locutus/esm/python/math/isqrt.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

const MAX_SAFE_ROOT = BigInt(Number.MAX_SAFE_INTEGER);
const FIRST_UNSAFE_ROOT_SQUARED = (MAX_SAFE_ROOT + 1n) * (MAX_SAFE_ROOT + 1n);
export function isqrt(n) {
    //      discuss at: https://locutus.io/python/isqrt/
    // parity verified: Python 3.12
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Returns the integer square root, rounding down to the nearest whole number.
    //       example 1: isqrt(15)
    //       returns 1: 3
    //       example 2: isqrt(16)
    //       returns 2: 4
    //       example 3: isqrt(0)
    //       returns 3: 0
    if (typeof n === 'string' && /^[-+]?\d+$/.test(n.trim())) {
        const parsed = BigInt(n);
        if (parsed < 0n) {
            throw new Error('isqrt() only accepts non-negative integers');
        }
        if (parsed >= FIRST_UNSAFE_ROOT_SQUARED) {
            throw new RangeError('isqrt() only supports roots within JS safe integer precision');
        }
        const root = bigintSqrt(parsed);
        if (root > MAX_SAFE_ROOT) {
            throw new RangeError('isqrt() only supports roots within JS safe integer precision');
        }
        return Number(root);
    }
    const value = Number(n);
    if (!Number.isFinite(value) || !Number.isSafeInteger(value) || value < 0) {
        throw new Error('isqrt() only accepts non-negative integers');
    }
    return Math.floor(Math.sqrt(value));
}
function bigintSqrt(value) {
    if (value < 2n) {
        return value;
    }
    let x0 = value;
    let x1 = (x0 + 1n) >> 1n;
    while (x1 < x0) {
        x0 = x1;
        x1 = (x1 + value / x1) >> 1n;
    }
    return x0;
}