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