minix/lib/libc/math/atan2.c

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2005-04-21 16:53:53 +02:00
/*
* (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
*/
/* $Header$ */
#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;
}