quicktime/ffmpeg/libavcodec/rangecoder.h

   1 /*
   2  * Range coder
   3  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18  *
  19  */
  20
  21 /**
  22  * @file rangecoder.h
  23  * Range coder.
  24  */
  25
  26 typedef struct RangeCoder{
  27     int low;
  28     int range;
  29     int outstanding_count;
  30     int outstanding_byte;
  31     uint8_t zero_state[256];
  32     uint8_t  one_state[256];
  33     uint8_t *bytestream_start;
  34     uint8_t *bytestream;
  35     uint8_t *bytestream_end;
  36 }RangeCoder;
  37
  38 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
  39 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
  40 int ff_rac_terminate(RangeCoder *c);
  41 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
  42
  43 static inline void renorm_encoder(RangeCoder *c){
  44     //FIXME optimize
  45     while(c->range < 0x100){
  46         if(c->outstanding_byte < 0){
  47             c->outstanding_byte= c->low>>8;
  48         }else if(c->low <= 0xFF00){
  49             *c->bytestream++ = c->outstanding_byte;
  50             for(;c->outstanding_count; c->outstanding_count--)
  51                 *c->bytestream++ = 0xFF;
  52             c->outstanding_byte= c->low>>8;
  53         }else if(c->low >= 0x10000){
  54             *c->bytestream++ = c->outstanding_byte + 1;
  55             for(;c->outstanding_count; c->outstanding_count--)
  56                 *c->bytestream++ = 0x00;
  57             c->outstanding_byte= (c->low>>8) & 0xFF;
  58         }else{
  59             c->outstanding_count++;
  60         }
  61
  62         c->low = (c->low & 0xFF)<<8;
  63         c->range <<= 8;
  64     }
  65 }
  66
  67 static inline void put_rac(RangeCoder *c, uint8_t * const state, int bit){
  68     int range1= (c->range * (*state)) >> 8;
  69
  70     assert(*state);
  71     assert(range1 < c->range);
  72     assert(range1 > 0);
  73     if(!bit){
  74         c->range -= range1;
  75         *state= c->zero_state[*state];
  76     }else{
  77         c->low += c->range - range1;
  78         c->range = range1;
  79         *state= c->one_state[*state];
  80     }
  81
  82     renorm_encoder(c);
  83 }
  84
  85 static inline void refill(RangeCoder *c){
  86     if(c->range < 0x100){
  87         c->range <<= 8;
  88         c->low <<= 8;
  89         if(c->bytestream < c->bytestream_end)
  90             c->low+= c->bytestream[0];
  91         c->bytestream++;
  92     }
  93 }
  94
  95 static inline int get_rac(RangeCoder *c, uint8_t * const state){
  96     int range1= (c->range * (*state)) >> 8;
  97     int attribute_unused one_mask;
  98
  99     c->range -= range1;
 100 #if 1
 101     if(c->low < c->range){
 102         *state= c->zero_state[*state];
 103         refill(c);
 104         return 0;
 105     }else{
 106         c->low -= c->range;
 107         *state= c->one_state[*state];
 108         c->range = range1;
 109         refill(c);
 110         return 1;
 111     }
 112 #else
 113     one_mask= (c->range - c->low-1)>>31;
 114
 115     c->low -= c->range & one_mask;
 116     c->range += (range1 - c->range) & one_mask;
 117
 118     *state= c->zero_state[(*state) + (256&one_mask)];
 119
 120     refill(c);
 121
 122     return one_mask&1;
 123 #endif
 124 }
 125