numtheory/fastFactorize.cpp

• View this file on GitHub
• Last update: 2024-01-23 02:14:10+08:00
• Link: https://github.com/kth-competitive-programming/kactl)

Verified with

• test/chromatic_number.test.cpp
• test/factorize.test.cpp
• test/primality_test.test.cpp
• test/primitive_root.test.cpp

Code

//source: KACTL(https://github.com/kth-competitive-programming/kactl)

ull modmul(ull a, ull b, ull M) {
	ll ret = a * b - M * ull(1.L / M * a * b);
	return ret + M * (ret < 0) - M * (ret >= (ll)M);
}

ull modpow(ull b, ull e, ull mod) {
	ull ans = 1;
	for (; e; b = modmul(b, b, mod), e /= 2)
		if (e & 1) ans = modmul(ans, b, mod);
	return ans;
}

bool isPrime(ull n) {
	if (n < 2 || n % 6 % 4 != 1) return (n | 1) == 3;
	ull A[] = {2, 325, 9375, 28178, 450775, 9780504, 1795265022},
	    s = __builtin_ctzll(n-1), d = n >> s;
	for (ull a : A) {   // ^ count trailing zeroes
		ull p = modpow(a%n, d, n), i = s;
		while (p != 1 && p != n - 1 && a % n && i--)
			p = modmul(p, p, n);
		if (p != n-1 && i != s) return 0;
	}
	return 1;
}

ull pollard(ull n) {
  static mt19937_64 rng(clock);
  uniform_int_distribution<ull> unif(0, n - 1);
  ull c = 1;
	auto f = [n, &c](ull x) { return modmul(x, x, n) + c % n; };
	ull x = 0, y = 0, t = 30, prd = 2, i = 1, q;
	while (t++ % 40 || __gcd(prd, n) == 1) {
		if (x == y) c = unif(rng), x = ++i, y = f(x);
		if ((q = modmul(prd, max(x,y) - min(x,y), n))) prd = q;
		x = f(x), y = f(f(y));
	}
	return __gcd(prd, n);
}

vector<ull> factor(ull n) {
	if (n == 1) return {};
	if (isPrime(n)) return {n};
	ull x = pollard(n);
	auto l = factor(x), r = factor(n / x);
	l.insert(l.end(), r.begin(), r.end());
	return l;
}

#line 1 "numtheory/fastFactorize.cpp"
//source: KACTL(https://github.com/kth-competitive-programming/kactl)

ull modmul(ull a, ull b, ull M) {
	ll ret = a * b - M * ull(1.L / M * a * b);
	return ret + M * (ret < 0) - M * (ret >= (ll)M);
}

ull modpow(ull b, ull e, ull mod) {
	ull ans = 1;
	for (; e; b = modmul(b, b, mod), e /= 2)
		if (e & 1) ans = modmul(ans, b, mod);
	return ans;
}

bool isPrime(ull n) {
	if (n < 2 || n % 6 % 4 != 1) return (n | 1) == 3;
	ull A[] = {2, 325, 9375, 28178, 450775, 9780504, 1795265022},
	    s = __builtin_ctzll(n-1), d = n >> s;
	for (ull a : A) {   // ^ count trailing zeroes
		ull p = modpow(a%n, d, n), i = s;
		while (p != 1 && p != n - 1 && a % n && i--)
			p = modmul(p, p, n);
		if (p != n-1 && i != s) return 0;
	}
	return 1;
}

ull pollard(ull n) {
  static mt19937_64 rng(clock);
  uniform_int_distribution<ull> unif(0, n - 1);
  ull c = 1;
	auto f = [n, &c](ull x) { return modmul(x, x, n) + c % n; };
	ull x = 0, y = 0, t = 30, prd = 2, i = 1, q;
	while (t++ % 40 || __gcd(prd, n) == 1) {
		if (x == y) c = unif(rng), x = ++i, y = f(x);
		if ((q = modmul(prd, max(x,y) - min(x,y), n))) prd = q;
		x = f(x), y = f(f(y));
	}
	return __gcd(prd, n);
}

vector<ull> factor(ull n) {
	if (n == 1) return {};
	if (isPrime(n)) return {n};
	ull x = pollard(n);
	auto l = factor(x), r = factor(n / x);
	l.insert(l.end(), r.begin(), r.end());
	return l;
}

Back to top page