Only recompute level_cost_[] when needed

Add a dirty_ flag to keep track of updated probabilities and the need to
recompute the level costs.
This only makes a difference for "-m 2" method which was sub-optimal.
But it's overall cleaner to have this flag.

Change-Id: I21c71201e1d07a923d97a3adf2fbbd7d67d35433

src/enc/cost.c

@@ -354,6 +354,9 @@ static int VariableLevelCost(int level, const uint8_t probas[NUM_PROBAS]) {
 
 void VP8CalculateLevelCosts(VP8Proba* const proba) {
   int ctype, band, ctx;
+
+  if (!proba->dirty_) return;  // nothing to do.
+
   for (ctype = 0; ctype < NUM_TYPES; ++ctype) {
     for (band = 0; band < NUM_BANDS; ++band) {
       for(ctx = 0; ctx < NUM_CTX; ++ctx) {
@@ -370,6 +373,7 @@ void VP8CalculateLevelCosts(VP8Proba* const proba) {
       }
     }
   }
+  proba->dirty_ = 0;
 }
 
 //------------------------------------------------------------------------------

src/enc/frame.c

@@ -54,9 +54,9 @@ static const uint8_t kCat6[] =
 //------------------------------------------------------------------------------
 // Reset the statistics about: number of skips, token proba, level cost,...
 
-static void ResetStats(VP8Encoder* const enc, int precalc_cost) {
+static void ResetStats(VP8Encoder* const enc) {
   VP8Proba* const proba = &enc->proba_;
-  if (precalc_cost) VP8CalculateLevelCosts(proba);
+  VP8CalculateLevelCosts(proba);
   proba->nb_skip_ = 0;
 }
 
@@ -123,7 +123,7 @@ static int RecordCoeffs(int ctx, const VP8Residual* const res) {
     Record(1, s + 0);
     while ((v = res->coeffs[n++]) == 0) {
       Record(0, s + 1);
-      s = res->stats[VP8EncBands[n]][0];      
+      s = res->stats[VP8EncBands[n]][0];
     }
     Record(1, s + 1);
     if (!Record(2u < (unsigned int)(v + 1), s + 2)) {  // v = -1 or 1
@@ -176,6 +176,7 @@ static int BranchCost(int nb, int total, int proba) {
 
 static int FinalizeTokenProbas(VP8Encoder* const enc) {
   VP8Proba* const proba = &enc->proba_;
+  int has_changed = 0;
   int size = 0;
   int t, b, c, p;
   for (t = 0; t < NUM_TYPES; ++t) {
@@ -197,6 +198,7 @@ static int FinalizeTokenProbas(VP8Encoder* const enc) {
           size += VP8BitCost(use_new_p, update_proba);
           if (use_new_p) {  // only use proba that seem meaningful enough.
             proba->coeffs_[t][b][c][p] = new_p;
+            has_changed |= (new_p != old_p);
             size += 8 * 256;
           } else {
             proba->coeffs_[t][b][c][p] = old_p;
@@ -205,6 +207,7 @@ static int FinalizeTokenProbas(VP8Encoder* const enc) {
       }
     }
   }
+  proba->dirty_ = has_changed;
   return size;
 }
 
@@ -773,7 +776,7 @@ int VP8EncLoop(VP8Encoder* const enc) {
     VP8BitWriterInit(enc->parts_ + p, bytes_per_parts);
   }
 
-  ResetStats(enc, rd_opt != 0);
+  ResetStats(enc);
   ResetSSE(enc);
 
   VP8IteratorInit(enc, &it);
@@ -845,7 +848,7 @@ static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
 
   VP8SetSegmentParams(enc, q);      // setup segment quantizations and filters
 
-  ResetStats(enc, rd_opt != 0);
+  ResetStats(enc);
   ResetTokenStats(enc);
 
   VP8IteratorInit(enc, &it);

src/enc/quant.c

@@ -421,8 +421,8 @@ static int TrellisQuantizeBlock(const VP8EncIterator* const it,
                                 int ctx0, int coeff_type,
                                 const VP8Matrix* const mtx,
                                 int lambda) {
-  ProbaArray* const last_costs = it->enc_->proba_.coeffs_[coeff_type];
-  CostArray* const costs = it->enc_->proba_.level_cost_[coeff_type];
+  const ProbaArray* const last_costs = it->enc_->proba_.coeffs_[coeff_type];
+  const CostArray* const costs = it->enc_->proba_.level_cost_[coeff_type];
   const int first = (coeff_type == 0) ? 1 : 0;
   Node nodes[17][NUM_NODES];
   int best_path[3] = {-1, -1, -1};   // store best-last/best-level/best-previous

src/enc/tree.c

@@ -158,9 +158,12 @@ const uint8_t
 
 void VP8DefaultProbas(VP8Encoder* const enc) {
   VP8Proba* const probas = &enc->proba_;
+  probas->use_skip_proba_ = 0;
   memset(probas->segments_, 255u, sizeof(probas->segments_));
   memcpy(probas->coeffs_, VP8CoeffsProba0, sizeof(VP8CoeffsProba0));
-  probas->use_skip_proba_ = 0;
+  // Note: we could hard-code the level_costs_ corresponding to VP8CoeffsProba0,
+  // but that's ~11k of static data. Better call VP8CalculateLevelCosts() later.
+  probas->dirty_ = 1;
 }
 
 // Paragraph 11.5.  900bytes.

src/enc/vp8enci.h

@@ -188,6 +188,7 @@ typedef struct {
   ProbaArray coeffs_[NUM_TYPES][NUM_BANDS];      // 924 bytes
   StatsArray stats_[NUM_TYPES][NUM_BANDS];       // 4224 bytes
   CostArray level_cost_[NUM_TYPES][NUM_BANDS];   // 11.4k
+  int dirty_;               // if true, need to call VP8CalculateLevelCosts()
   int use_skip_proba_;      // Note: we always use skip_proba for now.
   int nb_skip_;             // number of skipped blocks
 } VP8Proba;