The below is released under the GPL http://www.gnu.org/licenses/gpl.html

xorshift.js

//Webkit2's crazy invertible mapping generator
// Theory is here: http://dl.acm.org/citation.cfm?id=752741
var xorshift = (function(seed) {
  // We can't reach the maximal period inside JS because numbers above
  // 2^53 aren't 'safe'
  seed = seed || Math.round(Math.random() *  Math.pow(2, 32));

  return {
    rand : function() {
      // creates randomness...somehow...
      seed += (seed * seed) | 5;
      // Shift off bits, discarding the sign. Discarding the sign is
      // important because OR w/ 5 can give us + or - numbers.
      return (seed >>> 32) / max;
    }
  };
}(seed));