������ 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.