tor-browser

refmvs.c (36817B)

---

/*
* Copyright © 2020, VideoLAN and dav1d authors
* Copyright © 2020, Two Orioles, LLC
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
*    list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
*    this list of conditions and the following disclaimer in the documentation
*    and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#include "config.h"

#include <limits.h>
#include <stdlib.h>

#include "dav1d/common.h"

#include "common/intops.h"

#include "src/env.h"
#include "src/mem.h"
#include "src/refmvs.h"

static void add_spatial_candidate(refmvs_candidate *const mvstack, int *const cnt,
                                 const int weight, const refmvs_block *const b,
                                 const union refmvs_refpair ref, const mv gmv[2],
                                 int *const have_newmv_match,
                                 int *const have_refmv_match)
{
   if (b->mv.mv[0].n == INVALID_MV) return; // intra block, no intrabc

   if (ref.ref[1] == -1) {
       for (int n = 0; n < 2; n++) {
           if (b->ref.ref[n] == ref.ref[0]) {
               const mv cand_mv = ((b->mf & 1) && gmv[0].n != INVALID_MV) ?
                                  gmv[0] : b->mv.mv[n];

               *have_refmv_match = 1;
               *have_newmv_match |= b->mf >> 1;

               const int last = *cnt;
               for (int m = 0; m < last; m++)
                   if (mvstack[m].mv.mv[0].n == cand_mv.n) {
                       mvstack[m].weight += weight;
                       return;
                   }

               if (last < 8) {
                   mvstack[last].mv.mv[0] = cand_mv;
                   mvstack[last].weight = weight;
                   *cnt = last + 1;
               }
               return;
           }
       }
   } else if (b->ref.pair == ref.pair) {
       const refmvs_mvpair cand_mv = { .mv = {
           [0] = ((b->mf & 1) && gmv[0].n != INVALID_MV) ? gmv[0] : b->mv.mv[0],
           [1] = ((b->mf & 1) && gmv[1].n != INVALID_MV) ? gmv[1] : b->mv.mv[1],
       }};

       *have_refmv_match = 1;
       *have_newmv_match |= b->mf >> 1;

       const int last = *cnt;
       for (int n = 0; n < last; n++)
           if (mvstack[n].mv.n == cand_mv.n) {
               mvstack[n].weight += weight;
               return;
           }

       if (last < 8) {
           mvstack[last].mv = cand_mv;
           mvstack[last].weight = weight;
           *cnt = last + 1;
       }
   }
}

static int scan_row(refmvs_candidate *const mvstack, int *const cnt,
                   const union refmvs_refpair ref, const mv gmv[2],
                   const refmvs_block *b, const int bw4, const int w4,
                   const int max_rows, const int step,
                   int *const have_newmv_match, int *const have_refmv_match)
{
   const refmvs_block *cand_b = b;
   const enum BlockSize first_cand_bs = cand_b->bs;
   const uint8_t *const first_cand_b_dim = dav1d_block_dimensions[first_cand_bs];
   int cand_bw4 = first_cand_b_dim[0];
   int len = imax(step, imin(bw4, cand_bw4));

   if (bw4 <= cand_bw4) {
       // FIXME weight can be higher for odd blocks (bx4 & 1), but then the
       // position of the first block has to be odd already, i.e. not just
       // for row_offset=-3/-5
       // FIXME why can this not be cand_bw4?
       const int weight = bw4 == 1 ? 2 :
                          imax(2, imin(2 * max_rows, first_cand_b_dim[1]));
       add_spatial_candidate(mvstack, cnt, len * weight, cand_b, ref, gmv,
                             have_newmv_match, have_refmv_match);
       return weight >> 1;
   }

   for (int x = 0;;) {
       // FIXME if we overhang above, we could fill a bitmask so we don't have
       // to repeat the add_spatial_candidate() for the next row, but just increase
       // the weight here
       add_spatial_candidate(mvstack, cnt, len * 2, cand_b, ref, gmv,
                             have_newmv_match, have_refmv_match);
       x += len;
       if (x >= w4) return 1;
       cand_b = &b[x];
       cand_bw4 = dav1d_block_dimensions[cand_b->bs][0];
       assert(cand_bw4 < bw4);
       len = imax(step, cand_bw4);
   }
}

static int scan_col(refmvs_candidate *const mvstack, int *const cnt,
                   const union refmvs_refpair ref, const mv gmv[2],
                   /*const*/ refmvs_block *const *b, const int bh4, const int h4,
                   const int bx4, const int max_cols, const int step,
                   int *const have_newmv_match, int *const have_refmv_match)
{
   const refmvs_block *cand_b = &b[0][bx4];
   const enum BlockSize first_cand_bs = cand_b->bs;
   const uint8_t *const first_cand_b_dim = dav1d_block_dimensions[first_cand_bs];
   int cand_bh4 = first_cand_b_dim[1];
   int len = imax(step, imin(bh4, cand_bh4));

