@hugoalh/is-numeric-prime/_bigint_root_approximate.js

A module to determine whether the numeric is prime.

/**
 * Return the root of the big integer, approximate. From https://stackoverflow.com/a/64190462.
 * @param {bigint} radicand Radicand.
 * @param {bigint} [index=2n] Index.
 * @returns {BigIntRootApproximateResult} Root, approximate.
 */
export function bigintRootApproximate(radicand, index = 2n) {
    if (!(radicand >= 0n)) {
        throw new RangeError(`\`${radicand}\` (parameter \`radicand\`) is not a bigint which is positive!`);
    }
    if (!(index > 0n)) {
        throw new RangeError(`\`${index}\` (parameter \`index\`) is not a bigint which is > 0!`);
    }
    if (radicand === 0n ||
        index === 1n) {
        return {
            ceil: radicand,
            floor: radicand
        };
    }
    let s = radicand + 1n;
    let u = radicand;
    while (u < s) {
        s = u;
        u = (u * (index - 1n) + radicand / (u ** (index - 1n))) / index;
    }
    return {
        ceil: (s ** index === radicand) ? s : s + 1n,
        floor: s
    };
}