libwebp: update snapshot to v0.3.0-rc6

third_party/libwebp/enc/frame.c

Index: third_party/libwebp/enc/frame.c
diff --git a/third_party/libwebp/enc/frame.c b/third_party/libwebp/enc/frame.c
index d0ddb467e07bd85faa578c4cdaf08e1b6f354982..95206185b7a086ca5f5c5a62767ade4e3ffc76e1 100644
--- a/third_party/libwebp/enc/frame.c
+++ b/third_party/libwebp/enc/frame.c
@@ -9,6 +9,7 @@
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
+#include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 #include <math.h>
@@ -44,18 +45,18 @@ const uint8_t VP8EncBands[16 + 1] = {
   0  // sentinel
 };
 
-static const uint8_t kCat3[] = { 173, 148, 140 };
-static const uint8_t kCat4[] = { 176, 155, 140, 135 };
-static const uint8_t kCat5[] = { 180, 157, 141, 134, 130 };
-static const uint8_t kCat6[] =
+const uint8_t VP8Cat3[] = { 173, 148, 140 };
+const uint8_t VP8Cat4[] = { 176, 155, 140, 135 };
+const uint8_t VP8Cat5[] = { 180, 157, 141, 134, 130 };
+const uint8_t VP8Cat6[] =
     { 254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129 };
 
 //------------------------------------------------------------------------------
 // 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;
 }
 
@@ -94,9 +95,14 @@ static void ResetTokenStats(VP8Encoder* const enc) {
 }
 
 // Record proba context used
-static int Record(int bit, uint64_t* const stats) {
-  stats[0] += bit;
-  stats[1] += 1;
+static int Record(int bit, proba_t* const stats) {
+  proba_t p = *stats;
+  if (p >= 0xffff0000u) {               // an overflow is inbound.
+    p = ((p + 1u) >> 1) & 0x7fff7fffu;  // -> divide the stats by 2.
+  }
+  // record bit count (lower 16 bits) and increment total count (upper 16 bits).
+  p += 0x00010000u + bit;
+  *stats = p;
   return bit;
 }
 
@@ -107,31 +113,34 @@ static int Record(int bit, uint64_t* const stats) {
 // Note: no need to record the fixed probas.
 static int RecordCoeffs(int ctx, const VP8Residual* const res) {
   int n = res->first;
-  uint64_t (*s)[2] = res->stats[VP8EncBands[n]][ctx];
-  if (!Record(res->last >= 0, s[0])) {
+  // should be stats[VP8EncBands[n]], but it's equivalent for n=0 or 1
+  proba_t* s = res->stats[n][ctx];
+  if (res->last  < 0) {
+    Record(0, s + 0);
     return 0;
   }
-
-  while (1) {
-    int v = res->coeffs[n++];
-    if (!Record(v != 0, s[1])) {
+  while (n <= res->last) {
+    int v;
+    Record(1, s + 0);  // order of record doesn't matter
+    while ((v = res->coeffs[n++]) == 0) {
+      Record(0, s + 1);
       s = res->stats[VP8EncBands[n]][0];
-      continue;
     }
-    if (!Record(2u < (unsigned int)(v + 1), s[2])) {  // v = -1 or 1
+    Record(1, s + 1);
+    if (!Record(2u < (unsigned int)(v + 1), s + 2)) {  // v = -1 or 1
       s = res->stats[VP8EncBands[n]][1];
     } else {
       v = abs(v);
 #if !defined(USE_LEVEL_CODE_TABLE)
-      if (!Record(v > 4, s[3])) {
-        if (Record(v != 2, s[4]))
-          Record(v == 4, s[5]);
-      } else if (!Record(v > 10, s[6])) {
-        Record(v > 6, s[7]);
-      } else if (!Record((v >= 3 + (8 << 2)), s[8])) {
-        Record((v >= 3 + (8 << 1)), s[9]);
+      if (!Record(v > 4, s + 3)) {
+        if (Record(v != 2, s + 4))
+          Record(v == 4, s + 5);
+      } else if (!Record(v > 10, s + 6)) {
+        Record(v > 6, s + 7);
+      } else if (!Record((v >= 3 + (8 << 2)), s + 8)) {
+        Record((v >= 3 + (8 << 1)), s + 9);
       } else {
-        Record((v >= 3 + (8 << 3)), s[10]);
+        Record((v >= 3 + (8 << 3)), s + 10);
       }
 #else
       if (v > MAX_VARIABLE_LEVEL)
@@ -143,44 +152,53 @@ static int RecordCoeffs(int ctx, const VP8Residual* const res) {
         int i;
         for (i = 0; (pattern >>= 1) != 0; ++i) {
           const int mask = 2 << i;
-          if (pattern & 1) Record(!!(bits & mask), s[3 + i]);
+          if (pattern & 1) Record(!!(bits & mask), s + 3 + i);
         }
       }
 #endif
       s = res->stats[VP8EncBands[n]][2];
     }
-    if (n == 16 || !Record(n <= res->last, s[0])) {
-      return 1;
-    }
   }
+  if (n < 16) Record(0, s + 0);
+  return 1;
 }
 
