/*
 * Copyright (c) 2024, Alliance for Open Media. All rights reserved.
 *
 * This source code is subject to the terms of the BSD 2 Clause License and
 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
 * was not distributed with this source code in the LICENSE file, you can
 * obtain it at www.aomedia.org/license/software. If the Alliance for Open
 * Media Patent License 1.0 was not distributed with this source code in the
 * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
 */

#include <arm_neon.h>
#include <assert.h>
#include <stdint.h>

#include "config/aom_config.h"
#include "config/av1_rtcd.h"

#include "aom_dsp/aom_dsp_common.h"
#include "aom_dsp/aom_filter.h"
#include "aom_dsp/arm/mem_neon.h"
#include "aom_dsp/arm/transpose_neon.h"
#include "av1/common/arm/convolve_scale_neon.h"
#include "av1/common/convolve.h"
#include "av1/common/filter.h"

static inline int16x4_t convolve8_4_h(const int16x4_t s0, const int16x4_t s1,
                                      const int16x4_t s2, const int16x4_t s3,
                                      const int16x4_t s4, const int16x4_t s5,
                                      const int16x4_t s6, const int16x4_t s7,
                                      const int16x8_t filter,
                                      const int32x4_t horiz_const) {
  int16x4_t filter_lo = vget_low_s16(filter);
  int16x4_t filter_hi = vget_high_s16(filter);

  int32x4_t sum = horiz_const;
  sum = vmlal_lane_s16(sum, s0, filter_lo, 0);
  sum = vmlal_lane_s16(sum, s1, filter_lo, 1);
  sum = vmlal_lane_s16(sum, s2, filter_lo, 2);
  sum = vmlal_lane_s16(sum, s3, filter_lo, 3);
  sum = vmlal_lane_s16(sum, s4, filter_hi, 0);
  sum = vmlal_lane_s16(sum, s5, filter_hi, 1);
  sum = vmlal_lane_s16(sum, s6, filter_hi, 2);
  sum = vmlal_lane_s16(sum, s7, filter_hi, 3);

  return vshrn_n_s32(sum, ROUND0_BITS);
}

static inline int16x8_t convolve8_8_h(const int16x8_t s0, const int16x8_t s1,
                                      const int16x8_t s2, const int16x8_t s3,
                                      const int16x8_t s4, const int16x8_t s5,
                                      const int16x8_t s6, const int16x8_t s7,
                                      const int16x8_t filter,
                                      const int16x8_t horiz_const) {
  int16x4_t filter_lo = vget_low_s16(filter);
  int16x4_t filter_hi = vget_high_s16(filter);

  int16x8_t sum = horiz_const;
  sum = vmlaq_lane_s16(sum, s0, filter_lo, 0);
  sum = vmlaq_lane_s16(sum, s1, filter_lo, 1);
  sum = vmlaq_lane_s16(sum, s2, filter_lo, 2);
  sum = vmlaq_lane_s16(sum, s3, filter_lo, 3);
  sum = vmlaq_lane_s16(sum, s4, filter_hi, 0);
  sum = vmlaq_lane_s16(sum, s5, filter_hi, 1);
  sum = vmlaq_lane_s16(sum, s6, filter_hi, 2);
  sum = vmlaq_lane_s16(sum, s7, filter_hi, 3);

  return vshrq_n_s16(sum, ROUND0_BITS - 1);
}

static inline void convolve_horiz_scale_8tap_neon(const uint8_t *src,
                                                  int src_stride, int16_t *dst,
                                                  int dst_stride, int w, int h,
                                                  const int16_t *x_filter,
                                                  const int subpel_x_qn,
                                                  const int x_step_qn) {
  DECLARE_ALIGNED(16, int16_t, temp[8 * 8]);
  const int bd = 8;

  if (w == 4) {
    // The shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding shifts.
    const int32x4_t horiz_offset =
        vdupq_n_s32((1 << (bd + FILTER_BITS - 1)) + (1 << (ROUND0_BITS - 1)));

    do {
      int x_qn = subpel_x_qn;

