asin, asinf---arc sine

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

asin computes the inverse sine (arc sine) of the argument x. Arguments to asin must be in the range -1 to 1.

asinf is identical to asin, other than taking and returning floats.

You can modify error handling for these routines using matherr.

Returns

If x is not in the range -1 to 1, asin and asinf return NaN (not a number), set the global variable errno to EDOM, and issue a DOMAIN error message.

You can change this error treatment using matherr.