[FFmpeg-devel] [PATCH 09/10] avfilter/vsrc_mandelbrot: use hypot()

[Ganesh Ajjanagadde]

On Sun, Nov 22, 2015 at 3:07 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Sun, Nov 22, 2015 at 12:05:49PM -0500, Ganesh Ajjanagadde wrote:
>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at 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".

>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> No great genius has ever existed without some touch of madness. -- Aristotle
>
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