   if (bh4 <= cand_bh4) {
       // FIXME weight can be higher for odd blocks (by4 & 1), but then the
       // position of the first block has to be odd already, i.e. not just
       // for col_offset=-3/-5
       // FIXME why can this not be cand_bh4?
       const int weight = bh4 == 1 ? 2 :
                          imax(2, imin(2 * max_cols, first_cand_b_dim[0]));
       add_spatial_candidate(mvstack, cnt, len * weight, cand_b, ref, gmv,
                           have_newmv_match, have_refmv_match);
       return weight >> 1;
   }

   for (int y = 0;;) {
       // FIXME if we overhang above, we could fill a bitmask so we don't have
       // to repeat the add_spatial_candidate() for the next row, but just increase
       // the weight here
       add_spatial_candidate(mvstack, cnt, len * 2, cand_b, ref, gmv,
                             have_newmv_match, have_refmv_match);
       y += len;
       if (y >= h4) return 1;
       cand_b = &b[y][bx4];
       cand_bh4 = dav1d_block_dimensions[cand_b->bs][1];
       assert(cand_bh4 < bh4);
       len = imax(step, cand_bh4);
   }
}

static inline union mv mv_projection(const union mv mv, const int num, const int den) {
   static const uint16_t div_mult[32] = {
          0, 16384, 8192, 5461, 4096, 3276, 2730, 2340,
       2048,  1820, 1638, 1489, 1365, 1260, 1170, 1092,
       1024,   963,  910,  862,  819,  780,  744,  712,
        682,   655,  630,  606,  585,  564,  546,  528
   };
   assert(den > 0 && den < 32);
   assert(num > -32 && num < 32);
   const int frac = num * div_mult[den];
   const int y = mv.y * frac, x = mv.x * frac;
   // Round and clip according to AV1 spec section 7.9.3
   return (union mv) { // 0x3fff == (1 << 14) - 1
       .y = iclip((y + 8192 + (y >> 31)) >> 14, -0x3fff, 0x3fff),
       .x = iclip((x + 8192 + (x >> 31)) >> 14, -0x3fff, 0x3fff)
   };
}

static void add_temporal_candidate(const refmvs_frame *const rf,
                                  refmvs_candidate *const mvstack, int *const cnt,
                                  const refmvs_temporal_block *const rb,
                                  const union refmvs_refpair ref, int *const globalmv_ctx,
                                  const union mv gmv[])
{
   if (rb->mv.n == INVALID_MV) return;

   union mv mv = mv_projection(rb->mv, rf->pocdiff[ref.ref[0] - 1], rb->ref);
   fix_mv_precision(rf->frm_hdr, &mv);

   const int last = *cnt;
   if (ref.ref[1] == -1) {
       if (globalmv_ctx)
           *globalmv_ctx = (abs(mv.x - gmv[0].x) | abs(mv.y - gmv[0].y)) >= 16;

       for (int n = 0; n < last; n++)
           if (mvstack[n].mv.mv[0].n == mv.n) {
               mvstack[n].weight += 2;
               return;
           }
       if (last < 8) {
           mvstack[last].mv.mv[0] = mv;
           mvstack[last].weight = 2;
           *cnt = last + 1;
       }
   } else {
       refmvs_mvpair mvp = { .mv = {
           [0] = mv,
           [1] = mv_projection(rb->mv, rf->pocdiff[ref.ref[1] - 1], rb->ref),
       }};
       fix_mv_precision(rf->frm_hdr, &mvp.mv[1]);

       for (int n = 0; n < last; n++)
           if (mvstack[n].mv.n == mvp.n) {
               mvstack[n].weight += 2;
               return;
           }
       if (last < 8) {
           mvstack[last].mv = mvp;
           mvstack[last].weight = 2;
           *cnt = last + 1;
       }
   }
}

static void add_compound_extended_candidate(refmvs_candidate *const same,
                                           int *const same_count,
                                           const refmvs_block *const cand_b,
                                           const int sign0, const int sign1,
                                           const union refmvs_refpair ref,
                                           const uint8_t *const sign_bias)
{
   refmvs_candidate *const diff = &same[2];
   int *const diff_count = &same_count[2];

   for (int n = 0; n < 2; n++) {
       const int cand_ref = cand_b->ref.ref[n];

       if (cand_ref <= 0) break;

       mv cand_mv = cand_b->mv.mv[n];
       if (cand_ref == ref.ref[0]) {
           if (same_count[0] < 2)
               same[same_count[0]++].mv.mv[0] = cand_mv;
           if (diff_count[1] < 2) {
               if (sign1 ^ sign_bias[cand_ref - 1]) {
                   cand_mv.y = -cand_mv.y;
                   cand_mv.x = -cand_mv.x;
               }
               diff[diff_count[1]++].mv.mv[1] = cand_mv;
           }
       } else if (cand_ref == ref.ref[1]) {
           if (same_count[1] < 2)
               same[same_count[1]++].mv.mv[1] = cand_mv;
           if (diff_count[0] < 2) {
               if (sign0 ^ sign_bias[cand_ref - 1]) {
                   cand_mv.y = -cand_mv.y;
                   cand_mv.x = -cand_mv.x;
               }
               diff[diff_count[0]++].mv.mv[0] = cand_mv;
           }
       } else {
           mv i_cand_mv = (union mv) {
               .x = -cand_mv.x,
               .y = -cand_mv.y
           };

