HP-UX Reference (11i v2 07/12) - 3 Library Functions A-M (vol 6)

a
atan2(3M) atan2(3M)
NAME
atan2( ), atan2f( ), atan2l( ), atan2w( ), atan2q() - arctangent and quadrant functions
SYNOPSIS
#include <math.h>
double atan2(double y, double x);
float atan2f(float y, float x);
HP Integrity Server Only
long double atan2l(long double y, long double x);
extended atan2w(extended y, extended x);
quad atan2q(quad y, quad x);
DESCRIPTION
atan2() returns the arctangent of y/x, in the range −π to π, using the signs of both arguments to deter-
mine the quadrant of the return value.
atan2f() is a float version of atan2(); it takes float arguments and returns a float result.
Integrity Server Only
atan2l() is a long double version of atan2(); it takes long double arguments and returns a
long double result.
atan2w() is an extended version of atan2(); it takes extended arguments and returns an
extended result.
atan2q() is equivalent to atan2l() on HP-UX systems.
USAGE
To use these functions, compile either with the default -Ae option or with the -Aa
and the
-D_HPUX_SOURCE options.
To use (for Integrity servers)
atan2w() or atan2q(), compile also with the -fpwidetypes
option.
To use any of these functions, make sure your program includes
<math.h>, and link in the math library
by specifying -lm on the compiler or linker command line.
For more information, see the HP-UX floating-point guide for HP Integrity servers at the following site:
http://www.hp.com/go/fp
.
PA-RISC Only
Millicode versions of the
atan2() function are available. Millicode versions of math library functions are
usually faster than their counterparts in the standard library. To use these versions, compile your program
with the +Olibcalls or the +Oaggressive optimization option.
For special cases, the millicode versions return the same values as their standard library counterparts (see
the RETURN VALUE section).
RETURN VALUE
If y is ±0 and x is −0 atan2() returns ±π respectively.
If y is ±0 and x is +0 atan2() returns ±0 respectively.
If y is ±0 and x is less than zero, atan2() returns returns ±π respectively.
If y is ±0 and x is greater than zero, atan2() returns returns ±0 respectively.
If y is less than zero and x is zero, atan2() returns −π/2.
If y is greater than zero and x is zero, atan2() returns π/2.
If y is greater than zero and x is −INFINITY, atan2() returns Pi.
If y is less than zero and x is −INFINITY, atan2() returns −π.
If y is greater than zero and x is INFINITY, atan2() returns +0.
If y is less than zero and x is INFINITY, atan2() returns −0.
112 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: December 2007 Update