 // Collect statistics and deduce probabilities for next coding pass.
 // Return the total bit-cost for coding the probability updates.
-static int CalcTokenProba(uint64_t nb, uint64_t total) {
-  return (int)(nb ? ((total - nb) * 255 + total / 2) / total : 255);
+static int CalcTokenProba(int nb, int total) {
+  assert(nb <= total);
+  return nb ? (255 - nb * 255 / total) : 255;
 }
 
-static int FinalizeTokenProbas(VP8Encoder* const enc) {
-  VP8Proba* const proba = &enc->proba_;
+// Cost of coding 'nb' 1's and 'total-nb' 0's using 'proba' probability.
+static int BranchCost(int nb, int total, int proba) {
+  return nb * VP8BitCost(1, proba) + (total - nb) * VP8BitCost(0, proba);
+}
+
+static int FinalizeTokenProbas(VP8Proba* const proba) {
+  int has_changed = 0;
   int size = 0;
   int t, b, c, p;
   for (t = 0; t < NUM_TYPES; ++t) {
     for (b = 0; b < NUM_BANDS; ++b) {
       for (c = 0; c < NUM_CTX; ++c) {
         for (p = 0; p < NUM_PROBAS; ++p) {
-          const uint64_t* const cnt = proba->stats_[t][b][c][p];
+          const proba_t stats = proba->stats_[t][b][c][p];
+          const int nb = (stats >> 0) & 0xffff;
+          const int total = (stats >> 16) & 0xffff;
           const int update_proba = VP8CoeffsUpdateProba[t][b][c][p];
           const int old_p = VP8CoeffsProba0[t][b][c][p];
-          const int new_p = CalcTokenProba(cnt[0], cnt[1]);
-          const uint64_t old_cost = VP8BranchCost(cnt[0], cnt[1], old_p)
-                                  + VP8BitCost(0, update_proba);
-          const uint64_t new_cost = VP8BranchCost(cnt[0], cnt[1], new_p)
-                                  + VP8BitCost(1, update_proba) + 8 * 256;
+          const int new_p = CalcTokenProba(nb, total);
+          const int old_cost = BranchCost(nb, total, old_p)
+                             + VP8BitCost(0, update_proba);
+          const int new_cost = BranchCost(nb, total, new_p)
+                             + VP8BitCost(1, update_proba)
+                             + 8 * 256;
           const int use_new_p = (old_cost > new_cost);
           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;
@@ -189,10 +207,52 @@ static int FinalizeTokenProbas(VP8Encoder* const enc) {
       }
     }
   }
+  proba->dirty_ = has_changed;
   return size;
 }
 
 //------------------------------------------------------------------------------
+// Finalize Segment probability based on the coding tree
+
+static int GetProba(int a, int b) {
+  const int total = a + b;
+  return (total == 0) ? 255     // that's the default probability.
+                      : (255 * a + total / 2) / total;  // rounded proba
+}
+
+static void SetSegmentProbas(VP8Encoder* const enc) {
+  int p[NUM_MB_SEGMENTS] = { 0 };
+  int n;
+
+  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
+    const VP8MBInfo* const mb = &enc->mb_info_[n];
+    p[mb->segment_]++;
+  }
+  if (enc->pic_->stats != NULL) {
+    for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
+      enc->pic_->stats->segment_size[n] = p[n];
+    }
+  }
+  if (enc->segment_hdr_.num_segments_ > 1) {
+    uint8_t* const probas = enc->proba_.segments_;
+    probas[0] = GetProba(p[0] + p[1], p[2] + p[3]);
+    probas[1] = GetProba(p[0], p[1]);
+    probas[2] = GetProba(p[2], p[3]);
+
+    enc->segment_hdr_.update_map_ =
+        (probas[0] != 255) || (probas[1] != 255) || (probas[2] != 255);
+    enc->segment_hdr_.size_ =
+        p[0] * (VP8BitCost(0, probas[0]) + VP8BitCost(0, probas[1])) +
+        p[1] * (VP8BitCost(0, probas[0]) + VP8BitCost(1, probas[1])) +
+        p[2] * (VP8BitCost(1, probas[0]) + VP8BitCost(0, probas[2])) +
+        p[3] * (VP8BitCost(1, probas[0]) + VP8BitCost(1, probas[2]));
+  } else {
+    enc->segment_hdr_.update_map_ = 0;
+    enc->segment_hdr_.size_ = 0;
+  }
+}
+
+//------------------------------------------------------------------------------
 // helper functions for residuals struct VP8Residual.
 
 static void InitResidual(int first, int coeff_type,
@@ -220,40 +280,49 @@ static void SetResidualCoeffs(const int16_t* const coeffs,
 //------------------------------------------------------------------------------
 // Mode costs
 
