CubixChess Engine

CubixChess is a lightweight UCI chess engine, designed as a C++ translation of the engine I had written in Go (Simplex).

Features

Evaluation

The engine uses a NNUE evaluation function, with architecture (768 -> 128)x2 -> 1. It was trained with the Bullet trainer, using Leela self-play data.

Search

• Negamax with Alpha-Beta pruning
• Iterative deepening
• Principal variation search (PVS)
• Late move reductions (LMR)
• Quiescence search
• Transposition table
• Aspiration windows
• Move ordering with:
  • Hash move first
  • MVV-LVA
  • Killer heuristic
  • History heuristic
• Null-move pruning
• Reverse futility pruning
• Razoring
• Futility pruning
• Late move pruning
• Delta pruning

Chess internals

For move generation and board representation, the engine uses Disservin/chess-library (contained in header file chess.hpp).

UCI options

The only UCI option available is Hash to set the desired size (in MB) of the transposition table. The engine is single-threaded, hence it does not support the Threads option.

Building

1. First clone the repository:

   git clone https://github.com/Cubix1729/CubixChess.git
   cd CubixChess
   

2. Build the project using CMake:

   cmake -B build -DCMAKE_BUILD_TYPE=Release
   cmake --build build
   

   If your CPU does not support AVX2, then use cmake -B build -DCMAKE_BUILD_TYPE=Release -DUSE_AVX2=OFF

Special thanks

• Engines like PZChessBot or Weak for providing some inspiration
• Disservin for his great chess library
• jw1912 for the Bullet NNUE trainer
• linrock for the NNUE training data used (linrock/test80-2024)