HP-UX Reference (11i v2 04/09) - 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);
Itanium-based System 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 −Pi to Pi, using the signs of both arguments to
determine the quadrant of the return value.
atan2f() is a float version of atan2(); it takes
float arguments and returns a float result.
Itanium-based System 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
atan2w() or atan2q() (on Itanium-based systems), 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.
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 ±Pi 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 ±Pi 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 −Pi/2.
If y is greater than zero and x is zero,
atan2() returns Pi/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 −Pi.
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.
HP-UX 11i Version 2: September 2004 − 1 − Hewlett-Packard Company Section 3−−41