-static int GetResidualCost(int ctx, const VP8Residual* const res) {
+static int GetResidualCost(int ctx0, const VP8Residual* const res) {
   int n = res->first;
-  const uint8_t* p = res->prob[VP8EncBands[n]][ctx];
-  const uint16_t *t = res->cost[VP8EncBands[n]][ctx];
-  int last_p0 = p[0];
+  // should be prob[VP8EncBands[n]], but it's equivalent for n=0 or 1
+  int p0 = res->prob[n][ctx0][0];
+  const uint16_t* t = res->cost[n][ctx0];
   int cost;
 
   if (res->last < 0) {
-    return VP8BitCost(0, last_p0);
+    return VP8BitCost(0, p0);
   }
   cost = 0;
-  while (n <= res->last) {
-    const int v = res->coeffs[n];
+  while (n < res->last) {
+    int v = res->coeffs[n];
     const int b = VP8EncBands[n + 1];
     ++n;
     if (v == 0) {
-      cost += VP8LevelCost(t, 0);
-      p = res->prob[b][0];
+      // short-case for VP8LevelCost(t, 0) (note: VP8LevelFixedCosts[0] == 0):
+      cost += t[0];
       t = res->cost[b][0];
       continue;
     }
-    cost += VP8BitCost(1, last_p0);
-    if (2u >= (unsigned int)(v + 1)) {   // v = -1 or 1
-      cost += VP8LevelCost(t, 1);
-      p = res->prob[b][1];
-      t = res->cost[b][1];
-    } else {
-      cost += VP8LevelCost(t, abs(v));
-      p = res->prob[b][2];
-      t = res->cost[b][2];
+    v = abs(v);
+    cost += VP8BitCost(1, p0);
+    cost += VP8LevelCost(t, v);
+    {
+      const int ctx = (v == 1) ? 1 : 2;
+      p0 = res->prob[b][ctx][0];
+      t = res->cost[b][ctx];
+    }
+  }
+  // Last coefficient is always non-zero
+  {
+    const int v = abs(res->coeffs[n]);
+    assert(v != 0);
+    cost += VP8BitCost(1, p0);
+    cost += VP8LevelCost(t, v);
+    if (n < 15) {
+      const int b = VP8EncBands[n + 1];
+      const int ctx = (v == 1) ? 1 : 2;
+      const int last_p0 = res->prob[b][ctx][0];
+      cost += VP8BitCost(0, last_p0);
     }
-    last_p0 = p[0];
   }
-  if (n < 16) cost += VP8BitCost(0, last_p0);
   return cost;
 }
 
@@ -324,7 +393,8 @@ int VP8GetCostUV(VP8EncIterator* const it, const VP8ModeScore* const rd) {
 
 static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
   int n = res->first;
-  const uint8_t* p = res->prob[VP8EncBands[n]][ctx];
+  // should be prob[VP8EncBands[n]], but it's equivalent for n=0 or 1
+  const uint8_t* p = res->prob[n][ctx];
   if (!VP8PutBit(bw, res->last >= 0, p[0])) {
     return 0;
   }
@@ -353,30 +423,30 @@ static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
       } else {
         int mask;
         const uint8_t* tab;
-        if (v < 3 + (8 << 1)) {          // kCat3  (3b)
+        if (v < 3 + (8 << 1)) {          // VP8Cat3  (3b)
           VP8PutBit(bw, 0, p[8]);
           VP8PutBit(bw, 0, p[9]);
           v -= 3 + (8 << 0);
           mask = 1 << 2;
-          tab = kCat3;
-        } else if (v < 3 + (8 << 2)) {   // kCat4  (4b)
+          tab = VP8Cat3;
+        } else if (v < 3 + (8 << 2)) {   // VP8Cat4  (4b)
           VP8PutBit(bw, 0, p[8]);
           VP8PutBit(bw, 1, p[9]);
           v -= 3 + (8 << 1);
           mask = 1 << 3;
-          tab = kCat4;
-        } else if (v < 3 + (8 << 3)) {   // kCat5  (5b)
+          tab = VP8Cat4;
+        } else if (v < 3 + (8 << 3)) {   // VP8Cat5  (5b)
           VP8PutBit(bw, 1, p[8]);
           VP8PutBit(bw, 0, p[10]);
           v -= 3 + (8 << 2);
           mask = 1 << 4;
-          tab = kCat5;
-        } else {                         // kCat6 (11b)
+          tab = VP8Cat5;
+        } else {                         // VP8Cat6 (11b)
           VP8PutBit(bw, 1, p[8]);
           VP8PutBit(bw, 1, p[10]);
           v -= 3 + (8 << 3);
           mask = 1 << 10;
-          tab = kCat6;
+          tab = VP8Cat6;
         }
         while (mask) {
           VP8PutBit(bw, !!(v & mask), *tab++);
@@ -393,8 +463,7 @@ static int PutCoeffs(VP8BitWriter* const bw, int ctx, const VP8Residual* res) {
   return 1;
 }
 
