Problem Description
Claris loves bitwise operations very much, especially XOR, because it has many beautiful features. He gets four positive integers a,b,c,d that satisfies a≤b and c≤d. He wants to choose two integers x,y that satisfies a≤x≤b and c≤y≤d, and maximize the value of x XOR y. But he doesn't know how to do it, so please tell him the maximum value of x XOR y.
Input
The first line contains an integer T(1≤T≤10,000)——The number of the test cases.
For each test case, the only line contains four integers a,b,c,d(1≤a,b,c,d≤1018). Between each two adjacent integers there is a white space separated.
Output
For each test case, the only line contains a integer that is the maximum value of x XOR y.
Sample Input
2
1 2 3 4
5 7 13 15
Sample Output
6
11
https://blog.csdn.net/yeweiyang16/article/details/51115393
1 2 3 4 : x=0010 , y=0100 > x xor y =0110
5 7 13 15: x=0101 , y=1110 > x xor y =1011
有两个思路： 1。从高位向低位逐步推导；
2。把所有可能的x和y都列出来， 遍历判断。