[FFmpeg-devel] [PATCH] avcodec/aacenc_is: replace pow(x, 0.75) by x/sqrtf(sqrtf(x))

Claudio Freire klaussfreire at gmail.com
Thu Jan 14 05:27:26 CET 2016

On Mon, Jan 11, 2016 at 7:23 PM, Ganesh Ajjanagadde
<gajjanagadde at gmail.com> wrote:
> This is quite an accurate approximation; testing shows ~ 2ulp error in
> the floating point result. Tested with FATE.
> Alternatively, if one wants "full accuracy", one can use powf, or sqrt
> instead of sqrtf. With powf, one gets 1 ulp error (theoretically should be 0, as
> 0.75 is exactly representable) on GNU libm, with sqrt, 0 ulp error.
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>


Took the liberty of abstracting out the pow implementation we
discussed on IRC into a utility function and push that. It's more
readable, and next time we'll know clearly that's the way to go.

More information about the ffmpeg-devel mailing list