hilbbits.c

#include <stdio.h>

int main(void) {
	int i, x, y, e, o;
	for (i=0; i < 64; i++){
		//d2xy(8,i,&x,&y);
		e =((i & 0x20) >> 3)
		  |((i & 0x08) >> 2)
		  |((i & 0x02) >> 1);
		o =((i & 0x10) >> 2)
		  |((i & 0x04) >> 1)
		  |(i & 0x01);
		printf("%d%d%d\n",
			((e^o) & 0x04 ? 1 : 0),
  			((e^o) & 0x02 ? 1 : 0),
  			((e^o) & 0x01 ? 1 : 0) );
	}
	
	return 0;
}

//convert (x,y) to d
int xy2d (int n, int x, int y) {
    int rx, ry, s, d=0;
    for (s=n/2; s>0; s/=2) {
        rx = (x & s) > 0;
        ry = (y & s) > 0;
        d += s * s * ((3 * rx) ^ ry);
        rot(s, &x, &y, rx, ry);
    }
    return d;
}
 
//convert d to (x,y)
void d2xy(int n, int d, int *x, int *y) {
    int rx, ry, s, t=d;
    *x = *y = 0;
    for (s=1; s<n; s*=2) {
        rx = 1 & (t/2);
        ry = 1 & (t ^ rx);
        rot(s, x, y, rx, ry);
        *x += s * rx;
        *y += s * ry;
        t /= 4;
    }
}
 
//rotate/flip a quadrant appropriately
void rot(int n, int *x, int *y, int rx, int ry) {
    if (ry == 0) {
        if (rx == 1) {
            *x = n-1 - *x;
            *y = n-1 - *y;
        }
 
        //Swap x and y
        int t  = *x;
        *x = *y;
        *y = t;
    }
}