# 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 of x.

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

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

## Returns:

The inverse hyperbolic tangent of x.

If x is: These functions return: Errors:
±0.0 x
±1.0 Inf, with the same sign as x FE_DIVBYZERO
Finite and |x| > 1 NaN FE_INVALID
±Inf NaN FE_INVALID
NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

## 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_ALL_EXCEPT);
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