#include <bits/stdc++.h>
using namespace std;
using int64 = long long;
 
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int T;
    cin >> T;
    while(T--){
        int n;
        int64 a, b;
        cin >> n >> a >> b;
        vector<int64> c(n);
        for(int i = 0; i < n; i++)
            cin >> c[i];
 
        int64 g = __gcd(a, b);
        int64 C = *max_element(c.begin(), c.end());
        int64 R = C % g;
 
        int64 ans = 0;
        for(int i = 0; i < n; i++){
            int64 r = c[i] % g;
            int64 diff = (R - r + g) % g;
            ans = max(ans, diff);
        }
 
        cout << ans << "\n";
    }
 
    return 0;
}
 

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10
4 5 5
1 3 4 4
4 2 3
1 3 4 6
4 7 7
1 1 2 6
3 15 9
1 9 5
3 18 12
1 4 5
7 27 36
33 13 23 12 35 24 41
10 6 9
15 5 6 9 8 2 12 15 3 8
2 1 1000000000
1 1000000000
6 336718728 709848696
552806726 474775724 15129785 371139304 178408298 13106071
6 335734893 671469786
138885253 70095920 456876775 9345665 214704906 375508929