           if (diff_count[0] < 2) {
               diff[diff_count[0]++].mv.mv[0] =
                   sign0 ^ sign_bias[cand_ref - 1] ?
                   i_cand_mv : cand_mv;
           }

           if (diff_count[1] < 2) {
               diff[diff_count[1]++].mv.mv[1] =
                   sign1 ^ sign_bias[cand_ref - 1] ?
                   i_cand_mv : cand_mv;
           }
       }
   }
}

static void add_single_extended_candidate(refmvs_candidate mvstack[8], int *const cnt,
                                         const refmvs_block *const cand_b,
                                         const int sign, const uint8_t *const sign_bias)
{
   for (int n = 0; n < 2; n++) {
       const int cand_ref = cand_b->ref.ref[n];

       if (cand_ref <= 0) break;
       // we need to continue even if cand_ref == ref.ref[0], since
       // the candidate could have been added as a globalmv variant,
       // which changes the value
       // FIXME if scan_{row,col}() returned a mask for the nearest
       // edge, we could skip the appropriate ones here

       mv cand_mv = cand_b->mv.mv[n];
       if (sign ^ sign_bias[cand_ref - 1]) {
           cand_mv.y = -cand_mv.y;
           cand_mv.x = -cand_mv.x;
       }

       int m;
       const int last = *cnt;
       for (m = 0; m < last; m++)
           if (cand_mv.n == mvstack[m].mv.mv[0].n)
               break;
       if (m == last) {
           mvstack[m].mv.mv[0] = cand_mv;
           mvstack[m].weight = 2; // "minimal"
           *cnt = last + 1;
       }
   }
}

/*
* refmvs_frame allocates memory for one sbrow (32 blocks high, whole frame
* wide) of 4x4-resolution refmvs_block entries for spatial MV referencing.
* mvrefs_tile[] keeps a list of 35 (32 + 3 above) pointers into this memory,
* and each sbrow, the bottom entries (y=27/29/31) are exchanged with the top
* (-5/-3/-1) pointers by calling dav1d_refmvs_tile_sbrow_init() at the start
* of each tile/sbrow.
*
* For temporal MV referencing, we call dav1d_refmvs_save_tmvs() at the end of
* each tile/sbrow (when tile column threading is enabled), or at the start of
* each interleaved sbrow (i.e. once for all tile columns together, when tile
* column threading is disabled). This will copy the 4x4-resolution spatial MVs
* into 8x8-resolution refmvs_temporal_block structures. Then, for subsequent
* frames, at the start of each tile/sbrow (when tile column threading is
* enabled) or at the start of each interleaved sbrow (when tile column
* threading is disabled), we call load_tmvs(), which will project the MVs to
* their respective position in the current frame.
*/

void dav1d_refmvs_find(const refmvs_tile *const rt,
                      refmvs_candidate mvstack[8], int *const cnt,
                      int *const ctx,
                      const union refmvs_refpair ref, const enum BlockSize bs,
                      const enum EdgeFlags edge_flags,
                      const int by4, const int bx4)
{
   const refmvs_frame *const rf = rt->rf;
   const uint8_t *const b_dim = dav1d_block_dimensions[bs];
   const int bw4 = b_dim[0], w4 = imin(imin(bw4, 16), rt->tile_col.end - bx4);
   const int bh4 = b_dim[1], h4 = imin(imin(bh4, 16), rt->tile_row.end - by4);
   mv gmv[2], tgmv[2];

   *cnt = 0;
   assert(ref.ref[0] >=  0 && ref.ref[0] <= 8 &&
          ref.ref[1] >= -1 && ref.ref[1] <= 8);
   if (ref.ref[0] > 0) {
       tgmv[0] = get_gmv_2d(&rf->frm_hdr->gmv[ref.ref[0] - 1],
                            bx4, by4, bw4, bh4, rf->frm_hdr);
       gmv[0] = rf->frm_hdr->gmv[ref.ref[0] - 1].type > DAV1D_WM_TYPE_TRANSLATION ?
                tgmv[0] : (mv) { .n = INVALID_MV };
   } else {
       tgmv[0] = (mv) { .n = 0 };
       gmv[0] = (mv) { .n = INVALID_MV };
   }
   if (ref.ref[1] > 0) {
       tgmv[1] = get_gmv_2d(&rf->frm_hdr->gmv[ref.ref[1] - 1],
                            bx4, by4, bw4, bh4, rf->frm_hdr);
       gmv[1] = rf->frm_hdr->gmv[ref.ref[1] - 1].type > DAV1D_WM_TYPE_TRANSLATION ?
                tgmv[1] : (mv) { .n = INVALID_MV };
   }