-static void CodeResiduals(VP8BitWriter* const bw,
-                          VP8EncIterator* const it,
+static void CodeResiduals(VP8BitWriter* const bw, VP8EncIterator* const it,
                           const VP8ModeScore* const rd) {
   int x, y, ch;
   VP8Residual res;
@@ -494,146 +563,23 @@ static void RecordResiduals(VP8EncIterator* const it,
 //------------------------------------------------------------------------------
 // Token buffer
 
-#ifdef USE_TOKEN_BUFFER
-
-void VP8TBufferInit(VP8TBuffer* const b) {
-  b->rows_ = NULL;
-  b->tokens_ = NULL;
-  b->last_ = &b->rows_;
-  b->left_ = 0;
-  b->error_ = 0;
-}
-
-int VP8TBufferNewPage(VP8TBuffer* const b) {
-  VP8Tokens* const page = b->error_ ? NULL : (VP8Tokens*)malloc(sizeof(*page));
-  if (page == NULL) {
-    b->error_ = 1;
-    return 0;
-  }
-  *b->last_ = page;
-  b->last_ = &page->next_;
-  b->left_ = MAX_NUM_TOKEN;
-  b->tokens_ = page->tokens_;
-  return 1;
-}
-
-void VP8TBufferClear(VP8TBuffer* const b) {
-  if (b != NULL) {
-    const VP8Tokens* p = b->rows_;
-    while (p != NULL) {
-      const VP8Tokens* const next = p->next_;
-      free((void*)p);
-      p = next;
-    }
-    VP8TBufferInit(b);
-  }
-}
-
-int VP8EmitTokens(const VP8TBuffer* const b, VP8BitWriter* const bw,
-                  const uint8_t* const probas) {
-  VP8Tokens* p = b->rows_;
-  if (b->error_) return 0;
-  while (p != NULL) {
-    const int N = (p->next_ == NULL) ? b->left_ : 0;
-    int n = MAX_NUM_TOKEN;
-    while (n-- > N) {
-      VP8PutBit(bw, (p->tokens_[n] >> 15) & 1, probas[p->tokens_[n] & 0x7fff]);
-    }
-    p = p->next_;
-  }
-  return 1;
-}
-
-#define TOKEN_ID(b, ctx, p) ((p) + NUM_PROBAS * ((ctx) + (b) * NUM_CTX))
-
-static int RecordCoeffTokens(int ctx, const VP8Residual* const res,
-                             VP8TBuffer* tokens) {
-  int n = res->first;
-  int b = VP8EncBands[n];
-  if (!VP8AddToken(tokens, res->last >= 0, TOKEN_ID(b, ctx, 0))) {
-    return 0;
-  }
-
-  while (n < 16) {
-    const int c = res->coeffs[n++];
-    const int sign = c < 0;
-    int v = sign ? -c : c;
-    const int base_id = TOKEN_ID(b, ctx, 0);
-    if (!VP8AddToken(tokens, v != 0, base_id + 1)) {
-      b = VP8EncBands[n];
-      ctx = 0;
-      continue;
-    }
-    if (!VP8AddToken(tokens, v > 1, base_id + 2)) {
-      b = VP8EncBands[n];
-      ctx = 1;
-    } else {
-      if (!VP8AddToken(tokens, v > 4, base_id + 3)) {
-        if (VP8AddToken(tokens, v != 2, base_id + 4))
-          VP8AddToken(tokens, v == 4, base_id + 5);
-      } else if (!VP8AddToken(tokens, v > 10, base_id + 6)) {
-        if (!VP8AddToken(tokens, v > 6, base_id + 7)) {
-//          VP8AddToken(tokens, v == 6, 159);
-        } else {
-//          VP8AddToken(tokens, v >= 9, 165);
-//          VP8AddToken(tokens, !(v & 1), 145);
-        }
-      } else {
-        int mask;
-        const uint8_t* tab;
-        if (v < 3 + (8 << 1)) {          // kCat3  (3b)
-          VP8AddToken(tokens, 0, base_id + 8);
-          VP8AddToken(tokens, 0, base_id + 9);
-          v -= 3 + (8 << 0);
-          mask = 1 << 2;
-          tab = kCat3;
-        } else if (v < 3 + (8 << 2)) {   // kCat4  (4b)
-          VP8AddToken(tokens, 0, base_id + 8);
-          VP8AddToken(tokens, 1, base_id + 9);
-          v -= 3 + (8 << 1);
-          mask = 1 << 3;
-          tab = kCat4;
-        } else if (v < 3 + (8 << 3)) {   // kCat5  (5b)
-          VP8AddToken(tokens, 1, base_id + 8);
-          VP8AddToken(tokens, 0, base_id + 10);
-          v -= 3 + (8 << 2);
-          mask = 1 << 4;
-          tab = kCat5;
-        } else {                         // kCat6 (11b)
-          VP8AddToken(tokens, 1, base_id + 8);
-          VP8AddToken(tokens, 1, base_id + 10);
-          v -= 3 + (8 << 3);
-          mask = 1 << 10;
-          tab = kCat6;
-        }
-        while (mask) {
-          // VP8AddToken(tokens, !!(v & mask), *tab++);
-          mask >>= 1;
-        }
-      }
-      ctx = 2;
-    }
-    b = VP8EncBands[n];
-    // VP8PutBitUniform(bw, sign);
-    if (n == 16 || !VP8AddToken(tokens, n <= res->last, TOKEN_ID(b, ctx, 0))) {
-      return 1;   // EOB
-    }
-  }
-  return 1;
-}
+#if !defined(DISABLE_TOKEN_BUFFER)
 
