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

acos(3) OSS Library Calls Reference Manual
NAME
acos - Computes the inverse trigonometric 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 acos(
double x);
PARAMETERS
x Is the value for which the inverse trigonometric cosine function is to be com-
puted.
DESCRIPTION
The acos( ) function computes the principal value of the arc cosine of x, in the range [0, π] radi-
ans. The value of x must be in the domain [-1,+1].
NOTES
This function supports both IEEE Std 754-1985 floating-point and Tandem floating-point values
in the native environment. 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 acos( ) function returns the principal value of the arc cosine of x.
For IEEE floating-point values, if the value of x is NaN, the acos( ) function returns NaN. If the
value of x is positive or negative infinity, the acos( ) function returns NaN and sets errno to
[EDOM]. If the value of x is not in the domain [-1, +1], the acos( ) function returns NaN and sets
errno to [EDOM].
For Tandem floating-point values, if the value of x is not in the domain [-1, +1], the acos( ) func-
tion returns 0.0 (zero) and sets errno to [EDOM].
ERRORS
If the following condition occurs, the acos( ) function sets errno to the corresponding value:
[EDOM] The value of the x parameter is infinite or not in the domain [-1,+1].
RELATED INFORMATION
Functions: acosh(3), asin(3), asinh(3), atan(3), atan2(3), atanh(3), cos(3), cosh(3), fp_class(3),
isnan(3), sin(3), sinh(3), tan(3), tanh(3).
Files: float(4), math(4).
STANDARDS CONFORMANCE
This function conforms to the XPG4 Version 2 specification with extensions when used for IEEE
floating-point format data. This function conforms to the XPG4 Version 2 specification without
extensions when used for Tandem floating-point data.
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