JNT_COMP: clamp distance

Let maximum distance be INT16_MAX - 1.

To decide distance weights, use multiplication
instead of a division.

Google test shows +0.05% on lowres.

Change-Id: I2be25aec3c921773b0d776cf5ae00e3cd4cc27cd

av1/common/common_data.h

@@ -1815,6 +1815,9 @@ static const int intra_mode_context[INTRA_MODES] = {
 #if CONFIG_JNT_COMP
 // Note: this is also used in unit tests. So whenever one changes the table,
 // the unit tests need to be changed accordingly.
+static const int quant_dist_weight[4][2] = {
+  { 2, 3 }, { 2, 5 }, { 2, 7 }, { 1, MAX_FRAME_DISTANCE }
+};
 static const double quant_dist_category[4] = { 1.5, 2.5, 3.5, 255 };
 static const int quant_dist_lookup_table[2][4][2] = {
   { { 9, 7 }, { 11, 5 }, { 12, 4 }, { 13, 3 } },

av1/common/enums.h

@@ -108,6 +108,8 @@ extern "C" {
 #define USE_LOOP_FILTER_SUPERBLOCK 1
 #endif  // CONFIG_LPF_SB
 
+#define MAX_FRAME_DISTANCE (INT16_MAX - 1)
+
 #if CONFIG_JNT_COMP
 typedef enum COMPOUND_DIST_WEIGHT_MODE {
   DIST,

av1/common/reconinter.c

@@ -926,57 +926,44 @@ void av1_jnt_comp_weight_assign(const AV1_COMMON *cm, const MB_MODE_INFO *mbmi,
                                 int order_idx, int *fwd_offset, int *bck_offset,
                                 int is_compound) {
   assert(fwd_offset != NULL && bck_offset != NULL);
+  if (!is_compound || mbmi->compound_idx) {
+    *fwd_offset = -1;
+    *bck_offset = -1;
+    return;
+  }
 
-  if (is_compound) {
-    int bck_idx = cm->frame_refs[mbmi->ref_frame[0] - LAST_FRAME].idx;
-    int fwd_idx = cm->frame_refs[mbmi->ref_frame[1] - LAST_FRAME].idx;
-    int bck_frame_index = 0, fwd_frame_index = 0;
-    int cur_frame_index = cm->cur_frame->cur_frame_offset;
+  const int bck_idx = cm->frame_refs[mbmi->ref_frame[0] - LAST_FRAME].idx;
+  const int fwd_idx = cm->frame_refs[mbmi->ref_frame[1] - LAST_FRAME].idx;
+  const int cur_frame_index = cm->cur_frame->cur_frame_offset;
+  int bck_frame_index = 0, fwd_frame_index = 0;
 
-    if (bck_idx >= 0) {
-      bck_frame_index = cm->buffer_pool->frame_bufs[bck_idx].cur_frame_offset;
-    }
+  if (bck_idx >= 0) {
+    bck_frame_index = cm->buffer_pool->frame_bufs[bck_idx].cur_frame_offset;
+  }
 
-    if (fwd_idx >= 0) {
-      fwd_frame_index = cm->buffer_pool->frame_bufs[fwd_idx].cur_frame_offset;
-    }
+  if (fwd_idx >= 0) {
+    fwd_frame_index = cm->buffer_pool->frame_bufs[fwd_idx].cur_frame_offset;
+  }
 
-    *bck_offset = abs(cur_frame_index - bck_frame_index);
-    *fwd_offset = abs(fwd_frame_index - cur_frame_index);
+  int d0 = clamp(abs(fwd_frame_index - cur_frame_index), 0, MAX_FRAME_DISTANCE);
+  int d1 = clamp(abs(cur_frame_index - bck_frame_index), 0, MAX_FRAME_DISTANCE);
 
-    const double fwd = abs(fwd_frame_index - cur_frame_index);
-    const double bck = abs(cur_frame_index - bck_frame_index);
-    int order;
-    double ratio;
+  const int order = d0 <= d1;
 
-    if (COMPOUND_WEIGHT_MODE == DIST) {
-      if (fwd > bck) {
-        ratio = (bck != 0) ? fwd / bck : 5.0;
-        order = 0;
-      } else {
-        ratio = (fwd != 0) ? bck / fwd : 5.0;
-        order = 1;
-      }
-      int quant_dist_idx;
-      for (quant_dist_idx = 0; quant_dist_idx < 4; ++quant_dist_idx) {
-        if (ratio < quant_dist_category[quant_dist_idx]) break;
-      }
-      *fwd_offset = quant_dist_lookup_table[order_idx][quant_dist_idx][order];
-      *bck_offset =
-          quant_dist_lookup_table[order_idx][quant_dist_idx][1 - order];
-    } else {
-      *fwd_offset = (DIST_PRECISION >> 1);
-      *bck_offset = (DIST_PRECISION >> 1);
-    }
+  if (d0 == 0 || d1 == 0) {
+    *fwd_offset = quant_dist_lookup_table[order_idx][3][order];
+    *bck_offset = quant_dist_lookup_table[order_idx][3][1 - order];
+    return;
+  }
 
-    if (mbmi->compound_idx) {
-      *fwd_offset = -1;
-      *bck_offset = -1;
-    }
-  } else {
-    *bck_offset = -1;
-    *fwd_offset = -1;
+  int i;
+  for (i = 0; i < 4; ++i) {
+    int c0 = quant_dist_weight[i][0];
+    int c1 = quant_dist_weight[i][1];
+    if (d0 * c0 < d1 * c1) break;
   }
+  *fwd_offset = quant_dist_lookup_table[order_idx][i][order];
+  *bck_offset = quant_dist_lookup_table[order_idx][i][1 - order];
 }
 #endif  // CONFIG_JNT_COMP