lfg.h (1976B)
1 /* 2 * Lagged Fibonacci PRNG 3 * Copyright (c) 2008 Michael Niedermayer 4 * 5 * This file is part of Libav. 6 * 7 * Libav is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2.1 of the License, or (at your option) any later version. 11 * 12 * Libav is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with Libav; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22 #ifndef AVUTIL_LFG_H 23 #define AVUTIL_LFG_H 24 25 typedef struct { 26 unsigned int state[64]; 27 int index; 28 } AVLFG; 29 30 void av_lfg_init(AVLFG *c, unsigned int seed); 31 32 /** 33 * Get the next random unsigned 32-bit number using an ALFG. 34 * 35 * Please also consider a simple LCG like state= state*1664525+1013904223, 36 * it may be good enough and faster for your specific use case. 37 */ 38 static inline unsigned int av_lfg_get(AVLFG *c){ 39 c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63]; 40 return c->state[c->index++ & 63]; 41 } 42 43 /** 44 * Get the next random unsigned 32-bit number using a MLFG. 45 * 46 * Please also consider av_lfg_get() above, it is faster. 47 */ 48 static inline unsigned int av_mlfg_get(AVLFG *c){ 49 unsigned int a= c->state[(c->index-55) & 63]; 50 unsigned int b= c->state[(c->index-24) & 63]; 51 return c->state[c->index++ & 63] = 2*a*b+a+b; 52 } 53 54 /** 55 * Get the next two numbers generated by a Box-Muller Gaussian 56 * generator using the random numbers issued by lfg. 57 * 58 * @param out array where the two generated numbers are placed 59 */ 60 void av_bmg_get(AVLFG *lfg, double out[2]); 61 62 #endif /* AVUTIL_LFG_H */