Register Machine code for Fibonacci Numbers
Here is some code in C, which you can "compile" into your assembly language:

int x = 0, y = 1, z;
while (n--) {
  z = x;
  x = y;
  y += z;
}
return x;


After $n$ iterations of the loop, $x = F_n$ and $y = F_{n+1}$.