-static void RecordTokens(VP8EncIterator* const it,
-                         const VP8ModeScore* const rd, VP8TBuffer tokens[2]) {
+static void RecordTokens(VP8EncIterator* const it, const VP8ModeScore* const rd,
+                         VP8TBuffer* const tokens) {
   int x, y, ch;
   VP8Residual res;
   VP8Encoder* const enc = it->enc_;
 
   VP8IteratorNzToBytes(it);
   if (it->mb_->type_ == 1) {   // i16x16
+    const int ctx = it->top_nz_[8] + it->left_nz_[8];
     InitResidual(0, 1, enc, &res);
     SetResidualCoeffs(rd->y_dc_levels, &res);
-// TODO(skal): FIX ->    it->top_nz_[8] = it->left_nz_[8] =
-      RecordCoeffTokens(it->top_nz_[8] + it->left_nz_[8], &res, &tokens[0]);
+    it->top_nz_[8] = it->left_nz_[8] =
+        VP8RecordCoeffTokens(ctx, 1,
+                             res.first, res.last, res.coeffs, tokens);
+    RecordCoeffs(ctx, &res);
     InitResidual(1, 0, enc, &res);
   } else {
     InitResidual(0, 3, enc, &res);
@@ -645,7 +591,9 @@ static void RecordTokens(VP8EncIterator* const it,
       const int ctx = it->top_nz_[x] + it->left_nz_[y];
       SetResidualCoeffs(rd->y_ac_levels[x + y * 4], &res);
       it->top_nz_[x] = it->left_nz_[y] =
-          RecordCoeffTokens(ctx, &res, &tokens[0]);
+          VP8RecordCoeffTokens(ctx, res.coeff_type,
+                               res.first, res.last, res.coeffs, tokens);
+      RecordCoeffs(ctx, &res);
     }
   }
 
@@ -657,13 +605,16 @@ static void RecordTokens(VP8EncIterator* const it,
         const int ctx = it->top_nz_[4 + ch + x] + it->left_nz_[4 + ch + y];
         SetResidualCoeffs(rd->uv_levels[ch * 2 + x + y * 2], &res);
         it->top_nz_[4 + ch + x] = it->left_nz_[4 + ch + y] =
-            RecordCoeffTokens(ctx, &res, &tokens[1]);
+            VP8RecordCoeffTokens(ctx, 2,
+                                 res.first, res.last, res.coeffs, tokens);
+        RecordCoeffs(ctx, &res);
       }
     }
   }
+  VP8IteratorBytesToNz(it);
 }
 
-#endif    // USE_TOKEN_BUFFER
+#endif    // !DISABLE_TOKEN_BUFFER
 
 //------------------------------------------------------------------------------
 // ExtraInfo map / Debug function
@@ -679,7 +630,10 @@ static void SetBlock(uint8_t* p, int value, int size) {
 #endif
 
 static void ResetSSE(VP8Encoder* const enc) {
-  memset(enc->sse_, 0, sizeof(enc->sse_));
+  enc->sse_[0] = 0;
+  enc->sse_[1] = 0;
+  enc->sse_[2] = 0;
+  // Note: enc->sse_[3] is managed by alpha.c
   enc->sse_count_ = 0;
 }
 
@@ -718,6 +672,7 @@ static void StoreSideInfo(const VP8EncIterator* const it) {
         const int b = (int)((it->luma_bits_ + it->uv_bits_ + 7) >> 3);
         *info = (b > 255) ? 255 : b; break;
       }
+      case 7: *info = mb->alpha_; break;
       default: *info = 0; break;
     };
   }
@@ -729,99 +684,13 @@ static void StoreSideInfo(const VP8EncIterator* const it) {
 }
 
