double __far atan2(double y, double x);
Returns the arc tangent (arctangent) of y / x. The returned value is in radian and in a range of [-, ].
When either x or y is Not-a-Number, x and y are both 0, or x and y are both , this function returns Not-a-Number and sets macro EDOM to global variable errno.
If the solution is a denormal number or has disappeared and became 0, atan2 sets macro ERANGE to global variable errno.
This function calculates the arc tangent of y / x. At this time, the quadrant of the return value is determined based on the sign of both arguments.