atanh, atanhf---inverse hyperbolic tangent

#include <math.h>
double atanh(double x);
float atanhf(float x);

atanhf is identical, other than taking and returning float values.

Returns
atanh and atanhf return the calculated value.

If is greater than 1, the global errno is set to EDOM and the result is a NaN. A DOMAIN error is reported.

If is 1, the global errno is set to EDOM; and the result is infinity with the same sign as x. A SING error is reported.

You can modify the error handling for these routines using matherr.

Portability
Neither atanh nor atanhf are ANSI C.