Fibbonaci Fast dobule Algo

fibonacci_fast_double.js

var yourself = {
    fibonacci: function(n) {
        return this._fib(n)[0]
    },
    _fib : function(n) {
        if (n === 0) {
            return [0, 1]
        } else {
            let half = this._fib(Math.floor(n / 2));
            let a = half[0]
            let b = half[1]
            let c = a * (b * 2 - a)
            let d = a * a + b * b
            if (n % 2 === 0) {
                return [c, d]
            } else {
                return [d, c + d]
            }
        }
    }
};