PH Evaluator
A Poker Hand Evaluator based on a Pefect Hash Algorithm
Overview
Efficiently evaluating a poker hand has been an interesting but challenging problem. Given two different poker hands, how to determine which one is stronger? Or more generally, given one poker hand, can we assign a score to it indicating its strength?
Cactus Kev once gave an answer for a five-card poker hand evaluation. With smart encoding, it ranks each hand to 7462 distinct values.
Still, Kev's solution is specific for a five-card hand. To evaluate a seven-card poker hand (which is more popular because of Texas Hold'em) using Kev's algorithm, one brute force solution is to iterate all 7 choose 5 combination, running his five-card evaluation algorithm 21 times to find the best answer, which is apparently too time-inefficient. Omaha poker would be even more complicated, as it requires picking exactly two cards from four player's cards, and exactly three cards from five community cards. Using brute force, it would take 60 iterations (5 choose 3 multiplied by 4 choose 2) of Kev's 5-card evaluation algorithm.
PH Evaluator is designed for evaluating poker hands with more than 5 cards. Instead of traversing all the combinations, it uses a perfect hash algorithm to get the hand strength from a pre-computed hash table, which only costs very few CPU cycles and considerably small memory (~100kb for the 7 card evaluation). With slight modification, the same algorithm can be also applied to evaluating Omaha poker hands.
Algorithm
This documentation has the description of the underlying algorithm.
C/C++ Implementation
The cpp subdirectory has the C/C++ implementation of the algorithm, offering evaluation from 5-card hands to 7-card hands, as well as Omaha poker hands.
One of the latest benchmark report generated by Google Benchmark:
2020-05-25 03:29:00
Running ./benchmark_phevaluator
Run on (2 X 2800.16 MHz CPU s)
CPU Caches:
L1 Data 32 KiB (x1)
L1 Instruction 32 KiB (x1)
L2 Unified 1024 KiB (x1)
L3 Unified 33792 KiB (x1)
Load Average: 0.84, 0.29, 0.11
-------------------------------------------------------------------
Benchmark Time CPU Iterations
-------------------------------------------------------------------
EvaluateAllFiveCards 42539892 ns 42539339 ns 16
EvaluateAllSixCards 358763068 ns 358754423 ns 2
EvaluateAllSevenCards 2712988225 ns 2712943774 ns 1
EvaluateRandomFiveCards 1924 ns 1924 ns 366811
EvaluateRandomSixCards 2031 ns 2031 ns 347350
EvaluateRandomSevenCards 2296 ns 2296 ns 306389
EvaluateRandomOmahaCards 3709 ns 3709 ns 189019| Number of Hands | Time Used | Hands per Second | Memory Used | |
|---|---|---|---|---|
| All 5-card Hands | 2598960 | 42539892 ns | 61 M/s | 404K |
| All 6-card Hands | 20358520 | 358763068 ns | 56 M/s | 404K |
| All 7-card Hands | 133784560 | 2712988225 ns | 49 M/s | 404K |
| Random 5-card Hands | 100 | 1924 ns | 51 M/s | 404K |
| Random 6-card Hands | 100 | 2031 ns | 49 M/s | 404K |
| Random 7-card Hands | 100 | 2296 ns | 43 M/s | 404K |
| Random Omaha Hands | 100 | 3709 ns | 26 M/s | 404K |
- I didn't measure the memory properly. Basically 404K is the maximum memory used in all the evaluation methods.
- The performance on random samples are slightly worse due to the overhead of accessing the pre-generated random samples in the memory.
Python Implementation
The python subdirectory has the latest Python implementation, which is still in active development. Contributions are welcome.
Other Implementations
PHE is a Javascript port, developed by Thorsten Lorenz.
41Poker is another Javascript port, developed by 41semicolon.