float __far powf(float x, float y);
If x < 0 and y is a non-integer or if x = 0 and y <= 0, powf returns a Not-a-Number (NaN) and sets the macro EDOM for the global variable errno.
If an overflow occurs, powf returns ±∞ and sets the macro ERANGE for errno.
If an underflow occurs, powf returns a denormal number and sets the macro ERANGE for errno.