Add WebP library to Chromium...

third_party/libwebp/bits.h

+// Copyright 2010 Google Inc.
+//
+// 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)
+
+#ifndef WEBP_DECODE_BITS_H_
+#define WEBP_DECODE_BITS_H_
+
+#include <assert.h>
+#include "webp/decode_vp8.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+//-----------------------------------------------------------------------------
+// Bitreader and code-tree reader
+
+typedef struct {
+  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 left_;                  // how many unused bits (negated)
+} VP8BitReader;
+
+// Initialize the bit reader and the boolean decoder. Return true if ok.
+int VP8Init(VP8BitReader* const br, const uint8_t* buf, uint32_t size);
+
+// 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) {
+  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_++;
+  }
+  br->eof_ = 1;
+  return 0x80;
+}
+
+static inline void VP8Shift(VP8BitReader* const br) {
+  // range_ is in [0..127] interval here.
+  const int shift = kVP8Log2Range[br->range_];
+  br->range_ = kVP8NewRange[br->range_];
+  br->value_ <<= shift;
+  br->left_ += shift;
+  if (br->left_ > 0) {
+    br->value_ |= VP8GetByte(br) << br->left_;
+    br->left_ -= 8;
+  }
+}
+
+static inline uint32_t VP8GetBit(VP8BitReader* const br, int prob) {
+  const uint32_t split = (br->range_ * prob) >> 8;
+  const uint32_t bit = ((br->value_ >> 8) > split);
+  if (bit) {
+    br->range_ -= split + 1;
+    br->value_ -= (split + 1) << 8;
+  } else {
+    br->range_ = split;
+  }
+  if (br->range_ < 0x7f) {
+    VP8Shift(br);
+  }
+  return bit;
+}
+
+static inline int VP8GetSigned(VP8BitReader* const br, int v) {
+  const uint32_t split = br->range_ >> 1;
+  const uint32_t bit = ((br->value_ >> 8) > split);
+  if (bit) {
+    br->range_ -= split + 1;
+    br->value_ -= (split + 1) << 8;
+    v = -v;
+  } else {
+    br->range_ = split;
+  }
+  VP8Shift(br);
+  return v;
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  // WEBP_DECODE_BITS_H_