[FFmpeg-devel] [PATCH 03/15] lavfi/f_ebur128: replace pow(10, x) by exp10(x)

[Ronald S. Bultje]

Hi,

On Wed, Dec 23, 2015 at 2:00 PM, Ganesh Ajjanagadde <gajjanag at mit.edu>
wrote:

> On Wed, Dec 23, 2015 at 10:54 AM, Clément Bœsch <u at pkh.me> wrote:
> > On Wed, Dec 23, 2015 at 10:47:23AM -0800, Ganesh Ajjanagadde wrote:
> >> exp10, recently introduced, is superior for the purpose.
> >>
> >> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> >> ---
> >>  libavfilter/f_ebur128.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/libavfilter/f_ebur128.c b/libavfilter/f_ebur128.c
> >> index b9577c5..6749bcd 100644
> >> --- a/libavfilter/f_ebur128.c
> >> +++ b/libavfilter/f_ebur128.c
> >> @@ -435,7 +435,7 @@ static int config_audio_output(AVFilterLink
> *outlink)
> >>      return 0;
> >>  }
> >>
> >> -#define ENERGY(loudness) (pow(10, ((loudness) + 0.691) / 10.))
> >> +#define ENERGY(loudness) (exp10(((loudness) + 0.691) / 10.))
> >>  #define LOUDNESS(energy) (-0.691 + 10 * log10(energy))
> >>  #define DBFS(energy) (20 * log10(energy))
> >
> > OK if FATE is happy
>
> FATE is happy on GNU/Linux, where exp10 is correctly rounded. Can't
> speak for the fallback; it was a risk that I explained in detail. Now
> that I see its use, I am myself leaning towards a pow(10,x) fallback
> instead of the exp2 based one.


That's because your refactoring origin is biased. If you had started from
libavcodec/acelp_pitch_delay.c:135 (the only place I could find where we
use exp2 but where we should use exp10), you'd say the opposite.

(I think the current fallback is fine.)

Ronald