Math.ease

(function(math) {
	"use strict";

	function ease(value, start, end, pow) {
		/// <summary>
		///     Returns eased value for the input in the [start..end] range.
		/// </summary>
		/// <param name="value">Input value in the [start..end] range to ease.</param>
		/// <param name="start">Value range start, default 0.</param>
		/// <param name="end">Value range end, default 1.</param>
		/// <param name="pow">Easing power factor, default 2.</param>
		
		return get(start, end, pow)(value);
	}

	function get(start, end, pow) {
		/// <summary>
		///     Returns an easing function for input value in the [start..end] range.
		/// </summary>
		/// <param name="start">Value range start, default 0.</param>
		/// <param name="end">Value range end, default 1.</param>
		/// <param name="pow">Easing power factor, default 2.</param>
		
		switch (arguments.length) {
		case 0:
			start = 0;
			end = 1;
			pow = 2;
			break;
		case 1:
			end = start;
			start = 0;
			pow = 2;
			break;
		case 2:
			pow = 2;
			break;
		}

		if (!isFinite(pow) || !(pow > 0)) {
			pow = 2;
		}
		if (!isFinite(start)) {
			start = 0;
		}
		if (!isFinite(end)) {
			end = 1;
		}
		if (start > end) {
			start = end;
		}

		return function(value) {
			return unchecked(value, start, end, pow);
		};
	}

	function unchecked(value, start, end, pow) {
		var ratio = math.pow(value, pow) / (math.pow(value, pow) + math.pow(1 - value, pow));
		return start + (end - start) * ratio;
	}

	math.ease = ease;
	math.ease.get = get;

})(Math);