text: /*
   * Mersenne Twister Random Algorithm
   * Copyright (c) 2006 Ryan Martell.
   * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
   * Takuji Nishimura and Makoto Matsumoto.
   *
   * 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
   */
  
  #ifndef FFMPEG_RANDOM_H
  #define FFMPEG_RANDOM_H
  
  #define AV_RANDOM_N 624
  
  typedef struct {
      unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
      int index; ///< current untempered value we use as the base.
  } AVRandomState;
  
  
  void av_init_random(unsigned int seed, AVRandomState *state); ///< to be inlined, the struct must be visible, so it doesn't make sense to try and keep it opaque with malloc/free like calls
  void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop)
  
  /** generates a random number on [0,0xffffffff]-interval */
  static inline unsigned int av_random(AVRandomState *state)
  {
      unsigned int y;
  
      // regenerate the untempered numbers if we should...
      if (state->index >= AV_RANDOM_N)
          av_random_generate_untempered_numbers(state);
  
      // grab one...
      y = state->mt[state->index++];
  
      /* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
      y ^= (y >> 11);
      y ^= (y << 7) & 0x9d2c5680;
      y ^= (y << 15) & 0xefc60000;
      y ^= (y >> 18);
  
      return y;
  }
  
  /** return random in range [0-1] as double */
  static inline double av_random_real1(AVRandomState *state)
  {
      /* divided by 2^32-1 */
      return av_random(state) * (1.0 / 4294967296.0);
  }
  
  // only available if DEBUG is defined in the .c file
  void av_benchmark_random(void);
  
  #endif /* FFMPEG_RANDOM_H */
  