mirror of
https://github.com/FFmpeg/FFmpeg.git
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139 lines
3.8 KiB
C
139 lines
3.8 KiB
C
/*
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* Range coder
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* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file
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* Range coder.
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*/
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#ifndef AVCODEC_RANGECODER_H
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#define AVCODEC_RANGECODER_H
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#include <stdint.h>
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#include "libavutil/avassert.h"
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#include "libavutil/intmath.h"
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typedef struct RangeCoder {
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int low;
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int range;
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int outstanding_count;
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int outstanding_byte;
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uint8_t zero_state[256];
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uint8_t one_state[256];
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uint8_t *bytestream_start;
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uint8_t *bytestream;
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uint8_t *bytestream_end;
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int overread;
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#define MAX_OVERREAD 2
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} RangeCoder;
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void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
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void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
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/**
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* Terminates the range coder
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* @param version version 0 requires the decoder to know the data size in bytes
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* version 1 needs about 1 bit more space but does not need to
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* carry the size from encoder to decoder
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*/
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int ff_rac_terminate(RangeCoder *c, int version);
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void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
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static inline void renorm_encoder(RangeCoder *c)
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{
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if (c->low - 0xFF01 >= 0x10000 - 0xFF01U) {
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int mask = c->low - 0xFF01 >> 31;
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*c->bytestream = c->outstanding_byte + 1 + mask;
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c->bytestream += c->outstanding_byte >= 0;
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for (; c->outstanding_count; c->outstanding_count--)
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*c->bytestream++ = mask;
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c->outstanding_byte = c->low >> 8;
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} else {
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c->outstanding_count++;
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}
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c->low = (c->low & 0xFF) << 8;
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c->range <<= 8;
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}
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static inline int get_rac_count(RangeCoder *c)
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{
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int x = c->bytestream - c->bytestream_start + c->outstanding_count;
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if (c->outstanding_byte >= 0)
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x++;
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return 8 * x - av_log2(c->range);
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}
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static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
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{
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int range1 = (c->range * (*state)) >> 8;
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av_assert2(*state);
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av_assert2(range1 < c->range);
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av_assert2(range1 > 0);
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if (!bit) {
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c->range -= range1;
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*state = c->zero_state[*state];
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} else {
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c->low += c->range - range1;
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c->range = range1;
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*state = c->one_state[*state];
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}
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if (c->range < 0x100)
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renorm_encoder(c);
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}
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static inline void refill(RangeCoder *c)
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{
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c->range <<= 8;
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c->low <<= 8;
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if (c->bytestream < c->bytestream_end) {
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c->low += c->bytestream[0];
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c->bytestream++;
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} else
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c->overread ++;
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}
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static inline int get_rac(RangeCoder *c, uint8_t *const state)
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{
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int range1 = (c->range * (*state)) >> 8;
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c->range -= range1;
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if (c->low < c->range) {
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*state = c->zero_state[*state];
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if (c->range < 0x100)
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refill(c);
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return 0;
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} else {
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c->low -= c->range;
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*state = c->one_state[*state];
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c->range = range1;
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if (c->range < 0x100)
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refill(c);
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return 1;
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}
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}
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#endif /* AVCODEC_RANGECODER_H */
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