1 28994509 2004-04-21 devnull #include <u.h>
 2 28994509 2004-04-21 devnull #include <libc.h>
 3 28994509 2004-04-21 devnull #include "map.h"
 4 28994509 2004-04-21 devnull 
 5 28994509 2004-04-21 devnull double
 6 28994509 2004-04-21 devnull cubrt(double a)
 7 28994509 2004-04-21 devnull {
 8 28994509 2004-04-21 devnull 	double x,y,x1;
 9 fa325e9b 2020-01-10 cross 	if(a==0)
10 28994509 2004-04-21 devnull 		return(0.);
11 28994509 2004-04-21 devnull 	y = 1;
12 28994509 2004-04-21 devnull 	if(a<0) {
13 28994509 2004-04-21 devnull 		y = -y;
14 28994509 2004-04-21 devnull 		a = -a;
15 28994509 2004-04-21 devnull 	}
16 28994509 2004-04-21 devnull 	while(a<1) {
17 28994509 2004-04-21 devnull 		a *= 8;
18 28994509 2004-04-21 devnull 		y /= 2;
19 28994509 2004-04-21 devnull 	}
20 28994509 2004-04-21 devnull 	while(a>1) {
21 28994509 2004-04-21 devnull 		a /= 8;
22 28994509 2004-04-21 devnull 		y *= 2;
23 28994509 2004-04-21 devnull 	}
24 28994509 2004-04-21 devnull 	x = 1;
25 28994509 2004-04-21 devnull 	do {
26 28994509 2004-04-21 devnull 		x1 = x;
27 28994509 2004-04-21 devnull 		x = (2*x1+a/(x1*x1))/3;
28 28994509 2004-04-21 devnull 	} while(fabs(x-x1)>10.e-15);
29 28994509 2004-04-21 devnull 	return(x*y);
30 28994509 2004-04-21 devnull }