The Open Group Base Specifications Issue 7

IEEE Std 1003.1-2008

Copyright © 2001-2008 The IEEE and The Open Group

#### NAME

asinh, asinhf, asinhl - inverse hyperbolic sine functions

#### SYNOPSIS

`#include <math.h>`

double asinh(double *x*`);`

float asinhf(float *x*`);`

long double asinhl(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 POSIX.1-2008 defers to the ISO C
standard.

These functions shall compute the inverse hyperbolic sine 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 sine of their argument.

^{[MX]} If
*x* is NaN, a NaN shall be returned.

If *x* is ±0, or ±Inf, *x* shall be returned.

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

#### ERRORS

These functions may fail if:

- Range Error
^{[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.

*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

*feclearexcept* , *fetestexcept* , *sinh*

XBD *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 *asinh*() function is no longer marked as an extension.

The *asinhf*() and *asinhl*() 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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