[FFmpeg-devel] [PATCH] avfilter/window_func: use a constant instead of acosh()

[James Almer]

On 8/20/2016 2:46 AM, Paul B Mahol wrote:
> On Saturday, August 20, 2016, James Almer <jamrial at gmail.com> wrote:
> 
>> Should fix compilation with non C99 compilers like msvc 2012, where
>> acosh() is not available.
>>
>> Signed-off-by: James Almer <jamrial at gmail.com <javascript:;>>
>> ---
>> A fallback function like
>>
>> static av_always_inline double acosh(double x)
>> {
>>     return log(x + sqrt((x * x) - 1.0));
>> }
>>
>> could be added to libm.h if acosh() is needed sometime in the
>> future for values that can't be computed at compile time.
>> The above example doesn't take into account things like x == NaN
>> and x < 1.0, though.
>>
>>  libavfilter/window_func.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/libavfilter/window_func.c b/libavfilter/window_func.c
>> index fcdf6ea..acf1b20 100644
>> --- a/libavfilter/window_func.c
>> +++ b/libavfilter/window_func.c
>> @@ -117,7 +117,7 @@ void ff_generate_window_func(float *lut, int N, int
>> win_func, float *overlap)
>>          *overlap = 0.33;
>>          break;
>>      case WFUNC_DOLPH: {
>> -        double b = cosh(acosh(pow(10., 3)) / (N-1)), sum, t, c, norm = 0;
>> +        double b = cosh(7.6009022095419887 / (N-1)), sum, t, c, norm = 0;
>>          int j;
>>          for (c = 1 - 1 / (b*b), n = (N-1) / 2; n >= 0; --n) {
>>              for (sum = !n, b = t = j = 1; j <= n && sum != t; b *= (n-j)
>> * (1./j), ++j)
> 
> 
>>
> 
> 
> 
>  LGTM

Pushed, thanks.