Open System Services Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

OSS Library Calls (a - d) acosh(3)
NAME
acosh - Computes the inverse hyperbolic cosine function
LIBRARY
G-series native Guardian processes: $SYSTEM.SYSnn.ZCRESRL
G-series native OSS processes: /G/system/sysnn/zcresrl
H-series and J-series native Guardian processes: $SYSTEM.ZDLLnnn.ZCREDLL
32-bit H-series and J-series OSS processes: /G/system/zdllnnn/zcredll
64-bit H-series and J-series OSS processes: /G/system/zdllnnn/ycredll
SYNOPSIS
#include <math.h>
double acosh(
double x);
PARAMETERS
x Is the value for which the inverse hyperbolic cosine function is to be computed.
DESCRIPTION
The acosh( ) function computes the inverse hyperbolic cosine of x.
The acosh( ) function can be called only by native processes.
NOTES
This function supports both IEEE Std 754-1985 floating-point and Tandem floating-point values.
IEEE values can include NaN and infinity, and the sign of 0.0 (zero) can be either positive or
negative. Refer to the fp_class(3) reference page for a description of IEEE value classes.
Guardian functions are available to convert between floating-point formats. Refer to the Guar-
dian Programmer’s Guide for a discussion of floating-point conversions.
RETURN VALUES
The acosh( ) function returns the inverse hyperbolic cosine of the x parameter.
For IEEE floating-point values, when the value of x is NaN, the acosh( ) function returns NaN.
When the value of x is positive infinity, the acosh( ) function returns positive infinity. When the
value of x is less than 1.0, the acosh( ) function returns NaN and sets errno to [EDOM]. When
the value of x is negative infinity, the acosh( ) function returns NaN and sets errno to [EDOM].
For Tandem floating-point values, when the value of x is less than 1.0, the acosh( ) function
returns -HUGE_VAL and sets errno to [EDOM].
ERRORS
If the following condition occurs, the acosh( ) function sets errno to the corresponding value:
[EDOM] The value of the x parameter is less than 1.0 or, for IEEE floating-point values,
the value of x is negative infinity.
RELATED INFORMATION
Functions: fp_class(3), isnan(3).
STANDARDS CONFORMANCE
The XPG4 Version 2 specification leaves some features to the implementing vendor to define.
The following feature is affected in the HP implementation:
• When used for IEEE floating-point values, this function does not set errno to [EDOM]
when the value of x is NaN.
• When used for Tandem floating-point values, this function does not return the value NaN
when an invalid parameter is passed.
527187-017 Hewlett-Packard Company 1−11