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// 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_
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