Seedable random numbers using a hash

random-seed.js

"use strict";
const crypto = require("crypto");

/**
 * @param {string|number} [seed]
 * @param {number} [offset]
 */
const createRng = (seed = 0, offset = 0) => {
    const numBytes = 6; // 48 bits
    const maxInt = 2 ** 48;

    let count = offset;

    /**
     * @param {number|string} seed
     */
    const createHash = (seed) => {
        const hash = crypto.createHash("sha256");
        hash.update(seed.toString());
        return hash;
    };

    /**
     * @param {crypto.Hash} hash
     */
    const getInt = (hash) => {
        const bytes = hash.digest("hex").slice(-2 * numBytes);
        return parseInt(bytes, 16);
    };

    const randomFloat = () => {
        count = (count % Number.MAX_SAFE_INTEGER) + 1;
        const hash = createHash(seed);
        hash.update(count.toString());
        return getInt(hash) / maxInt;
    };

    /**
     * @param {number} min inclusive
     * @param {number} max exclusive
     */
    const randomInt = (min = 0, max = maxInt) => {
        const f = randomFloat();
        return Math.floor(min + f * (max - min));
    };

    return Object.freeze({
        maxInt,
        /**
         * Produce a random int
         */
        randomInt,
        /**
         * Produce a random float
         */
        randomFloat,
        /**
         * Produce a random float
         */
        get value() {
            return randomFloat();
        },
    });
};

const rng = createRng(0);
const iters = 1e5;

let hist = {};
for (let i = 0; i < iters; i++) {
    const n = rng.randomInt(0, 10);
    hist[n] = (hist[n] || 0) + 1;
}
console.log(hist);

hist = {};
for (let i = 0; i < iters; i++) {
    const n = crypto.randomInt(0, 10);
    hist[n] = (hist[n] || 0) + 1;
}
console.log(hist);