Cleans up mbskip encoding

Refactors mbskip coding to be compatible with coding of the rest of
the symbols. Adds forward/backward adaptation and removes a lot of
the legacy code.

Results:
fast50: +1.6%
derfraw300: +0.317%

Change-Id: I395a2976d15af044d3b8ded5acfa45f6f065f980

3 files changed, 16 insertions, 5 deletions

diff --git a/vp9/common/vp9_entropymode.c b/vp9/common/vp9_entropymode.c
index bf57e7ecc..a70d1a5d4 100644
--- a/vp9/common/vp9_entropymode.c
+++ b/vp9/common/vp9_entropymode.c
@@ -197,6 +197,10 @@ const vp9_prob vp9_default_tx_probs[TX_SIZE_PROBS] = {
 };
 #endif
 
+const vp9_prob vp9_default_mbskip_probs[MBSKIP_CONTEXTS] = {
+  192, 128, 64
+};
+
 void vp9_init_mbmode_probs(VP9_COMMON *x) {
   vpx_memcpy(x->fc.uv_mode_prob, default_if_uv_probs,
              sizeof(default_if_uv_probs));
@@ -221,6 +225,8 @@ void vp9_init_mbmode_probs(VP9_COMMON *x) {
              sizeof(default_single_ref_p));
   vpx_memcpy(x->fc.tx_probs, vp9_default_tx_probs,
              sizeof(vp9_default_tx_probs));
+  vpx_memcpy(x->fc.mbskip_probs, vp9_default_mbskip_probs,
+             sizeof(vp9_default_mbskip_probs));
 }
 
 #if VP9_SWITCHABLE_FILTERS == 3
@@ -321,7 +327,7 @@ void vp9_adapt_mode_context(VP9_COMMON *pc) {
 
 #define MODE_COUNT_SAT 20
 #define MODE_MAX_UPDATE_FACTOR 144
-static int update_mode_ct(int pre_prob, int prob,
+static int update_mode_ct(vp9_prob pre_prob, vp9_prob prob,
                           unsigned int branch_ct[2]) {
   int factor, count = branch_ct[0] + branch_ct[1];
   count = count > MODE_COUNT_SAT ? MODE_COUNT_SAT : count;
@@ -344,7 +350,7 @@ static void update_mode_probs(int n_modes,
     dst_probs[t] = update_mode_ct(pre_probs[t], probs[t], branch_ct[t]);
 }
 
-static int update_mode_ct2(int pre_prob, unsigned int branch_ct[2]) {
+static int update_mode_ct2(vp9_prob pre_prob, unsigned int branch_ct[2]) {
   return update_mode_ct(pre_prob, get_binary_prob(branch_ct[0],
                                                   branch_ct[1]), branch_ct);
 }
@@ -438,6 +444,9 @@ void vp9_adapt_mode_probs(VP9_COMMON *cm) {
       cm->fc.tx_probs[i] = weighted_prob(cm->fc.pre_tx_probs[i], prob, factor);
     }
   }
+  for (i = 0; i < MBSKIP_CONTEXTS; ++i)
+    fc->mbskip_probs[i] = update_mode_ct2(fc->pre_mbskip_probs[i],
+                                          fc->mbskip_count[i]);
 }
 
 static void set_default_lf_deltas(MACROBLOCKD *xd) {
diff --git a/vp9/common/vp9_onyxc_int.h b/vp9/common/vp9_onyxc_int.h
index dedda2069..4cb60f196 100644
--- a/vp9/common/vp9_onyxc_int.h
+++ b/vp9/common/vp9_onyxc_int.h
@@ -94,6 +94,10 @@ typedef struct frame_contexts {
   unsigned int tx_count_32x32p[TX_SIZE_MAX_SB];
   unsigned int tx_count_16x16p[TX_SIZE_MAX_SB - 1];
   unsigned int tx_count_8x8p[TX_SIZE_MAX_SB - 2];
+
+  vp9_prob mbskip_probs[MBSKIP_CONTEXTS];
+  vp9_prob pre_mbskip_probs[MBSKIP_CONTEXTS];
+  unsigned int mbskip_count[MBSKIP_CONTEXTS][2];
 } FRAME_CONTEXT;
 
 typedef enum {
@@ -244,8 +248,6 @@ typedef struct VP9Common {
   MV_REFERENCE_FRAME comp_var_ref[2];
   COMPPREDMODE_TYPE comp_pred_mode;
 
-  vp9_prob mbskip_pred_probs[MBSKIP_CONTEXTS];
-
   FRAME_CONTEXT fc;  /* this frame entropy */
   FRAME_CONTEXT frame_contexts[NUM_FRAME_CONTEXTS];
   unsigned int  frame_context_idx; /* Context to use/update */
diff --git a/vp9/common/vp9_pred_common.c b/vp9/common/vp9_pred_common.c
index 73c7278b0..f5ea9a48a 100644
--- a/vp9/common/vp9_pred_common.c
+++ b/vp9/common/vp9_pred_common.c
@@ -368,7 +368,7 @@ vp9_prob vp9_get_pred_prob(const VP9_COMMON *const cm,
     case PRED_SEG_ID:
       return cm->segment_pred_probs[pred_context];
     case PRED_MBSKIP:
-      return cm->mbskip_pred_probs[pred_context];
+      return cm->fc.mbskip_probs[pred_context];
     case PRED_INTRA_INTER:
       return cm->fc.intra_inter_prob[pred_context];
     case PRED_COMP_INTER_INTER: