atanh(), atanhf(), atanhl()

Compute an inverse hyperbolic tangent

Synopsis:

```#include <math.h>

double atanh( double x );

float atanhf( float x );

long double atanhl( long double x );
```

Arguments:

x
The value for which you want to compute the inverse hyperbolic tangent.

Library:

libm

Use the -l m option to qcc to link against this library.

Description:

These functions compute the inverse hyperbolic tangent (in radians) of x.

To check for error situations, use feclearexcept() and fetestexcept():

• Call feclearexcept(FE_ALL_EXCEPT) before calling atanh(), atanhf(), or atanhl().
• On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is nonzero, then an error has occurred.

Returns:

The inverse hyperbolic tangent of x.

If x is: These functions return:
±1 HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively, with the same sign as the correct value of the function, and a pole error occurs
finite and |x| > 1 NaN, and a domain error occurs
NaN NaN
±0 x
±Inf NaN, and a domain error occurs
Subnormal x, and a range error occurs

Errors:

FE_DIVBYZERO
The x argument is ±1.
FE_INVALID
The absolute value of x argument is greater than 1.
FE_UNDERFLOW
The value of x is subnormal.

Examples:

```#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
int except_flags;

feclearexcept(FE_ALL_EXCEPT);

printf( "%f\n", atanh( 0.5 ) );

except_flags = fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

return EXIT_SUCCESS;
}
```

produces the output:

```0.549306
```

Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No