/* On my old laptop without fastcall: $ time ./fib 40
   165580141
   real	0m0.913s
   That’s 181 million leaf calls per second.

   More recent GCC sometimes does extensive enough optimization to
   make this pointless, converting recursion to iteration and inlining
   leaf calls.

   See dumbfib.S for an overview.
 */
__attribute__((fastcall)) int fib(int n)
{
    return n < 2 ? 1 : fib(n-1) + fib(n-2);
}
main(int c, char **v) { printf("%d\n", fib(atoi(v[1]))); }