Nyx Chess Engine

A high-performance UCI chess engine written in C++17

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Overview

Nyx is a bitboard-based chess engine with alpha-beta search, quiescence search, transposition tables, and iterative deepening with time management. It speaks the UCI protocol for compatibility with any chess GUI (Arena, ChessBase, etc.) and includes a built-in CLI for direct terminal play.

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Architecture

graph TB
    subgraph Interface[Interface Layer]
        UCI[UCI Protocol - uci.cpp]
        CLI[CLI Mode - cli.cpp]
    end

    subgraph Search[Search Layer]
        AB[Alpha-Beta Search - search.cpp]
        QS[Quiescence Search - search.cpp]
        TT[Transposition Table - transposition.cpp]
        AB --> QS
        AB <--> TT
    end

    subgraph Evaluation[Evaluation Layer]
        EVAL[Evaluator - eval.cpp]
        PST[Piece-Square Tables]
        MOB[Mobility Scoring]
        KING[King Safety]
        EVAL --> PST
        EVAL --> MOB
        EVAL --> KING
    end

    subgraph Core[Core Layer]
        BOARD[Board Representation - board.cpp]
        MG[Move Generator - movegen.cpp]
        MV[Move Validator - move_validator.cpp]
        BB[Bitboard Attacks - bitboards.cpp]
        ZOB[Zobrist Hashing - zobrist.cpp]
        TYPES[Type System - types.h]
    end

    UCI --> Search
    CLI --> Search
    Search --> Evaluation
    Evaluation --> Core
    Search --> Core

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Data flow

1. Interface receives a position (UCI position or CLI board/move) and delegates to Search
2. Search explores the game tree using alpha-beta pruning, consulting the Transposition Table for cached results
3. Evaluation scores leaf nodes by material, piece-square tables, mobility, and king safety
4. Core provides bitboard move generation, legal move validation, and incremental board state updates

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Project structure

nyx/
├── src/
│   ├── core/                  # Core chess primitives
│   │   ├── board.cpp          # Board representation, make/unmake move, FEN
│   │   ├── bitboards.cpp      # Precomputed sliding-piece attack tables
│   │   ├── movegen.cpp        # Bitboard legal move generation
│   │   ├── move_validator.cpp # UCI move parsing and legality checks
│   │   ├── eval.cpp           # Position evaluation (material, PST, mobility, king safety)
│   │   ├── zobrist.cpp        # Zobrist hashing implementation
│   │   ├── bitops.h           # Portable popcount/ctz intrinsics (GCC, Clang, MSVC)
│   │   └── types.h            # Enums, bitboard typedefs, square utilities
│   ├── search/
│   │   ├── search.cpp         # Alpha-beta, quiescence, aspiration, time management
│   │   └── transposition.cpp  # Transposition table with Zobrist key storage
│   └── interface/
│       ├── uci.cpp            # UCI protocol handler
│       └── cli.cpp            # Command-line REPL
├── tests/                     # Unit test suites
│   ├── test_movegen.cpp
│   ├── test_eval.cpp
│   └── test_search.cpp
└── Makefile                   # Build system

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Features

Search

Feature	Status
Alpha-beta pruning with PVS	Done
Quiescence search (8-ply limit)	Done
Transposition table (Zobrist-keyed)	Done
Iterative deepening	Done
Aspiration windows	Done
Time management (check_time)	Done
Null move pruning	Done
Principal Variation collection	Done
Repetition detection	Done

Evaluation

Component	Description	Status
Material	Piece value summation (P=100, N=320, B=330, R=500, Q=900)	Done
Piece-Square Tables	Middlegame and endgame PST with game-phase interpolation	Done
Mobility	Bonus per non-pawn legal move	Done
King safety	Pawn shield bonus, exposed-king penalty	Done
Game-phase tapering	Opening to endgame smooth blend	Done

Interface

Protocol	Description	Status
UCI	Full protocol for GUI integration	Done
CLI	Interactive REPL with board/move/eval commands	Done

Portability

Platform	Support
Linux / macOS	GCC / Clang, Makefile build
Windows	MinGW-w64 (MSYS2) with CPU intrinsics dispatch

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License

Nyx is open source software released under the MIT License.

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Contributing

Contributions are welcome! Open an issue or submit a pull request on GitHub.

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Project Stats

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