      // Process a 4x4 tile.
      for (int r = 0; r < 4; ++r) {
        const uint8_t *const s = &src[x_qn >> SCALE_SUBPEL_BITS];

        const ptrdiff_t filter_offset =
            SUBPEL_TAPS * ((x_qn & SCALE_SUBPEL_MASK) >> SCALE_EXTRA_BITS);
        const int16x8_t filter = vld1q_s16(x_filter + filter_offset);

        uint8x8_t t0, t1, t2, t3;
        load_u8_8x4(s, src_stride, &t0, &t1, &t2, &t3);

        transpose_elems_inplace_u8_8x4(&t0, &t1, &t2, &t3);

        int16x4_t s0 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t0)));
        int16x4_t s1 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t1)));
        int16x4_t s2 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t2)));
        int16x4_t s3 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t3)));
        int16x4_t s4 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t0)));
        int16x4_t s5 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t1)));
        int16x4_t s6 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t2)));
        int16x4_t s7 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t3)));

        int16x4_t d0 =
            convolve8_4_h(s0, s1, s2, s3, s4, s5, s6, s7, filter, horiz_offset);

        vst1_s16(&temp[r * 4], d0);
        x_qn += x_step_qn;
      }

      // Transpose the 4x4 result tile and store.
      int16x4_t d0, d1, d2, d3;
      load_s16_4x4(temp, 4, &d0, &d1, &d2, &d3);

      transpose_elems_inplace_s16_4x4(&d0, &d1, &d2, &d3);

      store_s16_4x4(dst, dst_stride, d0, d1, d2, d3);

      dst += 4 * dst_stride;
      src += 4 * src_stride;
      h -= 4;
    } while (h > 0);
  } else {
    // The shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding shifts.
    // The additional -1 is needed because we are halving the filter values.
    const int16x8_t horiz_offset =
        vdupq_n_s16((1 << (bd + FILTER_BITS - 2)) + (1 << (ROUND0_BITS - 2)));

    do {
      int x_qn = subpel_x_qn;
      int16_t *d = dst;
      int width = w;

      do {
        // Process an 8x8 tile.
        for (int r = 0; r < 8; ++r) {
          const uint8_t *const s = &src[(x_qn >> SCALE_SUBPEL_BITS)];

          const ptrdiff_t filter_offset =
              SUBPEL_TAPS * ((x_qn & SCALE_SUBPEL_MASK) >> SCALE_EXTRA_BITS);
          int16x8_t filter = vld1q_s16(x_filter + filter_offset);
          // Filter values are all even so halve them to allow convolution
          // kernel computations to stay in 16-bit element types.
          filter = vshrq_n_s16(filter, 1);

          uint8x8_t t0, t1, t2, t3, t4, t5, t6, t7;
          load_u8_8x8(s, src_stride, &t0, &t1, &t2, &t3, &t4, &t5, &t6, &t7);

          transpose_elems_u8_8x8(t0, t1, t2, t3, t4, t5, t6, t7, &t0, &t1, &t2,
                                 &t3, &t4, &t5, &t6, &t7);

          int16x8_t s0 = vreinterpretq_s16_u16(vmovl_u8(t0));
          int16x8_t s1 = vreinterpretq_s16_u16(vmovl_u8(t1));
          int16x8_t s2 = vreinterpretq_s16_u16(vmovl_u8(t2));
          int16x8_t s3 = vreinterpretq_s16_u16(vmovl_u8(t3));
          int16x8_t s4 = vreinterpretq_s16_u16(vmovl_u8(t4));
          int16x8_t s5 = vreinterpretq_s16_u16(vmovl_u8(t5));
          int16x8_t s6 = vreinterpretq_s16_u16(vmovl_u8(t6));
          int16x8_t s7 = vreinterpretq_s16_u16(vmovl_u8(t7));

          int16x8_t d0 = convolve8_8_h(s0, s1, s2, s3, s4, s5, s6, s7, filter,
                                       horiz_offset);

          vst1q_s16(&temp[r * 8], d0);

          x_qn += x_step_qn;
        }

        // Transpose the 8x8 result tile and store.
        int16x8_t d0, d1, d2, d3, d4, d5, d6, d7;
        load_s16_8x8(temp, 8, &d0, &d1, &d2, &d3, &d4, &d5, &d6, &d7);

        transpose_elems_inplace_s16_8x8(&d0, &d1, &d2, &d3, &d4, &d5, &d6, &d7);

        store_s16_8x8(d, dst_stride, d0, d1, d2, d3, d4, d5, d6, d7);

        d += 8;
        width -= 8;
      } while (width != 0);

      dst += 8 * dst_stride;
      src += 8 * src_stride;
      h -= 8;
    } while (h > 0);
  }
}

static inline int16x4_t convolve6_4_h(const int16x4_t s0, const int16x4_t s1,
                                      const int16x4_t s2, const int16x4_t s3,
                                      const int16x4_t s4, const int16x4_t s5,
                                      const int16x8_t filter,
                                      const int32x4_t horiz_const) {
  int16x4_t filter_lo = vget_low_s16(filter);
  int16x4_t filter_hi = vget_high_s16(filter);

