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
  24  * Range coder.
  25  */
  26
  27 #ifndef AVCODEC_RANGECODER_H
  28 #define AVCODEC_RANGECODER_H
  29
  30 #include <stdint.h>
  31
  32 #include "libavutil/avassert.h"
  33 #include "libavutil/intmath.h"
  34
  35 typedef struct RangeCoder {
  36     int low;
  37     int range;
  38     int outstanding_count;
  39     int outstanding_byte;
  40     uint8_t zero_state[256];
  41     uint8_t one_state[256];
  42     uint8_t *bytestream_start;
  43     uint8_t *bytestream;
  44     uint8_t *bytestream_end;
  45     int overread;
  46 #define MAX_OVERREAD 2
  47 } RangeCoder;
  48
  49 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
  50 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
  51
  52 /**
  53  * Terminates the range coder
  54  * @param version version 0 requires the decoder to know the data size in bytes
  55  *                version 1 needs about 1 bit more space but does not need to
  56  *                          carry the size from encoder to decoder
  57  */
  58 int ff_rac_terminate(RangeCoder *c, int version);
  59
  60 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
  61
  62 static inline void renorm_encoder(RangeCoder *c)
  63 {
  64     // FIXME: optimize
  65         if (c->outstanding_byte < 0) {
  66             c->outstanding_byte = c->low >> 8;
  67         } else if (c->low <= 0xFF00) {
  68             *c->bytestream++ = c->outstanding_byte;
  69             for (; c->outstanding_count; c->outstanding_count--)
  70                 *c->bytestream++ = 0xFF;
  71             c->outstanding_byte = c->low >> 8;
  72         } else if (c->low >= 0x10000) {
  73             *c->bytestream++ = c->outstanding_byte + 1;
  74             for (; c->outstanding_count; c->outstanding_count--)
  75                 *c->bytestream++ = 0x00;
  76             c->outstanding_byte = (c->low >> 8) & 0xFF;
  77         } else {
  78             c->outstanding_count++;
  79         }
  80
  81         c->low     = (c->low & 0xFF) << 8;
  82         c->range <<= 8;
  83 }
  84
  85 static inline int get_rac_count(RangeCoder *c)
  86 {
  87     int x = c->bytestream - c->bytestream_start + c->outstanding_count;
  88     if (c->outstanding_byte >= 0)
  89         x++;
  90     return 8 * x - av_log2(c->range);
  91 }
  92
  93 static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
  94 {
  95     int range1 = (c->range * (*state)) >> 8;
  96
  97     av_assert2(*state);
  98     av_assert2(range1 < c->range);
  99     av_assert2(range1 > 0);
 100     if (!bit) {
 101         c->range -= range1;
 102         *state    = c->zero_state[*state];
 103     } else {
 104         c->low  += c->range - range1;
 105         c->range = range1;
 106         *state   = c->one_state[*state];
 107     }
 108
 109     while (c->range < 0x100)
 110         renorm_encoder(c);
 111 }
 112
 113 static inline void refill(RangeCoder *c)
 114 {
 115     if (c->range < 0x100) {
 116         c->range <<= 8;
 117         c->low   <<= 8;
 118         if (c->bytestream < c->bytestream_end) {
 119             c->low += c->bytestream[0];
 120             c->bytestream++;
 121         } else
 122             c->overread ++;
 123     }
 124 }
 125
 126 static inline int get_rac(RangeCoder *c, uint8_t *const state)
 127 {
 128     int range1 = (c->range * (*state)) >> 8;
 129
 130     c->range -= range1;
 131     if (c->low < c->range) {
 132         *state = c->zero_state[*state];
 133         refill(c);
 134         return 0;
 135     } else {
 136         c->low  -= c->range;
 137         *state   = c->one_state[*state];
 138         c->range = range1;
 139         refill(c);
 140         return 1;
 141     }
 142 }
 143
 144 #endif /* AVCODEC_RANGECODER_H */