prng.test.ts

describe('newPRNG', () => {
  test('should generate seeded random values', () => {
    expect(newPRNG(123)(new Array(5))).toEqual([-220828386, -1556571610, 1450074142, -2011800852, 1359997245]);
    expect(Buffer.from(newPRNG(123)(new Int8Array(20))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
    expect(Buffer.from(newPRNG(123)(new Int8Array(20))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
    expect(Buffer.from(newPRNG(123)(new Uint8ClampedArray(10))).toString('hex')).toBe('1ef2d66d26a3389a1e56');
    expect(Buffer.from(newPRNG(123)(new Int16Array(10))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
    expect(Buffer.from(newPRNG(123)(new Uint16Array(10))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
    expect(Buffer.from(newPRNG(123)(new Uint32Array(5))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
    expect(Buffer.from(newPRNG(123)(new Int32Array(5))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
    expect(Buffer.from(newPRNG(123)(new BigInt64Array(3))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe945489fa0',
    );
    expect(Buffer.from(newPRNG(123)(new BigUint64Array(3))).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe945489fa0',
    );
    expect(Buffer.from(newPRNG(123)(new DataView(new ArrayBuffer(20))).buffer).toString('hex')).toBe(
      '1ef2d66d26a3389a1e566e60ec88165a3d510fe9',
    );
  });
  test('should call randomizer if provided', () => {
    let x = 0;
    expect(Buffer.from(newPRNG(1, () => ++x)(new Uint8Array(200))).toString('hex')).toBe(
      'db12adaf757fe47e954775b89bd6afd5be384f6981f9929c463a143e7dc208ddbf2e660be05c67303854fe1215e68c469b45f13a11ca31' +
        'da7ef1c8f9930bd7ef983605d0c72afcd33bdcec65b9bab1204f571141e33a296167428f0cf80d76d787987e608e541f9d287da3d021d' +
        '908a9be8bbb75d4c1e8fb195f5c7ac7379375ee31bfa3d2ae6867c288c59fd2205ab7d71768fbc1b43a1b00b28e30f71cf0be140b6a10' +
        '827ce3d012296aaea8100089794abb717a940393fc03f0bcdf51cab7cbe4b45676e54c33',
    );
    expect(x).toBe(10);
  });
});

prng.ts

/** A pseudo random number generator */
export interface PRNG {
  /** Returns a pseudorandom 32 bit unsigned integer */
  (): number;

  /** Fills the given typed array with pseudorandom values */
  <T extends IntegerTypedArray | DataView | ArrayBuffer | number[] | null>(typedArray?: T): T;
}

/**
 * Returns a new pseudo random generator function that can be used to fill typed arrays with random values.
 * Based on xoshiro algorithm, see http://prng.di.unimi.it/
 * Extremely compact when minified, ~445 bytes.
 * Useful for generating testing data or to obtain a repeatable sequence of pseudorandom numbers.
 * @param seed The seed to use, a 53 bit integer
 * @param randomizer An optional function that can returns a random integer to be mixed.
 * @example
 * const prng = newPRNG(123);
 * const randomUint32: number = prng();
 * const bytes: Uint8Array = prng(new Uint8Array(10));
 * const random32bitInts: number[] = prng(new Array(12))
 */
export const newPRNG = /*@__PURE__*/ (seed: number, randomizer?: () => number): PRNG => {
  let q!: number;
  let n!: number;
  let ab!: number; // accumulator for bytes
  let an = 0; // number of bits available in acc
  let state = 0x3a522fb3; // initialization and randomization
  let s0 = 0x54e241; // xoshiro state 0
  let s1 = state * 97; // xoshiro state 1
  let s2 = s0 * 13; // xoshiro state 2
  let s3 = seed; // xoshiro state 3
  const prng = (out?: UnsafeAny) => {
    if (out !== undefined) {
      if (out) {
        n = out.BYTES_PER_ELEMENT * 8;
        if (!n || n > 4) {
          n = out.byteLength;
          out = n ? new Uint8Array(out.buffer || out, out.byteOffset | 0, n) : out;
          n = n ? 8 : 32;
        }
        for (let i = 0, m = -1 >>> (32 - n); i < out.length; ++i) {
          if (an < n) {
            an = 32;
            ab = prng();
          }
          out[i] = m & (ab >>> an);
          an -= n;
        }
      }
      return out;
    }
    if (state > 23) {
      state >>= 2;
      seed = prng() - seed / 7;
      s1 ^= (seed * 17) ^ (state & 1 && randomizer! && randomizer());
    }
    if (!--state) {
      state = 16 ^ (s2 & 7);
      seed ^= state ^ (randomizer! && randomizer());
    }
    q = s1;
    s2 ^= s0;
    s3 ^= s1;
    s1 ^= s2;
    s0 ^= s3;
    s2 ^= q << 9;
    s3 = (s3 << 11) ^ (s3 >> 21);
    q *= 5;
    return (seed ^ (((q << 7) ^ (q >> 25)) * 9)) >>> 0;
  };
  return prng;
};