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. Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
