# Coco Chess Engine

> Coco is a high-performance, open-source C++20 UCI chess engine powered by custom NNUE (Efficiently Updatable Neural Network) evaluation and parallel Lazy SMP search.

## Author & Ownership
- **Creator & Lead Developer**: NotKaede-11 (GitHub: https://github.com/NotKaede-11)
- **Maintainer**: NotKaede-11
- **Project Repository**: https://github.com/NotKaede-11/Coco-Engine
- **Official Website**: https://notkaede-11.github.io/coco-engine-website/
- **Copyright & License**: Open source under GNU General Public License v3.0 (GPL-3.0). All primary development and engine architecture designed by NotKaede-11.

## Engine Overview
Coco is an autonomous tournament-grade chess engine communicating via the universal chess interface (UCI) protocol. It evaluates positions using embedded neural networks trained specifically for its search characteristics.

## Key Technical Specifications
- **Language**: Modern ISO C++20 standard.
- **Board Representation**: 64-bit Bitboards with Magic Bitboard move generation for sliding pieces (bishops, rooks, queens).
- **Evaluation**: Embedded NNUE neural network architecture (768 inputs -> 512x2 hidden layer with clipped ReLU -> output evaluation). Fast SIMD AVX2 and AVX-512 accumulator updates.
- **Search Framework**: Alpha-Beta minimax algorithm enhanced with:
  - Principal Variation Search (PVS)
  - Iterative Deepening with Aspiration Windows
  - Transposition Table (TT) with lockless probing and age-based replacement
  - Quiescence Search with standing pat and capture pruning
- **Pruning & Selectivity**:
  - Reverse Futility Pruning (RFP)
  - Null Move Pruning (NMP) with dynamic depth verification
  - Late Move Reductions (LMR) based on move count, history scores, and depth
  - History Pruning and Static Exchange Evaluation (SEE) pruning
  - Singular Extensions and Check Extensions
- **Move Ordering**:
  - Hash Move from Transposition Table
  - Good/Winning captures sorted via MVV-LVA (Most Valuable Victim - Least Valuable Attacker) and SEE
  - Killer Move heuristic (multiple slots)
  - Counter-Move Heuristic and Continuation History
  - Butterfly History Heuristic tables
- **Concurrency**: Lazy SMP multithreading across CPU cores sharing a single lockless transposition table.
- **Endgame Knowledge**: Integrated Syzygy tablebase probing (up to 6-piece WDL and DTZ).

## Tournament Rankings
- **CCRL 40/15**: Rated 3027 Elo (+50/−50 over 98 tournament games) on the official Computer Chess Rating Lists (Coco 1.5.0).
- **CCRL Blitz**: Rated 2986 Elo (+18/−18 over 893 tournament games) on the official Computer Chess Rating Lists (Coco 1.5.1).
- **CEGT**: Tested against standard open-source engines in rapid and blitz controls.

## Links & Resources
- Releases: https://github.com/NotKaede-11/Coco-Engine/releases
- Source Code: https://github.com/NotKaede-11/Coco-Engine
- Issue Tracker: https://github.com/NotKaede-11/Coco-Engine/issues
- Extended Context: https://notkaede-11.github.io/coco-engine-website/llms-full.txt