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Introduce capture history pruning

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This patch introduces a heuristic that is similar to countermove based pruning but for captures - capture history pruning. The idea is that we can (almost) safely prune really late captures with negative history if they don't give check so will most likely not produce some king-attacking tactic.

passed STC
https://tests.stockfishchess.org/tests/view/5e8c60d40ffd2be7f15e5470
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 23748 W: 4758 L: 4529 D: 14461
Ptnml(0-2): 421, 2712, 5400, 2899, 442

passed LTC
https://tests.stockfishchess.org/tests/view/5e8c72bf0ffd2be7f15e547f
LLR: 2.96 (-2.94,2.94) {0.25,1.75}
Total: 17330 W: 2415 L: 2190 D: 12725
Ptnml(0-2): 126, 1561, 5107, 1704, 167

closes https://github.com/official-stockfish/Stockfish/pull/2618

bench 4417023
This commit is contained in:
Vizvezdenec 2020-04-07 16:53:24 +03:00 • committed by Joost VandeVondele
parent 85bcf4741e
commit 195a4fec6d
1 changed files with 17 additions and 7 deletions
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22
src/search.cpp
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@ -789,6 +789,8 @@ namespace {
}
}
CapturePieceToHistory& captureHistory = thisThread->captureHistory;
// Step 6. Static evaluation of the position
if (inCheck)
{
@ -899,7 +901,7 @@ namespace {
&& abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
{
Value raisedBeta = std::min(beta + 189 - 45 * improving, VALUE_INFINITE);
MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &captureHistory);
int probCutCount = 0;
while ( (move = mp.next_move()) != MOVE_NONE
@ -954,7 +956,7 @@ moves_loop: // When in check, search starts from here
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->lowPlyHistory,
&thisThread->captureHistory,
&captureHistory,
contHist,
countermove,
ss->killers,
@ -1010,12 +1012,12 @@ moves_loop: // When in check, search starts from here
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
moveCountPruning = moveCount >= futility_move_count(improving, depth);
if ( !captureOrPromotion
&& !givesCheck)
{
// Reduced depth of the next LMR search
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
if ( !captureOrPromotion
&& !givesCheck)
{
// Countermoves based pruning (~20 Elo)
if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
@ -1035,8 +1037,16 @@ moves_loop: // When in check, search starts from here
if (!pos.see_ge(move, Value(-(32 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
else if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
else
{
if ( !givesCheck
&& lmrDepth < 1
&& captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
continue;
if (!pos.see_ge(move, Value(-194) * depth)) // (~25 Elo)
continue;
}
}
// Step 14. Extensions (~75 Elo)