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highbd_variance_neon.c (19940B)


      1 /*
      2 * Copyright (c) 2023 The WebM project authors. All rights reserved.
      3 * Copyright (c) 2022, Alliance for Open Media. All rights reserved.
      4 *
      5 * This source code is subject to the terms of the BSD 2 Clause License and
      6 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
      7 * was not distributed with this source code in the LICENSE file, you can
      8 * obtain it at www.aomedia.org/license/software. If the Alliance for Open
      9 * Media Patent License 1.0 was not distributed with this source code in the
     10 * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
     11 */
     12 
     13 #include <arm_neon.h>
     14 
     15 #include "config/aom_config.h"
     16 #include "config/aom_dsp_rtcd.h"
     17 
     18 #include "aom_dsp/aom_filter.h"
     19 #include "aom_dsp/arm/mem_neon.h"
     20 #include "aom_dsp/arm/sum_neon.h"
     21 #include "aom_dsp/variance.h"
     22 
     23 // Process a block of width 4 two rows at a time.
     24 static inline void highbd_variance_4xh_neon(const uint16_t *src_ptr,
     25                                            int src_stride,
     26                                            const uint16_t *ref_ptr,
     27                                            int ref_stride, int h,
     28                                            uint64_t *sse, int64_t *sum) {
     29  int16x8_t sum_s16 = vdupq_n_s16(0);
     30  int32x4_t sse_s32 = vdupq_n_s32(0);
     31 
     32  int i = h;
     33  do {
     34    const uint16x8_t s = load_unaligned_u16_4x2(src_ptr, src_stride);
     35    const uint16x8_t r = load_unaligned_u16_4x2(ref_ptr, ref_stride);
     36 
     37    int16x8_t diff = vreinterpretq_s16_u16(vsubq_u16(s, r));
     38    sum_s16 = vaddq_s16(sum_s16, diff);
     39 
     40    sse_s32 = vmlal_s16(sse_s32, vget_low_s16(diff), vget_low_s16(diff));
     41    sse_s32 = vmlal_s16(sse_s32, vget_high_s16(diff), vget_high_s16(diff));
     42 
     43    src_ptr += 2 * src_stride;
     44    ref_ptr += 2 * ref_stride;
     45    i -= 2;
     46  } while (i != 0);
     47 
     48  *sum = horizontal_add_s16x8(sum_s16);
     49  *sse = horizontal_add_s32x4(sse_s32);
     50 }
     51 
     52 // For 8-bit and 10-bit data, since we're using two int32x4 accumulators, all
     53 // block sizes can be processed in 32-bit elements (1023*1023*128*32 =
     54 // 4286582784 for a 128x128 block).
     55 static inline void highbd_variance_large_neon(const uint16_t *src_ptr,
     56                                              int src_stride,
     57                                              const uint16_t *ref_ptr,
     58                                              int ref_stride, int w, int h,
     59                                              uint64_t *sse, int64_t *sum) {
     60  int32x4_t sum_s32 = vdupq_n_s32(0);
     61  int32x4_t sse_s32[2] = { vdupq_n_s32(0), vdupq_n_s32(0) };
     62 
     63  int i = h;
     64  do {
     65    int j = 0;
     66    do {
     67      const uint16x8_t s = vld1q_u16(src_ptr + j);
     68      const uint16x8_t r = vld1q_u16(ref_ptr + j);
     69 
     70      const int16x8_t diff = vreinterpretq_s16_u16(vsubq_u16(s, r));
     71      sum_s32 = vpadalq_s16(sum_s32, diff);
     72 
     73      sse_s32[0] =
     74          vmlal_s16(sse_s32[0], vget_low_s16(diff), vget_low_s16(diff));
     75      sse_s32[1] =
     76          vmlal_s16(sse_s32[1], vget_high_s16(diff), vget_high_s16(diff));
     77 
     78      j += 8;
     79    } while (j < w);
     80 
     81    src_ptr += src_stride;
     82    ref_ptr += ref_stride;
     83  } while (--i != 0);
