[lv_map] Add read_coeffs_reverse()

Move coeff decoding logics into read_coeffs_reverse()

Change-Id: Iea7fa09d387af1d797de3df1cf2878516e039203

av1/common/txb_common.h

@@ -507,6 +507,10 @@ static INLINE int get_nz_map_ctx_from_stats(
     return ctx + map[AOMMIN(idx, 2)];
   }
 }
+
+typedef aom_cdf_prob (*base_cdf_arr)[CDF_SIZE(4)];
+typedef aom_cdf_prob (*br_cdf_arr)[CDF_SIZE(BR_CDF_SIZE)];
+
 static INLINE int get_lower_levels_ctx_eob(int bwl, int height, int scan_idx) {
   if (scan_idx == 0) return 0;
   if (scan_idx <= (height << bwl) / 8) return 1;

av1/decoder/decodetxb.c

@@ -63,6 +63,35 @@ static INLINE int get_dqv(const int16_t *dequant, int coeff_idx,
   return dqv;
 }
 
+static INLINE void read_coeffs_reverse(aom_reader *r, TX_SIZE tx_size,
+                                       TX_TYPE tx_type, int start_si,
+                                       int end_si, const int16_t *scan, int bwl,
+                                       uint8_t *levels, base_cdf_arr base_cdf,
+                                       br_cdf_arr br_cdf, int *num_updates,
+                                       uint16_t *update_pos) {
+  for (int c = end_si; c >= start_si; --c) {
+    const int pos = scan[c];
+    const int coeff_ctx =
+        get_lower_levels_ctx(levels, pos, bwl, tx_size, tx_type);
+    const int nsymbs = 4;
+    int level = aom_read_symbol(r, base_cdf[coeff_ctx], nsymbs, ACCT_STR);
+    if (level > NUM_BASE_LEVELS) {
+      const int br_ctx = get_br_ctx(levels, pos, bwl, tx_type);
+      aom_cdf_prob *cdf = br_cdf[br_ctx];
+      for (int idx = 0; idx < COEFF_BASE_RANGE; idx += BR_CDF_SIZE - 1) {
+        const int k = aom_read_symbol(r, cdf, BR_CDF_SIZE, ACCT_STR);
+        level += k;
+        if (k < BR_CDF_SIZE - 1) break;
+      }
+      if (level > NUM_BASE_LEVELS + COEFF_BASE_RANGE) {
+        update_pos[*num_updates] = pos;
+        ++*num_updates;
+      }
+    }
+    levels[get_padded_idx(pos, bwl)] = level;
+  }
+}
+
 uint8_t av1_read_coeffs_txb(const AV1_COMMON *const cm, MACROBLOCKD *const xd,
                             aom_reader *const r, const int blk_row,
                             const int blk_col, const int plane,
@@ -221,31 +250,11 @@ uint8_t av1_read_coeffs_txb(const AV1_COMMON *const cm, MACROBLOCKD *const xd,
     }
     levels[get_padded_idx(pos, bwl)] = level;
   }
-  for (int i = 1; i < *eob; ++i) {
-    const int c = *eob - 1 - i;
-    const int pos = scan[c];
-    const int coeff_ctx =
-        get_lower_levels_ctx(levels, pos, bwl, tx_size, tx_type);
-    aom_cdf_prob *cdf = ec_ctx->coeff_base_cdf[txs_ctx][plane_type][coeff_ctx];
-    const int nsymbs = 4;
-    int level = aom_read_symbol(r, cdf, nsymbs, ACCT_STR);
-    if (level > NUM_BASE_LEVELS) {
-      const int br_ctx = get_br_ctx(levels, pos, bwl, tx_type);
-      for (int idx = 0; idx < COEFF_BASE_RANGE; idx += BR_CDF_SIZE - 1) {
-        const int k = aom_read_symbol(
-            r,
-            ec_ctx->coeff_br_cdf[AOMMIN(txs_ctx, TX_32X32)][plane_type][br_ctx],
-            BR_CDF_SIZE, ACCT_STR);
-        level += k;
-        if (k < BR_CDF_SIZE - 1) break;
-      }
-      if (level > NUM_BASE_LEVELS + COEFF_BASE_RANGE) {
-        update_pos[num_updates] = pos;
-        ++num_updates;
-      }
-    }
-    levels[get_padded_idx(pos, bwl)] = level;
-  }
+  base_cdf_arr base_cdf = ec_ctx->coeff_base_cdf[txs_ctx][plane_type];
+  br_cdf_arr br_cdf =
+      ec_ctx->coeff_br_cdf[AOMMIN(txs_ctx, TX_32X32)][plane_type];
+  read_coeffs_reverse(r, tx_size, tx_type, 0, *eob - 1 - 1, scan, bwl, levels,
+                      base_cdf, br_cdf, &num_updates, update_pos);
 
   for (int i = 0; i < num_updates; ++i) {
     const int pos = update_pos[i];