Deringing cleanup: don't hardcode the number of levels

No change in code behaviour.

Change-Id: If612c1340b4ca30e290947607ecb64a0cb30e95e

vp10/common/dering.c

@@ -20,7 +20,7 @@
 
 
 int compute_level_from_index(int global_level, int gi) {
-  static const int dering_gains[4] = {0, 11, 16, 22};
+  static const int dering_gains[DERING_REFINEMENT_LEVELS] = {0, 11, 16, 22};
   int level;
   if (global_level == 0) return 0;
   level = (global_level*dering_gains[gi] + 8) >> 4;

vp10/common/dering.h

@@ -15,6 +15,8 @@ extern "C" {
 #define MAX_DERING_LEVEL (1 << DERING_LEVEL_BITS)
 
 #define DERING_REFINEMENT 1
+#define DERING_REFINEMENT_BITS 2
+#define DERING_REFINEMENT_LEVELS 4
 
 int compute_level_from_index(int global_level, int gi);
 int sb_all_skip(const VP10_COMMON *const cm, int mi_row, int mi_col);

vp10/decoder/decodeframe.c

@@ -976,7 +976,7 @@ static void decode_partition(VP10Decoder *const pbi, MACROBLOCKD *const xd,
   if (bsize == BLOCK_64X64) {
     if (cm->dering_level != 0 && !sb_all_skip(cm, mi_row, mi_col)) {
       cm->mi_grid_visible[mi_row*cm->mi_stride + mi_col]->mbmi.dering_gain =
-          vpx_read_literal(r, 2);
+          vpx_read_literal(r, DERING_REFINEMENT_BITS);
     } else {
       cm->mi_grid_visible[mi_row*cm->mi_stride + mi_col]->mbmi.dering_gain = 0;
     }

vp10/encoder/bitstream.c

@@ -611,7 +611,7 @@ static void write_modes_sb(VP10_COMP *cpi, const TileInfo *const tile,
       !sb_all_skip(cm, mi_row, mi_col)) {
     vpx_write_literal(
         w, cm->mi_grid_visible[mi_row*cm->mi_stride + mi_col]->mbmi.dering_gain,
-        2);
+        DERING_REFINEMENT_BITS);
   }
 #endif
 }

vp10/encoder/pickdering.c

@@ -155,7 +155,7 @@ int vp10_dering_search(YV12_BUFFER_CONFIG *frame, const YV12_BUFFER_CONFIG *ref,
       int best_gi;
       int best_mse = mse[nhsb*sbr+sbc][0];
       best_gi = 0;
-      for (gi = 1; gi < 4; gi++) {
+      for (gi = 1; gi < DERING_REFINEMENT_LEVELS; gi++) {
         level = compute_level_from_index(best_level, gi);
         if (mse[nhsb*sbr+sbc][level] < best_mse) {
           best_gi = gi;