pokerlib

A library of poker primitives in go

Features:

• Foundation data types for Card, Hand and Deck
• Hand ranking. Calculates best 5 card hand out of any set of cards.
• Hand rank encoding
• English language hand descriptions Ex: Full house, Kings full of 8's, An Ace high flush, etc.]]
• Hand evaluation logging
• Odds calculations

Rank representation:

Each 5 card hand has a unique 32-bit encoding, this value is called the Hand Rank.
The 32 bits contains info about the type of hand (Flush, straight, etc), as well as the index of each of the 5 cards. The encoding is arranged such that a better hand will be represented by bigger value (interpreting the handrank bits as a 32-bit unsigned int with simple BCD encoding)

32 bit encoding:

  bits 27-20 contains the hand kind 
  bits 19-16 card
  bits 15-12 card
  bits 11-8  card
  bits 7-4   card
  bits 3-0   card

Each card in the hand is represented as a 4 bit value. The least signaficant 20 bits of the rank represent the 5 cards in order of hand evaluation signficance. I.e. for a pair, the 2 cards in the pair are the left most 2 cards, no matter if they are Kings or 2's...

Examples:   

            hand:   A♥ A♣ K♦ K♣ Q♥   (2 Pair, Ace's and King's)

            (2 pair)     (Ace)  (Ace)  (King)  (King) (Queen)
    rank:   00000011     1110   1110   1101    1101   1100       = 4124124


            hand:   2♥ 2♣ 2♦ 7♣ 7♥   (2 Pair, Ace's and King's)

            (Full House) (Two)  (Two)  (Two)  (Seven) (Seven)
    rank:   00000111     0010   0010   0010   0111    0111      = 7479927

Hand odds

Win and Tie probabilities can be calculated given a set of hand hole cards, and additionally 0-5 common cards and a deck.

The Monte Carlo method is used.