On Thu, Oct 29, 2015 at 9:35 AM, Ganesh Ajjanagadde <gajjanaga...@gmail.com> wrote: > > On Oct 29, 2015 9:26 AM, "Ronald S. Bultje" <rsbul...@gmail.com> wrote: >> >> Hi, >> >> On Thu, Oct 29, 2015 at 8:47 AM, Ganesh Ajjanagadde <gajja...@mit.edu> >> wrote: >> >> > On Thu, Oct 29, 2015 at 8:22 AM, Paul B Mahol <one...@gmail.com> wrote: >> > > On 10/29/15, Ganesh Ajjanagadde <gajjanaga...@gmail.com> wrote: >> > >> This is likely more precise and conveys the intent better. >> > >> >> > >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> >> > >> --- >> > >> libavfilter/avf_showvolume.c | 2 +- >> > >> 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> >> > >> diff --git a/libavfilter/avf_showvolume.c >> > >> b/libavfilter/avf_showvolume.c >> > >> index 95b5388..395375a 100644 >> > >> --- a/libavfilter/avf_showvolume.c >> > >> +++ b/libavfilter/avf_showvolume.c >> > >> @@ -197,7 +197,7 @@ static int filter_frame(AVFilterLink *inlink, >> > AVFrame >> > >> *insamples) >> > >> max = FFMAX(max, src[i]); >> > >> >> > >> max = av_clipf(max, 0, 1); >> > >> - values[VAR_VOLUME] = 20.0 * log(max) / M_LN10; >> > >> + values[VAR_VOLUME] = 20.0 * log10(max); >> > >> values[VAR_CHANNEL] = c; >> > >> color = av_expr_eval(s->c_expr, values, NULL); >> > >> >> > >> -- >> > >> 2.6.2 >> > > >> > > Have you checked which one is faster? >> > > I really have no opinion on this but gain is neglible. >> > >> > No, I have not. I suspect, but have not confirmed that log10 is >> > slightly slower: >> > >> > >> > https://stackoverflow.com/questions/10810105/explanation-wanted-log10-faster-than-log-and-log2-but-only-with-o2-and-greater >> > (janneb's comment). Keep in mind their benchmark did not include the >> > cost of a division. >> >> >> A good compiler (including yours) will merge the division into the >> multiply: >> a * func(x) / c >> is the same as: >> (a / c) * func(x) >> >> and the compiler can pre-calculate the output of a/c into a single >> constant. > > Not necessarily, floating point is not associative.
pushed, thanks. > >> >> Ronald >> _______________________________________________ >> ffmpeg-devel mailing list >> ffmpeg-devel@ffmpeg.org >> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
