libavcodec/rangecoder.h

   1 /*
   2  * Range coder
   3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file libavcodec/rangecoder.h
  24  * Range coder.
  25  */
  26
  27 #ifndef AVCODEC_RANGECODER_H
  28 #define AVCODEC_RANGECODER_H
  29
  30 #include <stdint.h>
  31 #include <assert.h>
  32 #include "libavutil/common.h"
  33
  34 typedef struct RangeCoder{
  35     int low;
  36     int range;
  37     int outstanding_count;
  38     int outstanding_byte;
  39     uint8_t zero_state[256];
  40     uint8_t  one_state[256];
  41     uint8_t *bytestream_start;
  42     uint8_t *bytestream;
  43     uint8_t *bytestream_end;
  44 }RangeCoder;
  45
  46 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
  47 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
  48 int ff_rac_terminate(RangeCoder *c);
  49 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
  50
  51 static inline void renorm_encoder(RangeCoder *c){
  52     //FIXME optimize
  53     while(c->range < 0x100){
  54         if(c->outstanding_byte < 0){
  55             c->outstanding_byte= c->low>>8;
  56         }else if(c->low <= 0xFF00){
  57             *c->bytestream++ = c->outstanding_byte;
  58             for(;c->outstanding_count; c->outstanding_count--)
  59                 *c->bytestream++ = 0xFF;
  60             c->outstanding_byte= c->low>>8;
  61         }else if(c->low >= 0x10000){
  62             *c->bytestream++ = c->outstanding_byte + 1;
  63             for(;c->outstanding_count; c->outstanding_count--)
  64                 *c->bytestream++ = 0x00;
  65             c->outstanding_byte= (c->low>>8) & 0xFF;
  66         }else{
  67             c->outstanding_count++;
  68         }
  69
  70         c->low = (c->low & 0xFF)<<8;
  71         c->range <<= 8;
  72     }
  73 }
  74
  75 static inline int get_rac_count(RangeCoder *c){
  76     int x= c->bytestream - c->bytestream_start + c->outstanding_count;
  77     if(c->outstanding_byte >= 0)
  78         x++;
  79     return 8*x - av_log2(c->range);
  80 }
  81
  82 static inline void put_rac(RangeCoder *c, uint8_t * const state, int bit){
  83     int range1= (c->range * (*state)) >> 8;
  84
  85     assert(*state);
  86     assert(range1 < c->range);
  87     assert(range1 > 0);
  88     if(!bit){
  89         c->range -= range1;
  90         *state= c->zero_state[*state];
  91     }else{
  92         c->low += c->range - range1;
  93         c->range = range1;
  94         *state= c->one_state[*state];
  95     }
  96
  97     renorm_encoder(c);
  98 }
  99
 100 static inline void refill(RangeCoder *c){
 101     if(c->range < 0x100){
 102         c->range <<= 8;
 103         c->low <<= 8;
 104         if(c->bytestream < c->bytestream_end)
 105             c->low+= c->bytestream[0];
 106         c->bytestream++;
 107     }
 108 }
 109
 110 static inline int get_rac(RangeCoder *c, uint8_t * const state){
 111     int range1= (c->range * (*state)) >> 8;
 112     int av_unused one_mask;
 113
 114     c->range -= range1;
 115 #if 1
 116     if(c->low < c->range){
 117         *state= c->zero_state[*state];
 118         refill(c);
 119         return 0;
 120     }else{
 121         c->low -= c->range;
 122         *state= c->one_state[*state];
 123         c->range = range1;
 124         refill(c);
 125         return 1;
 126     }
 127 #else
 128     one_mask= (c->range - c->low-1)>>31;
 129
 130     c->low -= c->range & one_mask;
 131     c->range += (range1 - c->range) & one_mask;
 132
 133     *state= c->zero_state[(*state) + (256&one_mask)];
 134
 135     refill(c);
 136
 137     return one_mask&1;
 138 #endif
 139 }
 140
 141 #endif /* AVCODEC_RANGECODER_H */