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Add a multiplicative LFG for those thinking the additive is not good

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enough, just 4 lines of code.

Originally committed as revision 14478 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2008-07-30 23:08:07 +00:00
parent 62f2523062
commit 310d442456
1 changed files with 12 additions and 1 deletions
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13
libavutil/lfg.h
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@ -30,7 +30,7 @@ typedef struct {
void av_lfg_init(AVLFG *c, unsigned int seed); void av_lfg_init(AVLFG *c, unsigned int seed);
/** /**
* Gets the next random unsigned 32bit number. * Gets the next random unsigned 32bit number using a ALFG.
* *
* Please also consider a simple LCG like state= state*1664525+1013904223, * Please also consider a simple LCG like state= state*1664525+1013904223,
* it may be good enough and faster for your specific use case. * it may be good enough and faster for your specific use case.
@ -40,4 +40,15 @@ static inline unsigned int av_lfg_get(AVLFG *c){
return c->state[c->index++ & 63]; return c->state[c->index++ & 63];
} }
/**
* Gets the next random unsigned 32bit number using a MLFG.
*
* Please also consider the av_lfg_get() above, it is faster.
*/
static inline unsigned int av_mlfg_get(AVLFG *c){
unsigned int a= c->state[(c->index-55) & 63];
unsigned int b= c->state[(c->index-24) & 63];
return c->state[c->index++ & 63] = a*b+a+b;
}
#endif //FFMPEG_LFG_H #endif //FFMPEG_LFG_H