xref: /plan9/sys/src/libc/port/atan2.c (revision 3e12c5d1bb89fc02707907988834ef147769ddaf) 
1 #include <u.h>
2 #include <libc.h>
3 /*
4 	atan2 discovers what quadrant the angle
5 	is in and calls atan.
6 */
7 
8 double
atan2(double arg1,double arg2)9 atan2(double arg1, double arg2)
10 {
11 
12 	if(arg1+arg2 == arg1) {
13 		if(arg1 >= 0)
14 			return PIO2;
15 		return -PIO2;
16 	}
17 	arg1 = atan(arg1/arg2);
18 	if(arg2 < 0) {
19 		if(arg1 <= 0)
20 			return arg1 + PI;
21 		return arg1 - PI;
22 	}
23 	return arg1;
24 }
25