Eubos v2.27
Thanks to the Author Chris Bolt cjbolt
A Java chess engine. Uses UCI protocol. Playable on lichess .
Download : https://github.com/cjbolt/EubosChess/releases/tag/v2.27
Homepage / Instructions : https://github.com/cjbolt/EubosChess
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.
Contributors 4 :
@cjbolt
cjbolt Chris Bolt
@ddugovic
ddugovic Daniel Dugovic
@dependabot[bot]
dependabot[bot]
@yit6
yit6
"Life is a little similar to illness as it proceeds through crises and lysis and has daily improvements and worsening. Unlike other diseases, life is always fatal and cannot bear treatment"
book "The Conscience of Zeno" by Italo Svevo
