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Code Issues Releases Wiki Activity

Simplify SEE pruning for captures

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It seems that the current search is smart enough to allow us to remove
(again) the block of code that checks for discovered attacks after the
first pruning condition for captures.

STC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 278848 W: 70856 L: 70903 D: 137089
Ptnml(0-2): 960, 32829, 71894, 32780, 961
https://tests.stockfishchess.org/tests/view/64d0af095b17f7c21c0dc440

LTC:
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 100704 W: 25564 L: 25425 D: 49715
Ptnml(0-2): 56, 10858, 28381, 11005, 52
https://tests.stockfishchess.org/tests/view/64d293e85b17f7c21c0df844

closes https://github.com/official-stockfish/Stockfish/pull/4736

Bench: 1470572
This commit is contained in:
Stéphane Nicolet 2023-08-10 06:31:48 +02:00 • committed by Disservin
parent c02ee70927
commit 495852fecd
1 changed files with 3 additions and 22 deletions
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25
src/search.cpp
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@ -989,28 +989,9 @@ moves_loop: // When in check, search starts here
+ captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha)
continue;
Bitboard occupied;
// SEE based pruning (~11 Elo)
if (!pos.see_ge(move, occupied, Value(-205) * depth))
{
if (depth < 2 - capture)
continue;
// Don't prune the move if opponent Queen/Rook is under discovered attack after the exchanges
// Don't prune the move if opponent King is under discovered attack after or during the exchanges
Bitboard leftEnemies = (pos.pieces(~us, KING, QUEEN, ROOK)) & occupied;
Bitboard attacks = 0;
occupied |= to_sq(move);
while (leftEnemies && !attacks)
{
Square sq = pop_lsb(leftEnemies);
attacks |= pos.attackers_to(sq, occupied) & pos.pieces(us) & occupied;
// Don't consider pieces that were already threatened/hanging before SEE exchanges
if (attacks && (sq != pos.square<KING>(~us) && (pos.attackers_to(sq, pos.pieces()) & pos.pieces(us))))
attacks = 0;
}
if (!attacks)
continue;
}
// SEE based pruning for captures and checks (~11 Elo)
if (!pos.see_ge(move, Value(-205) * depth))
continue;
}
else
{