An iterative algorithm for Fibonacci numbers

Question

I am interested in an iterative algorithm for Fibonacci numbers, so I found the formula on wiki...it looks straight forward so I tried it in Python...it doesn\'t have a prob

Answer 1

I came across this on another thread and it is significantly faster than anything else I have tried and wont time out on large numbers. Here is a link to the math.

def fib(n):
    v1, v2, v3 = 1, 1, 0  
    for rec in bin(n)[3:]: 
        calc = v2*v2
        v1, v2, v3 = v1*v1+calc, (v1+v3)*v2, calc+v3*v3
        if rec=='1':    v1, v2, v3 = v1+v2, v1, v2
    return v2