octo-deno/lib/random/mersennetwister.js

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
 * JavaScript version of Mersenne Twister
 *
 * @author Yasuharu Okada
 *
 */

function MersenneTwister () {
  const N = 624
  const M = 397
  const UPPER_MASK = 0x80000000
  const LOWER_MASK = 0x7fffffff
  const MAG01 = new Int32Array([0, 0x9908b0df])

  let mt = new Int32Array(N)
  /* the array for the state vector */
  let mti = 625

  this.seed = function (s) {
    mt[0] = s | 0
    for (mti = 1; mti < N; mti++) {
      mt[mti] = Math.imul(1812433253, mt[mti - 1] ^ (mt[mti - 1] >>> 30)) + mti
    }
  }

  this.export_state = function () {
    return [mt, mti]
  }

  this.import_state = function (s) {
    mt = s[0]
    mti = s[1]
  }

  this.export_mta = function () {
    return mt
  }

  this.import_mta = function (_mta) {
    mt = _mta
  }

  this.export_mti = function () {
    return mti
  }

  this.import_mti = function (_mti) {
    mti = _mti
  }

  this.int32 = function () {
    let y, kk

    if (mti >= N) { /* generate N words at one time */
      for (kk = 0; kk < N - M; kk++) {
        y = ((mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK))
        mt[kk] = (mt[kk + M] ^ (y >>> 1) ^ MAG01[y & 0x1])
      }
      for (; kk < N - 1; kk++) {
        y = ((mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK))
        mt[kk] = (mt[kk + (M - N)] ^ (y >>> 1) ^ MAG01[y & 0x1])
      }
      y = ((mt[N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK))
      mt[N - 1] = (mt[M - 1] ^ (y >>> 1) ^ MAG01[y & 0x1])
      mti = 0
    }

    y = mt[mti++]

    /* Tempering */
    y = y ^ (y >>> 11)
    y = y ^ ((y << 7) & 0x9d2c5680)
    y = y ^ ((y << 15) & 0xefc60000)
    y = y ^ (y >>> 18)

    return y >>> 0
  }

  this.real2 = function () {
    return ((this.int32() >>> 5) * 67108864.0 + (this.int32() >>> 6)) / 9007199254740992.0
  }
}