Chess engine: Eubos 2.27 (java engine)

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=2480

v.2.27

This release contains a major bug fix. A bug existed since Eubos 2.24 and perhaps earlier. The defect is more prevalent at longer time controls, as it related to the hash table, which is more important in longer searches. The best move that was returned could be legal, but spurious. It could result in not moving away an attacked piece, or even making a losing capture for no positional/mating benefit.

I have also, as a consequence of trying to corner the defect, added a validation search and extra diagnostic logging, which is switched off in the released binary.

Also as a consequence, I have revisited the search functions and made various refactors and improvements to aid maintenance of the code. The best of these being reworking the move iterator for the lazy move generation to be more logical and efficient.

I have also added storage of extended/quiescent search transposition data in the hash table.

Some more gory details on the defect...

The processing that returned the best move failed to check the depth of the transposition table entry, which could mean that if a hash entry was overwritten during the search, after backing up a hash move (for example, if the root hash got overwritten by the replacement scheme and then a transposition of moves meant the same position was reached further down the search tree, but searched to a lower depth) then the best move could be legal but spurious. The regular search correctly checked the depth.

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 - Rating CEDR progres

Pl	Engines	Rating	score	Games	%
1492	Eubos 2.20	2480.6	4.00	38	10.53
1493	Eubos 2.21	2479.9	79.00	269	29.37
1503	Eubos 2.23	2462.8	69.00	327	21.10
1531	Eubos 2.22	2414.6	41.50	138	30.07
1552	Eubos 2.16	2388.8	34.00	100	34.00
1555	Eubos 2.14	2388.4	17.50	82	21.34
1576	Eubos 2.15	2356.4	49.50	154	32.14
1591	Eubos 2.24	2333.7	15.50	114	13.60
1603	Eubos 2.17	2314.9	20.50	140	14.64
1644	Eubos 2.19	2241.6	6.00	28	21.43
1658	Eubos 2.12	2223.3	13.00	83	15.66
1683	Eubos 2.10	2168.2	6.00	30	20.00
1815	Eubos 2.3	1850.9	5.50	62	8.87
1851	Eubos 1.0.8	1678.1	9.00	42	21.43

Eubos 2.27 download