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

atan(3) OSS Library Calls Reference Manual
NAME
atan - Computes the inverse trigonometric tangent 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 atan(
double x);
PARAMETERS
x Is the value for which the inverse trigonometric tangent function is to be com-
puted.
DESCRIPTION
The atan( ) function computes the principal value of the arc tangent of x, in the domain
[-π/2, π/2] radians.
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 atan( ) function returns the principal value of the arc tangent of x.
For IEEE floating-point values, if the value of x is NaN, the atan( ) function returns NaN.
If the result would underflow, the atan( ) function returns 0.0 (zero).
ERRORS
The atan( ) function does not set errno.
RELATED INFORMATION
Functions: acos(3), acosh(3), asin(3), asinh(3), atanh(3), atan2(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.
The XPG4 Version 2 specification leaves some features to the implementing vendor to define.
The following features are affected in the HP implementation:
• When used for IEEE floating-point data, this function does not set errno to [EDOM]
when the value of x is NaN.
• This function does not set errno to [ERANGE] when the result would underflow.
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