The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> acosh, acoshf, acoshl - inverse hyperbolic cosine functions

#### SYNOPSIS

> ``#include <math.h>
> double acosh(double` x`);
> float acoshf(float` x`);
> long double acoshl(long double` x`);
> ``

#### DESCRIPTION

> [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 IEEE Std 1003.1-2001 defers to the ISO C standard.

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

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

#### RETURN VALUE

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

> For finite values of 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 +1, +0 shall be returned.

> If x is +Inf, +Inf 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.

#### ERRORS

> These functions shall fail if:

> Domain Error
>   The x argument is finite and less than +1.0, [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 following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> 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.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> cosh(), feclearexcept(), fetestexcept(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>

#### CHANGE HISTORY

> First released in Issue 4, Version 2.

#### Issue 5

> Moved from X/OPEN UNIX extension to BASE.

#### Issue 6

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

> The acoshf() and acoshl() 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.

End of informative text.

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