  VP8LPredictorsAdd_C[7](in + i, upper + i, num_pixels - i, out + i);
}
#undef DO_PRED67

#define GENERATE_PREDICTOR_2(X, IN)                                       \
static void PredictorAdd##X##_NEON(const uint32_t* in,                    \
                                   const uint32_t* upper, int num_pixels, \
                                   uint32_t* WEBP_RESTRICT out) {         \
  int i;                                                                  \
  for (i = 0; i + 4 <= num_pixels; i += 4) {                              \
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);                      \
    const uint8x16_t Tother = LOADQ_U32P_AS_U8(&(IN));                    \
    const uint8x16_t T = LOADQ_U32P_AS_U8(&upper[i]);                     \
    const uint8x16_t avg = vhaddq_u8(T, Tother);                          \
    const uint8x16_t res = vaddq_u8(avg, src);                            \
    STOREQ_U8_AS_U32P(&out[i], res);                                      \
  }                                                                       \
  VP8LPredictorsAdd_C[(X)](in + i, upper + i, num_pixels - i, out + i);   \
}
// Predictor8: average TL T.
GENERATE_PREDICTOR_2(8, upper[i - 1])
// Predictor9: average T TR.
GENERATE_PREDICTOR_2(9, upper[i + 1])
#undef GENERATE_PREDICTOR_2

// Predictor10: average of (average of (L,TL), average of (T, TR)).
#define DO_PRED10(LANE) do {                                             \
  const uint8x16_t avgLTL = vhaddq_u8(L, TL);                            \
  const uint8x16_t avg = vhaddq_u8(avgTTR, avgLTL);                      \
  const uint8x16_t res = vaddq_u8(avg, src);                             \
  vst1q_lane_u32(&out[i + (LANE)], vreinterpretq_u32_u8(res), (LANE));   \
  L = ROTATE32_LEFT(res);                                                \
} while (0)

static void PredictorAdd10_NEON(const uint32_t* in, const uint32_t* upper,
                                int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint8x16_t L = LOADQ_U32_AS_U8(out[-1]);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t TL = LOADQ_U32P_AS_U8(&upper[i - 1]);
    const uint8x16_t T = LOADQ_U32P_AS_U8(&upper[i]);
    const uint8x16_t TR = LOADQ_U32P_AS_U8(&upper[i + 1]);
    const uint8x16_t avgTTR = vhaddq_u8(T, TR);
    DO_PRED10(0);
    DO_PRED10(1);
    DO_PRED10(2);
    DO_PRED10(3);
  }
  VP8LPredictorsAdd_C[10](in + i, upper + i, num_pixels - i, out + i);
}
#undef DO_PRED10

// Predictor11: select.
#define DO_PRED11(LANE) do {                                                   \
  const uint8x16_t sumLin = vaddq_u8(L, src);  /* in + L */                    \
  const uint8x16_t pLTL = vabdq_u8(L, TL);  /* |L - TL| */                     \
  const uint16x8_t sum_LTL = vpaddlq_u8(pLTL);                                 \
  const uint32x4_t pa = vpaddlq_u16(sum_LTL);                                  \
  const uint32x4_t mask = vcleq_u32(pa, pb);                                   \
  const uint8x16_t res = vbslq_u8(vreinterpretq_u8_u32(mask), sumTin, sumLin); \
  vst1q_lane_u32(&out[i + (LANE)], vreinterpretq_u32_u8(res), (LANE));         \
  L = ROTATE32_LEFT(res);                                                      \
} while (0)

static void PredictorAdd11_NEON(const uint32_t* in, const uint32_t* upper,
                                int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint8x16_t L = LOADQ_U32_AS_U8(out[-1]);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t T = LOADQ_U32P_AS_U8(&upper[i]);
    const uint8x16_t TL = LOADQ_U32P_AS_U8(&upper[i - 1]);
    const uint8x16_t pTTL = vabdq_u8(T, TL);   // |T - TL|
    const uint16x8_t sum_TTL = vpaddlq_u8(pTTL);
    const uint32x4_t pb = vpaddlq_u16(sum_TTL);
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t sumTin = vaddq_u8(T, src);   // in + T
    DO_PRED11(0);
    DO_PRED11(1);
    DO_PRED11(2);
    DO_PRED11(3);
  }
  VP8LPredictorsAdd_C[11](in + i, upper + i, num_pixels - i, out + i);
}
#undef DO_PRED11

