This addresses the issue where Stockfish may output non-proven checkmate
scores if the search is prematurely halted, either due to a time control
or node limit, before it explores other possibilities where the
checkmate score could have been delayed or refuted.
The fix also replaces staving off from proven mated scores in a
multithread environment making use of the threads instead of a negative
effect with multithreads (1t was better in proving mated in scores than
more threads).
Issue reported on mate tracker repo by and this PR is co-authored with
@robertnurnberg Special thanks to @AndyGrant for outlining that a fix is
eventually possible.
Passed Adj off SMP STC:
https://tests.stockfishchess.org/tests/view/65a125d779aa8af82b96c3eb
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 303256 W: 75823 L: 75892 D: 151541
Ptnml(0-2): 406, 35269, 80395, 35104, 454
Passed Adj off SMP LTC:
https://tests.stockfishchess.org/tests/view/65a37add79aa8af82b96f0f7
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 56056 W: 13951 L: 13770 D: 28335
Ptnml(0-2): 11, 5910, 16002, 6097, 8
Passed all tests in matetrack without any better mate for opponent found in 1t and multithreads.
Fixed bugs in https://github.com/official-stockfish/Stockfish/pull/4976
closes https://github.com/official-stockfish/Stockfish/pull/4990
Bench: 1308279
Co-Authored-By: Robert Nürnberg <28635489+robertnurnberg@users.noreply.github.com>
This fixes futility pruning return values after recent tweaks, `eval` is
guaranteed to be less than the mate-in range but it can be as low value such
that the average between eval and beta can still fall in the mated-in range when
beta is as low in mated range. i.e. (eval + beta) / 2 being at mated-range which
can break mates.
Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/658f3eed79aa8af82b955139
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 117408 W: 29891 L: 29761 D: 57756
Ptnml(0-2): 386, 13355, 31120, 13429, 414
Passed non-regression LTC:
https://tests.stockfishchess.org/tests/view/658f8b7a79aa8af82b9557bd
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 60240 W: 14962 L: 14786 D: 30492
Ptnml(0-2): 22, 6257, 17390, 6425, 26
changes signature at higher depth e.g. `128 1 15`
closes https://github.com/official-stockfish/Stockfish/pull/4944
Bench: 1304666
This patch is a simplification and a fix to dealing with null moves scores that returns proven mates or TB scores by preventing 'null move pruning' if the nullvalue is in that range.
Current solution downgrades nullValues on the non-PV node but the value can be used in a transposed PV-node to the same position afterwards (Triangulation), the later is prone to propagate a wrong score (96.05) to root that will not be refuted unless we search further.
Score of (96.05) can be obtained be two methods,
maxim static-eval returned on Pv update (mostly qSearch)
this downgrade (clamp) in NMP
and theoretically can happen with or without TBs but the second scenario is more dangerous than the first.
This fixes the reproducible case in very common scenarios with TBs as shown in the debugging at discord.
Fixes: #4699
Passed STC:
https://tests.stockfishchess.org/tests/view/64c1eca8dc56e1650abba6f9
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 670048 W: 171132 L: 171600 D: 327316
Ptnml(0-2): 2134, 75687, 179820, 75279, 2104
Passed LTC:
https://tests.stockfishchess.org/tests/view/64c5e130dc56e1650abc0438
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 92868 W: 23642 L: 23499 D: 45727
Ptnml(0-2): 52, 9509, 27171, 9648, 54
closes https://github.com/official-stockfish/Stockfish/pull/4715
Bench: 1327410
Increase reduction on retrying a move we just retreated that falls in a repetition:
if current move can be the same move from previous previous turn then we retreated
that move on the previous turn, this patch increases reduction if retrying that move
results in a repetition.
How to continue from there? Maybe we some variants of this idea could bring Elo too
(only testing the destination square, or triangulations, etc.)
Passed STC:
https://tests.stockfishchess.org/tests/view/64e1aede883cbb7cbd9ad976
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 424000 W: 108675 L: 107809 D: 207516
Ptnml(0-2): 1296, 47350, 113896, 48108, 1350
Passed LTC:
https://tests.stockfishchess.org/tests/view/64e32d629970091252666872
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 89682 W: 22976 L: 22569 D: 44137
Ptnml(0-2): 39, 8843, 26675, 9240, 44
closes https://github.com/official-stockfish/Stockfish/pull/4757
bench: 1574347