  int32x4_t sum = horiz_const;
  // Filter values at indices 0 and 7 are 0.
  sum = vmlal_lane_s16(sum, s0, filter_lo, 1);
  sum = vmlal_lane_s16(sum, s1, filter_lo, 2);
  sum = vmlal_lane_s16(sum, s2, filter_lo, 3);
  sum = vmlal_lane_s16(sum, s3, filter_hi, 0);
  sum = vmlal_lane_s16(sum, s4, filter_hi, 1);
  sum = vmlal_lane_s16(sum, s5, filter_hi, 2);

  return vshrn_n_s32(sum, ROUND0_BITS);
}

static inline int16x8_t convolve6_8_h(const int16x8_t s0, const int16x8_t s1,
                                      const int16x8_t s2, const int16x8_t s3,
                                      const int16x8_t s4, const int16x8_t s5,
                                      const int16x8_t filter,
                                      const int16x8_t horiz_const) {
  int16x4_t filter_lo = vget_low_s16(filter);
  int16x4_t filter_hi = vget_high_s16(filter);

  int16x8_t sum = horiz_const;
  // Filter values at indices 0 and 7 are 0.
  sum = vmlaq_lane_s16(sum, s0, filter_lo, 1);
  sum = vmlaq_lane_s16(sum, s1, filter_lo, 2);
  sum = vmlaq_lane_s16(sum, s2, filter_lo, 3);
  sum = vmlaq_lane_s16(sum, s3, filter_hi, 0);
  sum = vmlaq_lane_s16(sum, s4, filter_hi, 1);
  sum = vmlaq_lane_s16(sum, s5, filter_hi, 2);

  // We halved the filter values so -1 from right shift.
  return vshrq_n_s16(sum, ROUND0_BITS - 1);
}

static inline void convolve_horiz_scale_6tap_neon(const uint8_t *src,
                                                  int src_stride, int16_t *dst,
                                                  int dst_stride, int w, int h,
                                                  const int16_t *x_filter,
                                                  const int subpel_x_qn,
                                                  const int x_step_qn) {
  DECLARE_ALIGNED(16, int16_t, temp[8 * 8]);
  const int bd = 8;

  if (w == 4) {
    // The shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding shifts.
    const int32x4_t horiz_offset =
        vdupq_n_s32((1 << (bd + FILTER_BITS - 1)) + (1 << (ROUND0_BITS - 1)));

    do {
      int x_qn = subpel_x_qn;

      // Process a 4x4 tile.
      for (int r = 0; r < 4; ++r) {
        const uint8_t *const s = &src[x_qn >> SCALE_SUBPEL_BITS];

        const ptrdiff_t filter_offset =
            SUBPEL_TAPS * ((x_qn & SCALE_SUBPEL_MASK) >> SCALE_EXTRA_BITS);
        const int16x8_t filter = vld1q_s16(x_filter + filter_offset);

        uint8x8_t t0, t1, t2, t3;
        load_u8_8x4(s, src_stride, &t0, &t1, &t2, &t3);

        transpose_elems_inplace_u8_8x4(&t0, &t1, &t2, &t3);

        int16x4_t s0 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t1)));
        int16x4_t s1 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t2)));
        int16x4_t s2 = vget_low_s16(vreinterpretq_s16_u16(vmovl_u8(t3)));
        int16x4_t s3 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t0)));
        int16x4_t s4 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t1)));
        int16x4_t s5 = vget_high_s16(vreinterpretq_s16_u16(vmovl_u8(t2)));

        int16x4_t d0 =
            convolve6_4_h(s0, s1, s2, s3, s4, s5, filter, horiz_offset);

        vst1_s16(&temp[r * 4], d0);
        x_qn += x_step_qn;
      }

      // Transpose the 4x4 result tile and store.
      int16x4_t d0, d1, d2, d3;
      load_s16_4x4(temp, 4, &d0, &d1, &d2, &d3);

      transpose_elems_inplace_s16_4x4(&d0, &d1, &d2, &d3);

      store_s16_4x4(dst, dst_stride, d0, d1, d2, d3);

      dst += 4 * dst_stride;
      src += 4 * src_stride;
      h -= 4;
    } while (h > 0);
  } else {
    // The shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding shifts.
    // The additional -1 is needed because we are halving the filter values.
    const int16x8_t horiz_offset =
        vdupq_n_s16((1 << (bd + FILTER_BITS - 2)) + (1 << (ROUND0_BITS - 2)));

