text: /*
   * Range coder
   * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
   *
   * This file is part of FFmpeg.
   *
   * FFmpeg is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * FFmpeg is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with FFmpeg; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  /**
   * @file
   * Range coder.
   */
  
  #ifndef AVCODEC_RANGECODER_H
  #define AVCODEC_RANGECODER_H
  
  #include <stdint.h>
  
  #include "libavutil/common.h"
  #include "libavutil/avassert.h"
  
  typedef struct RangeCoder {
      int low;
      int range;
      int outstanding_count;
      int outstanding_byte;
      uint8_t zero_state[256];
      uint8_t one_state[256];
      uint8_t *bytestream_start;
      uint8_t *bytestream;
      uint8_t *bytestream_end;
      int overread;
  #define MAX_OVERREAD 2
  } RangeCoder;
  
  void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
  void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
  
  /**
   * Terminates the range coder
   * @param version version 0 requires the decoder to know the data size in bytes
   *                version 1 needs about 1 bit more space but does not need to
   *                          carry the size from encoder to decoder
   */
  int ff_rac_terminate(RangeCoder *c, int version);
  
  void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
  
  static inline void renorm_encoder(RangeCoder *c)
  {
      // FIXME: optimize
      while (c->range < 0x100) {
          if (c->outstanding_byte < 0) {
              c->outstanding_byte = c->low >> 8;
          } else if (c->low <= 0xFF00) {
              *c->bytestream++ = c->outstanding_byte;
              for (; c->outstanding_count; c->outstanding_count--)
                  *c->bytestream++ = 0xFF;
              c->outstanding_byte = c->low >> 8;
          } else if (c->low >= 0x10000) {
              *c->bytestream++ = c->outstanding_byte + 1;
              for (; c->outstanding_count; c->outstanding_count--)
                  *c->bytestream++ = 0x00;
              c->outstanding_byte = (c->low >> 8) & 0xFF;
          } else {
              c->outstanding_count++;
          }
  
          c->low     = (c->low & 0xFF) << 8;
          c->range <<= 8;
      }
  }
  
  static inline int get_rac_count(RangeCoder *c)
  {
      int x = c->bytestream - c->bytestream_start + c->outstanding_count;
      if (c->outstanding_byte >= 0)
          x++;
      return 8 * x - av_log2(c->range);
  }
  
  static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)
  {
      int range1 = (c->range * (*state)) >> 8;
  
      av_assert2(*state);
      av_assert2(range1 < c->range);
      av_assert2(range1 > 0);
      if (!bit) {
          c->range -= range1;
          *state    = c->zero_state[*state];
      } else {
          c->low  += c->range - range1;
          c->range = range1;
          *state   = c->one_state[*state];
      }
  
      renorm_encoder(c);
  }
  
  static inline void refill(RangeCoder *c)
  {
      if (c->range < 0x100) {
          c->range <<= 8;
          c->low   <<= 8;
          if (c->bytestream < c->bytestream_end) {
              c->low += c->bytestream[0];
              c->bytestream++;
          } else
              c->overread ++;
      }
  }
  
  static inline int get_rac(RangeCoder *c, uint8_t *const state)
  {
      int range1 = (c->range * (*state)) >> 8;
  
      c->range -= range1;
      if (c->low < c->range) {
          *state = c->zero_state[*state];
          refill(c);
          return 0;
      } else {
          c->low  -= c->range;
          *state   = c->one_state[*state];
          c->range = range1;
          refill(c);
          return 1;
      }
  }
  
  #endif /* AVCODEC_RANGECODER_H */
  