   // top
   int have_newmv = 0, have_col_mvs = 0, have_row_mvs = 0;
   unsigned max_rows = 0, n_rows = ~0;
   const refmvs_block *b_top;
   if (by4 > rt->tile_row.start) {
       max_rows = imin((by4 - rt->tile_row.start + 1) >> 1, 2 + (bh4 > 1));
       b_top = &rt->r[(by4 & 31) - 1 + 5][bx4];
       n_rows = scan_row(mvstack, cnt, ref, gmv, b_top,
                         bw4, w4, max_rows, bw4 >= 16 ? 4 : 1,
                         &have_newmv, &have_row_mvs);
   }

   // left
   unsigned max_cols = 0, n_cols = ~0U;
   refmvs_block *const *b_left;
   if (bx4 > rt->tile_col.start) {
       max_cols = imin((bx4 - rt->tile_col.start + 1) >> 1, 2 + (bw4 > 1));
       b_left = &rt->r[(by4 & 31) + 5];
       n_cols = scan_col(mvstack, cnt, ref, gmv, b_left,
                         bh4, h4, bx4 - 1, max_cols, bh4 >= 16 ? 4 : 1,
                         &have_newmv, &have_col_mvs);
   }

   // top/right
   if (n_rows != ~0U && edge_flags & EDGE_I444_TOP_HAS_RIGHT &&
       imax(bw4, bh4) <= 16 && bw4 + bx4 < rt->tile_col.end)
   {
       add_spatial_candidate(mvstack, cnt, 4, &b_top[bw4], ref, gmv,
                             &have_newmv, &have_row_mvs);
   }

   const int nearest_match = have_col_mvs + have_row_mvs;
   const int nearest_cnt = *cnt;
   for (int n = 0; n < nearest_cnt; n++)
       mvstack[n].weight += 640;

   // temporal
   int globalmv_ctx = rf->frm_hdr->use_ref_frame_mvs;
   if (rf->use_ref_frame_mvs) {
       const ptrdiff_t stride = rf->rp_stride;
       const int by8 = by4 >> 1, bx8 = bx4 >> 1;
       const refmvs_temporal_block *const rbi = &rt->rp_proj[(by8 & 15) * stride + bx8];
       const refmvs_temporal_block *rb = rbi;
       const int step_h = bw4 >= 16 ? 2 : 1, step_v = bh4 >= 16 ? 2 : 1;
       const int w8 = imin((w4 + 1) >> 1, 8), h8 = imin((h4 + 1) >> 1, 8);
       for (int y = 0; y < h8; y += step_v) {
           for (int x = 0; x < w8; x+= step_h) {
               add_temporal_candidate(rf, mvstack, cnt, &rb[x], ref,
                                      !(x | y) ? &globalmv_ctx : NULL, tgmv);
           }
           rb += stride * step_v;
       }
       if (imin(bw4, bh4) >= 2 && imax(bw4, bh4) < 16) {
           const int bh8 = bh4 >> 1, bw8 = bw4 >> 1;
           rb = &rbi[bh8 * stride];
           const int has_bottom = by8 + bh8 < imin(rt->tile_row.end >> 1,
                                                   (by8 & ~7) + 8);
           if (has_bottom && bx8 - 1 >= imax(rt->tile_col.start >> 1, bx8 & ~7)) {
               add_temporal_candidate(rf, mvstack, cnt, &rb[-1], ref,
                                      NULL, NULL);
           }
           if (bx8 + bw8 < imin(rt->tile_col.end >> 1, (bx8 & ~7) + 8)) {
               if (has_bottom) {
                   add_temporal_candidate(rf, mvstack, cnt, &rb[bw8], ref,
                                          NULL, NULL);
               }
               if (by8 + bh8 - 1 < imin(rt->tile_row.end >> 1, (by8 & ~7) + 8)) {
                   add_temporal_candidate(rf, mvstack, cnt, &rb[bw8 - stride],
                                          ref, NULL, NULL);
               }
           }
       }
   }
   assert(*cnt <= 8);

   // top/left (which, confusingly, is part of "secondary" references)
   int have_dummy_newmv_match;
   if ((n_rows | n_cols) != ~0U) {
       add_spatial_candidate(mvstack, cnt, 4, &b_top[-1], ref, gmv,
                             &have_dummy_newmv_match, &have_row_mvs);
   }

   // "secondary" (non-direct neighbour) top & left edges
   // what is different about secondary is that everything is now in 8x8 resolution
   for (int n = 2; n <= 3; n++) {
       if ((unsigned) n > n_rows && (unsigned) n <= max_rows) {
           n_rows += scan_row(mvstack, cnt, ref, gmv,
                              &rt->r[(((by4 & 31) - 2 * n + 1) | 1) + 5][bx4 | 1],
                              bw4, w4, 1 + max_rows - n, bw4 >= 16 ? 4 : 2,
                              &have_dummy_newmv_match, &have_row_mvs);
       }

       if ((unsigned) n > n_cols && (unsigned) n <= max_cols) {
           n_cols += scan_col(mvstack, cnt, ref, gmv, &rt->r[((by4 & 31) | 1) + 5],
                              bh4, h4, (bx4 - n * 2 + 1) | 1,
                              1 + max_cols - n, bh4 >= 16 ? 4 : 2,
                              &have_dummy_newmv_match, &have_col_mvs);
       }
   }
   assert(*cnt <= 8);

   const int ref_match_count = have_col_mvs + have_row_mvs;

