[FFmpeg-user] Problem with signbit()

[Ulf Zibis]

Am 18.07.19 um 09:24 schrieb Moritz Barsnick:
> On Thu, Jul 18, 2019 at 01:41:02 +0200, Ulf Zibis wrote:
>> Given this code snippet:
>>     float a = 0.0F;
>>     float b = -0.0F;
>>     printf("a: %f, signbit(a): %d\n", a, signbit(a));
>>     printf("b: %f, signbit(b): %d\n", b, signbit(b));
>> Result:
>>     a: 0.000000, signbit(a): 0
>>     b: -0.000000, signbit(b): 0
>> I would expect:
>>     a: 0.000000, signbit(a): 0
>>     b: -0.000000, signbit(b): <something not 0>
>> ... according to: http://man7.org/linux/man-pages/man3/signbit.3.html
>>
>> Are there some flags in the your build script which cause this problem?
> Obviously "-fno-signed-zeros".
>
> Committed here with an explanation:
> https://github.com/FFmpeg/FFmpeg/commit/b2eb2ff098b
>
> It doesn't have an effect with all compilers, apparently. Not sure if
> that's important.
Much thanks for the finding, Moritz.

> Are you developing something use the libav* libraries? Or are you
> developing something for inclusion within ffmpeg? At least in the
> former case, I recommend the "libav-user" mailing list.
I'm developing a video filter.

Is it possible to compile and build a filter separate off FFmpeg and
link it with the command line application to use it?

-Ulf