使用一个数字移位4位

Question

I have to write a method that takes in an integer as a parameter (0, 1, 2, or 3). I have to use that to create a bitmask with a 0. So, if the parameter is 0, than the bitmask will be FFF0 , for 1: FF0F , 2: F0FF , 3: 0FFF . I am trying not to hardcode it.

What I have tried, but it only works partially:

int bob = 0xFFFF;
int multi = 2;

multi = multi << param;

this works with 1 and 2, and for even those, it makes it 0xFF00 , and 0xF000 .

I am trying not to use multiplication either (that would make it a lot easier, so I don't want to use it).

Answer 1

我会说：

0xFFFF - (0xF << (param * 4))

Answer 2

Something like this:

bitmask = 0xFFFF;
bitmaskmask = 0xF;
bitmaskmask = bitmaskmask << parameter * 4;
bitmask = bitmask ^ bitmaskmask;

Answer 3

Given your inputs, you can achieve what you are looking for using the bitwise XOR operation as follows:

xorMask = 0x000F << (4*multi) ;
result = bob ^ xorMask ;

This creates an XOR mask with 1 bits in the appropriate portion of the 16 bit value, then XORing it with the input to 0 those bits in the output.