export function gcd(a, b) {
	let x = Math.abs(a);
	let y = Math.abs(b);
	while (y !== 0) {
		const t = y;
		y = x % y;
		x = t;
	}
	return x;
}

export function modPow(base, exp, mod) {
	let result = 1;
	let b = base % mod;
	let e = exp;
	while (e > 0) {
		if (e % 2 === 1) {
			result = (result * b) % mod;
		}
		b = (b * b) % mod;
		e = Math.floor(e / 2);
	}
	return result;
}

export function modInverse(e, phi) {
	let oldR = e;
	let r = phi;
	let oldS = 1;
	let s = 0;

	while (r !== 0) {
		const q = Math.floor(oldR / r);
		[oldR, r] = [r, oldR - q * r];
		[oldS, s] = [s, oldS - q * s];
	}

	if (oldR !== 1) {
		return null;
	}

	return ((oldS % phi) + phi) % phi;
}

export function isPrime(n) {
	if (n < 2) {
		return false;
	}
	for (let i = 2; i * i <= n; i += 1) {
		if (n % i === 0) {
			return false;
		}
	}
	return true;
}