Chess engine: Eubos 2.10

- March 19, 2022

Eubos - a basic Java chess engine, written for kicks. Uses jcpi for the UCI protocol parts. Kind of weak, doesn't evaluate for king safety, for example. Now uses transpostion hashing, but because it runs in the Java VM on a bog standard PC, doesn't search very deeply (around 100K Nodes/s, though this is actually quite hard to evaluate due to the hashing).

Author: Chris Bolt Rating CEDR=2099

v.2.10

Features

Null Move Pruning added to the search, based on the implementation fromm the Chess Programming Wiki Engine

Added support for the 'move overhead' UCI configuration option, this is used for Eubos on Lichess

Added statistics collection for more advanced Lazy Evaluation tuning

Mate Distance Pruning

Tuning / Optimisation / Tweaks

Staged move generation implemented for the hash move at non-root and extended search nodes

Extracted a specific function for the search at the root node

Now tracks whether the Principal continuation has been fully searched and flags this using a boolean

Tweaked the lazy evaluation threshold, to produce more evaluation cut-offs

Use an auto-flushing stream for the UCI protocol output (send direction) to the chess GUI. This reduces time forfeits on Lichess.

Fixes

Bug fix for en passant hash moves, the en passant flag in the move integer was not getting set from the board state when retrieving from the hash table.

Quality

Potential Improvements

I would like to more fully utilise the staged move generation. For example it isn't too much work to include promotions as a special case in the move generation.

I would also like to refactor the staged move generation to use a loop rather than duplicating code in the search functions

The search node functions need to be optimised, I have some ideas about passing alpha and beta in an array, to help breaking down some function sizes and possibly better utilising hotspot compilation.

To install Eubos as an engine in Arena:
1. Select Engines > Install New Engine
2. In the file browser dialog that appears, change the drop down to *.bat
3. Navigate to the Eubos binary location, select the Eubos.bat
4. Select UCI protocol to communicate with Eubos
5. That's it!

Eubos 2.10 download