t = int(input())
for _ in range(t):
    n, x = map(int, input().split())
    c = list(map(int, input().split()))
    ans = 0
    for i in c:
        if x & (1 << i):
            continue
        plus = ((x >> i) + 1) << i
        minus = ((x >> i) << i) - 1
        if (minus < 0 and ans < (plus - x) * 2):
            ans = (plus - x) * 2
        elif (minus >= 0 and ans < min(plus - x, x - minus) * 2):
            ans = min(plus - x, x - minus) * 2
    print(ans)