make VP8LSetBitPos() set br->eos_ flag

ReadSymbol() finishes with a VP8LSetBitPos() call only and could miss an eos_ during the decode loop.

Things are faster because of inlining too.

Change-Id: I2d2a275f38834ba005bc767d45c5de72d032103e

src/dec/vp8l.c

@@ -891,6 +891,7 @@ static int DecodeAlphaData(VP8LDecoder* const dec, uint8_t* const data,
       ok = 0;
       goto End;
     }
+    assert(br->eos_ == VP8LIsEndOfStream(br));
     ok = !br->error_;
     if (!ok) goto End;
   }
@@ -1008,6 +1009,7 @@ static int DecodeImageData(VP8LDecoder* const dec, uint32_t* const data,
       ok = 0;
       goto End;
     }
+    assert(br->eos_ == VP8LIsEndOfStream(br));
     ok = !br->error_;
     if (!ok) goto End;
   }

src/utils/bit_reader.c

@@ -105,9 +105,7 @@ int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
 //------------------------------------------------------------------------------
 // VP8LBitReader
 
-#define LBITS 64      // Number of bits prefetched.
-#define WBITS 32      // Minimum number of bytes needed after VP8LFillBitWindow.
-#define LOG8_WBITS 4  // Number of bytes needed to store WBITS bits.
+#define VP8L_LOG8_WBITS 4  // Number of bytes needed to store VP8L_WBITS bits.
 
 #if !defined(WEBP_FORCE_ALIGNED) && \
     (defined(__arm__) || defined(_M_ARM) || defined(__aarch64__) || \
@@ -151,16 +149,6 @@ void VP8LInitBitReader(VP8LBitReader* const br, const uint8_t* const start,
   br->buf_ = start;
 }
 
-// Special version that assumes br->pos_ <= br_len_.
-static int IsEndOfStreamSpecial(const VP8LBitReader* const br) {
-  assert(br->pos_ <= br->len_);
-  return br->pos_ == br->len_ && br->bit_pos_ > LBITS;
-}
-
-static int IsEndOfStream(const VP8LBitReader* const br) {
-  return (br->pos_ > br->len_) || IsEndOfStreamSpecial(br);
-}
-
 void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
                             const uint8_t* const buf, size_t len) {
   assert(br != NULL);
@@ -168,38 +156,39 @@ void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
   assert(len < 0xfffffff8u);   // can't happen with a RIFF chunk.
   br->buf_ = buf;
   br->len_ = len;
-  br->eos_ = IsEndOfStream(br);
+  // pos_ > len_ should be considered a param error.
+  br->error_ = (br->pos_ > br->len_);
+  br->eos_ = br->error_ || VP8LIsEndOfStream(br);
 }
 
-// If not at EOS, reload up to LBITS byte-by-byte
+// If not at EOS, reload up to VP8L_LBITS byte-by-byte
 static void ShiftBytes(VP8LBitReader* const br) {
   while (br->bit_pos_ >= 8 && br->pos_ < br->len_) {
     br->val_ >>= 8;
-    br->val_ |= ((vp8l_val_t)br->buf_[br->pos_]) << (LBITS - 8);
+    br->val_ |= ((vp8l_val_t)br->buf_[br->pos_]) << (VP8L_LBITS - 8);
     ++br->pos_;
     br->bit_pos_ -= 8;
   }
+  br->eos_ = VP8LIsEndOfStream(br);
 }
 
-void VP8LFillBitWindow(VP8LBitReader* const br) {
-  if (br->bit_pos_ >= WBITS) {
+void VP8LDoFillBitWindow(VP8LBitReader* const br) {
+  assert(br->bit_pos_ >= VP8L_WBITS);
   // TODO(jzern): given the fixed read size it may be possible to force
   //              alignment in this block.
 #if defined(VP8L_USE_UNALIGNED_LOAD)
   if (br->pos_ + sizeof(br->val_) < br->len_) {
-      br->val_ >>= WBITS;
-      br->bit_pos_ -= WBITS;
+    br->val_ >>= VP8L_WBITS;
+    br->bit_pos_ -= VP8L_WBITS;
     // The expression below needs a little-endian arch to work correctly.
     // This gives a large speedup for decoding speed.
     br->val_ |= (vp8l_val_t)*(const uint32_t*)(br->buf_ + br->pos_) <<
-                  (LBITS - WBITS);
-      br->pos_ += LOG8_WBITS;
+                (VP8L_LBITS - VP8L_WBITS);
+    br->pos_ += VP8L_LOG8_WBITS;
     return;
   }
 #endif
   ShiftBytes(br);       // Slow path.
-    br->eos_ = IsEndOfStreamSpecial(br);
-  }
 }
 
 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits) {
@@ -210,8 +199,6 @@ uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits) {
         (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
     const int new_bits = br->bit_pos_ + n_bits;
     br->bit_pos_ = new_bits;
-    // If this read is going to cross the read buffer, set the eos flag.
-    br->eos_ = IsEndOfStreamSpecial(br);
     ShiftBytes(br);
     return val;
   } else {

src/utils/bit_reader.h

@@ -107,6 +107,9 @@ int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits);
 // maximum number of bits (inclusive) the bit-reader can handle:
 #define VP8L_MAX_NUM_BIT_READ 24
 
+#define VP8L_LBITS 64  // Number of bits prefetched.
+#define VP8L_WBITS 32  // Minimum number of bytes ready after VP8LFillBitWindow.
+
 typedef uint64_t vp8l_val_t;  // right now, this bit-reader can only use 64bit.
 
 typedef struct {
@@ -138,14 +141,26 @@ static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
   return (uint32_t)(br->val_ >> br->bit_pos_);
 }
 
+// Returns true if there was an attempt at reading bit past the end of
+// the buffer. Doesn't set br->eos_ flag.
+static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) {
+  assert(br->pos_ <= br->len_);
+  return (br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS);
+}
+
 // For jumping over a number of bits in the bit stream when accessed with
 // VP8LPrefetchBits and VP8LFillBitWindow.
 static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) {
   br->bit_pos_ = val;
+  br->eos_ = VP8LIsEndOfStream(br);
 }
 
 // Advances the read buffer by 4 bytes to make room for reading next 32 bits.
-void VP8LFillBitWindow(VP8LBitReader* const br);
+// Speed critical, but infrequent part of the code can be non-inligned.
+extern void VP8LDoFillBitWindow(VP8LBitReader* const br);
+static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) {
+  if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br);
+}
 
 #ifdef __cplusplus
 }    // extern "C"