Reckless – Chess Engine in Rust

Reckless is a UCI chess engine written in Rust as a personal project.

Guided by the insights from the chess programming community, it fearlessly combines established concepts with its reckless nature, as the name suggests.

Rating

Version	CCRL Blitz	CCRL 40/15	Release Date
Reckless v0.7.0	3505 +/- 16 [#59]	3407 +/- 25 [#61]	Aug 23, 2024
Reckless v0.6.0	3386 +/- 16 [#78]	3318 +/- 16 [#83]	Mar 22, 2024
Reckless v0.5.0	3243 +/- 19 [#94]	3213 +/- 21 [#94]	Feb 4, 2024
Reckless v0.4.0	2933 +/- 19 [#151]	2929 +/- 21 [#158]	Dec 13, 2023
Reckless v0.3.0	2617 +/- 20 [#229]	2615 +/- 21 [#251]	Nov 6, 2023
Reckless v0.2.0	2358 +/- 19 [#333]		Oct 7, 2023
Reckless v0.1.0	2020 +/- 20 [#471]		May 16, 2023

Getting started

Precompiled binaries

You can download precompiled builds from the GitHub Releases page.

• x86_64-v1: Slowest, compatible with any x86-64 CPU.
• x86_64-v2: Faster, requires support for POPCNT, SEE3, etc.
• x86_64-v3: Even faster, requires support for AVX2, etc.
• x86_64-v4: Fastest, requires support for AVX512.

For detailed information on the specific features needed for each level, refer to the x86-64 microarchitecture levels Wikipedia page.

Building from source

1. Make sure you have Rust 1.70.0 or a later version installed. If not, follow the official Rust installation guide.

2. Download the latest NNUE model either from the Reckless Networks repository or by running the following command:

# Fetch the latest NNUE model
make fetch

3. To build the engine, a compatible model must be present in ./networks/model.nnue. If the model is located elsewhere, specify the path manually:

# Build the engine
make

# Optionally, specify a custom path for the model file
make EVALFILE=path/to/model.nnue

Troubleshooting

If you're getting a cannot transmute between types of different sizes error, it's due to a mismatch between the model and the engine's architecture. In this case, update the source code and fetch the latest model.

Usage

Reckless is not a standalone chess program but a chess engine designed for use with UCI-compatible GUIs, such as Cute Chess or ChessBase.

Custom commands

Along with the standard UCI commands, Reckless supports additional commands for testing and debugging:

Command	Description
perft <depth>	Run a perft test to count the number of leaf nodes at a given depth
bench <depth>	Run a benchmark on a set of positions to measure the engine's performance
eval	Print the static evaluation of the current position from white's perspective

Features

Board representation

• Bitboards with Little-Endian Rank-File Mapping
• Magic Bitboards for sliding piece attacks
• Copy-Make approach

Move generation

• Pseudo legal move generator
• Pre-calculated attack maps using Fancy Magic Bitboards
• Magic numbers are pre-generated using Reckless Magics
• Compile time generation of move maps using a build script

Search

• Fail-Soft Alpha-Beta
• Principal Variation Search
• Quiescence Search
• Iterative Deepening
• Aspiration Windows
• Lockless Transposition Table
• Lazy SMP (Shared-Memory Parallel)

Selectivity

Pruning

• Reverse Futility Pruning
• Null Move Pruning
• Razoring
• Futility Pruning
• Late Move Pruning
• Delta Pruning
• Static Exchange Evaluation Pruning
• Mate Distance Pruning

Reductions

• Fractional Late Move Reductions
• Internal Iterative Reductions

Extensions

• Check Extensions

Move ordering

• Hash Move
• Killer Move Heuristic
• SEE with MVV-LVA as a tiebreaker for captures
• History Heuristic for quiet moves
  • Butterfly History
  • Counter Move History
  • Follow-Up History

Evaluation

• NNUE
• Architecture: (768 -> 384)x2 -> 1x4
• Activation Function: SCReLU (Squared Clipped Rectified Linear Unit)
• Quantization: i16 (256, 64)
• Trained on original data generated entirely through self-play
• Handwritten SIMD for AVX2 instructions

Time management

• Soft and hard bounds
• Best move stability
• Evaluation stability
• Distribution of root nodes

Acknowledgements

• OpenBench is the primary testing framework powered by Cute Chess.
• Open source chess engines, like Stockfish, Ethereal, Berserk, and numerous others, for serving as inspiration and providing ideas that fuel development.
• Stockfish Discord server members for providing relevant insights and feedback.
• Chess Programming Wiki for contributing to the project's foundation.
• Many thanks to the CCRL team and all chess engine testers for their valuable contributions.

License

This project is licensed with the MIT license.