boardgame.io/src/plugins/random/random.alea.js

library for turn-based games

// Inlined version of Alea from https://github.com/davidbau/seedrandom.

/*
 * Copyright 2015 David Bau.
 *
 * Permission is hereby granted, free of charge,
 * to any person obtaining a copy of this software
 * and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the
 * Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall
 * be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

function Alea(seed) {
  var me = this,
    mash = Mash();

  me.next = function() {
    var t = 2091639 * me.s0 + me.c * 2.3283064365386963e-10; // 2^-32
    me.s0 = me.s1;
    me.s1 = me.s2;
    return (me.s2 = t - (me.c = t | 0));
  };

  // Apply the seeding algorithm from Baagoe.
  me.c = 1;
  me.s0 = mash(' ');
  me.s1 = mash(' ');
  me.s2 = mash(' ');
  me.s0 -= mash(seed);
  if (me.s0 < 0) {
    me.s0 += 1;
  }
  me.s1 -= mash(seed);
  if (me.s1 < 0) {
    me.s1 += 1;
  }
  me.s2 -= mash(seed);
  if (me.s2 < 0) {
    me.s2 += 1;
  }
  mash = null;
}

function copy(f, t) {
  t.c = f.c;
  t.s0 = f.s0;
  t.s1 = f.s1;
  t.s2 = f.s2;
  return t;
}

function Mash() {
  var n = 0xefc8249d;

  var mash = function(data) {
    data = data.toString();
    for (var i = 0; i < data.length; i++) {
      n += data.charCodeAt(i);
      var h = 0.02519603282416938 * n;
      n = h >>> 0;
      h -= n;
      h *= n;
      n = h >>> 0;
      h -= n;
      n += h * 0x100000000; // 2^32
    }
    return (n >>> 0) * 2.3283064365386963e-10; // 2^-32
  };

  return mash;
}

export function alea(seed, opts) {
  var xg = new Alea(seed),
    state = opts && opts.state,
    prng = xg.next;
  prng.quick = prng;
  if (state) {
    if (typeof state == 'object') copy(state, xg);
    prng.state = function() {
      return copy(xg, {});
    };
  }
  return prng;
}