[FFmpeg-devel] [PATCH] avfilter/avf_showfreqs: avoid wasteful pow

[Paul B Mahol]

On 12/9/15, Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
> pow is a ridiculous function for computing a simple Gaussian.
>
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavfilter/avf_showfreqs.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/libavfilter/avf_showfreqs.c b/libavfilter/avf_showfreqs.c
> index a3665ef..3ed0155 100644
> --- a/libavfilter/avf_showfreqs.c
> +++ b/libavfilter/avf_showfreqs.c
> @@ -227,8 +227,9 @@ static void generate_window_func(float *lut, int N, int
> win_func, float *overlap
>          *overlap = 0.75;
>          break;
>      case WFUNC_GAUSS:
> +#define SQR(x) ((x)*(x))
>          for (n = 0; n < N; n++)
> -            lut[n] = pow(M_E,-0.5*pow((n-(N-1)/2)/(0.4*(N-1)/2.f),2));
> +            lut[n] = exp(-0.5 * SQR((n-(N-1)/2)/(0.4*(N-1)/2.f)));
>          *overlap = 0.75;
>          break;
>      default:
> --
> 2.6.3

OK