#include <bits/stdc++.h>   using namespace std;   int main() {     int t;     long long x, y, p, q;     cin >> t;     while (t--) {       cin >> x >> y >> p >> q;       long long l = 0, h = 1e9, ans = -1, mid, a, b;       while (l <= h) {         mid = (l + h) / 2;         a = p * mid;         b = q * mid;         if (b >= y && a >= x && b - a >= y - x) {           ans = b - y;           h = mid - 1;         } else           l = mid + 1;       }       cout << ans << endl;     }     return 0;   }   