Chessna

Chessna is a simple chess engine that is designed to beat most human players.

Features

Move Generation:

• Bitboards

Search:

• Iterative deepening in combination with Alpha-Beta Search
• Quiescence Search
• Transposition Table
• Move ordering (MVV-LVA, Killer moves, Promotions, Castling, best move from last iteration)
• Late Move Reduction
• Null-move heuristic (still experimental)

Evaluation:

• material difference
• position score (slightly different for endgame)
• Mop-up evaluation

Other:

• UCI (Universal chess interface): needed to communicate with lichess
• Pondering (think on opponent's time)

How to test the engine

Compile the engine and run it:

make 
build/chessna

Chessna uses UCI (partially implemented) for communication. You can setup the start position or any custom position using the according FEN followed by the moves:

position startpos moves e2e4 e7e5 

To calculate the best move for a certain depth type:

position 8/6p1/5n1p/3rpk2/1PB2b2/5P2/5PK1/8 b - - 0 52 
go depth 9

To calculate the best move given a time limit (in ms) type:

position 8/6p1/5n1p/3rpk2/1PB2b2/5P2/5PK1/8 b - - 0 52 moves d5d2 c4a6 
go movetime 10000

Note: The engine will only use 90% of the given time to calculate the best move. You can also tell the engine its remaining time (in ms) for a match and it will adjust its move time accordingly:

position 8/6p1/5n1p/3rpk2/1PB2b2/5P2/5PK1/8 b - - 0 52 moves d5d2 c4a6 
go wtime 300000 btime 300000 

Furthermore you can add an increment:

position 8/6p1/5n1p/3rpk2/1PB2b2/5P2/5PK1/8 b - - 0 52 moves d5d2 c4a6 
go wtime 300000 btime 300000 winc 2000 binc 2000 

You can also use a GUI to run Chessna. So far I've only tested that it works with Lichess as I use lichess-bot to let Chessna play against other bots and players.

Features to implement in the future:

• LAZY SMP: multithreading
• Opening Book
• better evaluation (king safety, mobility, pawn structure, ...)
• improve move generation (use array instead of vector, magic bitboards etc.)