[FFmpeg-devel] [PATCH] Box-Muller gaussian generator

[Michael Niedermayer]

On Fri, Dec 11, 2009 at 01:40:08AM +0100, Michael Niedermayer wrote:
> On Sun, Dec 06, 2009 at 11:13:37PM +0100, Stefano Sabatini wrote:
> > On date Sunday 2009-12-06 19:40:20 +0100, Vitor Sessak encoded:
> > > Stefano Sabatini wrote:
> > >> Hi,
> > >>
> > >> I'm going to use this for a noise filter, I believe this could be
> > >> useful in other part of libav* though.
> > >
> > >> +double av_bmg_get(AVBMG *bmg)
> > >> +{
> > >> +    double x1, x2, w, y;
> > >> +    AVLFG *lfg = &bmg->lfg;
> > >> +
> > >> +    do {
> > >> +        x1 = 2.0 * ranf(lfg) - 1.0;
> > >> +        x2 = 2.0 * ranf(lfg) - 1.0;
> > >> +        w = x1*x1 + x2*x2;
> > >> +    } while (w >= 1.0);
> > >> +
> > >> +    w = sqrt((-2.0 * log(w)) / w);
> > >> +    y = x2 * w;
> > >> +
> > >> +    return bmg->mean + y * bmg->std_dev;
> > >> +}
> > >
> > > This generates two numbers to use only one. Isn't it faster to store the  
> > > second number for the next call or have a function to fill a buffer of  
> > > random numbers?
> > 
> > Implemented the first idea.
> 
> void av_bmg_get(AVLFG *lfg, double out[2]);
>     double x1, x2, w;
> 
>     do {
>         x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0;
>         x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0;
>         w = x1*x1 + x2*x2;
>     } while (w >= 1.0);
> 
>     w = sqrt((-2.0 * log(w)) / w);
>     out[0] = x1 * w;
>     out[1] = x2 * w;
> }
> 
> comments welcome, if none ill commit above
> 
> libavutil is supposed to be clean and i wont tolerate it being filled up with

hmm, the word tolerate sounds a little harsh, i guess i could have said this
more diplomatically but the point stands we dont need a new file and whole
struct+API for something that could be a single 8 line function



[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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