Sarun_2_7 (UCI Compatible Chess Engine)

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A UCI-compatible chess engine written in C++.

Key MileStones

• Parses FEN and setups board internally
• Legal Move Generation in a given position and core engine system
• Achieved Search speed of 2.65M nodes/sec, validated via Basic & Perft testing
• Core Engine Logic: Implemented Zobrist Hashing, a Transposition Table for PV retrieval, and a move-ordering system Heuristics.
• UCI compatible and deployed it as a Lichess bot
• Integrated Polyglot Support: Implemented PolyKey generation and integrated komodo.bin for high-performance opening theory.

Overview

• Protocol: UCI (Universal Chess Interface)
• Language: C++ Build System: Make
• Start date: July 8, 2025
• Run targets:
  • UCI GUIs
  • Lichess via python lichess API

Features

Search

• Iterative deepening (SearchPosition)
• Alpha-beta search (AlphaBeta)
• Quiescence search on captures (Quiescence)
• Basic repetition / 50-move detection
• Null move pruning (R=3)
• Late move reduction (LMR)

Move ordering

• MVV-LVA capture scoring
• Killer moves
• History heuristic

Opening Book

• Format: Polyglot/Komodo binary books (e.g. komodo.bin).
• Usage: Place a book at openingBook/komodo.bin or set the POLYBOOK environment variable to a custom path.
• Behavior: When present the engine will load the book at startup and prefer book moves (weighted-random selection) before running the search.

Evaluation

• Material + piece-square tables (PST)
• Bishop pair bonus
• King safety / castling related terms
• Hanging piece penalties (with stronger opening penalties for hanging minors)
• Endgame-only passed pawn bonus

Hashing / transposition table

• Zobrist keys
• PV / hash move probing and storage

Time management (UCI)

• Parses go wtime/btime/winc/binc/movestogo/movetime/depth/infinite
• Sets a stoptime and stops search when time is exceeded
• Auto-reduces depth in very low time situations when depth is not specified

Project structure

src/ contains the engine implementation:

• uci.cpp: UCI loop + command parsing
• search.cpp: alpha-beta, quiescence, iterative deepening, time stop checks
• evaluate.cpp: evaluation function and terms
• movegen.cpp: move generation
• makemove.cpp: make/take moves
• moveorder.cpp: move scoring / ordering
• pvtable.cpp: transposition table and PV line handling
• init.cpp: initialization tables
• misc.cpp : to retrieve the current time in milliseconds
• attack.cpp: attack detection
• board.cpp: board parsing / FEN
• defs.h, struct.h: core constants and structures

Build instructions

Windows (MinGW-w64 / MSYS2)

Requirements:

• g++ (MinGW-w64)
• make (optional)

From the project root:

g++ -O2 -std=c++17 -Isrc src/*.cpp -o sarun.exe

Usage

Run as a UCI engine

./sarun

Example UCI session:

uci
isready
ucinewgame
position startpos
go wtime 60000 btime 60000 winc 0 binc 0 movestogo 30

Supported UCI commands

• uci
• isready
• ucinewgame
• position startpos [moves ...]
• position fen <fen> [moves ...]
• go depth N
• go movetime MS
• go wtime MS btime MS winc MS binc MS movestogo N
• go infinite
• stop
• quit

Motivation

This project was built to deeply understand:

• Low-level performance-oriented C++ systems
• Game Theory, Game tree search and optimization techniques
• Caching, hashing, and time-constrained decision making
• Debugging complex states and iterative development

Rather than using existing engines, everything was implemented from scratch to gain hands-on experience with real-world algorithmic trade-offs.

Credits & Links

• Stockfish for inspiration
• Chess Programming Wiki — implementation references and techniques
• BlueFever Software (VICE) for the educational foundation and core Algorithms
• Chess Stack Exchange - For community expertise and technical problem-solving.

#Opening Theory

• Polyglot format — For polyKey Generation and opening book interoperability based on the standard Polyglot specifications.
• Komodo Chess — This engine uses the komodo.bin Polyglot book provided by Komodo Chess to handle opening theory.