ml-xsadd/src/XSadd.ts

JavaScript implementation of the XORSHIFT-ADD (XSadd) pseudo random number generator

const LOOP = 8;
const FLOAT_MUL = 1 / 16777216;

const sh1 = 15;
const sh2 = 18;
const sh3 = 11;

function multiplyUint32(n: number, m: number) {
  n >>>= 0;
  m >>>= 0;
  const nlo = n & 0xffff;
  const nhi = n - nlo;
  return (((nhi * m) >>> 0) + nlo * m) >>> 0;
}

export class XSadd {
  public random: () => number;

  private state: Uint32Array;

  /**
   * create an instance of XSadd with the specified seed
   * @param [seed=Date.now()]
   */
  constructor(seed = Date.now()) {
    this.state = new Uint32Array(4);
    this.init(seed);
    this.random = this.getFloat.bind(this);
  }

  /**
   * Returns a 32-bit integer r (0 <= r < 2^32)
   */
  public getUint32() {
    this.nextState();
    return (this.state[3] + this.state[2]) >>> 0;
  }

  /**
   * Returns a floating point number r (0.0 <= r < 1.0)
   */
  public getFloat() {
    return (this.getUint32() >>> 8) * FLOAT_MUL;
  }

  public init(seed: number) {
    if (!Number.isInteger(seed)) {
      throw new TypeError("seed must be an integer");
    }
    this.state[0] = seed;
    this.state[1] = 0;
    this.state[2] = 0;
    this.state[3] = 0;
    for (let i = 1; i < LOOP; i++) {
      this.state[i & 3] ^=
        (i +
          multiplyUint32(
            1812433253,
            this.state[(i - 1) & 3] ^ ((this.state[(i - 1) & 3] >>> 30) >>> 0),
          )) >>>
        0;
    }
    this.periodCertification();
    for (let i = 0; i < LOOP; i++) {
      this.nextState();
    }
  }

  private periodCertification() {
    if (
      this.state[0] === 0 &&
      this.state[1] === 0 &&
      this.state[2] === 0 &&
      this.state[3] === 0
    ) {
      this.state[0] = 88; // X
      this.state[1] = 83; // S
      this.state[2] = 65; // A
      this.state[3] = 68; // D
    }
  }

  private nextState() {
    let t = this.state[0];
    t ^= t << sh1;
    t ^= t >>> sh2;
    t ^= this.state[3] << sh3;
    this.state[0] = this.state[1];
    this.state[1] = this.state[2];
    this.state[2] = this.state[3];
    this.state[3] = t;
  }
}