    do {
      int x_qn = subpel_x_qn;
      int16_t *d = dst;
      int width = w;

      do {
        // Process an 8x8 tile.
        for (int r = 0; r < 8; ++r) {
          const uint8_t *const s = &src[(x_qn >> SCALE_SUBPEL_BITS)];

          const ptrdiff_t filter_offset =
              SUBPEL_TAPS * ((x_qn & SCALE_SUBPEL_MASK) >> SCALE_EXTRA_BITS);
          int16x8_t filter = vld1q_s16(x_filter + filter_offset);
          // Filter values are all even so halve them to allow convolution
          // kernel computations to stay in 16-bit element types.
          filter = vshrq_n_s16(filter, 1);

          uint8x8_t t0, t1, t2, t3, t4, t5, t6, t7;
          load_u8_8x8(s, src_stride, &t0, &t1, &t2, &t3, &t4, &t5, &t6, &t7);

          transpose_elems_u8_8x8(t0, t1, t2, t3, t4, t5, t6, t7, &t0, &t1, &t2,
                                 &t3, &t4, &t5, &t6, &t7);

          int16x8_t s0 = vreinterpretq_s16_u16(vmovl_u8(t1));
          int16x8_t s1 = vreinterpretq_s16_u16(vmovl_u8(t2));
          int16x8_t s2 = vreinterpretq_s16_u16(vmovl_u8(t3));
          int16x8_t s3 = vreinterpretq_s16_u16(vmovl_u8(t4));
          int16x8_t s4 = vreinterpretq_s16_u16(vmovl_u8(t5));
          int16x8_t s5 = vreinterpretq_s16_u16(vmovl_u8(t6));

          int16x8_t d0 =
              convolve6_8_h(s0, s1, s2, s3, s4, s5, filter, horiz_offset);

          vst1q_s16(&temp[r * 8], d0);

          x_qn += x_step_qn;
        }

        // Transpose the 8x8 result tile and store.
        int16x8_t d0, d1, d2, d3, d4, d5, d6, d7;
        load_s16_8x8(temp, 8, &d0, &d1, &d2, &d3, &d4, &d5, &d6, &d7);

        transpose_elems_inplace_s16_8x8(&d0, &d1, &d2, &d3, &d4, &d5, &d6, &d7);

        store_s16_8x8(d, dst_stride, d0, d1, d2, d3, d4, d5, d6, d7);

        d += 8;
        width -= 8;
      } while (width != 0);

      dst += 8 * dst_stride;
      src += 8 * src_stride;
      h -= 8;
    } while (h > 0);
  }
}

static inline void convolve_horiz_scale_2_8tap_neon(
    const uint8_t *src, int src_stride, int16_t *dst, int dst_stride, int w,
    int h, const int16_t *x_filter) {
  const int bd = 8;

  if (w == 4) {
    // A shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding
    // shifts - which are generally faster than rounding shifts on modern CPUs.
    const int32x4_t horiz_offset =
        vdupq_n_s32((1 << (bd + FILTER_BITS - 1)) + (1 << (ROUND0_BITS - 1)));
    const int16x8_t filter = vld1q_s16(x_filter);

    do {
      uint8x16_t t0, t1, t2, t3;
      load_u8_16x4(src, src_stride, &t0, &t1, &t2, &t3);
      transpose_elems_inplace_u8_16x4(&t0, &t1, &t2, &t3);

      int16x8_t tt0 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t0)));
      int16x8_t tt1 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t1)));
      int16x8_t tt2 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t2)));
      int16x8_t tt3 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t3)));
      int16x8_t tt4 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t0)));
      int16x8_t tt5 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t1)));
      int16x8_t tt6 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t2)));
      int16x8_t tt7 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t3)));

      int16x4_t s0 = vget_low_s16(tt0);
      int16x4_t s1 = vget_low_s16(tt1);
      int16x4_t s2 = vget_low_s16(tt2);
      int16x4_t s3 = vget_low_s16(tt3);
      int16x4_t s4 = vget_high_s16(tt0);
      int16x4_t s5 = vget_high_s16(tt1);
      int16x4_t s6 = vget_high_s16(tt2);
      int16x4_t s7 = vget_high_s16(tt3);
      int16x4_t s8 = vget_low_s16(tt4);
      int16x4_t s9 = vget_low_s16(tt5);
      int16x4_t s10 = vget_low_s16(tt6);
      int16x4_t s11 = vget_low_s16(tt7);
      int16x4_t s12 = vget_high_s16(tt4);
      int16x4_t s13 = vget_high_s16(tt5);

