#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001

int main(){
	
	int _t;
	cin>>_t;
	
	rep(_,_t){
		long long n,x;
		cin>>n>>x;
		long long f = 0;
		rep(i,n){
			int a;
			cin>>a;
			f |= 1LL<<a;
		}
		long long ox = x;
		rep(i,60){
			if((x>>i)&1){
				f &= ~(1LL<<i);
			}
		}
		if(f==0){
			cout<<0<<endl;
			continue;
		}
		long long msb = 0;
		rep(i,60){
			if((f>>i)&1)msb = 1LL<<i;
		}
		long long ans = Inf64;
		if(ox>=msb){
			/*long long t = ox;
			rep(i,60){
				if((1LL<<i)<=msb){
					t |= 1LL<<i;
				}
				else{
					if((t>>i)&1){
						t ^= 1LL<<i;
						break;
					}
				}
			}
			ans = min(ans,abs(t-ox));*/
		}
		rep(i,60){
			if((1LL<<i)>=msb){
				x &= ~(1LL<<i);
			}
		}
		ans = min(ans,abs(msb-x));
		if(msb<=ox){
			ans = min(ans,x+1);
		}
		cout<<ans*2<<endl;
	}
	
    return 0;
}