The closed form will become inaccurate at some point. However, there is a way to calculate Fibonacci accurately with O(log(n)) time (ignoring the time to multip

The closed form will become inaccurate at some point. However, there is a way to calculate Fibonacci accurately with O(log(n)) time (ignoring the time to multiply - otherwise O(M(n) log(n)) where M(n) is the time to multiply two numbers of n digits).