Made of little things.

/** Small seeded PRNG (mulberry32) so a world can be regenerated from its seed. */
export interface Rng {
  next(): number;
  range(min: number, max: number): number;
  int(min: number, max: number): number;
  chance(p: number): boolean;
  sign(): 1 | -1;
}

export function createRng(seed: number): Rng {
  let a = seed >>> 0;
  const next = (): number => {
    a = (a + 0x6d2b79f5) >>> 0;
    let t = a;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
  return {
    next,
    range: (min, max) => min + next() * (max - min),
    int: (min, max) => Math.floor(min + next() * (max - min + 1)),
    chance: (p) => next() < p,
    sign: () => (next() < 0.5 ? -1 : 1),
  };
}