How to reverse bitwise AND (&) in C?

Question

How to reverse bitwise AND (&) in C?

For example I have an operation in C like this:

((unsigned int)ptr & 0xff000000))

The

Answer 1

You can't do that because you have thrown away information (i.e. bits) - you can't get information back from nowhere.

Note that both AND (&) and OR (|) are destructive. The only Boolean operations that are reversible are XOR (^) and NOT (~).

Answer 2

Impossible. Bitwise & of 0xff000000 is a lossy operation. You lose the lower 24-bits permanently.

Answer 3

You can only reverse XOR, as it's non-destructive.

Both OR and AND are destructive.

Answer 4

Bitwise & can't be reversed:

0 & 1 = 0
0 & 0 = 0