On date Tuesday 2024-01-02 03:28:45 +0100, Michael Niedermayer wrote: > rounding the 64bit integer state to double between each iteration > causes a reduction in quality of the random number generator. > For example its period drops from 2^64 to around 200 million > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > --- > libavutil/eval.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/libavutil/eval.c b/libavutil/eval.c > index bad9e4ecb8d..89c61ba4bf5 100644 > --- a/libavutil/eval.c > +++ b/libavutil/eval.c > @@ -55,6 +55,7 @@ typedef struct Parser { > void *log_ctx; > #define VARS 10 > double *var; > + uint64_t *var_uint64; > } Parser; > > static const AVClass eval_class = { > @@ -173,6 +174,7 @@ struct AVExpr { > } a; > struct AVExpr *param[3]; > double *var; > + uint64_t *var_uint64; > }; > > static double etime(double v) > @@ -230,9 +232,10 @@ static double eval_expr(Parser *p, AVExpr *e) > } > case e_random:{ > int idx= av_clip(eval_expr(p, e->param[0]), 0, VARS-1); > - uint64_t r= isnan(p->var[idx]) ? 0 : p->var[idx]; > + uint64_t r= p->var_uint64[idx] ? p->var_uint64[idx] : > (isnan(p->var[idx]) ? 0 : p->var[idx]); > r= r*1664525+1013904223; > p->var[idx]= r; > + p->var_uint64[idx]= r; > return e->value * (r * (1.0/UINT64_MAX)); > } > case e_while: { > @@ -319,7 +322,11 @@ static double eval_expr(Parser *p, AVExpr *e) > case e_div: return e->value * (d2 ? (d / d2) : d * INFINITY); > case e_add: return e->value * (d + d2); > case e_last:return e->value * d2; > - case e_st : return e->value * (p->var[av_clip(d, 0, > VARS-1)]= d2); > + case e_st : { > + int index = av_clip(d, 0, VARS-1);
> + p->var_uint64[index] = 0; can't you set this to d2 and then in case e_random: uint64_t r = isnan(p->var[idx]) ? 0 : p->var_uint64[idx]; ? _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".