Simple PRNG

example.js

let rng = createNumberGenerator(
  createSeedFromString("Hello friends!") // 2053374269
);

// Generate a boolean with 30% success
console.log(generateBoolean(rng, 0.3)); // false
console.log(generateBoolean(rng, 0.3)); // true

// Generate a D6
console.log(generateNumber(rng, 1, 6)); // 3
console.log(generateNumber(rng, 1, 6)); // 5
console.log(generateNumber(rng, 1, 6)); // 5

// Generate a float between 0 and 1
console.log(generateFloat(rng)); // 0.4461949771377712
console.log(generateFloat(rng)); // 0.22262383583528544

rng.js

function toUint32(x) {
  return x >>> 0;
}

function createSeedFromString(string) {
  let seed = 0;
  for (let i = 0; i < string.length; ++i) {
    seed ^= string.charCodeAt(i) << i % 4 * 8;
  }
  return toUint32(seed);
}

function createNumberGenerator(seed) {
  return new Uint32Array([
    Math.imul(seed, 0x85ebca6b), 
    Math.imul(seed, 0xc2b2ae35),
  ]);
}

function generate(rng) {
  let s0 = rng[0];
  let s1 = rng[1] ^ s0;
  rng[0] = (s0 << 26 | s0 >> 8) ^ s1 ^ s1 << 9;
  rng[1] = s1 << 13 | s1 >> 19;
  return toUint32(Math.imul(s0, 0x9e3779bb));
}

function generateBoolean(rng, probability) {
  return generate(rng) < toUint32(probability * 0xffffffff);
}

function generateFloat(rng) {
  return generate(rng) / 0xffffffff;
}

function generateNumber(rng, min, max) {
  return min + generate(rng) % (max - min + 1);
}