XorShiftRNG

XorShiftRNG.js

XorShiftRNG = (function(){
//from: http://d.hatena.ne.jp/uupaa/20091223/1261528727
var nowimpl = !!Date.now;

//from: http://homepage2.nifty.com/magicant/sjavascript/mt.html
function mul(a, b) {
	var a1 = a >>> 16, a2 = a & 0xffff;
	var b1 = b >>> 16, b2 = b & 0xffff;
	return (((a1 * b2 + a2 * b1) << 16) + a2 * b2) >>> 0;
}

function XorShiftRNG(seed){
	if (arguments.length == 0){
		this.setSeedByTime();
	} else {
		this.setSeed(seed);
	}
}

XorShiftRNG.prototype.setSeedByTime = function(){
	this.setSeed(nowimpl ? Date.now() : +new Date());
}

//from: http://unkar.org/r/tech/1192628099#l75
XorShiftRNG.prototype.setSeed = function(seed){
	var x = 1812433253;
	this._x = seed = mul(x, (seed^(seed>>>30)))+1;
	this._y = seed = mul(x, (seed^(seed>>>30)))+2;
	this._z = seed = mul(x, (seed^(seed>>>30)))+3;
	this._w = seed = mul(x, (seed^(seed>>>30)))+4;
}

XorShiftRNG.prototype.next = function(){
	return this.nextUInt32() / 4294967295;
}

XorShiftRNG.prototype.nextUInt32 = function(){
	var w = this._w, t = this._x ^ (this._x << 11);
	this._x = this._y;
	this._y = this._z;
	this._z = w;
	return this._w = ((w ^ w >>> 19) ^ (t ^ t >>> 8)) >>> 0;
}

return XorShiftRNG;
})();