What are your favorite bit hacks?

Besides the obvious set/get/clear bit mask (e.g. byte |= (1 << bit_we_want_to_set)).

Mine would be determining if an integer is a power of 2. Instead of using some
unnecessary complex loop, we simply do:
x && ((x & (x - 1)) == 0);

Simple, but clever. If you are nub (most likely are), read up more on bit manipulation/twiddling/hack, etc.

>>3
I'll have you know I graduated top of my class in the bit twiddlers and I have performed over one hundred bit twiddles, and that is just with my pen and paper.