     84 
     85  *sum = horizontal_add_s32x4(sum_s32);
     86  *sse = horizontal_long_add_u32x4(vaddq_u32(
     87      vreinterpretq_u32_s32(sse_s32[0]), vreinterpretq_u32_s32(sse_s32[1])));
     88 }
     89 
     90 static inline void highbd_variance_8xh_neon(const uint16_t *src, int src_stride,
     91                                            const uint16_t *ref, int ref_stride,
     92                                            int h, uint64_t *sse,
     93                                            int64_t *sum) {
     94  highbd_variance_large_neon(src, src_stride, ref, ref_stride, 8, h, sse, sum);
     95 }
     96 
     97 static inline void highbd_variance_16xh_neon(const uint16_t *src,
     98                                             int src_stride,
     99                                             const uint16_t *ref,
    100                                             int ref_stride, int h,
    101                                             uint64_t *sse, int64_t *sum) {
    102  highbd_variance_large_neon(src, src_stride, ref, ref_stride, 16, h, sse, sum);
    103 }
    104 
    105 static inline void highbd_variance_32xh_neon(const uint16_t *src,
    106                                             int src_stride,
    107                                             const uint16_t *ref,
    108                                             int ref_stride, int h,
    109                                             uint64_t *sse, int64_t *sum) {
    110  highbd_variance_large_neon(src, src_stride, ref, ref_stride, 32, h, sse, sum);
    111 }
    112 
    113 static inline void highbd_variance_64xh_neon(const uint16_t *src,
    114                                             int src_stride,
    115                                             const uint16_t *ref,
    116                                             int ref_stride, int h,
    117                                             uint64_t *sse, int64_t *sum) {
    118  highbd_variance_large_neon(src, src_stride, ref, ref_stride, 64, h, sse, sum);
    119 }
    120 
    121 static inline void highbd_variance_128xh_neon(const uint16_t *src,
    122                                              int src_stride,
    123                                              const uint16_t *ref,
    124                                              int ref_stride, int h,
    125                                              uint64_t *sse, int64_t *sum) {
    126  highbd_variance_large_neon(src, src_stride, ref, ref_stride, 128, h, sse,
    127                             sum);
    128 }
    129 
    130 // For 12-bit data, we can only accumulate up to 128 elements in the sum of
    131 // squares (4095*4095*128 = 2146435200), and because we're using two int32x4
    132 // accumulators, we can only process up to 32 32-element rows (32*32/8 = 128)
    133 // or 16 64-element rows before we have to accumulate into 64-bit elements.
    134 // Therefore blocks of size 32x64, 64x32, 64x64, 64x128, 128x64, 128x128 are
    135 // processed in a different helper function.
    136 
    137 // Process a block of any size where the width is divisible by 8, with
    138 // accumulation into 64-bit elements.
    139 static inline void highbd_variance_xlarge_neon(
    140    const uint16_t *src_ptr, int src_stride, const uint16_t *ref_ptr,
    141    int ref_stride, int w, int h, int h_limit, uint64_t *sse, int64_t *sum) {
    142  int32x4_t sum_s32 = vdupq_n_s32(0);
    143  int64x2_t sse_s64 = vdupq_n_s64(0);
    144 
    145  // 'h_limit' is the number of 'w'-width rows we can process before our 32-bit
    146  // accumulator overflows. After hitting this limit we accumulate into 64-bit
    147  // elements.