   // context build-up
   int refmv_ctx, newmv_ctx;
   switch (nearest_match) {
   case 0:
       refmv_ctx = imin(2, ref_match_count);
       newmv_ctx = ref_match_count > 0;
       break;
   case 1:
       refmv_ctx = imin(ref_match_count * 3, 4);
       newmv_ctx = 3 - have_newmv;
       break;
   case 2:
       refmv_ctx = 5;
       newmv_ctx = 5 - have_newmv;
       break;
   }

   // sorting (nearest, then "secondary")
   int len = nearest_cnt;
   while (len) {
       int last = 0;
       for (int n = 1; n < len; n++) {
           if (mvstack[n - 1].weight < mvstack[n].weight) {
#define EXCHANGE(a, b) do { refmvs_candidate tmp = a; a = b; b = tmp; } while (0)
               EXCHANGE(mvstack[n - 1], mvstack[n]);
               last = n;
           }
       }
       len = last;
   }
   len = *cnt;
   while (len > nearest_cnt) {
       int last = nearest_cnt;
       for (int n = nearest_cnt + 1; n < len; n++) {
           if (mvstack[n - 1].weight < mvstack[n].weight) {
               EXCHANGE(mvstack[n - 1], mvstack[n]);
#undef EXCHANGE
               last = n;
           }
       }
       len = last;
   }

   if (ref.ref[1] > 0) {
       if (*cnt < 2) {
           const int sign0 = rf->sign_bias[ref.ref[0] - 1];
           const int sign1 = rf->sign_bias[ref.ref[1] - 1];
           const int sz4 = imin(w4, h4);
           refmvs_candidate *const same = &mvstack[*cnt];
           int same_count[4] = { 0 };

           // non-self references in top
           if (n_rows != ~0U) for (int x = 0; x < sz4;) {
               const refmvs_block *const cand_b = &b_top[x];
               add_compound_extended_candidate(same, same_count, cand_b,
                                               sign0, sign1, ref, rf->sign_bias);
               x += dav1d_block_dimensions[cand_b->bs][0];
           }

           // non-self references in left
           if (n_cols != ~0U) for (int y = 0; y < sz4;) {
               const refmvs_block *const cand_b = &b_left[y][bx4 - 1];
               add_compound_extended_candidate(same, same_count, cand_b,
                                               sign0, sign1, ref, rf->sign_bias);
               y += dav1d_block_dimensions[cand_b->bs][1];
           }

           refmvs_candidate *const diff = &same[2];
           const int *const diff_count = &same_count[2];

           // merge together
           for (int n = 0; n < 2; n++) {
               int m = same_count[n];

               if (m >= 2) continue;

               const int l = diff_count[n];
               if (l) {
                   same[m].mv.mv[n] = diff[0].mv.mv[n];
                   if (++m == 2) continue;
                   if (l == 2) {
                       same[1].mv.mv[n] = diff[1].mv.mv[n];
                       continue;
                   }
               }
               do {
                   same[m].mv.mv[n] = tgmv[n];
               } while (++m < 2);
           }

           // if the first extended was the same as the non-extended one,
           // then replace it with the second extended one
           int n = *cnt;
           if (n == 1 && mvstack[0].mv.n == same[0].mv.n)
               mvstack[1].mv = mvstack[2].mv;
           do {
               mvstack[n].weight = 2;
           } while (++n < 2);
           *cnt = 2;
       }

       // clamping
       const int left = -(bx4 + bw4 + 4) * 4 * 8;
       const int right = (rf->iw4 - bx4 + 4) * 4 * 8;
       const int top = -(by4 + bh4 + 4) * 4 * 8;
       const int bottom = (rf->ih4 - by4 + 4) * 4 * 8;

       const int n_refmvs = *cnt;
       int n = 0;
       do {
           mvstack[n].mv.mv[0].x = iclip(mvstack[n].mv.mv[0].x, left, right);
           mvstack[n].mv.mv[0].y = iclip(mvstack[n].mv.mv[0].y, top, bottom);
           mvstack[n].mv.mv[1].x = iclip(mvstack[n].mv.mv[1].x, left, right);
           mvstack[n].mv.mv[1].y = iclip(mvstack[n].mv.mv[1].y, top, bottom);
       } while (++n < n_refmvs);

       switch (refmv_ctx >> 1) {
       case 0:
           *ctx = imin(newmv_ctx, 1);
           break;
       case 1:
           *ctx = 1 + imin(newmv_ctx, 3);
           break;
       case 2:
           *ctx = iclip(3 + newmv_ctx, 4, 7);
           break;
       }

       return;
   } else if (*cnt < 2 && ref.ref[0] > 0) {
       const int sign = rf->sign_bias[ref.ref[0] - 1];
       const int sz4 = imin(w4, h4);

