/*
 * Copyright (c) 2023, 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 "blend_a64_mask_neon.h"
#include "common_dsp_rtcd.h"
#include "definitions.h"
#include "mem_neon.h"

static inline uint8x16_t alpha_blend_a64_u8x16(uint8x16_t m, uint8x16_t a, uint8x16_t b) {
    uint16x8_t       blend_u16_lo, blend_u16_hi;
    uint8x8_t        blend_u8_lo, blend_u8_hi;
    const uint8x16_t m_inv = vsubq_u8(vdupq_n_u8(AOM_BLEND_A64_MAX_ALPHA), m);

    blend_u16_lo = vmull_u8(vget_low_u8(m), vget_low_u8(a));
    blend_u16_hi = vmull_u8(vget_high_u8(m), vget_high_u8(a));

    blend_u16_lo = vmlal_u8(blend_u16_lo, vget_low_u8(m_inv), vget_low_u8(b));
    blend_u16_hi = vmlal_u8(blend_u16_hi, vget_high_u8(m_inv), vget_high_u8(b));

    blend_u8_lo = vrshrn_n_u16(blend_u16_lo, AOM_BLEND_A64_ROUND_BITS);
    blend_u8_hi = vrshrn_n_u16(blend_u16_hi, AOM_BLEND_A64_ROUND_BITS);

    return vcombine_u8(blend_u8_lo, blend_u8_hi);
}

static inline uint8x8_t alpha_blend_a64_u8x8(uint8x8_t m, uint8x8_t a, uint8x8_t b) {
    uint16x8_t      blend_u16 = vmull_u8(m, a);
    const uint8x8_t m_inv     = vsub_u8(vdup_n_u8(AOM_BLEND_A64_MAX_ALPHA), m);

    blend_u16 = vmlal_u8(blend_u16, m_inv, b);

    return vrshrn_n_u16(blend_u16, AOM_BLEND_A64_ROUND_BITS);
}

void svt_aom_blend_a64_hmask_neon(uint8_t *dst, uint32_t dst_stride, const uint8_t *src0, uint32_t src0_stride,
                                  const uint8_t *src1, uint32_t src1_stride, const uint8_t *mask, int w, int h) {
    assert(IMPLIES(src0 == dst, src0_stride == dst_stride));
    assert(IMPLIES(src1 == dst, src1_stride == dst_stride));

    assert(h >= 2);
    assert(w >= 2);
    assert(IS_POWER_OF_TWO(h));
    assert(IS_POWER_OF_TWO(w));

    if (w >= 16) {
        do {
            int i = 0;
            do {
                uint8x16_t m0 = vld1q_u8(mask + i);
                uint8x16_t s0 = vld1q_u8(src0 + i);
                uint8x16_t s1 = vld1q_u8(src1 + i);

                uint8x16_t blend = alpha_blend_a64_u8x16(m0, s0, s1);

                vst1q_u8(dst + i, blend);

                i += 16;
            } while (i != w);

            src0 += src0_stride;
            src1 += src1_stride;
            dst += dst_stride;
        } while (--h != 0);
    } else if (w == 8) {
        const uint8x8_t m0 = vld1_u8(mask);
        do {
            uint8x8_t s0 = vld1_u8(src0);
            uint8x8_t s1 = vld1_u8(src1);

            uint8x8_t blend = alpha_blend_a64_u8x8(m0, s0, s1);

            vst1_u8(dst, blend);

            src0 += src0_stride;
            src1 += src1_stride;
            dst += dst_stride;
        } while (--h != 0);
    } else if (w == 4) {
        const uint8x8_t m0 = load_dup_u8_4x2(mask);
        do {
            uint8x8_t s0 = load_u8_4x2(src0, src0_stride);
            uint8x8_t s1 = load_u8_4x2(src1, src1_stride);

            uint8x8_t blend = alpha_blend_a64_u8x8(m0, s0, s1);

            store_u8x4_strided_x2(dst, dst_stride, blend);

