bitburner-src/src/Casino/RNG.ts

interface RNG {
  random(): number;
}

/*
 * very bad RNG, meant to be used as introduction to RNG manipulation. It has a
 * period of 1024.
 */
class RNG0 implements RNG {
  x: number;
  m = 1024;
  a = 341;
  c = 1;

  constructor() {
    this.x = 0;
    this.reset();
  }

  step(): void {
    this.x = (this.a * this.x + this.c) % this.m;
  }

  random(): number {
    this.step();
    return this.x / this.m;
  }

  reset(): void {
    this.x = new Date().getTime() % this.m;
  }
}

export const BadRNG: RNG0 = new RNG0();

/*
 * Wichmann–Hill PRNG
 * The period is 6e12.
 */
export class WHRNG implements RNG {
  s1 = 0;
  s2 = 0;
  s3 = 0;

  constructor(totalPlaytime: number) {
    // This one is seeded by the players total play time.
    const v: number = (totalPlaytime / 1000) % 30000;
    this.s1 = v;
    this.s2 = v;
    this.s3 = v;
  }

  step(): void {
    this.s1 = (171 * this.s1) % 30269;
    this.s2 = (172 * this.s2) % 30307;
    this.s3 = (170 * this.s3) % 30323;
  }

  random(): number {
    this.step();
    return (this.s1 / 30269.0 + this.s2 / 30307.0 + this.s3 / 30323.0) % 1.0;
  }
}