// Predictor12: ClampedAddSubtractFull.
#define DO_PRED12(DIFF, LANE) do {                                       \
  const uint8x8_t pred =                                                 \
      vqmovun_s16(vaddq_s16(vreinterpretq_s16_u16(L), (DIFF)));          \
  const uint8x8_t res =                                                  \
      vadd_u8(pred, (LANE <= 1) ? vget_low_u8(src) : vget_high_u8(src)); \
  const uint16x8_t res16 = vmovl_u8(res);                                \
  vst1_lane_u32(&out[i + (LANE)], vreinterpret_u32_u8(res), (LANE) & 1); \
  /* rotate in the left predictor for next iteration */                  \
  L = vextq_u16(res16, res16, 4);                                        \
} while (0)

static void PredictorAdd12_NEON(const uint32_t* in, const uint32_t* upper,
                                int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint16x8_t L = vmovl_u8(LOAD_U32_AS_U8(out[-1]));
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    // load four pixels of source
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    // precompute the difference T - TL once for all, stored as s16
    const uint8x16_t TL = LOADQ_U32P_AS_U8(&upper[i - 1]);
    const uint8x16_t T = LOADQ_U32P_AS_U8(&upper[i]);
    const int16x8_t diff_lo =
        vreinterpretq_s16_u16(vsubl_u8(vget_low_u8(T), vget_low_u8(TL)));
    const int16x8_t diff_hi =
        vreinterpretq_s16_u16(vsubl_u8(vget_high_u8(T), vget_high_u8(TL)));
    // loop over the four reconstructed pixels
    DO_PRED12(diff_lo, 0);
    DO_PRED12(diff_lo, 1);
    DO_PRED12(diff_hi, 2);
    DO_PRED12(diff_hi, 3);
  }
  VP8LPredictorsAdd_C[12](in + i, upper + i, num_pixels - i, out + i);
}
#undef DO_PRED12

// Predictor13: ClampedAddSubtractHalf
#define DO_PRED13(LANE, LOW_OR_HI) do {                                        \
  const uint8x16_t avg = vhaddq_u8(L, T);                                      \
  const uint8x16_t cmp = vcgtq_u8(TL, avg);                                    \
  const uint8x16_t TL_1 = vaddq_u8(TL, cmp);                                   \
  /* Compute half of the difference between avg and TL'. */                    \
  const int8x8_t diff_avg =                                                    \
      vreinterpret_s8_u8(LOW_OR_HI(vhsubq_u8(avg, TL_1)));                     \
  /* Compute the sum with avg and saturate. */                                 \
  const int16x8_t avg_16 = vreinterpretq_s16_u16(vmovl_u8(LOW_OR_HI(avg)));    \
  const uint8x8_t delta = vqmovun_s16(vaddw_s8(avg_16, diff_avg));             \
  const uint8x8_t res = vadd_u8(LOW_OR_HI(src), delta);                        \
  const uint8x16_t res2 = vcombine_u8(res, res);                               \
  vst1_lane_u32(&out[i + (LANE)], vreinterpret_u32_u8(res), (LANE) & 1);       \
  L = ROTATE32_LEFT(res2);                                                     \
} while (0)

static void PredictorAdd13_NEON(const uint32_t* in, const uint32_t* upper,
                                int num_pixels, uint32_t* WEBP_RESTRICT out) {
  int i;
  uint8x16_t L = LOADQ_U32_AS_U8(out[-1]);
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t src = LOADQ_U32P_AS_U8(&in[i]);
    const uint8x16_t T = LOADQ_U32P_AS_U8(&upper[i]);
    const uint8x16_t TL = LOADQ_U32P_AS_U8(&upper[i - 1]);
    DO_PRED13(0, vget_low_u8);
    DO_PRED13(1, vget_low_u8);
    DO_PRED13(2, vget_high_u8);
    DO_PRED13(3, vget_high_u8);
  }
  VP8LPredictorsAdd_C[13](in + i, upper + i, num_pixels - i, out + i);
}
#undef DO_PRED13