      int16x4_t d0 =
          convolve8_4_h(s0, s1, s2, s3, s4, s5, s6, s7, filter, horiz_offset);
      int16x4_t d1 =
          convolve8_4_h(s2, s3, s4, s5, s6, s7, s8, s9, filter, horiz_offset);
      int16x4_t d2 =
          convolve8_4_h(s4, s5, s6, s7, s8, s9, s10, s11, filter, horiz_offset);
      int16x4_t d3 = convolve8_4_h(s6, s7, s8, s9, s10, s11, s12, s13, filter,
                                   horiz_offset);

      transpose_elems_inplace_s16_4x4(&d0, &d1, &d2, &d3);

      store_s16_4x4(dst, dst_stride, d0, d1, d2, d3);

      dst += 4 * dst_stride;
      src += 4 * src_stride;
      h -= 4;
    } while (h > 0);
  } else {
    // A shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding
    // shifts - which are generally faster than rounding shifts on modern CPUs.
    // The additional -1 is needed because we are halving the filter values.
    const int16x8_t horiz_offset =
        vdupq_n_s16((1 << (bd + FILTER_BITS - 2)) + (1 << (ROUND0_BITS - 2)));
    // Filter values are all even so halve them to allow convolution
    // kernel computations to stay in 16-bit element types.
    const int16x8_t filter = vshrq_n_s16(vld1q_s16(x_filter), 1);

    do {
      const uint8_t *s = src;
      int16_t *d = dst;
      int width = w;

      uint8x8_t t0, t1, t2, t3, t4, t5, t6, t7;
      load_u8_8x8(s, src_stride, &t0, &t1, &t2, &t3, &t4, &t5, &t6, &t7);
      transpose_elems_u8_8x8(t0, t1, t2, t3, t4, t5, t6, t7, &t0, &t1, &t2, &t3,
                             &t4, &t5, &t6, &t7);

      s += 8;

      int16x8_t s0 = vreinterpretq_s16_u16(vmovl_u8(t0));
      int16x8_t s1 = vreinterpretq_s16_u16(vmovl_u8(t1));
      int16x8_t s2 = vreinterpretq_s16_u16(vmovl_u8(t2));
      int16x8_t s3 = vreinterpretq_s16_u16(vmovl_u8(t3));
      int16x8_t s4 = vreinterpretq_s16_u16(vmovl_u8(t4));
      int16x8_t s5 = vreinterpretq_s16_u16(vmovl_u8(t5));
      int16x8_t s6 = vreinterpretq_s16_u16(vmovl_u8(t6));
      int16x8_t s7 = vreinterpretq_s16_u16(vmovl_u8(t7));

      do {
        uint8x8_t t8, t9, t10, t11, t12, t13, t14, t15;
        load_u8_8x8(s, src_stride, &t8, &t9, &t10, &t11, &t12, &t13, &t14,
                    &t15);
        transpose_elems_u8_8x8(t8, t9, t10, t11, t12, t13, t14, t15, &t8, &t9,
                               &t10, &t11, &t12, &t13, &t14, &t15);

        int16x8_t s8 = vreinterpretq_s16_u16(vmovl_u8(t8));
        int16x8_t s9 = vreinterpretq_s16_u16(vmovl_u8(t9));
        int16x8_t s10 = vreinterpretq_s16_u16(vmovl_u8(t10));
        int16x8_t s11 = vreinterpretq_s16_u16(vmovl_u8(t11));
        int16x8_t s12 = vreinterpretq_s16_u16(vmovl_u8(t12));
        int16x8_t s13 = vreinterpretq_s16_u16(vmovl_u8(t13));
        int16x8_t s14 = vreinterpretq_s16_u16(vmovl_u8(t14));
        int16x8_t s15 = vreinterpretq_s16_u16(vmovl_u8(t15));

        int16x8_t d0 =
            convolve8_8_h(s0, s1, s2, s3, s4, s5, s6, s7, filter, horiz_offset);
        int16x8_t d1 =
            convolve8_8_h(s2, s3, s4, s5, s6, s7, s8, s9, filter, horiz_offset);
        int16x8_t d2 = convolve8_8_h(s4, s5, s6, s7, s8, s9, s10, s11, filter,
                                     horiz_offset);
        int16x8_t d3 = convolve8_8_h(s6, s7, s8, s9, s10, s11, s12, s13, filter,
                                     horiz_offset);

        transpose_elems_inplace_s16_8x4(&d0, &d1, &d2, &d3);

