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