xorshift.js/lib/xorshift128plus.js

xorshift* / xorshift+ generators

'use strict'
var inherits = require('inherits')
var XorShift = require('./xorshift')

function XorShift128Plus (seed) {
  XorShift.call(this)

  if (!seed) throw new TypeError('expected seed as array or hex string')
  if (typeof seed === 'string') seed = this._hex2seed(4, seed)
  if (seed.length !== 4) throw new TypeError('seed length should equal 4')

  this._s0H = seed[0] >>> 0
  this._s0L = seed[1] >>> 0
  this._s1H = seed[2] >>> 0
  this._s1L = seed[3] >>> 0
}

inherits(XorShift128Plus, XorShift)

XorShift128Plus.prototype.randomInt64 = function () {
  // uint64_t s1 = s[0];
  var s1H = this._s0H
  var s1L = this._s0L
  // const uint64_t s0 = s[1];
  var s0H = this._s1H
  var s0L = this._s1L
  // s[0] = s0;
  this._s0H = s0H
  this._s0L = s0L
  // s1 ^= s1 << 23;
  s1H ^= ((s1H & 0x000001ff) << 23) | (s1L >>> 9)
  s1L ^= (s1L & 0x000001ff) << 23
  // s[1] = s1 ^ s0 ^ (s1 >> 17) ^ (s0 >> 26);
  this._s1H ^= s1H ^ (s1H >>> 17) ^ (s0H >>> 26)
  this._s1H >>>= 0
  this._s1L ^= s1L ^ (((s1H & 0x0001ffff) << 15) | (s1L >>> 17)) ^ (((s0H & 0x03ffffff) << 6) | (s0L >>> 26))
  this._s1L >>>= 0
  // return s[1] + s0;
  var t = this._s1L + s0L
  return [
    (((t / 0x0100000000) | 0) + this._s1H + s0H) >>> 0,
    t >>> 0
  ]
}

module.exports = XorShift128Plus