Question

I’d need to perform a bitwise operation (or a serie) so that:

0 1 = 0
1 1 = 1
1 0 = 0

so far AND (&) works fine but I also need that

0 0 = 1

and here AND (&) is not the correct one.

I’m using it in a jquery grep function that reads:

jQuery.grep(json, function (e, index) {
            return (e.value & (onoff << 3)) != 0;
        });

where onoff could be either 1 or 0 and e.value is a representation of a 4 bits string (i.e. could be “1001”). In this above example I’m testing first bit on the left (<< 3).

Can this be done with a serie of AND, OR, XOR?

Answer 1

This is just XNOR(a, b), which is equal to NOT(XOR(a, b)), i.e. exclusive OR with the output inverted. In C and C-like languages this would be:

!(a ^ b)

or in your specific case:

return !((e.value >> 3) ^ onoff);

Having said that, you could just test for equality:

return (e.value >> 3) == onoff;