 //------------------------------------------------------------------------------
-// Main loops
-//
-//  VP8EncLoop(): does the final bitstream coding.
-
-static void ResetAfterSkip(VP8EncIterator* const it) {
-  if (it->mb_->type_ == 1) {
-    *it->nz_ = 0;  // reset all predictors
-    it->left_nz_[8] = 0;
-  } else {
-    *it->nz_ &= (1 << 24);  // preserve the dc_nz bit
-  }
-}
-
-int VP8EncLoop(VP8Encoder* const enc) {
-  int i, s, p;
-  int ok = 1;
-  VP8EncIterator it;
-  VP8ModeScore info;
-  const int dont_use_skip = !enc->proba_.use_skip_proba_;
-  const int rd_opt = enc->rd_opt_level_;
-  const int kAverageBytesPerMB = 5;     // TODO: have a kTable[quality/10]
-  const int bytes_per_parts =
-    enc->mb_w_ * enc->mb_h_ * kAverageBytesPerMB / enc->num_parts_;
-
-  // Initialize the bit-writers
-  for (p = 0; p < enc->num_parts_; ++p) {
-    VP8BitWriterInit(enc->parts_ + p, bytes_per_parts);
-  }
-
-  ResetStats(enc, rd_opt != 0);
-  ResetSSE(enc);
-
-  VP8IteratorInit(enc, &it);
-  VP8InitFilter(&it);
-  do {
-    VP8IteratorImport(&it);
-    // Warning! order is important: first call VP8Decimate() and
-    // *then* decide how to code the skip decision if there's one.
-    if (!VP8Decimate(&it, &info, rd_opt) || dont_use_skip) {
-      CodeResiduals(it.bw_, &it, &info);
-    } else {   // reset predictors after a skip
-      ResetAfterSkip(&it);
-    }
-#ifdef WEBP_EXPERIMENTAL_FEATURES
-    if (enc->use_layer_) {
-      VP8EncCodeLayerBlock(&it);
-    }
-#endif
-    StoreSideInfo(&it);
-    VP8StoreFilterStats(&it);
-    VP8IteratorExport(&it);
-    ok = VP8IteratorProgress(&it, 20);
-  } while (ok && VP8IteratorNext(&it, it.yuv_out_));
-
-  if (ok) {      // Finalize the partitions, check for extra errors.
-    for (p = 0; p < enc->num_parts_; ++p) {
-      VP8BitWriterFinish(enc->parts_ + p);
-      ok &= !enc->parts_[p].error_;
-    }
-  }
-
-  if (ok) {      // All good. Finish up.
-    if (enc->pic_->stats) {           // finalize byte counters...
-      for (i = 0; i <= 2; ++i) {
-        for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
-          enc->residual_bytes_[i][s] = (int)((it.bit_count_[s][i] + 7) >> 3);
-        }
-      }
-    }
-    VP8AdjustFilterStrength(&it);     // ...and store filter stats.
-  } else {
-    // Something bad happened -> need to do some memory cleanup.
-    VP8EncFreeBitWriters(enc);
-  }
-
-  return ok;
-}
-
-//------------------------------------------------------------------------------
-//  VP8StatLoop(): only collect statistics (number of skips, token usage, ...)
-//                 This is used for deciding optimal probabilities. It also
-//                 modifies the quantizer value if some target (size, PNSR)
-//                 was specified.
+//  StatLoop(): only collect statistics (number of skips, token usage, ...).
+//  This is used for deciding optimal probabilities. It also modifies the
+//  quantizer value if some target (size, PNSR) was specified.
 
 #define kHeaderSizeEstimate (15 + 20 + 10)      // TODO: fix better
 
-static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
-                       float* const PSNR, int percent_delta) {
-  VP8EncIterator it;
-  uint64_t size = 0;
-  uint64_t distortion = 0;
-  const uint64_t pixel_count = nb_mbs * 384;
-
+static void SetLoopParams(VP8Encoder* const enc, float q) {
   // Make sure the quality parameter is inside valid bounds
   if (q < 0.) {
     q = 0;
@@ -830,10 +699,23 @@ static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
   }
 
   VP8SetSegmentParams(enc, q);      // setup segment quantizations and filters
+  SetSegmentProbas(enc);            // compute segment probabilities
 
-  ResetStats(enc, rd_opt != 0);
+  ResetStats(enc);
   ResetTokenStats(enc);
 
+  ResetSSE(enc);
+}
+
+static int OneStatPass(VP8Encoder* const enc, float q, VP8RDLevel rd_opt,
+                       int nb_mbs, float* const PSNR, int percent_delta) {
+  VP8EncIterator it;
+  uint64_t size = 0;
+  uint64_t distortion = 0;
+  const uint64_t pixel_count = nb_mbs * 384;
+
+  SetLoopParams(enc, q);
+
   VP8IteratorInit(enc, &it);
   do {
     VP8ModeScore info;
@@ -849,7 +731,7 @@ static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
       return 0;
   } while (VP8IteratorNext(&it, it.yuv_out_) && --nb_mbs > 0);
   size += FinalizeSkipProba(enc);
-  size += FinalizeTokenProbas(enc);
+  size += FinalizeTokenProbas(&enc->proba_);
   size += enc->segment_hdr_.size_;
   size = ((size + 1024) >> 11) + kHeaderSizeEstimate;
 
