make the token page size be variable instead of fixed 8192

also changed the token-page layout a little bit to remove
a not-needed field.

This reduces the number of malloc()/free() calls substantially
with minimal increase in memory consumption (~2%).
For the tail of large sources, the number of malloc calls goes
typically from ~10000 to ~100 (e.g.: bryce_big.jpg: 22711 -> 105)

Change-Id: Ib847f41e618ed8c303d26b76da982fbc48de45b9

src/enc/token.c

@@ -27,23 +27,27 @@
 #if !defined(DISABLE_TOKEN_BUFFER)
 
 // we use pages to reduce the number of memcpy()
-#define MAX_NUM_TOKEN 8192          // max number of token per page
+#define MIN_PAGE_SIZE 8192          // minimum number of token per page
 #define FIXED_PROBA_BIT (1u << 14)
 
-struct VP8Tokens {
-  uint16_t tokens_[MAX_NUM_TOKEN];  // bit#15: bit
+typedef uint16_t token_t;  // bit#15: bit
                            // bit #14: constant proba or idx
                            // bits 0..13: slot or constant proba
-  VP8Tokens* next_;
+struct VP8Tokens {
+  VP8Tokens* next_;        // pointer to next page
 };
+// Token data is located in memory just after the next_ field.
+// This macro is used to return their address and hide the trick.
+#define TOKEN_DATA(p) ((token_t*)&(p)[1])
 
 //------------------------------------------------------------------------------
 
-void VP8TBufferInit(VP8TBuffer* const b) {
+void VP8TBufferInit(VP8TBuffer* const b, int page_size) {
   b->tokens_ = NULL;
   b->pages_ = NULL;
   b->last_page_ = &b->pages_;
   b->left_ = 0;
+  b->page_size_ = (page_size < MIN_PAGE_SIZE) ? MIN_PAGE_SIZE : page_size;
   b->error_ = 0;
 }
 
@@ -55,22 +59,26 @@ void VP8TBufferClear(VP8TBuffer* const b) {
       WebPSafeFree((void*)p);
       p = next;
     }
-    VP8TBufferInit(b);
+    VP8TBufferInit(b, b->page_size_);
   }
 }
 
 static int TBufferNewPage(VP8TBuffer* const b) {
-  VP8Tokens* const page =
-      b->error_ ? NULL : (VP8Tokens*)WebPSafeMalloc(1ULL, sizeof(*page));
+  VP8Tokens* page = NULL;
+  const size_t size = sizeof(*page) + b->page_size_ * sizeof(token_t);
+  if (!b->error_) {
+    page = (VP8Tokens*)WebPSafeMalloc(1ULL, size);
+  }
   if (page == NULL) {
     b->error_ = 1;
     return 0;
   }
+  page->next_ = NULL;
+
   *b->last_page_ = page;
   b->last_page_ = &page->next_;
-  b->left_ = MAX_NUM_TOKEN;
-  b->tokens_ = page->tokens_;
-  page->next_ = NULL;
+  b->left_ = b->page_size_;
+  b->tokens_ = TOKEN_DATA(page);
   return 1;
 }
 
@@ -197,8 +205,9 @@ void VP8TokenToStats(const VP8TBuffer* const b, proba_t* const stats) {
   while (p != NULL) {
     const int N = (p->next_ == NULL) ? b->left_ : 0;
     int n = MAX_NUM_TOKEN;
+    const token_t* const tokens = TOKEN_DATA(p);
     while (n-- > N) {
-      const uint16_t token = p->tokens_[n];
+      const token_t token = tokens[n];
       if (!(token & FIXED_PROBA_BIT)) {
         Record((token >> 15) & 1, stats + (token & 0x3fffu));
       }
@@ -220,9 +229,10 @@ int VP8EmitTokens(VP8TBuffer* const b, VP8BitWriter* const bw,
   while (p != NULL) {
     const VP8Tokens* const next = p->next_;
     const int N = (next == NULL) ? b->left_ : 0;
-    int n = MAX_NUM_TOKEN;
+    int n = b->page_size_;
+    const token_t* const tokens = TOKEN_DATA(p);
     while (n-- > N) {
-      const uint16_t token = p->tokens_[n];
+      const token_t token = tokens[n];
       const int bit = (token >> 15) & 1;
       if (token & FIXED_PROBA_BIT) {
         VP8PutBit(bw, bit, token & 0xffu);  // constant proba
@@ -245,9 +255,10 @@ size_t VP8EstimateTokenSize(VP8TBuffer* const b, const uint8_t* const probas) {
   while (p != NULL) {
     const VP8Tokens* const next = p->next_;
     const int N = (next == NULL) ? b->left_ : 0;
-    int n = MAX_NUM_TOKEN;
+    int n = b->page_size_;
+    const token_t* const tokens = TOKEN_DATA(p);
     while (n-- > N) {
-      const uint16_t token = p->tokens_[n];
+      const token_t token = tokens[n];
       const int bit = token & (1 << 15);
       if (token & FIXED_PROBA_BIT) {
         size += VP8BitCost(bit, token & 0xffu);

src/enc/vp8enci.h

@@ -363,12 +363,14 @@ typedef struct {
   VP8Tokens* pages_;        // first page
   VP8Tokens** last_page_;   // last page
   uint16_t* tokens_;        // set to (*last_page_)->tokens_
-  int left_;          // how many free tokens left before the page is full.
+  int left_;                // how many free tokens left before the page is full
+  int page_size_;           // number of tokens per page
 #endif
   int error_;         // true in case of malloc error
 } VP8TBuffer;
 
-void VP8TBufferInit(VP8TBuffer* const b);    // initialize an empty buffer
+// initialize an empty buffer
+void VP8TBufferInit(VP8TBuffer* const b, int page_size);
 void VP8TBufferClear(VP8TBuffer* const b);   // de-allocate pages memory
 
 #if !defined(DISABLE_TOKEN_BUFFER)

src/enc/webpenc.c

@@ -258,7 +258,12 @@ static VP8Encoder* InitVP8Encoder(const WebPConfig* const config,
   VP8EncInitLayer(enc);
 #endif
 
-  VP8TBufferInit(&enc->tokens_);
+  // lower quality means smaller output -> we modulate a little the page
+  // size based on quality. This is just a crude 1rst-order prediction.
+  {
+    const float scale = 1.f + config->quality * 5.f / 100.f;  // in [1,6]
+    VP8TBufferInit(&enc->tokens_, (int)(mb_w * mb_h * 4 * scale));
+  }
   return enc;
 }