ref: ad26dc48a6dc05da02f96e5f1e7b82de58ff5b2c
dir: /sys/src/cmd/map/libmap/cubrt.c/
#include <u.h> #include <libc.h> #include "map.h" double cubrt(double a) { double x,y,x1; if(a==0) return(0.); y = 1; if(a<0) { y = -y; a = -a; } while(a<1) { a *= 8; y /= 2; } while(a>1) { a /= 8; y *= 2; } x = 1; do { x1 = x; x = (2*x1+a/(x1*x1))/3; } while(fabs(x-x1)>10.e-15); return(x*y); }