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.
   * based upon
   *    "Range encoding: an algorithm for removing redundancy from a digitised
   *                     message.
   *     G. N. N. Martin                  Presented in March 1979 to the Video &
   *                                      Data Recording Conference,
   *     IBM UK Scientific Center         held in Southampton July 24-27 1979."
   *
   */
  
  #include <string.h>
  
  #include "libavutil/attributes.h"
  #include "libavutil/avassert.h"
  #include "avcodec.h"
  #include "rangecoder.h"
  #include "bytestream.h"
  
  av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
  {
      c->bytestream_start  =
      c->bytestream        = buf;
      c->bytestream_end    = buf + buf_size;
      c->low               = 0;
      c->range             = 0xFF00;
      c->outstanding_count = 0;
      c->outstanding_byte  = -1;
  }
  
  av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf,
                                     int buf_size)
  {
      /* cast to avoid compiler warning */
      ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
  
      c->low = bytestream_get_be16((const uint8_t **)&c->bytestream);
  }
  
  void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
  {
      const int64_t one = 1LL << 32;
      int64_t p;
      int last_p8, p8, i;
  
      memset(c->zero_state, 0, sizeof(c->zero_state));
      memset(c->one_state, 0, sizeof(c->one_state));
  
      last_p8 = 0;
      p       = one / 2;
      for (i = 0; i < 128; i++) {
          p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
          if (p8 <= last_p8)
              p8 = last_p8 + 1;
          if (last_p8 && last_p8 < 256 && p8 <= max_p)
              c->one_state[last_p8] = p8;
  
          p      += ((one - p) * factor + one / 2) >> 32;
          last_p8 = p8;
      }
  
      for (i = 256 - max_p; i <= max_p; i++) {
          if (c->one_state[i])
              continue;
  
          p  = (i * one + 128) >> 8;
          p += ((one - p) * factor + one / 2) >> 32;
          p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
          if (p8 <= i)
              p8 = i + 1;
          if (p8 > max_p)
              p8 = max_p;
          c->one_state[i] = p8;
      }
  
      for (i = 1; i < 255; i++)
          c->zero_state[i] = 256 - c->one_state[256 - i];
  }
  
  /* Return the number of bytes written. */
  int ff_rac_terminate(RangeCoder *c)
  {
      c->range = 0xFF;
      c->low  += 0xFF;
      renorm_encoder(c);
      c->range = 0xFF;
      renorm_encoder(c);
  
      av_assert1(c->low   == 0);
      av_assert1(c->range >= 0x100);
  
      return c->bytestream - c->bytestream_start;
  }
  
  #ifdef TEST
  #define SIZE 10240
  
  #include "libavutil/lfg.h"
  #include "libavutil/log.h"
  
  int main(void)
  {
      RangeCoder c;
      uint8_t b[9 * SIZE];
      uint8_t r[9 * SIZE];
      int i;
      uint8_t state[10];
      AVLFG prng;
  
      av_lfg_init(&prng, 1);
  
      ff_init_range_encoder(&c, b, SIZE);
      ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
  
      memset(state, 128, sizeof(state));
  
      for (i = 0; i < SIZE; i++)
          r[i] = av_lfg_get(&prng) % 7;
  
      for (i = 0; i < SIZE; i++)
          put_rac(&c, state, r[i] & 1);
  
      ff_rac_terminate(&c);
  
      ff_init_range_decoder(&c, b, SIZE);
  
      memset(state, 128, sizeof(state));
  
      for (i = 0; i < SIZE; i++)
          if ((r[i] & 1) != get_rac(&c, state)) {
              av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
              return 1;
          }
  
      return 0;
  }
  #endif /* TEST */
  