#undef LOAD_U32_AS_U8
#undef LOAD_U32P_AS_U8
#undef LOADQ_U32_AS_U8
#undef LOADQ_U32P_AS_U8
#undef GET_U8_AS_U32
#undef GETQ_U8_AS_U32
#undef STOREQ_U8_AS_U32P
#undef ROTATE32_LEFT

//------------------------------------------------------------------------------
// Subtract-Green Transform

// vtbl?_u8 are marked unavailable for iOS arm64 with Xcode < 6.3, use
// non-standard versions there.
#if defined(__APPLE__) && WEBP_AARCH64 && \
    defined(__apple_build_version__) && (__apple_build_version__< 6020037)
#define USE_VTBLQ
#endif

#ifdef USE_VTBLQ
// 255 = byte will be zeroed
static const uint8_t kGreenShuffle[16] = {
  1, 255, 1, 255, 5, 255, 5, 255, 9, 255, 9, 255, 13, 255, 13, 255
};

static WEBP_INLINE uint8x16_t DoGreenShuffle_NEON(const uint8x16_t argb,
                                                  const uint8x16_t shuffle) {
  return vcombine_u8(vtbl1q_u8(argb, vget_low_u8(shuffle)),
                     vtbl1q_u8(argb, vget_high_u8(shuffle)));
}
#else  // !USE_VTBLQ
// 255 = byte will be zeroed
static const uint8_t kGreenShuffle[8] = { 1, 255, 1, 255, 5, 255, 5, 255  };

static WEBP_INLINE uint8x16_t DoGreenShuffle_NEON(const uint8x16_t argb,
                                                  const uint8x8_t shuffle) {
  return vcombine_u8(vtbl1_u8(vget_low_u8(argb), shuffle),
                     vtbl1_u8(vget_high_u8(argb), shuffle));
}
#endif  // USE_VTBLQ

static void AddGreenToBlueAndRed_NEON(const uint32_t* src, int num_pixels,
                                      uint32_t* dst) {
  const uint32_t* const end = src + (num_pixels & ~3);
#ifdef USE_VTBLQ
  const uint8x16_t shuffle = vld1q_u8(kGreenShuffle);
#else
  const uint8x8_t shuffle = vld1_u8(kGreenShuffle);
#endif
  for (; src < end; src += 4, dst += 4) {
    const uint8x16_t argb = vld1q_u8((const uint8_t*)src);
    const uint8x16_t greens = DoGreenShuffle_NEON(argb, shuffle);
    vst1q_u8((uint8_t*)dst, vaddq_u8(argb, greens));
  }
  // fallthrough and finish off with plain-C
  VP8LAddGreenToBlueAndRed_C(src, num_pixels & 3, dst);
}

//------------------------------------------------------------------------------
// Color Transform

