libavutil/lfg.h

   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 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  * Gets 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  * Gets 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 #endif /* AVUTIL_LFG_H */