lfg.h (2541B)
1 /* 2 * Lagged Fibonacci PRNG 3 * Copyright (c) 2008 Michael Niedermayer 4 * 5 * This file is part of FFmpeg. 6 * 7 * FFmpeg 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 * FFmpeg 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 FFmpeg; 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 #include <stdint.h> 26 27 /** 28 * Context structure for the Lagged Fibonacci PRNG. 29 * The exact layout, types and content of this struct may change and should 30 * not be accessed directly. Only its `sizeof()` is guaranteed to stay the same 31 * to allow easy instanciation. 32 */ 33 typedef struct AVLFG { 34 unsigned int state[64]; 35 int index; 36 } AVLFG; 37 38 void av_lfg_init(AVLFG *c, unsigned int seed); 39 40 /** 41 * Seed the state of the ALFG using binary data. 42 * 43 * @return 0 on success, negative value (AVERROR) on failure. 44 */ 45 int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length); 46 47 /** 48 * Get the next random unsigned 32-bit number using an ALFG. 49 * 50 * Please also consider a simple LCG like state= state*1664525+1013904223, 51 * it may be good enough and faster for your specific use case. 52 */ 53 static inline unsigned int av_lfg_get(AVLFG *c){ 54 unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63]; 55 c->index += 1U; 56 return a; 57 } 58 59 /** 60 * Get the next random unsigned 32-bit number using a MLFG. 61 * 62 * Please also consider av_lfg_get() above, it is faster. 63 */ 64 static inline unsigned int av_mlfg_get(AVLFG *c){ 65 unsigned int a= c->state[(c->index-55) & 63]; 66 unsigned int b= c->state[(c->index-24) & 63]; 67 a = c->state[c->index & 63] = 2*a*b+a+b; 68 c->index += 1U; 69 return a; 70 } 71 72 /** 73 * Get the next two numbers generated by a Box-Muller Gaussian 74 * generator using the random numbers issued by lfg. 75 * 76 * @param lfg pointer to the contex structure 77 * @param out array where the two generated numbers are placed 78 */ 79 void av_bmg_get(AVLFG *lfg, double out[2]); 80 81 #endif /* AVUTIL_LFG_H */