快速乘？

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll rd()
{
    return rand()|(ll(rand())<<32);
}
ll md;
ll mul1(ll x,ll y)
{
    x%=md;y%=md;
    ll t=x*y-ll((long double)x/md*y+0.5)*md;
    return t<0?t+md:t;
}
ll mul2(ll x,ll y)
{
    x%=md;y%=md;
    ll t=x*y-ll((long double)x*y/md+0.5)*md;
    return t<0?t+md:t;
}
ll mul3(ll x,ll y)
{
    x%=md;y%=md;
    ll t=x*y-ll((long double)x/md*y+1e-8)*md;
    return t<0?t+md:t;
}
ll mul0(ll x,ll y)
{
    return __int128(x)*y%md;
}
ll a,b;
int main()
{
    int T=0;
    srand(3254244);
    while(1)
    {
        T++;
        ll a=rd(),b=rd();
        md=rd();//%ll(1e18);
        //cout<<a<<‘ ‘<<b<<‘ ‘<<md<<‘\n‘;
        ll t1=mul1(a,b),t2=mul0(a,b);//可将mul1改为mul2/mul3
        //cout<<t1<<‘ ‘<<t2<<‘\n‘;
        if(t1!=t2)
        {
            printf("%d\n",T);
            puts("test");
            int t;cin>>t;
        }
        //int t;cin>>t;
    }
    return 0;
}