gfiber / vendor / opensource / ffmpeg / d843e7dc941efab94c6756bf65d8421d80f9ce9a / . / libavutil / random.h

/* | |

* Mersenne Twister PRNG 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 AVUTIL_RANDOM_H | |

#define AVUTIL_RANDOM_H | |

#define AV_RANDOM_N 624 | |

#include "avutil.h" | |

#include "common.h" | |

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; | |

#if LIBAVUTIL_VERSION_MAJOR < 50 | |

attribute_deprecated void av_init_random(unsigned int seed, AVRandomState *state); | |

#endif | |

void av_random_init(AVRandomState *state, unsigned int seed); ///< To be inlined, the struct must be visible. So it does not 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 from the interval [0,0xffffffff]. | |

* | |

* Please do NOT use the Mersenne Twister, it is slow. Use the random number | |

* generator from lfg.c/h or a simple LCG like state = state*1664525+1013904223. | |

* If you still choose to use MT, expect that you will have to provide | |

* some evidence that it makes a difference for the case where you use it. | |

*/ | |

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; | |

} | |

/** Returns a random number in the 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); | |

} | |

#endif /* AVUTIL_RANDOM_H */ |