            src0 += 2 * src0_stride;
            src1 += 2 * src1_stride;
            dst += 2 * dst_stride;
            h -= 2;
        } while (h != 0);
    } else {
        assert(w == 2);
        const uint8x8_t m0 = vreinterpret_u8_u16(vld1_dup_u16((uint16_t *)mask));
        do {
            uint8x8_t s0 = load_u8_2x2(src0, src0_stride);
            uint8x8_t s1 = load_u8_2x2(src1, src1_stride);

            uint8x8_t blend = alpha_blend_a64_u8x8(m0, s0, s1);

            store_u8x2_strided_x2(dst, dst_stride, blend);

            src0 += 2 * src0_stride;
            src1 += 2 * src1_stride;
            dst += 2 * dst_stride;
            h -= 2;
        } while (h != 0);
    }
}

void svt_aom_blend_a64_vmask_neon(uint8_t *dst, uint32_t dst_stride, const uint8_t *src0, uint32_t src0_stride,
                                  const uint8_t *src1, uint32_t src1_stride, const uint8_t *mask, int w, int h) {
    assert(IMPLIES(src0 == dst, src0_stride == dst_stride));
    assert(IMPLIES(src1 == dst, src1_stride == dst_stride));

    assert(h >= 2);
    assert(w >= 2);
    assert(IS_POWER_OF_TWO(h));
    assert(IS_POWER_OF_TWO(w));

    if (w >= 16) {
        do {
            uint8x16_t m0 = vdupq_n_u8(mask[0]);
            int        i  = 0;
            do {
                uint8x16_t s0 = vld1q_u8(src0 + i);
                uint8x16_t s1 = vld1q_u8(src1 + i);

                uint8x16_t blend = alpha_blend_a64_u8x16(m0, s0, s1);

                vst1q_u8(dst + i, blend);

                i += 16;
            } while (i != w);

            mask += 1;
            src0 += src0_stride;
            src1 += src1_stride;
            dst += dst_stride;
        } while (--h != 0);
    } else if (w == 8) {
        do {
            uint8x8_t m0 = vdup_n_u8(mask[0]);
            uint8x8_t s0 = vld1_u8(src0);
            uint8x8_t s1 = vld1_u8(src1);

            uint8x8_t blend = alpha_blend_a64_u8x8(m0, s0, s1);

            vst1_u8(dst, blend);

            mask += 1;
            src0 += src0_stride;
            src1 += src1_stride;
            dst += dst_stride;
        } while (--h != 0);
    } else if (w == 4) {
        do {
            const uint16x4_t m0 = vdup_n_u16((uint16_t)mask[0]);
            const uint16x4_t m1 = vdup_n_u16((uint16_t)mask[1]);
            const uint8x8_t  m  = vmovn_u16(vcombine_u16(m0, m1));
            uint8x8_t        s0 = load_u8_4x2(src0, src0_stride);
            uint8x8_t        s1 = load_u8_4x2(src1, src1_stride);

            uint8x8_t blend = alpha_blend_a64_u8x8(m, s0, s1);

            store_u8x4_strided_x2(dst, dst_stride, blend);

            mask += 2;
            src0 += 2 * src0_stride;
            src1 += 2 * src1_stride;
            dst += 2 * dst_stride;
            h -= 2;
        } while (h != 0);
    } else {
        assert(w == 2);
        do {
            uint16x4_t m0 = vdup_n_u16(0);
            m0            = vld1_lane_u16((uint16_t *)mask, m0, 0);
            uint8x8_t m   = vzip_u8(vreinterpret_u8_u16(m0), vreinterpret_u8_u16(m0)).val[0];
            uint8x8_t s0  = load_u8_2x2(src0, src0_stride);
            uint8x8_t s1  = load_u8_2x2(src1, src1_stride);

            uint8x8_t blend = alpha_blend_a64_u8x8(m, s0, s1);

            store_u8x2_strided_x2(dst, dst_stride, blend);

            mask += 2;
            src0 += 2 * src0_stride;
            src1 += 2 * src1_stride;
            dst += 2 * dst_stride;
            h -= 2;
        } while (h != 0);
    }
}