    148  int h_tmp = h > h_limit ? h_limit : h;
    149 
    150  int i = 0;
    151  do {
    152    int32x4_t sse_s32[2] = { vdupq_n_s32(0), vdupq_n_s32(0) };
    153    do {
    154      int j = 0;
    155      do {
    156        const uint16x8_t s0 = vld1q_u16(src_ptr + j);
    157        const uint16x8_t r0 = vld1q_u16(ref_ptr + j);
    158 
    159        const int16x8_t diff = vreinterpretq_s16_u16(vsubq_u16(s0, r0));
    160        sum_s32 = vpadalq_s16(sum_s32, diff);
    161 
    162        sse_s32[0] =
    163            vmlal_s16(sse_s32[0], vget_low_s16(diff), vget_low_s16(diff));
    164        sse_s32[1] =
    165            vmlal_s16(sse_s32[1], vget_high_s16(diff), vget_high_s16(diff));
    166 
    167        j += 8;
    168      } while (j < w);
    169 
    170      src_ptr += src_stride;
    171      ref_ptr += ref_stride;
    172      i++;
    173    } while (i < h_tmp);
    174 
    175    sse_s64 = vpadalq_s32(sse_s64, sse_s32[0]);
    176    sse_s64 = vpadalq_s32(sse_s64, sse_s32[1]);
    177    h_tmp += h_limit;
    178  } while (i < h);
    179 
    180  *sum = horizontal_add_s32x4(sum_s32);
    181  *sse = (uint64_t)horizontal_add_s64x2(sse_s64);
    182 }
    183 
    184 static inline void highbd_variance_32xh_xlarge_neon(
    185    const uint16_t *src, int src_stride, const uint16_t *ref, int ref_stride,
    186    int h, uint64_t *sse, int64_t *sum) {
    187  highbd_variance_xlarge_neon(src, src_stride, ref, ref_stride, 32, h, 32, sse,
    188                              sum);
    189 }
    190 
    191 static inline void highbd_variance_64xh_xlarge_neon(
    192    const uint16_t *src, int src_stride, const uint16_t *ref, int ref_stride,
    193    int h, uint64_t *sse, int64_t *sum) {
    194  highbd_variance_xlarge_neon(src, src_stride, ref, ref_stride, 64, h, 16, sse,
    195                              sum);
    196 }
    197 
    198 static inline void highbd_variance_128xh_xlarge_neon(
    199    const uint16_t *src, int src_stride, const uint16_t *ref, int ref_stride,
    200    int h, uint64_t *sse, int64_t *sum) {
    201  highbd_variance_xlarge_neon(src, src_stride, ref, ref_stride, 128, h, 8, sse,
    202                              sum);
    203 }
    204 
    205 #define HBD_VARIANCE_WXH_8_NEON(w, h)                                 \
    206  uint32_t aom_highbd_8_variance##w##x##h##_neon(                     \
    207      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr, \
    208      int ref_stride, uint32_t *sse) {                                \
    209    int sum;                                                          \
    210    uint64_t sse_long = 0;                                            \
    211    int64_t sum_long = 0;                                             \
    212    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                     \
    213    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                     \
    214    highbd_variance_##w##xh_neon(src, src_stride, ref, ref_stride, h, \
    215                                 &sse_long, &sum_long);               \
    216    *sse = (uint32_t)sse_long;                                        \
    217    sum = (int)sum_long;                                              \
    218    return *sse - (uint32_t)(((int64_t)sum * sum) / (w * h));         \
    219  }
    220 
    221 #define HBD_VARIANCE_WXH_10_NEON(w, h)                                \
    222  uint32_t aom_highbd_10_variance##w##x##h##_neon(                    \
    223      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr, \
    224      int ref_stride, uint32_t *sse) {                                \
    225    int sum;                                                          \
    226    int64_t var;                                                      \
    227    uint64_t sse_long = 0;                                            \
    228    int64_t sum_long = 0;                                             \
    229    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                     \
