On Mon, Nov 23, 2015 at 01:57:24PM -0500, Ganesh Ajjanagadde wrote: > On Mon, Nov 23, 2015 at 1:02 PM, Michael Niedermayer <michae...@gmx.at> wrote: > > On Mon, Nov 23, 2015 at 12:43:52PM -0500, Ganesh Ajjanagadde wrote: > >> On Sun, Nov 22, 2015 at 3:56 PM, Ganesh Ajjanagadde <gajja...@mit.edu> > >> wrote: > >> > On Sun, Nov 22, 2015 at 3:07 PM, Michael Niedermayer <michae...@gmx.at> > >> > wrote: > >> >> On Sun, Nov 22, 2015 at 12:05:49PM -0500, Ganesh Ajjanagadde wrote: > >> >>> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> > >> >>> --- > >> >>> libavfilter/vsrc_mandelbrot.c | 2 +- > >> >>> 1 file changed, 1 insertion(+), 1 deletion(-) > >> >>> > >> >>> diff --git a/libavfilter/vsrc_mandelbrot.c > >> >>> b/libavfilter/vsrc_mandelbrot.c > >> >>> index 950c5c8..a0c101e 100644 > >> >>> --- a/libavfilter/vsrc_mandelbrot.c > >> >>> +++ b/libavfilter/vsrc_mandelbrot.c > >> >>> @@ -291,7 +291,7 @@ static void draw_mandelbrot(AVFilterContext *ctx, > >> >>> uint32_t *color, int linesize, > >> >>> > >> >>> use_zyklus= (x==0 || s->inner!=BLACK ||color[x-1 + > >> >>> y*linesize] == 0xFF000000); > >> >>> if(use_zyklus) > >> >>> - epsilon= scale*1*sqrt(SQR(x-s->w/2) + > >> >>> SQR(y-s->h/2))/s->w; > >> >>> + epsilon= scale*hypot(x-s->w/2, y-s->h/2)/s->w; > >> >> > >> >> old: > >> >> 704 decicycles in hypo, 1048570 runs, 6 skips > >> >> > >> >> new: > >> >> 1075 decicycles in hypo, 1048566 runs, 10 skips > >> >> > >> >> that is from START/STOP_TIMER over hypot() > >> >> > >> >> the code is speed relevant as its executed per pixel > >> > > >> > Thanks for testing. Looking more closely, I see no reason for > >> > expensive sqrt calls anyway: one can simply square both sides; it > >> > should be cheaper. Will rework, post benchmark if it is indeed faster > >> > and does not suffer from floating point overflow, else will simply > >> > push a trivial removal of the "1". > >> > >> It seems like getting rid of the sqrt altogether has a very slight > >> positive impact (if any at all). I can post the patch, but would like > >> to know what to benchmark. There are numerous choices, e.g > >> draw_mandelbrot as a whole, the outer loop, or the inner loop. > >> I personally think the inner x loop (lines 268-388) is a good place to > >> look at, since the difference is very small anyway, and further > >> localization is impossible. > >
> > please post the patch
>
> bench posted first to see if it is considered interesting enough.
> Bench over whole draw_mandelbrot using START/STOP timer on x86-64,
> Haswell, GNU/Linux, command line:
> ffmpeg -v error -f lavfi -i mandelbrot -f null -
> new (draw_mandelbrot):
[...]
> 20857881401 decicycles in draw_mandelbrot, 1024 runs, 0 skips
>
> old (draw_mandelbrot):
[...]
> 21393227201 decicycles in draw_mandelbrot, 1024 runs, 0 skips
if this is consistent over several tries then its interresting
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
No snowflake in an avalanche ever feels responsible. -- Voltaire
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