in reply to A (memory) poor man's <strike>hash</strike> lookup table.

Maybe I'm being brain-dead here (wouldn't be the first time), but you start off with a hash of a million integer keys, but you end up with something much less useful than a hash. No associated values, and no guarantee of a million unique "keys" unless you use the two-pronged test during insertion. It may or may not function as a memory efficient "set", but it isn't a hash (not even a poor man's hash).