    230    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                     \
    231    highbd_variance_##w##xh_neon(src, src_stride, ref, ref_stride, h, \
    232                                 &sse_long, &sum_long);               \
    233    *sse = (uint32_t)ROUND_POWER_OF_TWO(sse_long, 4);                 \
    234    sum = (int)ROUND_POWER_OF_TWO(sum_long, 2);                       \
    235    var = (int64_t)(*sse) - (((int64_t)sum * sum) / (w * h));         \
    236    return (var >= 0) ? (uint32_t)var : 0;                            \
    237  }
    238 
    239 #define HBD_VARIANCE_WXH_12_NEON(w, h)                                \
    240  uint32_t aom_highbd_12_variance##w##x##h##_neon(                    \
    241      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr, \
    242      int ref_stride, uint32_t *sse) {                                \
    243    int sum;                                                          \
    244    int64_t var;                                                      \
    245    uint64_t sse_long = 0;                                            \
    246    int64_t sum_long = 0;                                             \
    247    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                     \
    248    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                     \
    249    highbd_variance_##w##xh_neon(src, src_stride, ref, ref_stride, h, \
    250                                 &sse_long, &sum_long);               \
    251    *sse = (uint32_t)ROUND_POWER_OF_TWO(sse_long, 8);                 \
    252    sum = (int)ROUND_POWER_OF_TWO(sum_long, 4);                       \
    253    var = (int64_t)(*sse) - (((int64_t)sum * sum) / (w * h));         \
    254    return (var >= 0) ? (uint32_t)var : 0;                            \
    255  }
    256 
    257 #define HBD_VARIANCE_WXH_12_XLARGE_NEON(w, h)                                \
    258  uint32_t aom_highbd_12_variance##w##x##h##_neon(                           \
    259      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr,        \
    260      int ref_stride, uint32_t *sse) {                                       \
    261    int sum;                                                                 \
    262    int64_t var;                                                             \
    263    uint64_t sse_long = 0;                                                   \
    264    int64_t sum_long = 0;                                                    \
    265    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                            \
    266    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                            \
    267    highbd_variance_##w##xh_xlarge_neon(src, src_stride, ref, ref_stride, h, \
    268                                        &sse_long, &sum_long);               \
    269    *sse = (uint32_t)ROUND_POWER_OF_TWO(sse_long, 8);                        \
    270    sum = (int)ROUND_POWER_OF_TWO(sum_long, 4);                              \
    271    var = (int64_t)(*sse) - (((int64_t)sum * sum) / (w * h));                \
    272    return (var >= 0) ? (uint32_t)var : 0;                                   \
    273  }
    274 
    275 // 8-bit
    276 HBD_VARIANCE_WXH_8_NEON(4, 4)
    277 HBD_VARIANCE_WXH_8_NEON(4, 8)
    278 
    279 HBD_VARIANCE_WXH_8_NEON(8, 4)
    280 HBD_VARIANCE_WXH_8_NEON(8, 8)
    281 HBD_VARIANCE_WXH_8_NEON(8, 16)
    282 
    283 HBD_VARIANCE_WXH_8_NEON(16, 8)
    284 HBD_VARIANCE_WXH_8_NEON(16, 16)
    285 HBD_VARIANCE_WXH_8_NEON(16, 32)
    286 
    287 HBD_VARIANCE_WXH_8_NEON(32, 16)
    288 HBD_VARIANCE_WXH_8_NEON(32, 32)
    289 HBD_VARIANCE_WXH_8_NEON(32, 64)
    290 
    291 HBD_VARIANCE_WXH_8_NEON(64, 32)
    292 HBD_VARIANCE_WXH_8_NEON(64, 64)
    293 HBD_VARIANCE_WXH_8_NEON(64, 128)
    294 
    295 HBD_VARIANCE_WXH_8_NEON(128, 64)
    296 HBD_VARIANCE_WXH_8_NEON(128, 128)
    297 
    298 // 10-bit
    299 HBD_VARIANCE_WXH_10_NEON(4, 4)
    300 HBD_VARIANCE_WXH_10_NEON(4, 8)
