�� double CDECL MSVCRT_atan( double x )
�� {
-�� if (!isfinite(x)) *MSVCRT__errno() = MSVCRT_EDOM;
�� �� return atan(x);
�� }

I've done a little more testing. The function is not setting errno in INF and -INF case. It does set errno�� to EDOM when argument is NAN.