##### Synopsis

    #include <math.h>
    double asin(double x);

##### Description

asin returns the principal value, in radians, of the inverse circular sine of x. The principal value lies in the interval [-PI/2, +PI/2] radians.

##### Fast math library behavior

If |x| > 1, errno is set to EDOM and asin returns HUGE_VAL.

##### IEC 60559 math library behavior

If x is NaN, asin returns x.
If |x| > 1, asin returns NaN with invalid signal.

##### Portability

asin conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).