@@ -862,10 +744,10 @@ static int OneStatPass(VP8Encoder* const enc, float q, int rd_opt, int nb_mbs,
 // successive refinement increments.
 static const int dqs[] = { 20, 15, 10, 8, 6, 4, 2, 1, 0 };
 
-int VP8StatLoop(VP8Encoder* const enc) {
-  const int do_search =
-    (enc->config_->target_size > 0 || enc->config_->target_PSNR > 0);
-  const int fast_probe = (enc->method_ < 2 && !do_search);
+static int StatLoop(VP8Encoder* const enc) {
+  const int method = enc->method_;
+  const int do_search = enc->do_search_;
+  const int fast_probe = ((method == 0 || method == 3) && !do_search);
   float q = enc->config_->quality;
   const int max_passes = enc->config_->pass;
   const int task_percent = 20;
@@ -876,12 +758,18 @@ int VP8StatLoop(VP8Encoder* const enc) {
 
   // Fast mode: quick analysis pass over few mbs. Better than nothing.
   nb_mbs = enc->mb_w_ * enc->mb_h_;
-  if (fast_probe && nb_mbs > 100) nb_mbs = 100;
+  if (fast_probe) {
+    if (method == 3) {  // we need more stats for method 3 to be reliable.
+      nb_mbs = (nb_mbs > 200) ? nb_mbs >> 1 : 100;
+    } else {
+      nb_mbs = (nb_mbs > 200) ? nb_mbs >> 2 : 50;
+    }
+  }
 
   // No target size: just do several pass without changing 'q'
   if (!do_search) {
     for (pass = 0; pass < max_passes; ++pass) {
-      const int rd_opt = (enc->method_ > 2);
+      const VP8RDLevel rd_opt = (method >= 3) ? RD_OPT_BASIC : RD_OPT_NONE;
       if (!OneStatPass(enc, q, rd_opt, nb_mbs, NULL, percent_per_pass)) {
         return 0;
       }
@@ -889,15 +777,14 @@ int VP8StatLoop(VP8Encoder* const enc) {
   } else {
     // binary search for a size close to target
     for (pass = 0; pass < max_passes && (dqs[pass] > 0); ++pass) {
-      const int rd_opt = 1;
       float PSNR;
       int criterion;
-      const int size = OneStatPass(enc, q, rd_opt, nb_mbs, &PSNR,
+      const int size = OneStatPass(enc, q, RD_OPT_BASIC, nb_mbs, &PSNR,
                                    percent_per_pass);
 #if DEBUG_SEARCH
       printf("#%d size=%d PSNR=%.2f q=%.2f\n", pass, size, PSNR, q);
 #endif
-      if (!size) return 0;
+      if (size == 0) return 0;
       if (enc->config_->target_PSNR > 0) {
         criterion = (PSNR < enc->config_->target_PSNR);
       } else {
@@ -911,10 +798,179 @@ int VP8StatLoop(VP8Encoder* const enc) {
       }
     }
   }
+  VP8CalculateLevelCosts(&enc->proba_);  // finalize costs
   return WebPReportProgress(enc->pic_, final_percent, &enc->percent_);
 }
 
