1/* 2 * Mersenne Twister PRNG algorithm 3 * Copyright (c) 2006 Ryan Martell 4 * Based on a C program for MT19937, with initialization improved 2002/1/26. 5 * Coded by 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 AVUTIL_RANDOM_H 25#define AVUTIL_RANDOM_H 26 27#define AV_RANDOM_N 624 28 29#include "avutil.h" 30#include "common.h" 31 32typedef struct { 33 unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector 34 int index; ///< Current untempered value we use as the base. 35} AVRandomState; 36 37 38#if LIBAVUTIL_VERSION_MAJOR < 50 39attribute_deprecated void av_init_random(unsigned int seed, AVRandomState *state); 40#endif 41void 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. 42void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop). 43 44/** 45 * Generates a random number from the interval [0,0xffffffff]. 46 * 47 * Please do NOT use the Mersenne Twister, it is slow. Use the random number 48 * generator from lfg.c/h or a simple LCG like state = state*1664525+1013904223. 49 * If you still choose to use MT, expect that you will have to provide 50 * some evidence that it makes a difference for the case where you use it. 51 */ 52static inline unsigned int av_random(AVRandomState *state) 53{ 54 unsigned int y; 55 56 // Regenerate the untempered numbers if we should... 57 if (state->index >= AV_RANDOM_N) 58 av_random_generate_untempered_numbers(state); 59 60 // Grab one... 61 y = state->mt[state->index++]; 62 63 /* Now temper (Mersenne Twister coefficients). The coefficients for MT19937 are.. */ 64 y ^= (y >> 11); 65 y ^= (y << 7) & 0x9d2c5680; 66 y ^= (y << 15) & 0xefc60000; 67 y ^= (y >> 18); 68 69 return y; 70} 71 72/** Returns a random number in the range [0-1] as double. */ 73static inline double av_random_real1(AVRandomState *state) 74{ 75 /* divided by 2^32-1 */ 76 return av_random(state) * (1.0 / 4294967296.0); 77} 78 79#endif /* AVUTIL_RANDOM_H */ 80