I implemented a poker calculator many years ago, here are some things that I learned.

You can get excellent performance by representing cards as bits. A hand can be composed of 4 `u13`

, each one representing one suit. Bit 0 represents card 2 and bit 12 represents an Ace. Testing for a flush can be done by checking if the pop count of a suit is at least 5. Testing for a straight can be done by or’ing all suits and checking if the set bits are contiguous. Checking for a pair can be done by and’ing each pair of suits and checking if any of these is different from 0.

If you want to compare hands to determine the winner, you don’t want to test each hand agaisn’t each other hand, as that would result in combinatorial explosion. It’s better to set a score. Then it’s just a matter of finding the highest score, which is linear. Here’s the best way that I found for this: consider a hexadecimal number with 6 digits. Since there are 9 possible hand types, you can assign an exclusive number for each. 0 is a high card, 1 is a pair and so forth. The higher the number, the stronger the hand. If you put this number in the highest order digit (6th digit), a hand with a stronger hand type will always have a score higher than a weaker hand. For example, a pair could be assigned number 0x110000 (the most significant 1 represents a pair), while a high card could be assigned number 0x0BA987 (the 0 represents a high card). The following digits you fill by assigning the strongest cards that participate in the hand. Since there are 13 cards, you can also assign an exclusive digit for each. Here are some examples:

Hand A: 2 of spades, 2 of hearts, 3 of spades, 3 of hearts, king of hearts, queen of spades, 7 of clubs

(2 cards in hand, 5 on the table, it doesn’t matter which oneis which).

The hand type is two pairs, so the most significant digit is 2. The first tie breaker would be the 3, so we assign it number 1. The second tie breaker would be the 2, so we assign it number 0. The last tie breaker would be the king, number 0xB. The other cards don’t participate, so we pad the remaining two digits with 0. Te score would be 0x210B00

Hand B: 8 of diamonds, 4 of hearts, 3 of spades, 3 of hearts, king of hearts, queen of spades, 7 of clubs

(2 cards in hand, 5 on the table, it doesn’t matter which one is which).

The hand type is one pair, digit 1. The first tie breaker is 3, digit 1. Second tie breaker is king, digit 0xB. Third tie breaker is queen, digit 0xA. Fourth tie breaker is 8, digit 6. Other cards don’t participate, so the last digit is 0. The score is 0x11BA80

Since 0x210B00 > 0x11BA80, hand A wins.