[FFmpeg-devel] [PATCHv2] avfilter/vsrc_mandelbrot: avoid sqrt for epsilon calculation

[Michael Niedermayer]

On Tue, Nov 24, 2015 at 12:02:24PM -0500, Ganesh Ajjanagadde wrote:
> This rewrites into a similar expression avoiding sqrt. Similarity is
> assured since sqrt(x^2 + y^2)/(x+y) lies in [1/sqrt(2), 1] for x, y > 0.
> 
> Tested on x86-64, Haswell, GNU/Linux.
> Command:
> ffmpeg -f lavfi -i mandelbrot -f null -
> 
> old (draw_mandelbrot):
> 277625266 decicycles in draw_mandelbrot,     256 runs,      0 skips
> 304527322 decicycles in draw_mandelbrot,     512 runs,      0 skips
> 377593582 decicycles in draw_mandelbrot,    1024 runs,      0 skips
> 338539499 decicycles in draw_mandelbrot,    2048 runs,      0 skips
> 583630357 decicycles in draw_mandelbrot,    4096 runs,      0 skips
> 
> new (draw_mandelbrot):
> 274635709 decicycles in draw_mandelbrot,     256 runs,      0 skips
> 300287046 decicycles in draw_mandelbrot,     512 runs,      0 skips
> 371819935 decicycles in draw_mandelbrot,    1024 runs,      0 skips
> 336663765 decicycles in draw_mandelbrot,    2048 runs,      0 skips
> 581851016 decicycles in draw_mandelbrot,    4096 runs,      0 skips
> 
> Reviewed-by: Michael Niedermayer <michael at niedermayer.cc>
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavfilter/vsrc_mandelbrot.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

LGTM

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Rewriting code that is poorly written but fully understood is good.
Rewriting code that one doesnt understand is a sign that one is less smart
then the original author, trying to rewrite it will not make it better.
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