Guardian Native C Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

Guardian Native C Library Calls (a - e) 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.
527192-018 Hewlett-Packard Company 1−11