add VP8EstimateTokenSize()

estimates final size of coded tokens given a set of probabilities

Change-Id: Ia5a459422557d98b78b3cd8e1a88cb30835825b6

src/enc/token.c

@@ -20,6 +20,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "./cost.h"
 #include "./vp8enci.h"
 
 #if defined(__cplusplus) || defined(c_plusplus)
@@ -238,6 +239,29 @@ int VP8EmitTokens(VP8TBuffer* const b, VP8BitWriter* const bw,
   return 1;
 }
 
+// Size estimation
+size_t VP8EstimateTokenSize(VP8TBuffer* const b, const uint8_t* const probas) {
+  size_t size = 0;
+  const VP8Tokens* p = b->pages_;
+  if (b->error_) return 0;
+  while (p != NULL) {
+    const VP8Tokens* const next = p->next_;
+    const int N = (next == NULL) ? b->left_ : 0;
+    int n = MAX_NUM_TOKEN;
+    while (n-- > N) {
+      const uint16_t token = p->tokens_[n];
+      const int bit = token & (1 << 15);
+      if (token & FIXED_PROBA_BIT) {
+        size += VP8BitCost(bit, token & 0xffu);
+      } else {
+        size += VP8BitCost(bit, probas[token & 0x3fffu]);
+      }
+    }
+    p = next;
+  }
+  return size;
+}
+
 //------------------------------------------------------------------------------
 
 #else     // DISABLE_TOKEN_BUFFER

src/enc/vp8enci.h

@@ -379,6 +379,9 @@ int VP8RecordCoeffTokens(int ctx, int coeff_type, int first, int last,
                          const int16_t* const coeffs,
                          VP8TBuffer* const tokens);
 
+// Estimate the final coded size given a set of 'probas'.
+size_t VP8EstimateTokenSize(VP8TBuffer* const b, const uint8_t* const probas);
+
 // unused for now
 void VP8TokenToStats(const VP8TBuffer* const b, proba_t* const stats);