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 Optionally, you can also play from the command line

Strength

See Releases

Version	Release Date	CCRL Blitz	CCRL 40/15
5.0	2023-10-27	N/A	2680
6.0	2024-02-17	N/A	2955

Features

• Board representation
  • BitBoards
  • Mailbox 8x8
  • Zobrist hashing
• Move Generation
  • Magic Bitboards for sliding pieces
  • hybrid pseudo-legal/legal move generation
• Evaluation
  • Tapered Evaluation
  • Material
  • Piece Square Tables
  • Tuning via Texel's Tuning Method
• 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
  • Quiescence Search
    • SEE Pruning
  • Transposition Table
  • Selectivity
    • Check Extension
    • 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
    • tt score adjustment
    • Lazy SMP

CLI Usage

• Type "uci" for the UCI protocol(not recommended for direct use, usually used by a chess GUI)
  • Protocol is explained here
• Type "cmdline" for the CLI protocol(Mainly for convenience in certain situations)
  • Protocol is explained below

Non-standard UCI commands

• "d"
  • Prints a string representation of the board from white's perspective
  • Prints out various statistics about the board
• "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.

Building

• C++20, CMake, and 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 the chess programming
• The Chess Programming Wiki, a bit outdated but nonetheless an excellent resource
• Stockfish
• Ethereal, one of the best references for chess programming
• Berserk, another good reference engine
• Weiss
• Crafty
• Zurichess
• The Engine Programming Discord Server, and the people in it
  • @JW, developer of Akimbo, 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

Command Line Protocol

• "position" {"fen" | "startpos"} [fenString]
  • Set the board position to the starting position or the fenString
• "print"
  • Print the current state of the board - Piece positions
    • Number of plies since the start of the game(starts at 0)
    • Half Move Clock
      • Used to detect 50 move rule draws
      • Draw at 100 half moves
      • Castling Rights
      • Side to move
    • Square of en passant, if available
    • Zobrist hash
• "move" <move>
  • makes a move
  • Standard Algebraic Notation(FIDE notation)
  • Square is a file (a-h) and rank(1-8)
  • Promotion piece is either, q(queen), r(rook), b(bishop), or n(knight)
• "undo"
  • Undo the last move that was made
• "eval"
  • Prints the static evaluation of the position
• "qeval"
  • Prints the quiescence search evaluation of the position
  • Currently not working
• "search" "depth" <depth>
• "search" "time" <time>
• "search" "infinite"
  • Performs an iterative deepening search up to depth, until time time, or until interrupted
  • Prints out the evaluation, node count, and PV of each depth
• "stop"
  • Stops the search
• "tests"
  • Runs test suite
  • Currently, only perft tests are run
• "perft" <depth>
  • Performs are perft up to depth
  • A perft(performance test) searches all moves up to depth and returns the number of positions reached
  • WARNING: time usage increases exponentially with depth
• "book"
  • Returns all the moves in the opening book
  • Opening book is currently hardcoded to "Sirius/res/gaviota_trim.pgn"
  • Prints "No moves in book found" if position is not in book