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 <gajjanaga...@gmail.com> --- 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