@augment-vir/common/dist/augments/random/random-integer.js

A collection of augments, helpers types, functions, and classes for any JavaScript environment.

import { ensureMinMax } from '@augment-vir/core';
/**
 * Creates a random integer (no decimal points are included) between the given min and max values
 * (inclusive).
 *
 * This function uses cryptographically secure randomness.
 *
 * @category Random
 * @category Package : @augment-vir/common
 * @package [`@augment-vir/common`](https://www.npmjs.com/package/@augment-vir/common)
 */
export function randomInteger({ min: rawMin, max: rawMax }) {
    const { min, max } = ensureMinMax({ min: Math.floor(rawMin), max: Math.floor(rawMax) });
    const range = max - min + 1;
    const bitsNeeded = Math.ceil(Math.log2(range));
    const neededBytes = Math.ceil(bitsNeeded / 8);
    /**
     * Testing on my system maxes out at 65,536 (Node) or 65,537 (Safari / Chrome / Firefox) bytes.
     * I don't know why, and that may be system dependent, I don't know.
     */
    if (neededBytes > 65_000) {
        throw new RangeError(`Cannot create a random integer so large. ({min: ${min}, max: ${max}})`);
    }
    const cutoff = Math.floor(256 ** neededBytes / range) * range;
    const currentBytes = new Uint8Array(neededBytes);
    let value;
    do {
        crypto.getRandomValues(currentBytes);
        value = currentBytes.reduce((accum, byte, index) => {
            return accum + byte * 256 ** index;
        }, 0);
    } while (value >= cutoff);
    return min + (value % range);
}