static inline uint8x8_t alpha_blend_a64_d16_u16x8(uint16x8_t m, uint16x8_t a, uint16x8_t b, uint16x8_t round_offset) {
    const uint16x8_t m_inv = vsubq_u16(vdupq_n_u16(AOM_BLEND_A64_MAX_ALPHA), m);

    uint32x4_t blend_u32_lo = vmull_u16(vget_low_u16(m), vget_low_u16(a));
    uint32x4_t blend_u32_hi = vmull_u16(vget_high_u16(m), vget_high_u16(a));

    blend_u32_lo = vmlal_u16(blend_u32_lo, vget_low_u16(m_inv), vget_low_u16(b));
    blend_u32_hi = vmlal_u16(blend_u32_hi, vget_high_u16(m_inv), vget_high_u16(b));

    uint16x4_t blend_u16_lo = vshrn_n_u32(blend_u32_lo, AOM_BLEND_A64_ROUND_BITS);
    uint16x4_t blend_u16_hi = vshrn_n_u32(blend_u32_hi, AOM_BLEND_A64_ROUND_BITS);

    uint16x8_t res = vcombine_u16(blend_u16_lo, blend_u16_hi);

    res = vqsubq_u16(res, round_offset);

    return vqrshrn_n_u16(res, 2 * FILTER_BITS - ROUND0_BITS - COMPOUND_ROUND1_BITS);
}

void svt_aom_lowbd_blend_a64_d16_mask_neon(uint8_t *dst, uint32_t dst_stride, const CONV_BUF_TYPE *src0,
                                           uint32_t src0_stride, const CONV_BUF_TYPE *src1, uint32_t src1_stride,
                                           const uint8_t *mask, uint32_t mask_stride, int w, int h, int subw, int subh,
                                           ConvolveParams *conv_params) {
    (void)conv_params;

    const int bd           = 8;
    const int offset_bits  = bd + 2 * FILTER_BITS - ROUND0_BITS;
    const int round_offset = (1 << (offset_bits - COMPOUND_ROUND1_BITS)) +
        (1 << (offset_bits - COMPOUND_ROUND1_BITS - 1));
    const uint16x8_t offset_vec = vdupq_n_u16(round_offset);

    assert(IMPLIES((void *)src0 == dst, src0_stride == dst_stride));
    assert(IMPLIES((void *)src1 == dst, src1_stride == dst_stride));

    assert(h >= 4);
    assert(w >= 4);
    assert(IS_POWER_OF_TWO(h));
    assert(IS_POWER_OF_TWO(w));

    if (subw == 0 && subh == 0) {
        if (w >= 8) {
            do {
                int i = 0;
                do {
                    uint16x8_t m0 = vmovl_u8(vld1_u8(mask + i));
                    uint16x8_t s0 = vld1q_u16(src0 + i);
                    uint16x8_t s1 = vld1q_u16(src1 + i);

                    uint8x8_t blend = alpha_blend_a64_d16_u16x8(m0, s0, s1, offset_vec);

                    vst1_u8(dst + i, blend);
                    i += 8;
                } while (i != w);

                mask += mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                uint16x8_t m0 = vmovl_u8(load_u8_4x2(mask, mask_stride));
                uint16x8_t s0 = load_u16_4x2(src0, src0_stride);
                uint16x8_t s1 = load_u16_4x2(src1, src1_stride);

                uint8x8_t blend = alpha_blend_a64_d16_u16x8(m0, s0, s1, offset_vec);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 2 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    } else if (subw == 1 && subh == 1) {
        if (w >= 8) {
            do {
                int i = 0;
                do {
                    uint8x8_t  m0 = vld1_u8(mask + 0 * mask_stride + 2 * i);
                    uint8x8_t  m1 = vld1_u8(mask + 1 * mask_stride + 2 * i);
                    uint8x8_t  m2 = vld1_u8(mask + 0 * mask_stride + 2 * i + 8);
                    uint8x8_t  m3 = vld1_u8(mask + 1 * mask_stride + 2 * i + 8);
                    uint16x8_t s0 = vld1q_u16(src0 + i);
                    uint16x8_t s1 = vld1q_u16(src1 + i);

                    uint16x8_t m_avg = avg_blend_pairwise_long_u8x8_4(m0, m1, m2, m3);

