for _ in range(int(input())):
    n, x = map(int, input().split())
    c = map(int, input().split())
    mx = -1
    for ci in c:
        if x >> ci & 1 == 0:
            mx = max(mx, ci)
    if mx == -1:
        print(0)
        continue
    tgt = ((x & ((1 << mx) - 1)) ^ x) | (1 << mx)
    ans = tgt - x
    tgt -= (1 << mx) + 1
    if tgt >= 0:
        ans = min(ans, x - tgt)
    print(2 * ans)