What is the reverse operation of bitwise AND?

Question

How can I get a from b and c? What would be the reverse operation?

Here is the code:

class  s
{
    public static void main(String ar[])
    {

        int a = 20;

        int b = 5;

        int c = 0;

        c = (a & b) ;

        System.out.println(c);

        int d = (c & b);

        System.out.println(d);
    }
}

Answer 1

You can't. If a bit in c is 0 and the corresponding bit in b is 0, it's impossible to know whether the corresponding bit in a was 0 or 1. By a similar argument, bitwise OR (the | operator) is also irreversible. On the other hand, bitwise XOR (the ^ operator) is reversible.