Oh you just use public keys.

Just change the nkeys variable at the top to be the number of keys you want to receive (and make sure bits_toinspect is greater than or equal to log2(nkeys).)

That's equivalent to knowing the very lowest bit of the private key so you've effectively reduced your search range by a power of 2 e.g. 2^60 --- 2^59. It's not useful enough in a practical setting though. Not to mention there isn't a foolproof way to guess the private key's parity in the first place.