       // non-self references in top
       if (n_rows != ~0U) for (int x = 0; x < sz4 && *cnt < 2;) {
           const refmvs_block *const cand_b = &b_top[x];
           add_single_extended_candidate(mvstack, cnt, cand_b, sign, rf->sign_bias);
           x += dav1d_block_dimensions[cand_b->bs][0];
       }

       // non-self references in left
       if (n_cols != ~0U) for (int y = 0; y < sz4 && *cnt < 2;) {
           const refmvs_block *const cand_b = &b_left[y][bx4 - 1];
           add_single_extended_candidate(mvstack, cnt, cand_b, sign, rf->sign_bias);
           y += dav1d_block_dimensions[cand_b->bs][1];
       }
   }
   assert(*cnt <= 8);

   // clamping
   int n_refmvs = *cnt;
   if (n_refmvs) {
       const int left = -(bx4 + bw4 + 4) * 4 * 8;
       const int right = (rf->iw4 - bx4 + 4) * 4 * 8;
       const int top = -(by4 + bh4 + 4) * 4 * 8;
       const int bottom = (rf->ih4 - by4 + 4) * 4 * 8;

       int n = 0;
       do {
           mvstack[n].mv.mv[0].x = iclip(mvstack[n].mv.mv[0].x, left, right);
           mvstack[n].mv.mv[0].y = iclip(mvstack[n].mv.mv[0].y, top, bottom);
       } while (++n < n_refmvs);
   }

   for (int n = *cnt; n < 2; n++)
       mvstack[n].mv.mv[0] = tgmv[0];

   *ctx = (refmv_ctx << 4) | (globalmv_ctx << 3) | newmv_ctx;
}

void dav1d_refmvs_tile_sbrow_init(refmvs_tile *const rt, const refmvs_frame *const rf,
                                 const int tile_col_start4, const int tile_col_end4,
                                 const int tile_row_start4, const int tile_row_end4,
                                 const int sby, int tile_row_idx, const int pass)
{
   if (rf->n_tile_threads == 1) tile_row_idx = 0;
   rt->rp_proj = &rf->rp_proj[16 * rf->rp_stride * tile_row_idx];
   const ptrdiff_t r_stride = rf->rp_stride * 2;
   const ptrdiff_t pass_off = (rf->n_frame_threads > 1 && pass == 2) ?
       35 * 2 * rf->n_blocks : 0;
   refmvs_block *r = &rf->r[35 * r_stride * tile_row_idx + pass_off];
   const int sbsz = rf->sbsz;
   const int off = (sbsz * sby) & 16;
   for (int i = 0; i < sbsz; i++, r += r_stride)
       rt->r[off + 5 + i] = r;
   rt->r[off + 0] = r;
   r += r_stride;
   rt->r[off + 1] = NULL;
   rt->r[off + 2] = r;
   r += r_stride;
   rt->r[off + 3] = NULL;
   rt->r[off + 4] = r;
   if (sby & 1) {
#define EXCHANGE(a, b) do { void *const tmp = a; a = b; b = tmp; } while (0)
       EXCHANGE(rt->r[off + 0], rt->r[off + sbsz + 0]);
       EXCHANGE(rt->r[off + 2], rt->r[off + sbsz + 2]);
       EXCHANGE(rt->r[off + 4], rt->r[off + sbsz + 4]);
#undef EXCHANGE
   }

   rt->rf = rf;
   rt->tile_row.start = tile_row_start4;
   rt->tile_row.end = imin(tile_row_end4, rf->ih4);
   rt->tile_col.start = tile_col_start4;
   rt->tile_col.end = imin(tile_col_end4, rf->iw4);
}

static void load_tmvs_c(const refmvs_frame *const rf, int tile_row_idx,
                       const int col_start8, const int col_end8,
                       const int row_start8, int row_end8)
{
   if (rf->n_tile_threads == 1) tile_row_idx = 0;
   assert(row_start8 >= 0);
   assert((unsigned) (row_end8 - row_start8) <= 16U);
   row_end8 = imin(row_end8, rf->ih8);
   const int col_start8i = imax(col_start8 - 8, 0);
   const int col_end8i = imin(col_end8 + 8, rf->iw8);

   const ptrdiff_t stride = rf->rp_stride;
   refmvs_temporal_block *rp_proj =
       &rf->rp_proj[16 * stride * tile_row_idx + (row_start8 & 15) * stride];
   for (int y = row_start8; y < row_end8; y++) {
       for (int x = col_start8; x < col_end8; x++)
           rp_proj[x].mv.n = INVALID_MV;
       rp_proj += stride;
   }

   rp_proj = &rf->rp_proj[16 * stride * tile_row_idx];
   for (int n = 0; n < rf->n_mfmvs; n++) {
       const int ref2cur = rf->mfmv_ref2cur[n];
       if (ref2cur == INVALID_REF2CUR) continue;