                    uint8x8_t blend = alpha_blend_a64_d16_u16x8(m_avg, s0, s1, offset_vec);

                    vst1_u8(dst + i, blend);
                    i += 8;
                } while (i != w);

                mask += 2 * mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                uint8x8_t  m0 = vld1_u8(mask + 0 * mask_stride);
                uint8x8_t  m1 = vld1_u8(mask + 1 * mask_stride);
                uint8x8_t  m2 = vld1_u8(mask + 2 * mask_stride);
                uint8x8_t  m3 = vld1_u8(mask + 3 * mask_stride);
                uint16x8_t s0 = load_u16_4x2(src0, src0_stride);
                uint16x8_t s1 = load_u16_4x2(src1, src1_stride);

                uint16x8_t m_avg = avg_blend_pairwise_long_u8x8_4(m0, m1, m2, m3);
                uint8x8_t  blend = alpha_blend_a64_d16_u16x8(m_avg, s0, s1, offset_vec);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 4 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    } else if (subw == 1 && subh == 0) {
        if (w >= 8) {
            do {
                int i = 0;
                do {
                    uint8x8_t  m0 = vld1_u8(mask + 2 * i);
                    uint8x8_t  m1 = vld1_u8(mask + 2 * i + 8);
                    uint16x8_t s0 = vld1q_u16(src0 + i);
                    uint16x8_t s1 = vld1q_u16(src1 + i);

                    uint16x8_t m_avg = vmovl_u8(vrshr_n_u8(vpadd_u8(m0, m1), 1));
                    uint8x8_t  blend = alpha_blend_a64_d16_u16x8(m_avg, s0, s1, offset_vec);

                    vst1_u8(dst + i, blend);
                    i += 8;
                } while (i != w);

                mask += mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                uint8x8_t  m0 = vld1_u8(mask + 0 * mask_stride);
                uint8x8_t  m1 = vld1_u8(mask + 1 * mask_stride);
                uint16x8_t s0 = load_u16_4x2(src0, src0_stride);
                uint16x8_t s1 = load_u16_4x2(src1, src1_stride);

                uint16x8_t m_avg = vmovl_u8(vrshr_n_u8(vpadd_u8(m0, m1), 1));
                uint8x8_t  blend = alpha_blend_a64_d16_u16x8(m_avg, s0, s1, offset_vec);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 2 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    } else {
        if (w >= 8) {
            do {
                int i = 0;
                do {
                    uint8x8_t  m0 = vld1_u8(mask + 0 * mask_stride + i);
                    uint8x8_t  m1 = vld1_u8(mask + 1 * mask_stride + i);
                    uint16x8_t s0 = vld1q_u16(src0 + i);
                    uint16x8_t s1 = vld1q_u16(src1 + i);

                    uint16x8_t m_avg = vmovl_u8(vrhadd_u8(m0, m1));
                    uint8x8_t  blend = alpha_blend_a64_d16_u16x8(m_avg, s0, s1, offset_vec);

                    vst1_u8(dst + i, blend);
                    i += 8;
                } while (i != w);

                mask += 2 * mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                uint8x8_t  m0_2 = load_u8_4x2(mask + 0 * mask_stride, 2 * mask_stride);
                uint8x8_t  m1_3 = load_u8_4x2(mask + 1 * mask_stride, 2 * mask_stride);
                uint16x8_t s0   = load_u16_4x2(src0, src0_stride);
                uint16x8_t s1   = load_u16_4x2(src1, src1_stride);

                uint16x8_t m_avg = vmovl_u8(vrhadd_u8(m0_2, m1_3));
                uint8x8_t  blend = alpha_blend_a64_d16_u16x8(m_avg, s0, s1, offset_vec);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 4 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    }
}

void svt_aom_blend_a64_mask_neon(uint8_t *dst, uint32_t dst_stride, const uint8_t *src0, uint32_t src0_stride,
                                 const uint8_t *src1, uint32_t src1_stride, const uint8_t *mask, uint32_t mask_stride,
                                 int w, int h, int subw, int subh) {
    int i;

