source: trunk/minix/lib/math/atan2.c@ 9

/*
 * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
 * See the copyright notice in the ACK home directory, in the file "Copyright".
 *
 * Author: Ceriel J.H. Jacobs
 */
/* $Header: /cvsup/minix/src/lib/math/atan2.c,v 1.1.1.1 2005/04/21 14:56:24 beng Exp $ */

#include        <math.h>
#include        <errno.h>
#include        "localmath.h"

double
atan2(double y, double x)
{
        double absx, absy, val;

        if (x == 0 && y == 0) {
                errno = EDOM;
                return 0;
        }
        absy = y < 0 ? -y : y;
        absx = x < 0 ? -x : x;
        if (absy - absx == absy) {
                /* x negligible compared to y */
                return y < 0 ? -M_PI_2 : M_PI_2;
        }
        if (absx - absy == absx) {
                /* y negligible compared to x */
                val = 0.0;
        }
        else    val = atan(y/x);
        if (x > 0) {
                /* first or fourth quadrant; already correct */
                return val;
        }
        if (y < 0) {
                /* third quadrant */
                return val - M_PI;
        }
        return val + M_PI;
}