A simple implementation of Duff's device

duff.c

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


int main(int argc, char* argv[])
{
  int n, i;

  if (argc != 2)
    return 1;
  n = atoi(argv[1]);

  i = (n - 1) / 8 + 1;
  off = n % 8;

  if (n)
    switch (off) {
    case 0:  do {
      printf("%d\n", n--);
    case 7:
      printf("%d\n", n--);
    case 6:
      printf("%d\n", n--);
    case 5:
      printf("%d\n", n--);
    case 4:
      printf("%d\n", n--);
    case 3:
      printf("%d\n", n--);
    case 2:
      printf("%d\n", n--);
    case 1:
      printf("%d\n", n--);
      } while (--i);
    }

  printf("final value: %d\n", n);
  
  return 0;
}