[Lain]

Recursion, as cool of a concept as it is, is honestly pretty useless for fib unless you're only going after small terms. So yeah, 5-25. Anything more risks a complete stack overflow.

Here's a recursive example of what the call stack will look like:

Code:

call fib(20)
   call fib(19)
       call fib(18)
           call fib(17)
               ...
               return 0, 1
           }
       }
   }
}

Returning whatever value.

Now, iteratively:

Code:

uint_32 a, 0;
uint_32 b, 1;
uint_32 c;
uint_32 fib(int x){
   for(int i = 0; i < x; i++){
       c = a+b
       a = b;
       b = c;
   }
   return c;
}
fib(20)

There are probably errors in this, it's just pseudocode so scoping is probably f*** and I probably don't need to use 32bit integers for small terms.

But the call-stack will look more like:

Code:

call fib(20)
   loop
}

There's more intensive computation in the one function, but there's no need for a massive call-stack, which in turn makes it run quite a bit quicker.
Recursion is a pretty solution, but that's about it.