ATANH(3) Library Functions Manual ATANH(3)

atanh atanhf atanhl — inverse hyperbolic tangent functions

#include <math.h>

double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 (“POSIX.1”) defers to the ISO C standard.

These functions shall compute the inverse hyperbolic tangent of their argument x.

An application wishing to check for error situations should set errno to zero and call (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the inverse hyperbolic tangent of their argument.

If x is ±1, a pole error shall occur, and atanh (), atanhf (), and atanhl () shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively, with the same sign as the correct value of the function.

For finite | x |>1, a domain error shall occur, and [MX] either a NaN (if supported), or an implementation-defined value shall be returned.

[MX] If x is NaN, a NaN shall be returned.

If x is ±0, x shall be returned.

If x is ±Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.

If x is subnormal, a range error may occur and x should be returned.

These functions shall fail if:

The x argument is finite and not in the range [-1,1], [MX] or is ±Inf.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

The x argument is ±1.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.

These functions may fail if:

[MX] The value of x is subnormal.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

None.

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

None.

None.

feclearexcept(3) , fetestexcept(3) , tanh(3) , the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), xbd_chap04(7), <math.h>

First released in Issue 4, Version 2.

Moved from X/OPEN UNIX extension to BASE.

The atanh () function is no longer marked as an extension.

The atanhf () and atanhl () functions are added for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 (“ISO C99”) standard are marked.

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December 6, 2001 posix.fail