    assert(IMPLIES(src0 == dst, src0_stride == dst_stride));
    assert(IMPLIES(src1 == dst, src1_stride == dst_stride));

    assert(h >= 1);
    assert(w >= 1);
    assert(IS_POWER_OF_TWO(h));
    assert(IS_POWER_OF_TWO(w));

    if ((subw | subh) == 0) {
        if (w > 8) {
            do {
                i = 0;
                do {
                    const uint8x16_t m0 = vld1q_u8(mask + i);
                    const uint8x16_t s0 = vld1q_u8(src0 + i);
                    const uint8x16_t s1 = vld1q_u8(src1 + i);

                    const uint8x16_t blend = alpha_blend_a64_u8x16(m0, s0, s1);

                    vst1q_u8(dst + i, blend);
                    i += 16;
                } while (i < w);

                mask += mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else if (w == 8) {
            do {
                const uint8x8_t m0 = vld1_u8(mask);
                const uint8x8_t s0 = vld1_u8(src0);
                const uint8x8_t s1 = vld1_u8(src1);

                const uint8x8_t blend = alpha_blend_a64_u8x8(m0, s0, s1);

                vst1_u8(dst, blend);

                mask += mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                const uint8x8_t m0 = load_u8_4x2(mask, mask_stride);
                const uint8x8_t s0 = load_u8_4x2(src0, src0_stride);
                const uint8x8_t s1 = load_u8_4x2(src1, src1_stride);

                const uint8x8_t blend = alpha_blend_a64_u8x8(m0, s0, s1);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 2 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    } else if ((subw & subh) == 1) {
        if (w > 8) {
            do {
                i = 0;
                do {
                    const uint8x16_t m0 = vld1q_u8(mask + 0 * mask_stride + 2 * i);
                    const uint8x16_t m1 = vld1q_u8(mask + 1 * mask_stride + 2 * i);
                    const uint8x16_t m2 = vld1q_u8(mask + 0 * mask_stride + 2 * i + 16);
                    const uint8x16_t m3 = vld1q_u8(mask + 1 * mask_stride + 2 * i + 16);
                    const uint8x16_t s0 = vld1q_u8(src0 + i);
                    const uint8x16_t s1 = vld1q_u8(src1 + i);

                    const uint8x16_t m_avg = avg_blend_pairwise_u8x16_4(m0, m1, m2, m3);
                    const uint8x16_t blend = alpha_blend_a64_u8x16(m_avg, s0, s1);

                    vst1q_u8(dst + i, blend);

                    i += 16;
                } while (i < w);

                mask += 2 * mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else if (w == 8) {
            do {
                const uint8x8_t m0 = vld1_u8(mask + 0 * mask_stride);
                const uint8x8_t m1 = vld1_u8(mask + 1 * mask_stride);
                const uint8x8_t m2 = vld1_u8(mask + 0 * mask_stride + 8);
                const uint8x8_t m3 = vld1_u8(mask + 1 * mask_stride + 8);
                const uint8x8_t s0 = vld1_u8(src0);
                const uint8x8_t s1 = vld1_u8(src1);

                const uint8x8_t m_avg = avg_blend_pairwise_u8x8_4(m0, m1, m2, m3);
                const uint8x8_t blend = alpha_blend_a64_u8x8(m_avg, s0, s1);

                vst1_u8(dst, blend);

                mask += 2 * mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                const uint8x8_t m0 = vld1_u8(mask + 0 * mask_stride);
                const uint8x8_t m1 = vld1_u8(mask + 1 * mask_stride);
                const uint8x8_t m2 = vld1_u8(mask + 2 * mask_stride);
                const uint8x8_t m3 = vld1_u8(mask + 3 * mask_stride);
                const uint8x8_t s0 = load_u8_4x2(src0, src0_stride);
                const uint8x8_t s1 = load_u8_4x2(src1, src1_stride);

                const uint8x8_t m_avg = avg_blend_pairwise_u8x8_4(m0, m1, m2, m3);
                const uint8x8_t blend = alpha_blend_a64_u8x8(m_avg, s0, s1);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 4 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    } else if (subw == 1 && subh == 0) {
        if (w > 8) {
            do {
                i = 0;

