Re: [FFmpeg-devel] [PATCH] avcodec/aacenc_is: replace pow(x, 0.75) by x/sqrtf(sqrtf(x))
On Wed, Jan 13, 2016 at 11:27 PM, Claudio Freire wrote: > On Mon, Jan 11, 2016 at 7:23 PM, Ganesh Ajjanagadde > 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 > > > Pushed. > > 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. Good idea, thanks. ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] avcodec/aacenc_is: replace pow(x, 0.75) by x/sqrtf(sqrtf(x))
On Mon, Jan 11, 2016 at 7:23 PM, Ganesh Ajjanagadde 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 Pushed. 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. ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
[FFmpeg-devel] [PATCH] avcodec/aacenc_is: replace pow(x, 0.75) by x/sqrtf(sqrtf(x))
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 --- libavcodec/aacenc_is.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libavcodec/aacenc_is.c b/libavcodec/aacenc_is.c index 4f7ec19..846b8ec 100644 --- a/libavcodec/aacenc_is.c +++ b/libavcodec/aacenc_is.c @@ -54,7 +54,7 @@ struct AACISError ff_aac_is_encoding_err(AACEncContext *s, ChannelElement *cpe, FFPsyBand *band0 = &s->psy.ch[s->cur_channel+0].psy_bands[(w+w2)*16+g]; FFPsyBand *band1 = &s->psy.ch[s->cur_channel+1].psy_bands[(w+w2)*16+g]; int is_band_type, is_sf_idx = FFMAX(1, sce0->sf_idx[(w+w2)*16+g]-4); -float e01_34 = phase*pow(ener1/ener0, 3.0/4.0); +float e01_34 = phase*(ener1/ener0)/sqrtf(sqrtf(ener1/ener0)); float maxval, dist_spec_err = 0.0f; float minthr = FFMIN(band0->threshold, band1->threshold); for (i = 0; i < sce0->ics.swb_sizes[g]; i++) -- 2.7.0 ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
