[FFmpeg-devel] [PATCH 11/11] avutil/rational: use frexp rather than ad-hoc log to get floating point exponent

[Ganesh Ajjanagadde]

On Thu, Oct 29, 2015 at 12:20 AM, Ganesh Ajjanagadde
<gajjanagadde at gmail.com> wrote:
> This simplifies and cleans up the code.
> Furthermore, it is much faster due to absence of the slow log computation.
>
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavutil/rational.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/libavutil/rational.c b/libavutil/rational.c
> index 21d2bb7..81a9402 100644
> --- a/libavutil/rational.c
> +++ b/libavutil/rational.c
> @@ -106,14 +106,14 @@ AVRational av_sub_q(AVRational b, AVRational c)
>  AVRational av_d2q(double d, int max)
>  {
>      AVRational a;
> -#define LOG2  0.69314718055994530941723212145817656807550013436025
>      int exponent;
>      int64_t den;
>      if (isnan(d))
>          return (AVRational) { 0,0 };
>      if (fabs(d) > INT_MAX + 3LL)
>          return (AVRational) { d < 0 ? -1 : 1, 0 };
> -    exponent = FFMAX( (int)(log(fabs(d) + 1e-20)/LOG2), 0);
> +    frexp(d, &exponent);
> +    exponent = FFMAX(exponent-1, 0);
>      den = 1LL << (61 - exponent);
>      // (int64_t)rint() and llrint() do not work with gcc on ia64 and sparc64
>      av_reduce(&a.num, &a.den, floor(d * den + 0.5), den, max);
> --
> 2.6.2
>

Just a note, so that this is not buried: wm4's comment (which I still
disagree with) does not apply to this patch.