SeededRandom.test.ts

import SeededRandom from "../SeededRandom"

describe("SeededRandom.ts", () => {
  it("インスタンスが違っていても、シード値が同じなら同じ値が返ってくる", () => {
    const seed = 100
    const r1 = new SeededRandom(seed)
    const r2 = new SeededRandom(seed)
    expect(r1.next()).toBe(r2.next())
    expect(r1.next()).toBe(r2.next())
    expect(r1.next()).toBe(r2.next())
    expect(r1.next()).toBe(r2.next())
    expect(r1.next()).toBe(r2.next())
  })
  it("シード値が別なら違う値が返ってくる", () => {
    const r1 = new SeededRandom(100)
    const r2 = new SeededRandom(101)
    expect(r1.next()).not.toBe(r2.next())
  })
})

SeededRandom.ts

/**
 * SeedeRandom
 * シード指定可能なランダム変数
 * @ref https://qiita.com/hp0me/items/ec10a59d8e3a05d90c83
 */
export default class SeededRandom {
  private seed: number
  constructor(seed: number = 123456789) {
    this.seed = seed
  }
  next(max: number = 1, min: number = 0) {
    max = max || 1
    min = min || 0

    this.seed = (this.seed * 9301 + 49297) % 233280
    const rnd = this.seed / 233280

    return min + rnd * (max - min)
  }
}