IEEE Std 1003.1-2008

Copyright © 2001-2008 The IEEE and The Open Group

atanh, atanhf, atanhl - inverse hyperbolic tangent functions

#include <math.h>

double atanh(doublex);

float atanhf(floatx);

long double atanhl(long doublex);

^{[CX]}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 POSIX.1-2008 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

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(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

xis ±1, a pole error shall occur, andatanh(),atanhf(), andatanhl() 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]}Ifxis NaN, a NaN shall be returned.If

xis ±0,xshall be returned.If

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

xis subnormal, a range error may occur andxshould be returned.

These functions shall fail if:

- Domain Error
- The
xargument is finite and not in the range [-1,1],^{[MX]}or is ±Inf.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall be set to [EDOM]. If the integer expression (math_errhandling& MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.- Pole Error
- The
xargument is ±1.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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:

- Range Error
^{[MX]}The value ofxis subnormal.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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,fetestexcept,tanhXBD

Treatment of Error Conditions for Mathematical Functions,<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() andatanhl() functions are added for alignment with the ISO/IEC 9899:1999 standard.The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

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