long double __far asinl(long double x); (C99)
Returns the arc sine (arcsine) of x. The returned value is in radian and in a range of [-π / 2, π / 2].
If x is not between [-1, 1], asinl returns a Not-a-Number (NaN) and sets macro EDOM to global variable errno.
This function calculates the arc sine (arcsine) of x. Specify x as, -1 <= x <= 1.