Binet's Fibonacci

binet-fibonacci.js

/*
 * fibbonacci.js
 * Copyright (C) 2013 dhilipsiva <[email protected]>
 *
 * Distributed under terms of the MIT license.
 */

function isDigit(val) {
    /*
     * Find if given value is a digit or not.
     * If the ceil (or floor) of a given value is
     * equal to itself, then it is digit, obviously.
     */
    return val == Math.ceil(val);
}

function isPerfectSquare(num) {
    // Test if a number is perfect square or not.
    var numSqrt = Math.sqrt(num);

    // If numSqrt is a digit, then num is a perfect square.
    return isDigit(numSqrt)
}

function calcBinetNumber(num) {
    //Calcualte the binet number.
    return 5 * Math.pow(num, 2);
}

function calcInverseBinetNumber(num){
    return Math.sqrt(num / 5);
}

function isFibbonacciNumber(num) {
    // Function to find if a number is a fibbonacci number.

    var binetNumber = calcBinetNumber(num);

    if (isPerfectSquare(binetNumber + 4))
        return true;
    if (isPerfectSquare(binetNumber - 4))
        return true;

    /*
     * If none of the above calculations returned true,
     * then it is obviously not a fibbonacci number.
     */
    return false;
}

// Sorry, I couldnt get nextSmallestFibonacciNumber to working.

function nextSmallestFibonacciNumber(num) {
    // Function to calcualte the next smallest fibonacci number in the series.
    var binetFactor = Math.sqrt(calcBinetNumber(num));
    var binetNumber = Math.pow(Math.ceil(binetFactor), 2);
    var inverseBinetNumber;
    inverseBinetNumber = calcInverseBinetNumber(binetNumber + 4);
    if (isDigit(inverseBinetNumber))
       return inverseBinetNumber;
    inverseBinetNumber = calcInverseBinetNumber(binetNumber - 4);
    if (isDigit(inverseBinetNumber))
       return inverseBinetNumber;
}