Dragontooth Movegen | Dylan D. Hunn

Dragontooth Movegen is a fast, no-compromises chess move generator written entirely in Go. It provides a simple API for GenerateLegalMoves(). It also provides Board and Move types, Apply() and Unapply() functionality, and easy-to-use Zobrist-backed hashing of board positions. FEN parsing/serializing and Move parsing/serializing are supported out of the box.

Dragontoothmg is based on magic bitboards for maximum performance, and generates legal moves only using pinned piece tables.

This project is currently stable and fully functional. Optimizations are underway, to improve on the benchmarks listed below.

Repo summary

Here is a summary of the important files in the repo:

File	Description
movegen.go	This is the “primary” source file. Functions are located here if, and only if, they are performance critical and executed to generate moves in-game.
types.go	This file contains the Board and Moves types, along with some supporting helper functions and types.
constants.go	All constants for move generation are hard-coded here, along with functions to compute the magic bitboard lookup tables when the file loads.
util.go	This file contains supporting library functions, for FEN reading and conversions.
apply.go	This provides functions to apply and unapply moves to the board. (Useful for Perft as well.)
perft.go	The actual Perft implementation is contained in this file.

API

Here are significant API calls that this library provides. For invocation details, see the docs.

Function	Description
GenerateLegalMoves	A fast way to generate all moves in the current position.
Board.Apply	Apply a move to the board. Returns a function that allows it to be unapplied.
Perft	Standard “performance test,” which recursively counts all of the moves from a position to a given depth.
ParseFen	Construct a Board from a standard chess FEN string.
Board.ToFen	Convert a Board to a standard FEN string.
Board.Hash	Generate a hash value for a Board, using the Zobrist method.
ParseMove	Parse a long-algbraic notation move from a string.
Move.String	Convert a Move to a string, in normal long-algebraic notation.

Installing and building the library

This project requires Go 1.9. As of the time of writing, 1.9 is still a pre-release version. You can get it by cloning the official Go Repo, and building it yourself. There are instructions for this. (Once Go 1.9 comes out in a few weeks, this will become unnecessary.)

To use this package in your own code, make sure your GO_PATH environment variable is correctly set, and install it using go get:

go get github.com/dylhunn/dragontoothmg

Then, you can include it in your project:

import "github.com/dylhunn/dragontoothmg"

Alternatively, you can clone it yourself:

git clone https://github.com/dylhunn/dragontoothmg.git

Testing and benchmarking

To run all tests, cd into the directory and use:

go test -v

The -v shows verbose progress output, since some of the Perft tests can take some time.

To run benchmarks:

go run bench/runbench.go

Current benchmark results are around 60 million NPS (nodes per second) on a modern Intel i5. This significantly outperforms the best current Go chess engines, and is about 40% of the performance of the Stockfish move generator. (Not bad for a garbage-collected language!) Improvements are continually underway, and results will vary on your machine.

Documentation and examples

You can find the documentation here.

Here is a simple example invocation:

// Read a position from a FEN string
board := dragontoothmg.ParseFen("1Q2rk2/2p2p2/1n4b1/N7/2B1Pp1q/2B4P/1QPP4/4K2R b K e3 4 30")
// Generate all legal moves
moveList := board.GenerateLegalMoves()
// For every legal move
for _, currMove := range moveList {
    // Apply it to the board
    unapplyFunc := board.Apply(currMove)
    // Print the move, the new position, and the hash of the new position
    fmt.Println("Moved to:", &currMove) // Reference converts Move to string automatically
    fmt.Println("New position is:", b.ToFen())
    fmt.Println("This new position has Zobrist hash:", board.Hash())
    // Unapply the move
    unapplyFunc()
}