#include <stdlib.h>
#include <stdio.h>
#include <math.h>

double can(double x) { /* Returns Cantor function y=f(x)  */
  int t;               /* ternery (base 3) expansion of x */
  double z, y;

  for(t= 0, y= 0.0, z= 0.5; t!= 1 && x> 0 ; z/= 2) {
    x*= 3;
    x-= ( t= (int) floor(x) );
    if(t> 0) y+= z;
  }
  return y;
}

double ican(double y) { /* Returns inverse Cantor function x=f^-1(y) */
  int b;                /* binary (base 2) expansion of y            */
  double z, x;

  for(b= 0, x= 0.0, z= 2.0/3.0; y> 0 ; z/= 3) {
    y*= 2;
    y-= ( b= (int) floor(y) );
    if(b> 0) x+= z;
  }
  return x;
}

int main(int ac, char **av) {     /* Usage: cantor <n>         */
  double x, y, dx;
  int n, i, inv;
  n = (ac> 1) ? strtol(av[1],0,NULL) : 10;
  inv = (ac> 2) && (*av[2]=='i'); /* Inverse: cantor <n> i     */
  dx = 1.0/n - 1e-9;              /* Avoid dyadics & ternaries */
  for(i=0; i<= n; ++i) {
    x = i*dx;
    y = (inv) ? ican(x) : can(x);
    printf("%7.5f  %7.5f\n", x, y);
  }
}