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Use complexity in search

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This patch uses the complexity measure (from #3875) as a heuristic for null move pruning.
Hopefully, there may be room to use it in other pruning techniques.
I would like to thank vondele and locutus2 for the feedback and suggestions during testing.

Passed STC
LLR: 2.95 (-2.94,2.94) <0.00,2.50>
Total: 35000 W: 9624 L: 9347 D: 16029
Ptnml(0-2): 156, 3894, 9137, 4143, 170
https://tests.stockfishchess.org/tests/view/61dda784c65bf87d6c45ab80

Passed LTC
LLR: 2.94 (-2.94,2.94) <0.50,3.00>
Total: 230776 W: 64227 L: 63454 D: 103095
Ptnml(0-2): 1082, 23100, 66380, 23615, 1211
https://tests.stockfishchess.org/tests/view/61ddd0cf3ddbc32543e72c2b

Closes https://github.com/official-stockfish/Stockfish/pull/3890

Bench: 4464962
This commit is contained in:
Rui Coelho 2022-01-13 18:30:53 +00:00 • committed by Joost VandeVondele
parent c5d45d3220
commit 7678d63cf2
2 changed files with 5 additions and 2 deletions
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1
AUTHORS
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@ -166,6 +166,7 @@ Rodrigo Exterckötter Tjäder
Ron Britvich (Britvich)
Ronald de Man (syzygy1, syzygy)
rqs
Rui Coelho (ruicoelhopedro)
Ryan Schmitt
Ryan Takker
Sami Kiminki (skiminki)

6
src/search.cpp
View file

@ -589,7 +589,7 @@ namespace {
bool givesCheck, improving, didLMR, priorCapture;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
Piece movedPiece;
int moveCount, captureCount, quietCount, bestMoveCount, improvement;
int moveCount, captureCount, quietCount, bestMoveCount, improvement, complexity;
// Step 1. Initialize node
ss->inCheck = pos.checkers();
@ -760,6 +760,7 @@ namespace {
ss->staticEval = eval = VALUE_NONE;
improving = false;
improvement = 0;
complexity = 0;
goto moves_loop;
}
else if (ss->ttHit)
@ -803,6 +804,7 @@ namespace {
: 200;
improving = improvement > 0;
complexity = abs(ss->staticEval - (us == WHITE ? eg_value(pos.psq_score()) : -eg_value(pos.psq_score())));
// Step 7. Futility pruning: child node (~25 Elo).
// The depth condition is important for mate finding.
@ -818,7 +820,7 @@ namespace {
&& (ss-1)->statScore < 23767
&& eval >= beta
&& eval >= ss->staticEval
&& ss->staticEval >= beta - 20 * depth - improvement / 15 + 204
&& ss->staticEval >= beta - 20 * depth - improvement / 15 + 204 + complexity / 25
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))