yading@10: /*
yading@10:  * Range coder
yading@10:  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * Range coder.
yading@10:  */
yading@10: 
yading@10: #ifndef AVCODEC_RANGECODER_H
yading@10: #define AVCODEC_RANGECODER_H
yading@10: 
yading@10: #include <stdint.h>
yading@10: 
yading@10: #include "libavutil/common.h"
yading@10: #include "libavutil/avassert.h"
yading@10: 
yading@10: typedef struct RangeCoder {
yading@10:     int low;
yading@10:     int range;
yading@10:     int outstanding_count;
yading@10:     int outstanding_byte;
yading@10:     uint8_t zero_state[256];
yading@10:     uint8_t one_state[256];
yading@10:     uint8_t *bytestream_start;
yading@10:     uint8_t *bytestream;
yading@10:     uint8_t *bytestream_end;
yading@10: } RangeCoder;
yading@10: 
yading@10: void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
yading@10: void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
yading@10: int ff_rac_terminate(RangeCoder *c);
yading@10: void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
yading@10: 
yading@10: static inline void renorm_encoder(RangeCoder *c)
yading@10: {
yading@10:     // FIXME: optimize
yading@10:     while (c->range < 0x100) {
yading@10:         if (c->outstanding_byte < 0) {
yading@10:             c->outstanding_byte = c->low >> 8;
yading@10:         } else if (c->low <= 0xFF00) {
yading@10:             *c->bytestream++ = c->outstanding_byte;
yading@10:             for (; c->outstanding_count; c->outstanding_count--)
yading@10:                 *c->bytestream++ = 0xFF;
yading@10:             c->outstanding_byte = c->low >> 8;
yading@10:         } else if (c->low >= 0x10000) {
yading@10:             *c->bytestream++ = c->outstanding_byte + 1;
yading@10:             for (; c->outstanding_count; c->outstanding_count--)
yading@10:                 *c->bytestream++ = 0x00;
yading@10:             c->outstanding_byte = (c->low >> 8) & 0xFF;
yading@10:         } else {
yading@10:             c->outstanding_count++;
yading@10:         }
yading@10: 
yading@10:         c->low     = (c->low & 0xFF) << 8;
yading@10:         c->range <<= 8;
yading@10:     }
yading@10: }
yading@10: 
yading@10: static inline int get_rac_count(RangeCoder *c)
yading@10: {
yading@10:     int x = c->bytestream - c->bytestream_start + c->outstanding_count;
yading@10:     if (c->outstanding_byte >= 0)
yading@10:         x++;
yading@10:     return 8 * x - av_log2(c->range);
yading@10: }
yading@10: 
yading@10: static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
yading@10: {
yading@10:     int range1 = (c->range * (*state)) >> 8;
yading@10: 
yading@10:     av_assert2(*state);
yading@10:     av_assert2(range1 < c->range);
yading@10:     av_assert2(range1 > 0);
yading@10:     if (!bit) {
yading@10:         c->range -= range1;
yading@10:         *state    = c->zero_state[*state];
yading@10:     } else {
yading@10:         c->low  += c->range - range1;
yading@10:         c->range = range1;
yading@10:         *state   = c->one_state[*state];
yading@10:     }
yading@10: 
yading@10:     renorm_encoder(c);
yading@10: }
yading@10: 
yading@10: static inline void refill(RangeCoder *c)
yading@10: {
yading@10:     if (c->range < 0x100) {
yading@10:         c->range <<= 8;
yading@10:         c->low   <<= 8;
yading@10:         if (c->bytestream < c->bytestream_end)
yading@10:             c->low += c->bytestream[0];
yading@10:         c->bytestream++;
yading@10:     }
yading@10: }
yading@10: 
yading@10: static inline int get_rac(RangeCoder *c, uint8_t *const state)
yading@10: {
yading@10:     int range1 = (c->range * (*state)) >> 8;
yading@10:     int av_unused one_mask;
yading@10: 
yading@10:     c->range -= range1;
yading@10: #if 1
yading@10:     if (c->low < c->range) {
yading@10:         *state = c->zero_state[*state];
yading@10:         refill(c);
yading@10:         return 0;
yading@10:     } else {
yading@10:         c->low  -= c->range;
yading@10:         *state   = c->one_state[*state];
yading@10:         c->range = range1;
yading@10:         refill(c);
yading@10:         return 1;
yading@10:     }
yading@10: #else
yading@10:     one_mask = (c->range - c->low - 1) >> 31;
yading@10: 
yading@10:     c->low   -= c->range & one_mask;
yading@10:     c->range += (range1 - c->range) & one_mask;
yading@10: 
yading@10:     *state = c->zero_state[(*state) + (256 & one_mask)];
yading@10: 
yading@10:     refill(c);
yading@10: 
yading@10:     return one_mask & 1;
yading@10: #endif
yading@10: }
yading@10: 
yading@10: #endif /* AVCODEC_RANGECODER_H */