libavutil/random.h

   1 /*
   2  * Mersenne Twister Random Algorithm
   3  * Copyright (c) 2006 Ryan Martell.
   4  * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
   5  * Takuji Nishimura and Makoto Matsumoto.
   6  *
   7  * This file is part of FFmpeg.
   8  *
   9  * FFmpeg is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * FFmpeg is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with FFmpeg; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 #ifndef FFMPEG_RANDOM_H
  25 #define FFMPEG_RANDOM_H
  26
  27 #define AV_RANDOM_N 624
  28
  29 typedef struct {
  30     unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
  31     int index; ///< current untempered value we use as the base.
  32 } AVRandomState;
  33
  34
  35 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
  36 void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop)
  37
  38 /** generates a random number on [0,0xffffffff]-interval */
  39 static inline unsigned int av_random(AVRandomState *state)
  40 {
  41     unsigned int y;
  42
  43     // regenerate the untempered numbers if we should...
  44     if (state->index >= AV_RANDOM_N)
  45         av_random_generate_untempered_numbers(state);
  46
  47     // grab one...
  48     y = state->mt[state->index++];
  49
  50     /* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
  51     y ^= (y >> 11);
  52     y ^= (y << 7) & 0x9d2c5680;
  53     y ^= (y << 15) & 0xefc60000;
  54     y ^= (y >> 18);
  55
  56     return y;
  57 }
  58
  59 /** return random in range [0-1] as double */
  60 static inline double av_random_real1(AVRandomState *state)
  61 {
  62     /* divided by 2^32-1 */
  63     return av_random(state) * (1.0 / 4294967296.0);
  64 }
  65
  66 // only available if DEBUG is defined in the .c file
  67 void av_benchmark_random(void);
  68
  69 #endif /* FFMPEG_RANDOM_H */