                do {
                    const uint8x16_t m0 = vld1q_u8(mask + 2 * i);
                    const uint8x16_t m1 = vld1q_u8(mask + 2 * i + 16);
                    const uint8x16_t s0 = vld1q_u8(src0 + i);
                    const uint8x16_t s1 = vld1q_u8(src1 + i);

                    const uint8x16_t m_avg = vrshrq_n_u8(vpaddq_u8(m0, m1), 1);
                    const uint8x16_t blend = alpha_blend_a64_u8x16(m_avg, s0, s1);

                    vst1q_u8(dst + i, blend);

                    i += 16;
                } while (i < w);

                mask += mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else if (w == 8) {
            do {
                const uint8x8_t m0 = vld1_u8(mask);
                const uint8x8_t m1 = vld1_u8(mask + 8);
                const uint8x8_t s0 = vld1_u8(src0);
                const uint8x8_t s1 = vld1_u8(src1);

                const uint8x8_t m_avg = vrshr_n_u8(vpadd_u8(m0, m1), 1);
                const uint8x8_t blend = alpha_blend_a64_u8x8(m_avg, s0, s1);

                vst1_u8(dst, blend);

                mask += mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                const uint8x8_t m0 = vld1_u8(mask + 0 * mask_stride);
                const uint8x8_t m1 = vld1_u8(mask + 1 * mask_stride);
                const uint8x8_t s0 = load_u8_4x2(src0, src0_stride);
                const uint8x8_t s1 = load_u8_4x2(src1, src1_stride);

                const uint8x8_t m_avg = vrshr_n_u8(vpadd_u8(m0, m1), 1);
                const uint8x8_t blend = alpha_blend_a64_u8x8(m_avg, s0, s1);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 2 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    } else {
        if (w > 8) {
            do {
                i = 0;
                do {
                    const uint8x16_t m0 = vld1q_u8(mask + 0 * mask_stride + i);
                    const uint8x16_t m1 = vld1q_u8(mask + 1 * mask_stride + i);
                    const uint8x16_t s0 = vld1q_u8(src0 + i);
                    const uint8x16_t s1 = vld1q_u8(src1 + i);

                    const uint8x16_t m_avg = vrhaddq_u8(m0, m1);
                    const uint8x16_t blend = alpha_blend_a64_u8x16(m_avg, s0, s1);

                    vst1q_u8(dst + i, blend);

                    i += 16;
                } while (i < w);

                mask += 2 * mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else if (w == 8) {
            do {
                const uint8x8_t m0 = vld1_u8(mask + 0 * mask_stride);
                const uint8x8_t m1 = vld1_u8(mask + 1 * mask_stride);
                const uint8x8_t s0 = vld1_u8(src0);
                const uint8x8_t s1 = vld1_u8(src1);

                const uint8x8_t m_avg = vrhadd_u8(m0, m1);
                const uint8x8_t blend = alpha_blend_a64_u8x8(m_avg, s0, s1);

                vst1_u8(dst, blend);

                mask += 2 * mask_stride;
                src0 += src0_stride;
                src1 += src1_stride;
                dst += dst_stride;
            } while (--h != 0);
        } else {
            do {
                const uint8x8_t m0_2 = load_u8_4x2(mask + 0 * mask_stride, 2 * mask_stride);
                const uint8x8_t m1_3 = load_u8_4x2(mask + 1 * mask_stride, 2 * mask_stride);
                const uint8x8_t s0   = load_u8_4x2(src0, src0_stride);
                const uint8x8_t s1   = load_u8_4x2(src1, src1_stride);

                const uint8x8_t m_avg = vrhadd_u8(m0_2, m1_3);
                const uint8x8_t blend = alpha_blend_a64_u8x8(m_avg, s0, s1);

                store_u8x4_strided_x2(dst, dst_stride, blend);

                mask += 4 * mask_stride;
                src0 += 2 * src0_stride;
                src1 += 2 * src1_stride;
                dst += 2 * dst_stride;
                h -= 2;
            } while (h != 0);
        }
    }
}