        store_s16_4x8(d, dst_stride, vget_low_s16(d0), vget_low_s16(d1),
                      vget_low_s16(d2), vget_low_s16(d3), vget_high_s16(d0),
                      vget_high_s16(d1), vget_high_s16(d2), vget_high_s16(d3));

        s0 = s8;
        s1 = s9;
        s2 = s10;
        s3 = s11;
        s4 = s12;
        s5 = s13;
        s6 = s14;
        s7 = s15;

        s += 8;
        d += 4;
        width -= 4;
      } while (width != 0);

      dst += 8 * dst_stride;
      src += 8 * src_stride;
      h -= 8;
    } while (h > 0);
  }
}

static inline void convolve_horiz_scale_2_6tap_neon(
    const uint8_t *src, int src_stride, int16_t *dst, int dst_stride, int w,
    int h, const int16_t *x_filter) {
  const int bd = 8;

  if (w == 4) {
    // A shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding
    // shifts - which are generally faster than rounding shifts on modern CPUs.
    const int32x4_t horiz_offset =
        vdupq_n_s32((1 << (bd + FILTER_BITS - 1)) + (1 << (ROUND0_BITS - 1)));
    const int16x8_t filter = vld1q_s16(x_filter);

    do {
      uint8x16_t t0, t1, t2, t3;
      load_u8_16x4(src, src_stride, &t0, &t1, &t2, &t3);
      transpose_elems_inplace_u8_16x4(&t0, &t1, &t2, &t3);

      int16x8_t tt0 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t1)));
      int16x8_t tt1 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t2)));
      int16x8_t tt2 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t3)));
      int16x8_t tt3 = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(t0)));
      int16x8_t tt4 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t0)));
      int16x8_t tt5 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t1)));
      int16x8_t tt6 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t2)));
      int16x8_t tt7 = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(t3)));

      int16x4_t s0 = vget_low_s16(tt0);
      int16x4_t s1 = vget_low_s16(tt1);
      int16x4_t s2 = vget_low_s16(tt2);
      int16x4_t s3 = vget_high_s16(tt3);
      int16x4_t s4 = vget_high_s16(tt0);
      int16x4_t s5 = vget_high_s16(tt1);
      int16x4_t s6 = vget_high_s16(tt2);
      int16x4_t s7 = vget_low_s16(tt4);
      int16x4_t s8 = vget_low_s16(tt5);
      int16x4_t s9 = vget_low_s16(tt6);
      int16x4_t s10 = vget_low_s16(tt7);
      int16x4_t s11 = vget_high_s16(tt4);

      int16x4_t d0 =
          convolve6_4_h(s0, s1, s2, s3, s4, s5, filter, horiz_offset);
      int16x4_t d1 =
          convolve6_4_h(s2, s3, s4, s5, s6, s7, filter, horiz_offset);
      int16x4_t d2 =
          convolve6_4_h(s4, s5, s6, s7, s8, s9, filter, horiz_offset);
      int16x4_t d3 =
          convolve6_4_h(s6, s7, s8, s9, s10, s11, filter, horiz_offset);

      transpose_elems_inplace_s16_4x4(&d0, &d1, &d2, &d3);

      store_s16_4x4(dst, dst_stride, d0, d1, d2, d3);

      dst += 4 * dst_stride;
      src += 4 * src_stride;
      h -= 4;
    } while (h > 0);
  } else {
    // A shim of 1 << (ROUND0_BITS - 1) enables us to use non-rounding
    // shifts - which are generally faster than rounding shifts on modern CPUs.
    // The additional -1 is needed because we are halving the filter values.
    const int16x8_t horiz_offset =
        vdupq_n_s16((1 << (bd + FILTER_BITS - 2)) + (1 << (ROUND0_BITS - 2)));
    // Filter values are all even so halve them to allow convolution
    // kernel computations to stay in 16-bit element types.
    const int16x8_t filter = vshrq_n_s16(vld1q_s16(x_filter), 1);

    do {
      const uint8_t *s = src;
      int16_t *d = dst;
      int width = w;

      uint8x8_t t0, t1, t2, t3, t4, t5, t6, t7;
      load_u8_8x8(s, src_stride, &t0, &t1, &t2, &t3, &t4, &t5, &t6, &t7);
      transpose_elems_u8_8x8(t0, t1, t2, t3, t4, t5, t6, t7, &t0, &t1, &t2, &t3,
                             &t4, &t5, &t6, &t7);

      s += 8;

