Duff's Device

It looks like an invalid code, but it is valid! This code portion is known as Duff's device.

    switch (count % 8) {
       case 0:        do {  *to = *from++;
       case 7:              *to = *from++;
       case 6:              *to = *from++;
       case 5:              *to = *from++;
       case 4:              *to = *from++;
       case 3:              *to = *from++;
       case 2:              *to = *from++;
       case 1:              *to = *from++;
                      } while ((count -= 8) > 0);
   }

More http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html