for _ in range(int(input())):
    n,x = map(int,input().split())
    l = [x]; r = [x]; z = 1<<61
    for v in map(int,input().split()):
        if x>>v&1: l.append(v); r.append(v)
        else: y = (1<<v)-1&x^x; l.append(y-1); r.append(y|1<<v)
    for p in l:
        if p<0: continue
        q = x
        for li,ri in zip(l,r):
            if li<p: q = max(q,ri)
        z = min(z,2*(q-p))
    print(z)