      int16x8_t s0 = vreinterpretq_s16_u16(vmovl_u8(t1));
      int16x8_t s1 = vreinterpretq_s16_u16(vmovl_u8(t2));
      int16x8_t s2 = vreinterpretq_s16_u16(vmovl_u8(t3));
      int16x8_t s3 = vreinterpretq_s16_u16(vmovl_u8(t4));
      int16x8_t s4 = vreinterpretq_s16_u16(vmovl_u8(t5));
      int16x8_t s5 = vreinterpretq_s16_u16(vmovl_u8(t6));
      int16x8_t s6 = vreinterpretq_s16_u16(vmovl_u8(t7));

      do {
        uint8x8_t t8, t9, t10, t11, t12, t13, t14, t15;
        load_u8_8x8(s, src_stride, &t8, &t9, &t10, &t11, &t12, &t13, &t14,
                    &t15);
        transpose_elems_u8_8x8(t8, t9, t10, t11, t12, t13, t14, t15, &t8, &t9,
                               &t10, &t11, &t12, &t13, &t14, &t15);

        int16x8_t s7 = vreinterpretq_s16_u16(vmovl_u8(t8));
        int16x8_t s8 = vreinterpretq_s16_u16(vmovl_u8(t9));
        int16x8_t s9 = vreinterpretq_s16_u16(vmovl_u8(t10));
        int16x8_t s10 = vreinterpretq_s16_u16(vmovl_u8(t11));
        int16x8_t s11 = vreinterpretq_s16_u16(vmovl_u8(t12));
        int16x8_t s12 = vreinterpretq_s16_u16(vmovl_u8(t13));
        int16x8_t s13 = vreinterpretq_s16_u16(vmovl_u8(t14));
        int16x8_t s14 = vreinterpretq_s16_u16(vmovl_u8(t15));

        int16x8_t d0 =
            convolve6_8_h(s0, s1, s2, s3, s4, s5, filter, horiz_offset);
        int16x8_t d1 =
            convolve6_8_h(s2, s3, s4, s5, s6, s7, filter, horiz_offset);
        int16x8_t d2 =
            convolve6_8_h(s4, s5, s6, s7, s8, s9, filter, horiz_offset);
        int16x8_t d3 =
            convolve6_8_h(s6, s7, s8, s9, s10, s11, filter, horiz_offset);

        transpose_elems_inplace_s16_8x4(&d0, &d1, &d2, &d3);

        store_s16_4x8(d, dst_stride, vget_low_s16(d0), vget_low_s16(d1),
                      vget_low_s16(d2), vget_low_s16(d3), vget_high_s16(d0),
                      vget_high_s16(d1), vget_high_s16(d2), vget_high_s16(d3));

        s0 = s8;
        s1 = s9;
        s2 = s10;
        s3 = s11;
        s4 = s12;
        s5 = s13;
        s6 = s14;

        s += 8;
        d += 4;
        width -= 4;
      } while (width != 0);

      dst += 8 * dst_stride;
      src += 8 * src_stride;
      h -= 8;
    } while (h > 0);
  }
}

void av1_convolve_2d_scale_neon(const uint8_t *src, int src_stride,
                                uint8_t *dst, int dst_stride, int w, int h,
                                const InterpFilterParams *filter_params_x,
                                const InterpFilterParams *filter_params_y,
                                const int subpel_x_qn, const int x_step_qn,
                                const int subpel_y_qn, const int y_step_qn,
                                ConvolveParams *conv_params) {
  if (w < 4 || h < 4) {
    av1_convolve_2d_scale_c(src, src_stride, dst, dst_stride, w, h,
                            filter_params_x, filter_params_y, subpel_x_qn,
                            x_step_qn, subpel_y_qn, y_step_qn, conv_params);
    return;
  }

  // For the interpolation 8-tap filters are used.
  assert(filter_params_y->taps <= 8 && filter_params_x->taps <= 8);

  DECLARE_ALIGNED(32, int16_t,
                  im_block[(2 * MAX_SB_SIZE + MAX_FILTER_TAP) * MAX_SB_SIZE]);
  int im_h = (((h - 1) * y_step_qn + subpel_y_qn) >> SCALE_SUBPEL_BITS) +
             filter_params_y->taps;
  int im_stride = MAX_SB_SIZE;
  CONV_BUF_TYPE *dst16 = conv_params->dst;
  const int dst16_stride = conv_params->dst_stride;

  // Account for needing filter_taps / 2 - 1 lines prior and filter_taps / 2
  // lines post both horizontally and vertically.
  const ptrdiff_t horiz_offset = filter_params_x->taps / 2 - 1;
  const ptrdiff_t vert_offset = (filter_params_y->taps / 2 - 1) * src_stride;

