#include <iostream>
#include <algorithm>
#include <cassert>

using namespace std;

int main(int argc, const char * argv[]) {
    int tn;
    cin >> tn;
    assert(1 <= tn && tn <= 10000);
    while (tn--) {
        long long a, b, c, d;
        cin >> a >> b >> c >> d;
        assert(1 <= a && a <= 100000000000000LL);
        assert(1 <= b && b <= 100000000000000LL);
        assert(1 <= c && c <= 100000000000000LL);
        assert(1 <= d && d <= 100000000000000LL);
        long long t = abs(a - b);
        long long x = t % __gcd(c, d);
        long long y = __gcd(c, d) - x;
        cout << min(x, y) << endl;
    }
    return 0;
}