#include <math.h>
float asinf(float val);
asinf returns the principal value, in radians, of the inverse circular sine of val. The principal value lies in the interval [-PI/2, +PI/2] radians.
If |x| > 1, errno is set to EDOM and asinf returns HUGE_VALF.
If x is NaN, asinf returns x.
If |x| > 1, asinf returns NaN with invalid signal.
asinf conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).