    301 
    302 HBD_VARIANCE_WXH_10_NEON(8, 4)
    303 HBD_VARIANCE_WXH_10_NEON(8, 8)
    304 HBD_VARIANCE_WXH_10_NEON(8, 16)
    305 
    306 HBD_VARIANCE_WXH_10_NEON(16, 8)
    307 HBD_VARIANCE_WXH_10_NEON(16, 16)
    308 HBD_VARIANCE_WXH_10_NEON(16, 32)
    309 
    310 HBD_VARIANCE_WXH_10_NEON(32, 16)
    311 HBD_VARIANCE_WXH_10_NEON(32, 32)
    312 HBD_VARIANCE_WXH_10_NEON(32, 64)
    313 
    314 HBD_VARIANCE_WXH_10_NEON(64, 32)
    315 HBD_VARIANCE_WXH_10_NEON(64, 64)
    316 HBD_VARIANCE_WXH_10_NEON(64, 128)
    317 
    318 HBD_VARIANCE_WXH_10_NEON(128, 64)
    319 HBD_VARIANCE_WXH_10_NEON(128, 128)
    320 
    321 // 12-bit
    322 HBD_VARIANCE_WXH_12_NEON(4, 4)
    323 HBD_VARIANCE_WXH_12_NEON(4, 8)
    324 
    325 HBD_VARIANCE_WXH_12_NEON(8, 4)
    326 HBD_VARIANCE_WXH_12_NEON(8, 8)
    327 HBD_VARIANCE_WXH_12_NEON(8, 16)
    328 
    329 HBD_VARIANCE_WXH_12_NEON(16, 8)
    330 HBD_VARIANCE_WXH_12_NEON(16, 16)
    331 HBD_VARIANCE_WXH_12_NEON(16, 32)
    332 
    333 HBD_VARIANCE_WXH_12_NEON(32, 16)
    334 HBD_VARIANCE_WXH_12_NEON(32, 32)
    335 HBD_VARIANCE_WXH_12_XLARGE_NEON(32, 64)
    336 
    337 HBD_VARIANCE_WXH_12_XLARGE_NEON(64, 32)
    338 HBD_VARIANCE_WXH_12_XLARGE_NEON(64, 64)
    339 HBD_VARIANCE_WXH_12_XLARGE_NEON(64, 128)
    340 
    341 HBD_VARIANCE_WXH_12_XLARGE_NEON(128, 64)
    342 HBD_VARIANCE_WXH_12_XLARGE_NEON(128, 128)
    343 
    344 #if !CONFIG_REALTIME_ONLY
    345 // 8-bit
    346 HBD_VARIANCE_WXH_8_NEON(4, 16)
    347 
    348 HBD_VARIANCE_WXH_8_NEON(8, 32)
    349 
    350 HBD_VARIANCE_WXH_8_NEON(16, 4)
    351 HBD_VARIANCE_WXH_8_NEON(16, 64)
    352 
    353 HBD_VARIANCE_WXH_8_NEON(32, 8)
    354 
    355 HBD_VARIANCE_WXH_8_NEON(64, 16)
    356 
    357 // 10-bit
    358 HBD_VARIANCE_WXH_10_NEON(4, 16)
    359 
    360 HBD_VARIANCE_WXH_10_NEON(8, 32)
    361 
    362 HBD_VARIANCE_WXH_10_NEON(16, 4)
    363 HBD_VARIANCE_WXH_10_NEON(16, 64)
    364 
    365 HBD_VARIANCE_WXH_10_NEON(32, 8)
    366 
    367 HBD_VARIANCE_WXH_10_NEON(64, 16)
    368 
    369 // 12-bit
    370 HBD_VARIANCE_WXH_12_NEON(4, 16)
    371 
    372 HBD_VARIANCE_WXH_12_NEON(8, 32)
    373 
    374 HBD_VARIANCE_WXH_12_NEON(16, 4)
    375 HBD_VARIANCE_WXH_12_NEON(16, 64)
    376 
    377 HBD_VARIANCE_WXH_12_NEON(32, 8)
    378 
    379 HBD_VARIANCE_WXH_12_NEON(64, 16)
    380 
    381 #endif  // !CONFIG_REALTIME_ONLY
    382 
    383 static inline uint32_t highbd_mse_wxh_neon(const uint16_t *src_ptr,
    384                                           int src_stride,
    385                                           const uint16_t *ref_ptr,
    386                                           int ref_stride, int w, int h,
    387                                           unsigned int *sse) {
    388  uint32x4_t sse_u32[2] = { vdupq_n_u32(0), vdupq_n_u32(0) };
    389 
    390  int i = h;
    391  do {
    392    int j = 0;
    393    do {
    394      uint16x8_t s = vld1q_u16(src_ptr + j);
    395      uint16x8_t r = vld1q_u16(ref_ptr + j);
    396 
    397      uint16x8_t diff = vabdq_u16(s, r);
    398 
    399      sse_u32[0] =
    400          vmlal_u16(sse_u32[0], vget_low_u16(diff), vget_low_u16(diff));
    401      sse_u32[1] =
    402          vmlal_u16(sse_u32[1], vget_high_u16(diff), vget_high_u16(diff));
    403 
    404      j += 8;
    405    } while (j < w);
    406 
    407    src_ptr += src_stride;
    408    ref_ptr += ref_stride;
    409  } while (--i != 0);
    410 
    411  *sse = horizontal_add_u32x4(vaddq_u32(sse_u32[0], sse_u32[1]));
    412  return *sse;
    413 }
    414 
    415 #define HIGHBD_MSE_WXH_NEON(w, h)                                     \
    416  uint32_t aom_highbd_8_mse##w##x##h##_neon(                          \
    417      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr, \
    418      int ref_stride, uint32_t *sse) {                                \
    419    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                     \
    420    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                     \