       const int ref = rf->mfmv_ref[n];
       const int ref_sign = ref - 4;
       const refmvs_temporal_block *r = &rf->rp_ref[ref][row_start8 * stride];
       for (int y = row_start8; y < row_end8; y++) {
           const int y_sb_align = y & ~7;
           const int y_proj_start = imax(y_sb_align, row_start8);
           const int y_proj_end = imin(y_sb_align + 8, row_end8);
           for (int x = col_start8i; x < col_end8i; x++) {
               const refmvs_temporal_block *rb = &r[x];
               const int b_ref = rb->ref;
               if (!b_ref) continue;
               const int ref2ref = rf->mfmv_ref2ref[n][b_ref - 1];
               if (!ref2ref) continue;
               const mv b_mv = rb->mv;
               const mv offset = mv_projection(b_mv, ref2cur, ref2ref);
               int pos_x = x + apply_sign(abs(offset.x) >> 6,
                                          offset.x ^ ref_sign);
               const int pos_y = y + apply_sign(abs(offset.y) >> 6,
                                                offset.y ^ ref_sign);
               if (pos_y >= y_proj_start && pos_y < y_proj_end) {
                   const ptrdiff_t pos = (pos_y & 15) * stride;
                   for (;;) {
                       const int x_sb_align = x & ~7;
                       if (pos_x >= imax(x_sb_align - 8, col_start8) &&
                           pos_x < imin(x_sb_align + 16, col_end8))
                       {
                           rp_proj[pos + pos_x].mv = rb->mv;
                           rp_proj[pos + pos_x].ref = ref2ref;
                       }
                       if (++x >= col_end8i) break;
                       rb++;
                       if (rb->ref != b_ref || rb->mv.n != b_mv.n) break;
                       pos_x++;
                   }
               } else {
                   for (;;) {
                       if (++x >= col_end8i) break;
                       rb++;
                       if (rb->ref != b_ref || rb->mv.n != b_mv.n) break;
                   }
               }
               x--;
           }
           r += stride;
       }
   }
}

static void save_tmvs_c(refmvs_temporal_block *rp, const ptrdiff_t stride,
                       refmvs_block *const *const rr,
                       const uint8_t *const ref_sign,
                       const int col_end8, const int row_end8,
                       const int col_start8, const int row_start8)
{
   for (int y = row_start8; y < row_end8; y++) {
       const refmvs_block *const b = rr[(y & 15) * 2];

       for (int x = col_start8; x < col_end8;) {
           const refmvs_block *const cand_b = &b[x * 2 + 1];
           const int bw8 = (dav1d_block_dimensions[cand_b->bs][0] + 1) >> 1;

           if (cand_b->ref.ref[1] > 0 && ref_sign[cand_b->ref.ref[1] - 1] &&
               (abs(cand_b->mv.mv[1].y) | abs(cand_b->mv.mv[1].x)) < 4096)
           {
               for (int n = 0; n < bw8; n++, x++)
                   rp[x] = (refmvs_temporal_block) { .mv = cand_b->mv.mv[1],
                                                     .ref = cand_b->ref.ref[1] };
           } else if (cand_b->ref.ref[0] > 0 && ref_sign[cand_b->ref.ref[0] - 1] &&
                      (abs(cand_b->mv.mv[0].y) | abs(cand_b->mv.mv[0].x)) < 4096)
           {
               for (int n = 0; n < bw8; n++, x++)
                   rp[x] = (refmvs_temporal_block) { .mv = cand_b->mv.mv[0],
                                                     .ref = cand_b->ref.ref[0] };
           } else {
               for (int n = 0; n < bw8; n++, x++) {
                   rp[x].mv.n = 0;
                   rp[x].ref = 0; // "invalid"
               }
           }
       }
       rp += stride;
   }
}

int dav1d_refmvs_init_frame(refmvs_frame *const rf,
                           const Dav1dSequenceHeader *const seq_hdr,
                           const Dav1dFrameHeader *const frm_hdr,
                           const uint8_t ref_poc[7],
                           refmvs_temporal_block *const rp,
                           const uint8_t ref_ref_poc[7][7],
                           /*const*/ refmvs_temporal_block *const rp_ref[7],
                           const int n_tile_threads, const int n_frame_threads)
{
   const int rp_stride = ((frm_hdr->width[0] + 127) & ~127) >> 3;
   const int n_tile_rows = n_tile_threads > 1 ? frm_hdr->tiling.rows : 1;
   const int n_blocks = rp_stride * n_tile_rows;

   rf->sbsz = 16 << seq_hdr->sb128;
   rf->frm_hdr = frm_hdr;
   rf->iw8 = (frm_hdr->width[0] + 7) >> 3;
   rf->ih8 = (frm_hdr->height + 7) >> 3;
   rf->iw4 = rf->iw8 << 1;
   rf->ih4 = rf->ih8 << 1;
   rf->rp = rp;
   rf->rp_stride = rp_stride;
   rf->n_tile_threads = n_tile_threads;
   rf->n_frame_threads = n_frame_threads;

