#include <stdio.h>

int main() {
    printf("Enter 0 to print hello and 1 to print goodbye: ");
    unsigned long mask = 0;
    scanf("%ld", &mask);

    // ensure mask is 0 or 1
    mask = !(!(mask));

    // extend first bit to all bits
    int i = 0;
    mask = mask|(mask << i++);
    mask = mask|(mask << i);
    i *= 2;
    mask = mask|(mask << i);
    i *= 2;
    mask = mask|(mask << i);
    i *= 2;
    mask = mask|(mask << i);
    i *= 2;
    mask = mask|(mask << i);
    i *= 2;
    mask = mask|(mask << i);

    // Load the addresses of the labels. Only works in gcc.
    unsigned long h = (unsigned long) &&hello;
    unsigned long g = (unsigned long) &&goodbye;

    // The mask is either all zeros or all ones, so this will evaulate to one of the addresses,
    // which is then passed to a parametric goto
    goto *(void *)((h&(~mask)) | (g&mask));

  hello:
    printf("Hello!\n");
    goto end;

  goodbye:
    printf("Goodbye!\n");
    goto end;

  end:
    return 0;
}