    421    highbd_mse_wxh_neon(src, src_stride, ref, ref_stride, w, h, sse); \
    422    return *sse;                                                      \
    423  }                                                                   \
    424                                                                      \
    425  uint32_t aom_highbd_10_mse##w##x##h##_neon(                         \
    426      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr, \
    427      int ref_stride, uint32_t *sse) {                                \
    428    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                     \
    429    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                     \
    430    highbd_mse_wxh_neon(src, src_stride, ref, ref_stride, w, h, sse); \
    431    *sse = ROUND_POWER_OF_TWO(*sse, 4);                               \
    432    return *sse;                                                      \
    433  }                                                                   \
    434                                                                      \
    435  uint32_t aom_highbd_12_mse##w##x##h##_neon(                         \
    436      const uint8_t *src_ptr, int src_stride, const uint8_t *ref_ptr, \
    437      int ref_stride, uint32_t *sse) {                                \
    438    uint16_t *src = CONVERT_TO_SHORTPTR(src_ptr);                     \
    439    uint16_t *ref = CONVERT_TO_SHORTPTR(ref_ptr);                     \
    440    highbd_mse_wxh_neon(src, src_stride, ref, ref_stride, w, h, sse); \
    441    *sse = ROUND_POWER_OF_TWO(*sse, 8);                               \
    442    return *sse;                                                      \
    443  }
    444 
    445 HIGHBD_MSE_WXH_NEON(16, 16)
    446 HIGHBD_MSE_WXH_NEON(16, 8)
    447 HIGHBD_MSE_WXH_NEON(8, 16)
    448 HIGHBD_MSE_WXH_NEON(8, 8)
    449 
    450 #undef HIGHBD_MSE_WXH_NEON
    451 
    452 static inline uint64x2_t mse_accumulate_u16_8x2(uint64x2_t sum, uint16x8_t s0,
    453                                                uint16x8_t s1, uint16x8_t d0,
    454                                                uint16x8_t d1) {
    455  uint16x8_t e0 = vabdq_u16(s0, d0);
    456  uint16x8_t e1 = vabdq_u16(s1, d1);
    457 
    458  uint32x4_t mse = vmull_u16(vget_low_u16(e0), vget_low_u16(e0));
    459  mse = vmlal_u16(mse, vget_high_u16(e0), vget_high_u16(e0));
    460  mse = vmlal_u16(mse, vget_low_u16(e1), vget_low_u16(e1));
    461  mse = vmlal_u16(mse, vget_high_u16(e1), vget_high_u16(e1));
    462 
    463  return vpadalq_u32(sum, mse);
    464 }
    465 
    466 uint64_t aom_mse_wxh_16bit_highbd_neon(uint16_t *dst, int dstride,
    467                                       uint16_t *src, int sstride, int w,
    468                                       int h) {
    469  assert((w == 8 || w == 4) && (h == 8 || h == 4));
    470 
    471  uint64x2_t sum = vdupq_n_u64(0);
    472 
    473  if (w == 8) {
    474    do {
    475      uint16x8_t d0 = vld1q_u16(dst + 0 * dstride);
    476      uint16x8_t d1 = vld1q_u16(dst + 1 * dstride);
    477      uint16x8_t s0 = vld1q_u16(src + 0 * sstride);
    478      uint16x8_t s1 = vld1q_u16(src + 1 * sstride);
    479 
    480      sum = mse_accumulate_u16_8x2(sum, s0, s1, d0, d1);
    481 
    482      dst += 2 * dstride;
    483      src += 2 * sstride;
    484      h -= 2;
    485    } while (h != 0);
    486  } else {  // w == 4
    487    do {
    488      uint16x8_t d0 = load_unaligned_u16_4x2(dst + 0 * dstride, dstride);
    489      uint16x8_t d1 = load_unaligned_u16_4x2(dst + 2 * dstride, dstride);
    490      uint16x8_t s0 = load_unaligned_u16_4x2(src + 0 * sstride, sstride);
    491      uint16x8_t s1 = load_unaligned_u16_4x2(src + 2 * sstride, sstride);
    492 
    493      sum = mse_accumulate_u16_8x2(sum, s0, s1, d0, d1);
    494 
    495      dst += 4 * dstride;
    496      src += 4 * sstride;
    497      h -= 4;
    498    } while (h != 0);
    499  }
    500 
    501  return horizontal_add_u64x2(sum);
    502 }