   if (n_blocks != rf->n_blocks) {
       const size_t r_sz = sizeof(*rf->r) * 35 * 2 * n_blocks * (1 + (n_frame_threads > 1));
       const size_t rp_proj_sz = sizeof(*rf->rp_proj) * 16 * n_blocks;
       /* Note that sizeof(*rf->r) == 12, but it's accessed using 16-byte unaligned
        * loads in save_tmvs() asm which can overread 4 bytes into rp_proj. */
       dav1d_free_aligned(rf->r);
       rf->r = dav1d_alloc_aligned(ALLOC_REFMVS, r_sz + rp_proj_sz, 64);
       if (!rf->r) {
           rf->n_blocks = 0;
           return DAV1D_ERR(ENOMEM);
       }

       rf->rp_proj = (refmvs_temporal_block*)((uintptr_t)rf->r + r_sz);
       rf->n_blocks = n_blocks;
   }

   const int poc = frm_hdr->frame_offset;
   for (int i = 0; i < 7; i++) {
       const int poc_diff = get_poc_diff(seq_hdr->order_hint_n_bits,
                                         ref_poc[i], poc);
       rf->sign_bias[i] = poc_diff > 0;
       rf->mfmv_sign[i] = poc_diff < 0;
       rf->pocdiff[i] = iclip(get_poc_diff(seq_hdr->order_hint_n_bits,
                                           poc, ref_poc[i]), -31, 31);
   }

   // temporal MV setup
   rf->n_mfmvs = 0;
   rf->rp_ref = rp_ref;
   if (frm_hdr->use_ref_frame_mvs && seq_hdr->order_hint_n_bits) {
       int total = 2;
       if (rp_ref[0] && ref_ref_poc[0][6] != ref_poc[3] /* alt-of-last != gold */) {
           rf->mfmv_ref[rf->n_mfmvs++] = 0; // last
           total = 3;
       }
       if (rp_ref[4] && get_poc_diff(seq_hdr->order_hint_n_bits, ref_poc[4],
                                     frm_hdr->frame_offset) > 0)
       {
           rf->mfmv_ref[rf->n_mfmvs++] = 4; // bwd
       }
       if (rp_ref[5] && get_poc_diff(seq_hdr->order_hint_n_bits, ref_poc[5],
                                     frm_hdr->frame_offset) > 0)
       {
           rf->mfmv_ref[rf->n_mfmvs++] = 5; // altref2
       }
       if (rf->n_mfmvs < total && rp_ref[6] &&
           get_poc_diff(seq_hdr->order_hint_n_bits, ref_poc[6],
                        frm_hdr->frame_offset) > 0)
       {
           rf->mfmv_ref[rf->n_mfmvs++] = 6; // altref
       }
       if (rf->n_mfmvs < total && rp_ref[1])
           rf->mfmv_ref[rf->n_mfmvs++] = 1; // last2

       for (int n = 0; n < rf->n_mfmvs; n++) {
           const int rpoc = ref_poc[rf->mfmv_ref[n]];
           const int diff1 = get_poc_diff(seq_hdr->order_hint_n_bits,
                                          rpoc, frm_hdr->frame_offset);
           if (abs(diff1) > 31) {
               rf->mfmv_ref2cur[n] = INVALID_REF2CUR;
           } else {
               rf->mfmv_ref2cur[n] = rf->mfmv_ref[n] < 4 ? -diff1 : diff1;
               for (int m = 0; m < 7; m++) {
                   const int rrpoc = ref_ref_poc[rf->mfmv_ref[n]][m];
                   const int diff2 = get_poc_diff(seq_hdr->order_hint_n_bits,
                                                  rpoc, rrpoc);
                   // unsigned comparison also catches the < 0 case
                   rf->mfmv_ref2ref[n][m] = (unsigned) diff2 > 31U ? 0 : diff2;
               }
           }
       }
   }
   rf->use_ref_frame_mvs = rf->n_mfmvs > 0;

   return 0;
}

static void splat_mv_c(refmvs_block **rr, const refmvs_block *const rmv,
                      const int bx4, const int bw4, int bh4)
{
   do {
       refmvs_block *const r = *rr++ + bx4;
       for (int x = 0; x < bw4; x++)
           r[x] = *rmv;
   } while (--bh4);
}

#if HAVE_ASM
#if ARCH_AARCH64 || ARCH_ARM
#include "src/arm/refmvs.h"
#elif ARCH_LOONGARCH64
#include "src/loongarch/refmvs.h"
#elif ARCH_X86
#include "src/x86/refmvs.h"
#endif
#endif

COLD void dav1d_refmvs_dsp_init(Dav1dRefmvsDSPContext *const c)
{
   c->load_tmvs = load_tmvs_c;
   c->save_tmvs = save_tmvs_c;
   c->splat_mv = splat_mv_c;

#if HAVE_ASM
#if ARCH_AARCH64 || ARCH_ARM
   refmvs_dsp_init_arm(c);
#elif ARCH_LOONGARCH64
   refmvs_dsp_init_loongarch(c);
#elif ARCH_X86
   refmvs_dsp_init_x86(c);
#endif
#endif
}