_{~2650 Elo · C · UCI · Alpha–Beta · Magic Bitboards}

Echo is a bitboard chess engine focused on performance and a classical alpha–beta search architecture and evaluation.

Technical Deep Dive: For a detailed breakdown of Echo's architecture, search heuristics, and evaluation function, see DOCUMENTATION.md.

• Protocol: UCI (Universal Chess Interface) compatible.

• Algorithm: Negamax with Alpha–Beta Pruning.
• Refinements: PVS, Iterative Deepening, Aspiration Windows.
• Pruning: Null Move (NMP), Futility, Reverse Futility (RFP).
• Heuristics: Killer Moves, History Heuristic, LMR.
• Quiescence: Mitigating horizon effects with capture-only searches.
• Optimization: Transposition Table (TT) with Zobrist Hashing.
• Multi-threading: Parallel Search using OpenMP.

• Tapered Eval: Smooth interpolation between middlegame and endgame.
• Pawn Structure: Passed (connected!), isolated, and doubled pawn detection.
• King Safety: Pawn shields, storm detection, and battery threats.
• Piece Activity: Mobility, Knight outposts, and Rook open file bonuses.

The codebase is modularized into the src/ directory, separating concerns between board representation, search, evaluation, and protocol handling.

/
├── src/
│   ├── main.c           # Entry point
│   ├── board.c          # Board state, bitboard macros, FEN parsing
│   ├── search.c         # Search algorithms (Negamax, PVS, Quiescence)
│   ├── eval.c           # Static evaluation logic & PSTs
│   ├── move_gen.c       # Move generation (pseudo-legal & legal)
│   ├── tt.c             # Transposition table & Zobrist hashing
│   ├── uci.c            # UCI protocol handling & input loop
│   ├── magic.c          # Magic bitboard generation (Rook/Bishop sliders)
│   ├── masks.c          # Pre-calculated attack masks (Leapers)
│   ├── sliding_masks.c  # Sliding piece attack lookups
│   └── helper.c         # Debugging utilities (print board, etc.)
├── ref/
│   ├── colSelector.py   # Development helpers
│   └── rowSelector.py
├── Makefile
└── README.md

• GCC or Clang
• Make

mkdir -p bin
make        # Standard build
make rel    # Release build (Optimized -Ofast -flto)
make win    # Cross-compile for Windows (requires MinGW)

./bin/echo

Echo integrates with any UCI-compliant GUI (e.g., Arena, CuteChess, En Croissant).

Supported Commands:

uci
isready
ucinewgame
position startpos | position fen <FEN>
go depth <N> | go movetime <ms>
bench <depth>
stop
quit

Echo includes a built-in benchmark command to measure search performance across various positions.

To run the standard benchmark suite (8 positions to depth 10):

bench

To run benchmarks to a specific depth:

bench <depth>

Standard benchmark results (Depth 10):

Total Nodes: 626688
Total Time: 2297 ms
NPS: 272828

This table maps core engine concepts to their specific implementation files in the new structure.

Utility functions found in src/helper.c and src/board.c:

• print_board() — ASCII/Unicode board visualization
• print_bitboard() — Visualizes specific bitmasks
• print_move_list() — Lists generated moves for the current state

The development of Echo was informed and inspired by several key resources in the chess programming community:

• Maksim Korzh (Code Monkey King): Foundational concepts in bitboard representation and move generation.
• Sebastian Lague: Algorithmic clarity regarding search architecture and optimization.
• BluefeverSoftware (VICE): Architectural patterns for UCI protocol handling and search structures.