Illegal moves fix and other improvements #9
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FIX: Engine stalling/disconnecting around ply 320 FIX: En passant capture of a checking pawn not considered legal FIX: Corrected extraneous - appearing in FEN castle field
The TT reads updating the PV reduces illegal moves cropping up in the pv. Also not calling Eval::evaluate until after checking the TT should provide a healthy performance improvement.
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Wow, awesome! Seems like there are still some issues to be addressed, but you did a great job. I'll merge this. |
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The two illegal moves in #8 (against TSCP and the first against EnkoChess) have been resolved. An oversight in move generation caused Apollo to not see an en passant capture as a valid way to leave check, causing the last move of the
positioncommand to not be recognized and Apollo to think it was playing the opposite side of the board.Although I could not replicate the second illegal move against EnkoChess, I could replicate Apollo fumbling its way through winning endgames (especially KRvK). With some changes to how the mate score is returned from the evaluation function and how it is stored and retrieved in the transposition tables, Apollo should no later attempt such circuitous routes to mating.
Some other minor issues were touched on. Illegal moves should occur far less frequently in PV output (although they still show up occasionally). An issue with De Morgan's Law was fixed in FEN string creation. Also, the engine no longer stalls and/or disconnects at plies 319 and beyond. There are still time management issues, unfortunately. Finally, I found a way to push back calling
Eval::evaluateuntil after looking through the transposition table, which speeds up iterative deepening quite nicely.I ran 60 game pairs (4-ply book, 40 moves/1 minute) to compare versions.
PGN of the games
Do I think these fixes gained 180 ELO? No. I estimated they gained closer to 60. Considering there are a lot of TODOs still in the code and some pesky loses on time and illegal pv moves, there is still plenty of work to do. However, this is significant enough progress that I think it is worth making the pull request here.