Sirius

A UCI chess engine written in c++. Sirius does not come with a gui. To play against it, you should download a chess GUI that supports the Universal Chess Interface(UCI) protocol

Strength

See Releases

Version	Release Date	CCRL Blitz	CCRL 40/15
5.0	2023-10-27	N/A	2677
6.0	2024-02-17	N/A	2965
7.0	2024-07-09	N/A	3224
8.0	2024-10-05	3444	N/A

Usage

Sirius can be used with any UCI Chess GUI or matchrunner including Arena, Cutechess, Cutechess-cli, Fastchess, Banksia, and more. You can also play it on Lichess(Though it's not online very often)

Features

• Board representation
  • BitBoards
  • 8x8 Mailbox
  • Zobrist hashing
• Move Generation
  • Magic Bitboards for sliding pieces
  • Hybrid pseudo-legal/legal move generation
• Evaluation
  • Tapered Evaluation
  • Incrementally updated evaluation
  • Tempo bonus
  • Material
  • Piece Square Tables
    • Horizontally mirrored
  • Mobility
  • Threats
  • Knight outposts
  • Rook on semi-open/open file
  • Minors behind pawns
  • Bishop pair
  • Bishop same color pawns
  • Pawn Structure
    • Passed pawns
    • Isolated pawns
    • Defended pawns
    • Pawn phalanxes
    • Passed pawn Distance to Kings
  • King Safety
    • King-pawn storm/shield
    • Safe and unsafe checks from enemy pieces
    • King ring attacks
  • Complexity eval
  • Endgame scaling
  • Tuning via Texel's Tuning Method
    • https://github.com/mcthouacbb/Sirius-Tune-2
• Search
  • Fail-soft Alpha-Beta Pruning
  • Iterative Deepening
  • Aspiration Windows
  • Mate Distance Pruning
  • Move Ordering
    • TT Move Ordering
    • MVV LVA
    • SEE Move Ordering
    • Killer Moves Heuristic
    • History Heuristic
    • Continuation History
    • Capture History
  • Quiescence Search
    • SEE Pruning
    • Quiescence Search Futility Pruning
    • Quiescence Search Late Move Pruning
  • Transposition Table
  • Selectivity
    • Check Extensions
    • Singular Extensions
      • Multicut
      • Double Extensions
      • Negative Extensions
    • Principal Variation Search(PVS)
      • 3 Fold LMR
    • Reverse Futility Pruning
    • Null Move Pruning
    • Futility Pruning
    • Late Move Pruning
    • History Pruning
    • SEE Pruning
    • Late Move Reductions
    • Internal Iterative Reductions
  • Miscellaneous
    • Improving Heuristic
    • Node count time management
    • Best move stability time management
    • tt score adjustment
    • Various static evaluation correction histories
    • TTPV
    • Staged move generation
    • Lazy SMP

Non-standard UCI commands

• "d"
  • Prints a string representation of the board from white's perspective
  • Prints out various statistics about the board
• "perft <depth>"
  • Runs a perft, which counts the number of leaf nodes of a brute force depth search
• "eval"
  • Prints the static evaluation of the current position
• "bench"
  • Runs an depth 15 search on a set of internal benchmark positions and prints out the number of nodes and number of nodes searched per second.

UCI options

Name	Type	Default value	Valid values	Description
Hash	integer	64	[1, 65536]	Size of the transposition table in Megabytes.
Threads	integer	1	[1, 256]	Number of threads used to search.
MoveOverhead	integer	10	[1, 100]	Amount of time subtracted to account for overhead between engine and gui.
PrettyPrint	boolean	false	true, false	Whether to pretty print uci output. Defaults to true if UCI is not first command

Building

Do not use the Makefile, it is intended for building with OpenBench only

• C++20, CMake, and a decent C++ compiler required
• If you have ninja and clang, you can build the release builds by running the following commands

  cmake --preset ninja-clang-x86-64-v<version>
  cmake --build build/x86-64-<version>
  

  where <version> is 1-4. You can also use the other presets, though they are mainly a convenience feature.
• If you would like to build with your own settings, feel free to do so.
  • On their own, the CMake files only define what is absolutely necessary to build Sirius(With the exception of a flag that links msvc std lib statically), so you don't have to change the build files to build Sirius yourself

Credits/Thanks

• Sebastian Lague, for getting me into chess programming
• The Chess Programming Wiki, very outdated but has some good ideas, especially for move generation/board representation
• OpenBench, an very well made distributed SPRT testing framework for chess engines
• Stockfish
• Ethereal, one of the best references for chess programming
• Berserk, another good reference engine
• Weiss
• Stash
• Crafty
• Zurichess
• The Engine Programming Discord Server, and the people in it
  • @JW, developer of Akimbo, Bullet, and Monty, helped me a ton with developing and testing the engine
  • @Ciekce, developer of Stormphrax, who, along with JW, taught me many things about Chess Programming, and is an excellent c++ programmer
  • @Alex2262, developer of Altaire
  • @Cj5716, general contributor to many engines
• The Stockfish Discord Server
• The Sebastian Lague Chess-Challenge Discord Server
  • Not a direct resource, but led to me finding many of the above mentioned resources
• Rustic Chess Blog, currently a WIP but it has excellent explanations for the techniques it does explain.
• Many others