README

Nemorino is a UCI chess engine.

Features

• Syzygy Tablebase support
• Pondering
• Standard Chess and Chess960
• Multi Core support (Shared Hash Table)
• Multi PV analysis mode
• CECP support (experimental - all testing is done using UCI)

UCI parameters:

• UCI_Chess960: If set to true engine will play according to Chess960 rules (default false)
• Hash: Size in MBytes used for the transposition table (default is 32. Nemorino will use additional memory for other fixed-size hash tables)
• Clear Hash: Will clear the transposition table
• MultiPV: Number of principal variations shown (default 1)
• Threads: Maximum number of threads (cores) used (default determined by number of available hardware threads)
• Ponder: When set to true, engine will continue analysis while waiting for opponent's move (default false)
• Contempt: Score (in centipawns) for accepting draws. If Contempt > 0 then the engine will avoid draws (default 0)
• BookFile: Polyglot book file the engine shall use (default "book.bin"). Nemorino doesn't have an own book so far
• OwnBook: Use Polyglot book, specified by book file (default false)
• SyzygyPath: Path(es) to directories Syzygy tablebase files can be found. Seperate multiple directories by ';' on windows and by ':' on linux
• SyzygyProbeDepth: Minimum search depth for probing Syzygy Bases. The lower the number, more tablebase lookups will be done, but search speed will decrease (default 8)
• MoveOverhead: Safety Time(in ms) needed to avoid time-losses (default 100)
• UCI_Opponent: With this command the GUI can send the name, title, elo and if the engine is playing a human or computer to the engine (see UCI Specification)

Installation

Released executables can be downloaded in the Download section

The current development versions are also available:

• Main Nemorino dev version
• Nemorino dev version for old PC without POPCNT support

Nemorino doesn't bring it's own UI. So for running it, you need a GUI supporting UCI (like Arena).
The engine requires 64-bit Windows.

Internals

• Bitboard based (using magic bitboards for sliding move generation)
• Principal Variation Search (with Aspiration Windows, Null-Move Pruning, Killermoves, Futility Pruning, Razoring, ...)
• Tapered Eval based on Material, Mobility, Threats, King Safety, and Pawn Structure
• Special evaluation functions for some endgames
• Copy/Make

Version History

1.01:

•      Bugfix: rare crashes caused by hash collisions in transposition table
  

•      Code changes for non-popcount compiles
  

1.02:

•      New Parameters: SyzygyProbeDepth and MoveOverhead
  

•      Bugfix: Handling of EP-Squares in TB probing code
  

2.00:

•      Several Improvements in Search: Singular Extensions, Cut Node Extensions, improved IID,..
  

•      Improved SEE (consider promotions and pinned pieces)
  

•      Improved King Safety Evaluation
  

•      Scale down endgame values if there are opposite colored bishops
  

•      Several minor improvements and clean-ups
  

2.00a (only bugfixes relevant when running with more than one thread):

•      Fix for known issue with tablebase access (see https://github.com/basil00/Fathom/issues/15
  

•      Fix for other (rare) crashes
  

3.00:

•      Refactoring of SMP implementation => Improved stability
  

•      Several minor improvements in search and move ordering
  

4.00:

•      Improved King Safety evaluation
  

•      Some Improvements when running with many threads
  

•      Some Evaluation Improvements (added some material imbalance terms, knight center mobility, ... and removed some useless terms)
  

5.00:

•      Several minor Improvements especially for King Safety 
  

•      Several Bugfixes
  

•      Replaced Syzygy probing code. Now instead of Fathom library, probing code from Stockfish is used
  

License

GNU GENERAL PUBLIC LICENSE Version 3

Strength

Nemorino is listed in several rating lists:

Nemorino 5.00

• CCRL 40/40 (4 CPU) Elo 3161 #17
• CCRL 40/40 Elo 3084 #21
• CCRL 40/4 (4 CPU) Elo 3178 #25
• CCRL 40/4 Elo 3123 #21
• CCRL 40/4 (FRC) Elo 3180 #9
• FastGM Bullet Elo 2921 #24
• FastGM 10min Elo 2971 #18
• CEGT 40/4 Elo 2974 #23
• CEGT 40/20 Elo 2992 #21
• Owl Chess Elo 3097 #21

Nemorino 4.00

• CEGT 40/4 (2 CPU) Elo 2984 #24
• CEGT 5+3 PB=ON Elo 2903 #27

Remarks

I wrote this engine because I wanted to understand, how a chess engine is working. And the best way to learn is to write an engine from scratch by yourself. I first started with C#, but after some time I got the ambition to learn C++. Therefore don't expect a lot of new ideas within my code, and neither expect clean and well-structured code. Instead you will find a unique combination of all those ideas explained in the Chess Programming Wiki.

Acknowledgements

These are my sources of information I used for my engine:

• My main source of information: Chess Programming Wiki
• Computer Chess Club Forums
• The code of several Open Source Chess Engines, mainly:
  • Stockfish - I copied board and move representation and some lines of code from Stockfish (marked by source code comments)
  • Hakkapeliitta
  • Lozza
  • Senpai
• The blogs of Steve Maughan, Thomas Petzke and Jonatan Pettersson