msvcrt: Fix bugs in math.c

[Piotr Caban]

Hi,

On 03/22/15 12:28, 陈正 wrote:
> - Fixed the problem of atan(INF)/tanh(INF)/exp(INF) causing errno EDOM
> - Fixed the error of _copysign(1., -0.) returning 1
Please don't send unrelated changes in one patch, please split it into 2 
patches.

The changes that remove errno setting from atan, tanh and exp looks good 
for me.

>   float CDECL MSVCRT__copysignf( float num, float sign )
>   {
> -    /* FIXME: Behaviour for Nan/Inf? */
> -    if (sign < 0.0)
> -        return num < 0.0 ? num : -num;
> -    return num < 0.0 ? -num : num;
> +    /* FIXME: Behaviour for signbit(NAN) is different in Linux and
> +     *        Windows, where Windows gives a zero for -NAN
> +     */
> +    if (signbit(sign))
> +        return signbit(num) ? num : -num;
> +    return signbit(num) ? -num : num;
>   }
Why don't you add an isnan() check? Is there any reason for returning 
"signbit(num) ? -num : num" instead of returning num?

It would be nice to also change signbit definition on systems that 
doesn't support it, so it at least works for normal numbers.

Thanks,
Piotr