blob: cbb095c1be79e679af76bb687f931541a583bce1 [file] [log] [blame]
// Copyright 2011 Google Inc. All Rights Reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
// Bit writing and boolean coder
// Author: Skal (
#include "../webp/types.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
// Bit-writing
typedef struct VP8BitWriter VP8BitWriter;
struct VP8BitWriter {
int32_t range_; // range-1
int32_t value_;
int run_; // number of outstanding bits
int nb_bits_; // number of pending bits
uint8_t* buf_; // internal buffer. Re-allocated regularly. Not owned.
size_t pos_;
size_t max_pos_;
int error_; // true in case of error
// Initialize the object. Allocates some initial memory based on expected_size.
int VP8BitWriterInit(VP8BitWriter* const bw, size_t expected_size);
// Finalize the bitstream coding. Returns a pointer to the internal buffer.
uint8_t* VP8BitWriterFinish(VP8BitWriter* const bw);
// Release any pending memory and zeroes the object. Not a mandatory call.
// Only useful in case of error, when the internal buffer hasn't been grabbed!
void VP8BitWriterWipeOut(VP8BitWriter* const bw);
int VP8PutBit(VP8BitWriter* const bw, int bit, int prob);
int VP8PutBitUniform(VP8BitWriter* const bw, int bit);
void VP8PutValue(VP8BitWriter* const bw, int value, int nb_bits);
void VP8PutSignedValue(VP8BitWriter* const bw, int value, int nb_bits);
// Appends some bytes to the internal buffer. Data is copied.
int VP8BitWriterAppend(VP8BitWriter* const bw,
const uint8_t* data, size_t size);
// return approximate write position (in bits)
static WEBP_INLINE uint64_t VP8BitWriterPos(const VP8BitWriter* const bw) {
return (uint64_t)(bw->pos_ + bw->run_) * 8 + 8 + bw->nb_bits_;
// Returns a pointer to the internal buffer.
static WEBP_INLINE uint8_t* VP8BitWriterBuf(const VP8BitWriter* const bw) {
return bw->buf_;
// Returns the size of the internal buffer.
static WEBP_INLINE size_t VP8BitWriterSize(const VP8BitWriter* const bw) {
return bw->pos_;
// VP8LBitWriter
// TODO(vikasa): VP8LBitWriter is copied as-is from lossless code. There's scope
// of re-using VP8BitWriter. Will evaluate once basic lossless encoder is
// implemented.
typedef struct {
uint8_t* buf_;
size_t bit_pos_;
size_t max_bytes_;
// After all bits are written, the caller must observe the state of
// error_. A value of 1 indicates that a memory allocation failure
// has happened during bit writing. A value of 0 indicates successful
// writing of bits.
int error_;
} VP8LBitWriter;
static WEBP_INLINE size_t VP8LBitWriterNumBytes(VP8LBitWriter* const bw) {
return (bw->bit_pos_ + 7) >> 3;
static WEBP_INLINE uint8_t* VP8LBitWriterFinish(VP8LBitWriter* const bw) {
return bw->buf_;
// Returns 0 in case of memory allocation error.
int VP8LBitWriterInit(VP8LBitWriter* const bw, size_t expected_size);
void VP8LBitWriterDestroy(VP8LBitWriter* const bw);
// This function writes bits into bytes in increasing addresses, and within
// a byte least-significant-bit first.
// The function can write up to 16 bits in one go with WriteBits
// Example: let's assume that 3 bits (Rs below) have been written already:
// 0000 0RRR 0000 0000 0000 0000
// Now, we could write 5 or less bits in MSB by just sifting by 3
// and OR'ing to BYTE-0.
// For n bits, we take the last 5 bytes, OR that with high bits in BYTE-0,
// and locate the rest in BYTE+1 and BYTE+2.
// VP8LBitWriter's error_ flag is set in case of memory allocation error.
void VP8LWriteBits(VP8LBitWriter* const bw, int n_bits, uint32_t bits);
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"