Pure, splittable version of BurtlePRNG

prng.js

// BurtlePRNG ported from https://github.com/graue/burtleprng
// Immutable + splittable + ES2015 by @briancavalier

// newRandom :: UInt32 -> UInt32 -> UInt32 -> UInt32 -> Gen a
// Create a new prng with exact state
export const newRandom = (s0, s1, s2, s3) =>
  new BurtlePRNG(s0>>>0, s1>>>0, s2>>>0, s3>>>0);

// seedRandom :: UInt32 -> Gen a
// Create a new prng from a 32-bit int seed
export const seedRandom = seed => {
  const s123 = seed >>> 0;
  return prime(20, new BurtlePRNG(S0, s123, s123, s123));
}

// splitn :: Int -> Gen a -> [Gen a]
// Create n new distinct, but deterministic prngs based on g
// Ugly imperative impl for speed
export const splitn = (n, g) => {
  const a = new Array(n);
  for(let i = 0; i < n; ++i) {
    const { value, next } = g.next();
    a[i] = next;
    g = seedRandom(value);
  }
  return a;
}

// prime :: Int -> Gen a -> Gen a
// Consume n randoms to "prime" prng
// Ugly imperative impl for speed
const prime = (n, g) => {
  for (let i = 0; i < n; ++i) {
    const { value, next } = g.next();
    g = next;
  }
  return g;
};

const rot = (x, k) => (x << k) | (x >> (32-k));

const S0 = 0xf1ea5eed;
const REAL_DIVISOR = 4294967296.0;

class BurtlePRNG {
  constructor(s0, s1, s2, s3) {
    this.s0 = s0;
    this.s1 = s1;
    this.s2 = s2;
    this.s3 = s3;
  }

  next() {
    const e  = (this.s0 - rot(this.s1, 27))>>>0;
    const s0 = (this.s1 ^ rot(this.s2, 17))>>>0;
    const s1 = (this.s2 + this.s3)>>>0;
    const s2 = (this.s3 + e)>>>0;
    const s3 = (e       + s0)>>>0;
    return { value: s3, next: new BurtlePRNG(s0, s1, s2, s3) };
  }

  nextReal() {
    const { value, next } = this.next();
    return { value: value/REAL_DIVISOR, next };
  }
}