Interval modification multiplication and addition (a good example of understanding lazy tags)

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 1e5+10;
int n,m,p;
int a[N];
struct Node{
    
    int l,r;
    int sum,add,mul;
}tr[N*4];

void pushup(int u)
{
    
    tr[u].sum = (tr[u<<1].sum+tr[u<<1|1].sum)%p;
}

void eval(Node &t,int add,int mul)
{
    
    t.sum = ((LL)t.sum*mul+(LL)(t.r-t.l+1)*add)%p;
    t.mul = (LL) t.mul*mul%p;
    t.add = ((LL)t.add*mul+add)%p;
} 
void pushdown (int u)
{
    
    eval(tr[u<<1],tr[u].add,tr[u].mul);
    eval(tr[u<<1|1],tr[u].add,tr[u].mul);
    tr[u].add=0,tr[u].mul = 1;
    
}
void build(int u,int l,int r)
{
    
    if (l==r) tr[u] = {
    l,r,a[r],0,1};
    else
    {
    
        tr[u] = {
    l,r,0,0,1};
        int mid = l+r>>1;
        build (u<<1,l,mid);  build(u<<1|1,mid+1,r);
        pushup(u);
    }
}
void modify(int u,int l,int r,int add,int mul)
{
    
    if (tr[u].l>=l&&tr[u].r<=r) eval(tr[u],add,mul);
    else
    {
    
        pushdown(u);
        int mid = tr[u].l+tr[u].r>>1;
        if (l<=mid) modify(u<<1,l,r,add,mul);
        if (r>mid) modify(u<<1|1,l,r,add,mul);
        pushup(u);
        
    }
}

int query(int u,int l,int r)
{
    
    if (tr[u].l>=l&&tr[u].r<=r) return tr[u].sum;
        pushdown(u);
        int mid = tr[u].l+tr[u].r>>1;
        int sum=0;
        if (l<=mid) sum=query(u<<1,l,r)%p;
        if (r>mid) sum=(sum+query(u<<1|1,l,r))%p;
        return sum;
}
int main()
{
    
    scanf("%d%d", &n, &p);
    for (int i = 1; i <= n; i ++ ) scanf("%d", &a[i]);
    build(1,1,n);
    scanf("%d", &m);
    while (m -- )
    {
    
        int t,l,r,d;
        scanf("%d%d%d",&t,&l,&r);
        if (t==1)
        {
    
            scanf("%d", &d);
            modify(1,l,r,0,d);
        }
        else if (t==2)
        {
    
            scanf("%d", &d);
            modify(1,l,r,d,1);
        }
        else
        printf ("%d\n",query(1,l,r));
    }
    return 0;
}