func_code_string: #include <bits/stdc++.h>   using namespace std;   long long gcd(long long a, long long b) {     if (b == 0) {       return a;     }     return gcd(b, a % b);   }   signed main() {     long long n;     cin >> n;     for (long long i = 0; i < n; i++) {       long long a, b, c, d;       cin >> a >> b >> c >> d;       long long x = gcd(c, d);       c /= x;       d /= x;       if (c == 0 && a != 0) {         cout << -1 <<   n ;         continue;       }       if (c == 0 && a == 0) {         cout <<  0 n ;         continue;       }       if (c == d && a != b) {         cout << -1 <<   n ;         continue;       }       if (c == d && a == b) {         cout <<  0 n ;         continue;       }       long long l = (a + c - 1) / c - 1;       long long r = (long long)2e18 / d;       while (r - l > 1) {         long long m = (r + l) / 2;         if (m * d >= b + m * c - a) {           r = m;         } else {           l = m;         }       }       cout << r * d - b <<   n ;     }   }   