Steve Brecher's Holdem Showdown:

BHS

Card Representation: 64 bits : ...AKQJT98765432 repeated 4 times, once per suit.
Hand Representation: 64 bits : 7 cards OR'd together.
Hand Value: 32 bits : 0x0R0CCCCC. R=HandRank, C=significant card(12=A,0=2)

This evaluator uses a different bit to represent each card, two 13-bit lookup tables, and a lot of fast bit tricks to do the evaluation. The first step is to separate the hand into suits, then OR each suit together. This will result in a word with between 2 and 7 bits set. Looking up the word in the nbrOfRanks table returns that bit count, representing the number of unique card ranks. Knowing this lets you narrow the remainder of the evaluation. For example: only 2 unique ranks means you have "quads with trips kicker". so you can AND the suits together to find which card you have 4 of. 3 unique ranks means you have either full house or quads. You can refine further XORing the four suits together, which gives you the bits that are set 1 or 3 times - triples and singletons. And so on. Once you get over 5 unique ranks you also need to check for straights and flushes, which is done with the 'mStraitAndOrFlush' macro. It uses the nbrOfRanks table again to check the number of cards in each individual suit, calling it a flush if there are 5 or more. It uses a straightValue table on either the flush suit or on all cards to find straights. This table returns the high card for any input with 5 bits in a row, or 0 if no straight exists.

This evaluator also contains 5,6, and 8 card evaluators, as well as lowball variants like Razz.