101 lines
2.7 KiB
JavaScript
Executable File
101 lines
2.7 KiB
JavaScript
Executable File
/**
|
|
* Pseudo random number generator
|
|
* using the xorshift32 method.
|
|
*/
|
|
export class Xorshift32 {
|
|
/**
|
|
* State holds a single uint32.
|
|
* It's useful for staying within modulo 2**32.
|
|
*
|
|
* @type {Uint32Array}
|
|
*/
|
|
#state;
|
|
get state() {
|
|
return this.#state;
|
|
}
|
|
|
|
/** @param {number} seed */
|
|
constructor(seed) {
|
|
if (seed === undefined) {
|
|
const maxInt32 = 2 ** 32;
|
|
seed = Math.floor(Math.random() * (maxInt32 - 1)) + 1;
|
|
}
|
|
seed = seed | 0;
|
|
this.#state = Uint32Array.of(seed);
|
|
}
|
|
|
|
/** @protected Shuffle the internal state. */
|
|
shuffle() {
|
|
this.#state[0] ^= this.#state[0] << 13;
|
|
this.#state[0] ^= this.#state[0] >>> 17;
|
|
this.#state[0] ^= this.#state[0] << 5;
|
|
|
|
// We could also do something like this:
|
|
// x ^= x << 13;
|
|
// x ^= x >>> 17;
|
|
// x ^= x << 5;
|
|
// return x;
|
|
// And even though bitwise operations coerce numbers
|
|
// into int32 (except >>> which converts into uint32).
|
|
// But using Uint32Array ensures the number stays
|
|
// uint32 all the way through, thus avoiding the pitfalls
|
|
// of potentially dipping into negative number territory
|
|
}
|
|
|
|
/**
|
|
* Get a random number and shuffle the internal state.
|
|
* @returns {number} a pseudo-random positive integer.
|
|
*/
|
|
next() {
|
|
this.shuffle();
|
|
return this.#state[0];
|
|
}
|
|
|
|
/** @param {number} x @returns {number} a positive integer lower than x */
|
|
lowerThan(x) {
|
|
return this.next() % x;
|
|
}
|
|
|
|
/** @param {number} x @returns {number} a positive integer lower than or equal to x */
|
|
lowerThanOrEqual(x) {
|
|
return this.next() % (x + 1);
|
|
}
|
|
|
|
/**
|
|
* @template T
|
|
* @param {T[]} arr - The array to pick from.
|
|
* @returns {T} One element from the array. * @return {<T>}
|
|
*/
|
|
randomElement(arr) {
|
|
if (arr instanceof Set) {
|
|
arr = [...arr];
|
|
}
|
|
const idx = this.lowerThan(arr.length);
|
|
|
|
return arr[idx];
|
|
}
|
|
|
|
/**
|
|
* @method
|
|
* @template T
|
|
* @param {...T} args pick random function argument
|
|
* @returns {T}
|
|
*/
|
|
oneOf(...args) {
|
|
return this.randomElement(args)
|
|
}
|
|
|
|
/**
|
|
* @param {number} lowerThanOrEqual a positive integer
|
|
* @param {number} greaterThanOrEqual a positive integer greater than lowerThanOrEqual
|
|
* @returns {number} a pseudo-random integer
|
|
*/
|
|
within(greaterThanOrEqual, lowerThanOrEqual) {
|
|
const range = lowerThanOrEqual - greaterThanOrEqual;
|
|
|
|
const num = this.lowerThanOrEqual(range);
|
|
|
|
return num + greaterThanOrEqual;
|
|
}
|
|
}
|