 //------------------------------------------------------------------------------
+// Main loops
+//
+
+static const int kAverageBytesPerMB[8] = { 50, 24, 16, 9, 7, 5, 3, 2 };
+
+static int PreLoopInitialize(VP8Encoder* const enc) {
+  int p;
+  int ok = 1;
+  const int average_bytes_per_MB = kAverageBytesPerMB[enc->base_quant_ >> 4];
+  const int bytes_per_parts =
+      enc->mb_w_ * enc->mb_h_ * average_bytes_per_MB / enc->num_parts_;
+  // Initialize the bit-writers
+  for (p = 0; ok && p < enc->num_parts_; ++p) {
+    ok = VP8BitWriterInit(enc->parts_ + p, bytes_per_parts);
+  }
+  if (!ok) VP8EncFreeBitWriters(enc);  // malloc error occurred
+  return ok;
+}
+
+static int PostLoopFinalize(VP8EncIterator* const it, int ok) {
+  VP8Encoder* const enc = it->enc_;
+  if (ok) {      // Finalize the partitions, check for extra errors.
+    int p;
+    for (p = 0; p < enc->num_parts_; ++p) {
+      VP8BitWriterFinish(enc->parts_ + p);
+      ok &= !enc->parts_[p].error_;
+    }
+  }
+
+  if (ok) {      // All good. Finish up.
+    if (enc->pic_->stats) {           // finalize byte counters...
+      int i, s;
+      for (i = 0; i <= 2; ++i) {
+        for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
+          enc->residual_bytes_[i][s] = (int)((it->bit_count_[s][i] + 7) >> 3);
+        }
+      }
+    }
+    VP8AdjustFilterStrength(it);     // ...and store filter stats.
+  } else {
+    // Something bad happened -> need to do some memory cleanup.
+    VP8EncFreeBitWriters(enc);
+  }
+  return ok;
+}
+
+//------------------------------------------------------------------------------
+//  VP8EncLoop(): does the final bitstream coding.
+
+static void ResetAfterSkip(VP8EncIterator* const it) {
+  if (it->mb_->type_ == 1) {
+    *it->nz_ = 0;  // reset all predictors
+    it->left_nz_[8] = 0;
+  } else {
+    *it->nz_ &= (1 << 24);  // preserve the dc_nz bit
+  }
+}
+
+int VP8EncLoop(VP8Encoder* const enc) {
+  VP8EncIterator it;
+  int ok = PreLoopInitialize(enc);
+  if (!ok) return 0;
+
+  StatLoop(enc);  // stats-collection loop
+
+  VP8IteratorInit(enc, &it);
+  VP8InitFilter(&it);
+  do {
+    VP8ModeScore info;
+    const int dont_use_skip = !enc->proba_.use_skip_proba_;
+    const VP8RDLevel rd_opt = enc->rd_opt_level_;
+
+    VP8IteratorImport(&it);
+    // Warning! order is important: first call VP8Decimate() and
+    // *then* decide how to code the skip decision if there's one.
+    if (!VP8Decimate(&it, &info, rd_opt) || dont_use_skip) {
+      CodeResiduals(it.bw_, &it, &info);
+    } else {   // reset predictors after a skip
+      ResetAfterSkip(&it);
+    }
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+    if (enc->use_layer_) {
+      VP8EncCodeLayerBlock(&it);
+    }
+#endif
+    StoreSideInfo(&it);
+    VP8StoreFilterStats(&it);
+    VP8IteratorExport(&it);
+    ok = VP8IteratorProgress(&it, 20);
+  } while (ok && VP8IteratorNext(&it, it.yuv_out_));
+
+  return PostLoopFinalize(&it, ok);
+}
+
+//------------------------------------------------------------------------------
+// Single pass using Token Buffer.
+
+#if !defined(DISABLE_TOKEN_BUFFER)
+
+#define MIN_COUNT 96   // minimum number of macroblocks before updating stats
+
+int VP8EncTokenLoop(VP8Encoder* const enc) {
+  int ok;
+  // Roughly refresh the proba height times per pass
+  int max_count = (enc->mb_w_ * enc->mb_h_) >> 3;
+  int cnt;
+  VP8EncIterator it;
+  VP8Proba* const proba = &enc->proba_;
+  const VP8RDLevel rd_opt = enc->rd_opt_level_;
+
+  if (max_count < MIN_COUNT) max_count = MIN_COUNT;
+  cnt = max_count;
+
+  assert(enc->num_parts_ == 1);
+  assert(enc->use_tokens_);
+  assert(proba->use_skip_proba_ == 0);
+  assert(rd_opt >= RD_OPT_BASIC);   // otherwise, token-buffer won't be useful
+  assert(!enc->do_search_);         // TODO(skal): handle pass and dichotomy
+
+  SetLoopParams(enc, enc->config_->quality);
+
+  ok = PreLoopInitialize(enc);
+  if (!ok) return 0;
+
+  VP8IteratorInit(enc, &it);
+  VP8InitFilter(&it);
+  do {
+    VP8ModeScore info;
+    VP8IteratorImport(&it);
+    if (--cnt < 0) {
+      FinalizeTokenProbas(proba);
+      VP8CalculateLevelCosts(proba);  // refresh cost tables for rd-opt
+      cnt = max_count;
+    }
+    VP8Decimate(&it, &info, rd_opt);
+    RecordTokens(&it, &info, &enc->tokens_);
+#ifdef WEBP_EXPERIMENTAL_FEATURES
+    if (enc->use_layer_) {
+      VP8EncCodeLayerBlock(&it);
+    }
+#endif
+    StoreSideInfo(&it);
+    VP8StoreFilterStats(&it);
+    VP8IteratorExport(&it);
+    ok = VP8IteratorProgress(&it, 20);
+  } while (ok && VP8IteratorNext(&it, it.yuv_out_));
+
+  ok = ok && WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
+
+  if (ok) {
+    FinalizeTokenProbas(proba);
+    ok = VP8EmitTokens(&enc->tokens_, enc->parts_ + 0,
+                       (const uint8_t*)proba->coeffs_, 1);
+  }
+
+  return PostLoopFinalize(&it, ok);
+}
+
+#else
+
+int VP8EncTokenLoop(VP8Encoder* const enc) {
+  (void)enc;
+  return 0;   // we shouldn't be here.
+}
+
+#endif    // DISABLE_TOKEN_BUFFER
+
+//------------------------------------------------------------------------------
 
 #if defined(__cplusplus) || defined(c_plusplus)
 }    // extern "C"