A JavaScript module implementing the Alea pseudo-random number generator with seed, offering functions to generate float32, uint32, fract53, and Gaussian-distributed random numbers for non-cryptographic purposes. Original author: Baagøe https://github.com/nquinlan/better-random-numbers-for-javascript-mirror

alea-prng.ts

interface AleaPRNG {
  float32: () => number;
  uint32: () => number;
  fract53: () => number;
  gaussian: (mean?: number, std?: number) => number;
}
/**
 * Alea PRNG that is not cryptographically secure.
 */
export const mkAlea = (seed: string): AleaPRNG => {
  const randomFloat32 = (() => {
    let n = 0xefc8249d;
    const mash = (data: string) => {
      for (let i = 0; i < data.length; i++) {
        n += data.charCodeAt(i);
        let 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
    };
    // keeping the order of mash calls the same
    let s0 = mash(" ");
    let s1 = mash(" ");
    let s2 = mash(" ");
    let c = 1;
    s0 -= mash(seed);
    if (s0 < 0) {
      s0 += 1;
    }
    s1 -= mash(seed);
    if (s1 < 0) {
      s1 += 1;
    }
    s2 -= mash(seed);
    if (s2 < 0) {
      s2 += 1;
    }
    // state setup is done, now make randomFloat32()
    return () => {
      const t = 2091639 * s0 + c * 2.3283064365386963e-10; // 2^-32
      s0 = s1;
      s1 = s2;
      return (s2 = t - (c = t | 0));
    };
  })();
  const randomUint32 = () => {
    return randomFloat32() * 0x100000000; // 2^32
  };
  const randomFract53 = () => {
    return (
      randomFloat32() +
      ((randomFloat32() * 0x200000) | 0) * 1.1102230246251565e-16
    ); // 2^-53
  };
  const randomGaussian = (() => {
    // plotted 100k numbers, looks good enough on a histogram chart
    let spare: number | undefined;
    return (mean = 0, std = 1) => {
      if (spare != null) {
        const r = spare * std + mean;
        spare = undefined;
        return r;
      }
      let u: number;
      let v: number;
      let s: number;
      do {
        u = randomFloat32() * 2 - 1;
        v = randomFloat32() * 2 - 1;
        s = u * u + v * v;
      } while (s >= 1 || s === 0);
      s = Math.sqrt((-2 * Math.log(s)) / s);
      spare = v * s;
      return mean + std * u * s;
    };
  })();
  return {
    float32: randomFloat32,
    uint32: randomUint32,
    fract53: randomFract53,
    gaussian: randomGaussian,
  };
};