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Do less SEE pruning in qsearch

Browse source 
Current master prunes all moves with negative SEE values in qsearch.
This patch sets constant negative threshold thus allowing some moves with negative SEE values to be searched.
Value of threshold is completely arbitrary and can be tweaked - also it as function of depth can be tried.
Original idea by author of Alexandria engine.

Passed STC
https://tests.stockfishchess.org/tests/view/63d79a59a67dd929a5564976
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 34864 W: 9392 L: 9086 D: 16386
Ptnml(0-2): 113, 3742, 9429, 4022, 126

Passed LTC
https://tests.stockfishchess.org/tests/view/63d8074aa67dd929a5565bc2
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 91616 W: 24532 L: 24126 D: 42958
Ptnml(0-2): 32, 8840, 27662, 9238, 36

closes https://github.com/official-stockfish/Stockfish/pull/4376

Bench: 4010877
This commit is contained in:
Michael Chaly 2023-02-02 13:05:54 +03:00 • committed by Joost VandeVondele
parent 3589bd008a
commit da8513f0ea
1 changed files with 2 additions and 2 deletions
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4
src/search.cpp
View file

@ -1556,9 +1556,9 @@ moves_loop: // When in check, search starts here
}
}
// Do not search moves with negative SEE values (~5 Elo)
// Do not search moves with bad enough SEE values (~5 Elo)
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !pos.see_ge(move))
&& !pos.see_ge(move, Value(-108)))
continue;
// Speculative prefetch as early as possible