static void TransformColorInverse_NEON(const VP8LMultipliers* const m,
                                       const uint32_t* const src,
                                       int num_pixels, uint32_t* dst) {
// sign-extended multiplying constants, pre-shifted by 6.
#define CST(X)  (((int16_t)(m->X << 8)) >> 6)
  const int16_t rb[8] = {
    CST(green_to_blue_), CST(green_to_red_),
    CST(green_to_blue_), CST(green_to_red_),
    CST(green_to_blue_), CST(green_to_red_),
    CST(green_to_blue_), CST(green_to_red_)
  };
  const int16x8_t mults_rb = vld1q_s16(rb);
  const int16_t b2[8] = {
    0, CST(red_to_blue_), 0, CST(red_to_blue_),
    0, CST(red_to_blue_), 0, CST(red_to_blue_),
  };
  const int16x8_t mults_b2 = vld1q_s16(b2);
#undef CST
#ifdef USE_VTBLQ
  static const uint8_t kg0g0[16] = {
    255, 1, 255, 1, 255, 5, 255, 5, 255, 9, 255, 9, 255, 13, 255, 13
  };
  const uint8x16_t shuffle = vld1q_u8(kg0g0);
#else
  static const uint8_t k0g0g[8] = { 255, 1, 255, 1, 255, 5, 255, 5 };
  const uint8x8_t shuffle = vld1_u8(k0g0g);
#endif
  const uint32x4_t mask_ag = vdupq_n_u32(0xff00ff00u);
  int i;
  for (i = 0; i + 4 <= num_pixels; i += 4) {
    const uint8x16_t in = vld1q_u8((const uint8_t*)(src + i));
    const uint32x4_t a0g0 = vandq_u32(vreinterpretq_u32_u8(in), mask_ag);
    // 0 g 0 g
    const uint8x16_t greens = DoGreenShuffle_NEON(in, shuffle);
    // x dr  x db1
    const int16x8_t A = vqdmulhq_s16(vreinterpretq_s16_u8(greens), mults_rb);
    // x r'  x   b'
    const int8x16_t B = vaddq_s8(vreinterpretq_s8_u8(in),
                                 vreinterpretq_s8_s16(A));
    // r' 0   b' 0
    const int16x8_t C = vshlq_n_s16(vreinterpretq_s16_s8(B), 8);
    // x db2  0  0
    const int16x8_t D = vqdmulhq_s16(C, mults_b2);
    // 0  x db2  0
    const uint32x4_t E = vshrq_n_u32(vreinterpretq_u32_s16(D), 8);
    // r' x  b'' 0
    const int8x16_t F = vaddq_s8(vreinterpretq_s8_u32(E),
                                 vreinterpretq_s8_s16(C));
    // 0  r'  0  b''
    const uint16x8_t G = vshrq_n_u16(vreinterpretq_u16_s8(F), 8);
    const uint32x4_t out = vorrq_u32(vreinterpretq_u32_u16(G), a0g0);
    vst1q_u32(dst + i, out);
  }
  // Fall-back to C-version for left-overs.
  VP8LTransformColorInverse_C(m, src + i, num_pixels - i, dst + i);
}

#undef USE_VTBLQ

//------------------------------------------------------------------------------
// Entry point

extern void VP8LDspInitNEON(void);

WEBP_TSAN_IGNORE_FUNCTION void VP8LDspInitNEON(void) {
  VP8LPredictors[5] = Predictor5_NEON;
  VP8LPredictors[6] = Predictor6_NEON;
  VP8LPredictors[7] = Predictor7_NEON;
  VP8LPredictors[13] = Predictor13_NEON;

  VP8LPredictorsAdd[0] = PredictorAdd0_NEON;
  VP8LPredictorsAdd[1] = PredictorAdd1_NEON;
  VP8LPredictorsAdd[2] = PredictorAdd2_NEON;
  VP8LPredictorsAdd[3] = PredictorAdd3_NEON;
  VP8LPredictorsAdd[4] = PredictorAdd4_NEON;
  VP8LPredictorsAdd[5] = PredictorAdd5_NEON;
  VP8LPredictorsAdd[6] = PredictorAdd6_NEON;
  VP8LPredictorsAdd[7] = PredictorAdd7_NEON;
  VP8LPredictorsAdd[8] = PredictorAdd8_NEON;
  VP8LPredictorsAdd[9] = PredictorAdd9_NEON;
  VP8LPredictorsAdd[10] = PredictorAdd10_NEON;
  VP8LPredictorsAdd[11] = PredictorAdd11_NEON;
  VP8LPredictorsAdd[12] = PredictorAdd12_NEON;
  VP8LPredictorsAdd[13] = PredictorAdd13_NEON;

  VP8LConvertBGRAToRGBA = ConvertBGRAToRGBA_NEON;
  VP8LConvertBGRAToBGR = ConvertBGRAToBGR_NEON;
  VP8LConvertBGRAToRGB = ConvertBGRAToRGB_NEON;

  VP8LAddGreenToBlueAndRed = AddGreenToBlueAndRed_NEON;
  VP8LTransformColorInverse = TransformColorInverse_NEON;
}

#else  // !WEBP_USE_NEON

WEBP_DSP_INIT_STUB(VP8LDspInitNEON)

#endif  // WEBP_USE_NEON