Template-summation of one-dimensional tree array (interval modification, interval query)

#include<iostream>
using namespace std;

typedef long long ll;
const int maxn = 1e6 + 10;

int n, m;
ll u[maxn];
ll t1[maxn];
ll t2[maxn];

ll lowbit(ll x) {
    
    
	return x & (-x);
}
void Update(ll i, ll k) {
    
    
	ll x = i;
	while (i <= n) {
    
    
		t1[i] += k;
		t2[i] += k * (x - 1);
		i += lowbit(i);
	}
}
ll get_sum(ll i) {
    
    
	ll sum = 0, x = i;
	while (i >= 1) {
    
    
		sum += x * t1[i] - t2[i];
		i -= lowbit(i);
	}
	return sum;
}
int main() {
    
    

	cin >> n >> m;

	for (int i = 1; i <= n; i++) {
    
    
		cin >> u[i];
	}
	for (int i = 1; i <= n; i++) {
    
    
		ll d = u[i] - u[i - 1];
		Update(i, d);
	}

	while (m--) {
    
    
		int sign;
		cin >> sign;
		if (sign == 1) {
    
    		//区间修改
			int l, r, k;
			cin >> l >> r >> k;
			Update((ll)l, k);
			Update((ll)r + 1ll, -k);
		}
		else {
    
    		//区间查询
			ll l, r;
			cin >> l >> r;
			cout << get_sum(r) - get_sum(l - 1) << endl;
		}
	}

	return 0;
}