libwebp: update snapshot to v0.2.0-rc1

third_party/libwebp/utils/bit_reader.h

-// Copyright 2010 Google Inc.
+// Copyright 2010 Google Inc. All Rights Reserved.
 //
 // This code is licensed under the same terms as WebM:
 //  Software License Agreement:  http://www.webmproject.org/license/software/
 //  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
 // -----------------------------------------------------------------------------
 //
 // Boolean decoder
 //
 // Author: Skal (pascal.massimino@gmail.com)
+//         Vikas Arora (vikaas.arora@gmail.com)
 
 #ifndef WEBP_UTILS_BIT_READER_H_
 #define WEBP_UTILS_BIT_READER_H_
 
 #include <assert.h>
-#include "../webp/decode_vp8.h"
+#ifdef _MSC_VER
+#include <stdlib.h>  // _byteswap_ulong
+#endif
+#include <string.h>  // For memcpy
+#include "../webp/types.h"
 
 #if defined(__cplusplus) || defined(c_plusplus)
 extern "C" {
 #endif
 
+#define BITS 32     // can be 32, 16 or 8
+#define MASK ((((bit_t)1) << (BITS)) - 1)
+#if (BITS == 32)
+typedef uint64_t bit_t;   // natural register type
+typedef uint32_t lbit_t;  // natural type for memory I/O
+#elif (BITS == 16)
+typedef uint32_t bit_t;
+typedef uint16_t lbit_t;
+#else
+typedef uint32_t bit_t;
+typedef uint8_t lbit_t;
+#endif
+
 //------------------------------------------------------------------------------
 // Bitreader and code-tree reader
 
 typedef struct VP8BitReader VP8BitReader;
 struct VP8BitReader {
   const uint8_t* buf_;        // next byte to be read
   const uint8_t* buf_end_;    // end of read buffer
   int eof_;                   // true if input is exhausted
 
   // boolean decoder
-  uint32_t range_;            // current range minus 1. In [127, 254] interval.
-  uint32_t value_;            // current value
-  int missing_;               // number of missing bits in value_ (8bit)
+  bit_t range_;            // current range minus 1. In [127, 254] interval.
+  bit_t value_;            // current value
+  int missing_;            // number of missing bits in value_ (8bit)
 };
 
 // Initialize the bit reader and the boolean decoder.
 void VP8InitBitReader(VP8BitReader* const br,
                       const uint8_t* const start, const uint8_t* const end);
 
 // return the next value made of 'num_bits' bits
 uint32_t VP8GetValue(VP8BitReader* const br, int num_bits);
-static inline uint32_t VP8Get(VP8BitReader* const br) {
+static WEBP_INLINE uint32_t VP8Get(VP8BitReader* const br) {
   return VP8GetValue(br, 1);
 }
 
 // return the next value with sign-extension.
 int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits);
 
 // Read a bit with proba 'prob'. Speed-critical function!
 extern const uint8_t kVP8Log2Range[128];
-extern const uint8_t kVP8NewRange[128];
-static inline uint32_t VP8GetByte(VP8BitReader* const br) {
-  assert(br);
-  if (br->buf_ < br->buf_end_) {
-    assert(br->buf_);
-    return *br->buf_++;
+extern const bit_t kVP8NewRange[128];
+
+void VP8LoadFinalBytes(VP8BitReader* const br);    // special case for the tail
+
+static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
+  assert(br && br->buf_);
+  // Read 'BITS' bits at a time if possible.
+  if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) {
+    // convert memory type to register type (with some zero'ing!)
+    bit_t bits;
+    lbit_t in_bits = *(lbit_t*)br->buf_;
+    br->buf_ += (BITS) >> 3;
+#if !defined(__BIG_ENDIAN__)
+#if (BITS == 32)
+#if defined(__i386__) || defined(__x86_64__)
+    __asm__ volatile("bswap %k0" : "=r"(in_bits) : "0"(in_bits));
+    bits = (bit_t)in_bits;   // 32b -> 64b zero-extension
+#elif defined(_MSC_VER)
+    bits = _byteswap_ulong(in_bits);
+#else
+    bits = (bit_t)(in_bits >> 24) | ((in_bits >> 8) & 0xff00)
+         | ((in_bits << 8) & 0xff0000)  | (in_bits << 24);
+#endif  // x86
+#elif (BITS == 16)
+    // gcc will recognize a 'rorw $8, ...' here:
+    bits = (bit_t)(in_bits >> 8) | ((in_bits & 0xff) << 8);
+#endif
+#else    // LITTLE_ENDIAN
+    bits = (bit_t)in_bits;
+#endif
+    br->value_ |= bits << br->missing_;
+    br->missing_ -= (BITS);
+  } else {
+    VP8LoadFinalBytes(br);    // no need to be inlined
   }
-  br->eof_ = 1;
-  return 0xff;
 }
 
