#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int T;
    cin >> T;
    while(T--){
        ll n, x, S = 0;
        cin >> n >> x;
        ll ans = 0;
        for(int i = 0; i < n; i++){
            int v;
            cin >> v;
            S |= 1ll << v;
        }
        S &= ~x;
        if(S == 0){
            cout << 0 << '\n';
            continue;
        }
        ll T = 1ll << __lg(S);
        ans = T - (x & (T - 1));
        if(S <= x){
            for(int i = 0; i < 60; i++){
                if(S >> i & 1) continue;
                if(S + (1ll << i) <= x) S += 1ll << i;
            }
            ans = min(ans, x - S);
        }
        cout << 2 * ans << '\n';
    }
}