I’m excited to release Echo 1.0, an open-source, original chess engine written from scratch in C. I’m posting here to introduce the engine to the community and hopefully get Echo queued for testing and ranking on the CCRL index!
Architecture & Engine Details
Echo was independently written to explore high-performance classical engine architecture without relying on existing engine codebases or NNUE setups.
- Board Representation & Move Generation: Custom bitboard implementation utilizing native bitwise hardware instructions (__builtin_popcountll, __builtin_ctzll), pre-calculated attack masks for leaper pieces, and an original Magic Bitboard implementation for sliding pieces.
- Hybrid Tracking: Uses a bitboard core augmented by a mailbox board state array to ensure $O(1)$ piece lookups during move evaluation and quiet search.
- Search Architecture: Custom Negamax framework with Alpha-Beta pruning, Principal Variation Search (PVS), Iterative Deepening, and Aspiration Windows.
- Selective Pruning & Reductions: Null Move Pruning (NMP), Reverse Futility Pruning (RFP), Futility Pruning, and Late Move Reductions (LMR) tuned specifically for Echo's evaluation scale.
- Move Ordering & Transposition: Zobrist hash-backed Transposition Table, combined with MVV-LVA capture ordering, Killer Move slots, and dynamic History Heuristics.
- Hand-Crafted Evaluation: Tapered Middlegame/Endgame evaluation incorporating PeSTO PST values alongside custom terms for piece mobility, king safety (pawn shields/batteries), and structural pawn logic (passed, connected, isolated, doubled).
Source & Downloads
- Github Repository: https://github.com/AM-ML/Echo
- Release / Executable: https://github.com/AM-ML/Echo/releases/ ... ase-v1.0.1
Acknowledgments: While the codebase is entirely original, the theoretical design was informed by educational resources provided by Maksim Korzh (Code Monkey King), Bluefever Software (VICE), Sebastian Lague, and the Chess Programming Wiki.
Feedback, bug reports, and initial rating estimates are all welcome! Thanks for testing.