-static inline uint32_t VP8BitUpdate(VP8BitReader* const br, uint32_t split) {
-  uint32_t bit;
-  const uint32_t value_split = (split + 1) << 8;
-  // Make sure we have a least 8 bits in 'value_'
-  if (br->missing_ > 0) {
-    br->value_ |= VP8GetByte(br) << br->missing_;
-    br->missing_ -= 8;
+static WEBP_INLINE int VP8BitUpdate(VP8BitReader* const br, bit_t split) {
+  const bit_t value_split = split | (MASK);
+  if (br->missing_ > 0) {  // Make sure we have a least BITS bits in 'value_'
+    VP8LoadNewBytes(br);
   }
-  bit = (br->value_ >= value_split);
-  if (bit) {
-    br->range_ -= split + 1;
-    br->value_ -= value_split;
+  if (br->value_ > value_split) {
+    br->range_ -= value_split + 1;
+    br->value_ -= value_split + 1;
+    return 1;
   } else {
-    br->range_ = split;
+    br->range_ = value_split;
+    return 0;
   }
-  return bit;
 }
 
-static inline void VP8Shift(VP8BitReader* const br) {
+static WEBP_INLINE void VP8Shift(VP8BitReader* const br) {
   // range_ is in [0..127] interval here.
-  const int shift = kVP8Log2Range[br->range_];
-  br->range_ = kVP8NewRange[br->range_];
+  const int idx = br->range_ >> (BITS);
+  const int shift = kVP8Log2Range[idx];
+  br->range_ = kVP8NewRange[idx];
   br->value_ <<= shift;
   br->missing_ += shift;
 }
 
-static inline uint32_t VP8GetBit(VP8BitReader* const br, int prob) {
-  const uint32_t split = (br->range_ * prob) >> 8;
-  const uint32_t bit = VP8BitUpdate(br, split);
-  if (br->range_ < 0x7f) {
+static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
+  // It's important to avoid generating a 64bit x 64bit multiply here.
+  // We just need an 8b x 8b after all.
+  const bit_t split =
+      (bit_t)((uint32_t)(br->range_ >> (BITS)) * prob) << ((BITS) - 8);
+  const int bit = VP8BitUpdate(br, split);
+  if (br->range_ <= (((bit_t)0x7e << (BITS)) | (MASK))) {
     VP8Shift(br);
   }
   return bit;
 }
 
-static inline int VP8GetSigned(VP8BitReader* const br, int v) {
-  const uint32_t split = br->range_ >> 1;
-  const uint32_t bit = VP8BitUpdate(br, split);
+static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
+  const bit_t split = (br->range_ >> 1);
+  const int bit = VP8BitUpdate(br, split);
   VP8Shift(br);
   return bit ? -v : v;
 }
 
+
+// -----------------------------------------------------------------------------
+// Bitreader
+
+typedef struct {
+  uint64_t       val_;
+  const uint8_t* buf_;
+  size_t         len_;
+  size_t         pos_;
+  int            bit_pos_;
+  int            eos_;
+  int            error_;
+} VP8LBitReader;
+
+void VP8LInitBitReader(VP8LBitReader* const br,
+                       const uint8_t* const start,
+                       size_t length);
+
+//  Sets a new data buffer.
+void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
+                            const uint8_t* const buffer, size_t length);
+
+// Reads the specified number of bits from Read Buffer.
+// Flags an error in case end_of_stream or n_bits is more than allowed limit.
+// Flags eos if this read attempt is going to cross the read buffer.
+uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
+
+// Reads one bit from Read Buffer. Flags an error in case end_of_stream.
+// Flags eos after reading last bit from the buffer.
+uint32_t VP8LReadOneBit(VP8LBitReader* const br);
+
+// VP8LReadOneBitUnsafe is faster than VP8LReadOneBit, but it can be called only
+// 32 times after the last VP8LFillBitWindow. Any subsequent calls
+// (without VP8LFillBitWindow) will return invalid data.
+static WEBP_INLINE uint32_t VP8LReadOneBitUnsafe(VP8LBitReader* const br) {
+  const uint32_t val = (br->val_ >> br->bit_pos_) & 1;
+  ++br->bit_pos_;
+  return val;
+}
+
+// Advances the Read buffer by 4 bytes to make room for reading next 32 bits.
+void VP8LFillBitWindow(VP8LBitReader* const br);
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }    // extern "C"
 #endif
 
 #endif  /* WEBP_UTILS_BIT_READER_H_ */