Replaces Math.random() with a seedable pseudo-random number function

prng.js

/*
 * A seedable (deterministic) psuedo-random number generator
 *
 * This script replaces native Math.random() with a deterministic psuedo-random
 * number generator. It also adds a static method to reset the prng stream and
 * optionally set a new seed string.
 *
 * @function random
 * @memberof Math
 * @description Generates a deterministic psuedo-random number between zero and one
 * @returns {Number} psuedo-random number between zero and one
 *
 * @function reset
 * @static
 * @memberof Math.random
 * @description Resets the prng stream, optionally with a new seed
 * @param {String} [seed] - Optional seed text
 * @returns undefined
 *
 * @property {String} seed - Current seed string
 * @static
 * @memberof Math.random
 * @readonly
 *
 * @function native
 * @static
 * @memberof Math.random
 * @description Native random function
 * @returns {Number} random number between zero and one
 */
(function() {

	'use strict';

	var _native = Math.random;
	var _seed = _native().toString( 36 ).slice( 2 );
	var _state = new Uint8Array( 256 );
	var _i = 0;
	var _j = 0;
	var _t = 0;

	function swap ( i, j ) {
		_t = _state[ i ];
		_state[ i ] = _state[ j ];
		_state[ j ] = _t;
	}

	function next () {
		_i = ( _i + 1 ) % 256;
		_j = ( _j + _state[ _i ] ) % 256;
		swap( _i, _j );
		return _state[ ( _state[ _i ] + _state[ _j ] ) % 256 ];
	}

	Object.defineProperty( Math, 'random', {
		value: function () {
			return Object.defineProperties(
				function random () {
					var r = next();
					r = r * 256 + next();
					r = r * 256 + next();
					r = r * 256 + next();
					r = r * 256 + next();
					r = r * 256 + next();
					r = r * 256 + next();
					return r / 0x100000000000004;
				}, {
				reset: {
					value: function ( seed ) {
						_seed = seed ? String( seed ).trim().slice( 0, 256 ) : _seed;
						_state.set( Array.apply( 0, Array( 256 ) ).map( function ( x, y ) { return y; } ) );
						for ( var i = 0, j = 0; i < 256; i ++ ) {
							swap( i, j = ( j + _state[ i ] + _seed[ i % _seed.length ].charCodeAt( 0 ) ) % 256 );
						}
						_i = _j = 0;
					},
					enumerable: true
				},
				seed: { get: function () { return _seed; }, enumerable: true 	},
				native: { value: _native, enumerable: true }
			} );
		}()
	} );

	Math.random.reset();

}());