Recursion without recursion... or is it?

This works on 32-bit x86 Linux with gcc as long as you don't enable optimization.


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

static void factorial(int in, int *out) {
        *(&in-1)-=5-5*(1/in);
        *out*=in--;
}

int main(int argc, char **argv) {
        int result=1;
        int number=0;

        if(argc!=2) {
                exit(1);
        }

        number=atoi(argv[1]);

        if(number<1) {
                exit(2);
        }

        factorial(number, &result);

        printf("%d! = %d\n", number, result);

        return 0;
}

$ ./factorial 3
3! = 6
$ ./factorial 5
5! = 120

care to explain this black magic, OP?