  // Horizontal filter

  if (x_step_qn != 2 * (1 << SCALE_SUBPEL_BITS)) {
    if (filter_params_x->interp_filter == MULTITAP_SHARP) {
      convolve_horiz_scale_8tap_neon(
          src - horiz_offset - vert_offset, src_stride, im_block, im_stride, w,
          im_h, filter_params_x->filter_ptr, subpel_x_qn, x_step_qn);
    } else {
      convolve_horiz_scale_6tap_neon(
          src - horiz_offset - vert_offset, src_stride, im_block, im_stride, w,
          im_h, filter_params_x->filter_ptr, subpel_x_qn, x_step_qn);
    }
  } else {
    assert(subpel_x_qn < (1 << SCALE_SUBPEL_BITS));
    // The filter index is calculated using the
    // ((subpel_x_qn + x * x_step_qn) & SCALE_SUBPEL_MASK) >> SCALE_EXTRA_BITS
    // equation, where the values of x are from 0 to w. If x_step_qn is a
    // multiple of SCALE_SUBPEL_MASK we can leave it out of the equation.
    const ptrdiff_t filter_offset =
        SUBPEL_TAPS * ((subpel_x_qn & SCALE_SUBPEL_MASK) >> SCALE_EXTRA_BITS);
    const int16_t *x_filter = filter_params_x->filter_ptr + filter_offset;

    // The source index is calculated using the (subpel_x_qn + x * x_step_qn)
    // >> SCALE_SUBPEL_BITS, where the values of x are from 0 to w. If
    // subpel_x_qn < (1 << SCALE_SUBPEL_BITS) and x_step_qn % (1 <<
    // SCALE_SUBPEL_BITS) == 0, the source index can be determined using the
    // value x * (x_step_qn / (1 << SCALE_SUBPEL_BITS)).
    if (filter_params_x->interp_filter == MULTITAP_SHARP) {
      convolve_horiz_scale_2_8tap_neon(src - horiz_offset - vert_offset,
                                       src_stride, im_block, im_stride, w, im_h,
                                       x_filter);
    } else {
      convolve_horiz_scale_2_6tap_neon(src - horiz_offset - vert_offset,
                                       src_stride, im_block, im_stride, w, im_h,
                                       x_filter);
    }
  }

  // Vertical filter
  if (filter_params_y->interp_filter == MULTITAP_SHARP) {
    if (UNLIKELY(conv_params->is_compound)) {
      if (conv_params->do_average) {
        if (conv_params->use_dist_wtd_comp_avg) {
          compound_dist_wtd_convolve_vert_scale_8tap_neon(
              im_block, im_stride, dst, dst_stride, dst16, dst16_stride, w, h,
              filter_params_y->filter_ptr, conv_params, subpel_y_qn, y_step_qn);
        } else {
          compound_avg_convolve_vert_scale_8tap_neon(
              im_block, im_stride, dst, dst_stride, dst16, dst16_stride, w, h,
              filter_params_y->filter_ptr, subpel_y_qn, y_step_qn);
        }
      } else {
        compound_convolve_vert_scale_8tap_neon(
            im_block, im_stride, dst16, dst16_stride, w, h,
            filter_params_y->filter_ptr, subpel_y_qn, y_step_qn);
      }
    } else {
      convolve_vert_scale_8tap_neon(im_block, im_stride, dst, dst_stride, w, h,
                                    filter_params_y->filter_ptr, subpel_y_qn,
                                    y_step_qn);
    }
  } else {
    if (UNLIKELY(conv_params->is_compound)) {
      if (conv_params->do_average) {
        if (conv_params->use_dist_wtd_comp_avg) {
          compound_dist_wtd_convolve_vert_scale_6tap_neon(
              im_block + im_stride, im_stride, dst, dst_stride, dst16,
              dst16_stride, w, h, filter_params_y->filter_ptr, conv_params,
              subpel_y_qn, y_step_qn);
        } else {
          compound_avg_convolve_vert_scale_6tap_neon(
              im_block + im_stride, im_stride, dst, dst_stride, dst16,
              dst16_stride, w, h, filter_params_y->filter_ptr, subpel_y_qn,
              y_step_qn);
        }
      } else {
        compound_convolve_vert_scale_6tap_neon(
            im_block + im_stride, im_stride, dst16, dst16_stride, w, h,
            filter_params_y->filter_ptr, subpel_y_qn, y_step_qn);
      }
    } else {
      convolve_vert_scale_6tap_neon(
          im_block + im_stride, im_stride, dst, dst_stride, w, h,
          filter_params_y->filter_ptr, subpel_y_qn, y_step_qn);
    }
  }
}