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MCP more after a bad singular search

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The idea is, that if we have the information that the singular search failed low and therefore produced an upperbound score, we can use the score from singularsearch as approximate upperbound as to what bestValue our non ttMoves will produce. If this value is well below alpha, we assume that all non-ttMoves will score below alpha and therfore can skip more moves.
This patch also sets up variables for future patches wanting to use teh singular search result outside of singular extensions, in singularBound and singularValue, meaning further patches using this search result to affect various pruning techniques can be tried.

Passed STC:
https://tests.stockfishchess.org/tests/view/6658d13e6b0e318cefa90120
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 85632 W: 22112 L: 21725 D: 41795
Ptnml(0-2): 243, 10010, 21947, 10349, 267

Passed LTC:
https://tests.stockfishchess.org/tests/view/6658dd356b0e318cefa9016a
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 243978 W: 62014 L: 61272 D: 120692
Ptnml(0-2): 128, 26598, 67791, 27348, 124

closes https://github.com/official-stockfish/Stockfish/pull/5325

bench 1397172
This commit is contained in:
rn5f107s2 2024-05-30 21:18:42 +02:00 • committed by Joost VandeVondele
parent 0ef809ac71
commit b34a690cd4
1 changed files with 9 additions and 3 deletions
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12
src/search.cpp
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@ -550,11 +550,12 @@ Value Search::Worker::search(
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta, singularValue;
bool givesCheck, improving, priorCapture, opponentWorsening;
bool capture, moveCountPruning, ttCapture;
Piece movedPiece;
int moveCount, captureCount, quietCount;
Bound singularBound;
// Step 1. Initialize node
Worker* thisThread = this;
@ -923,6 +924,8 @@ moves_loop: // When in check, search starts here
value = bestValue;
moveCountPruning = false;
singularValue = VALUE_INFINITE;
singularBound = BOUND_NONE;
// Step 13. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
@ -972,7 +975,9 @@ moves_loop: // When in check, search starts here
if (!rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
{
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~8 Elo)
moveCountPruning = moveCount >= futility_move_count(improving, depth);
moveCountPruning =
moveCount >= futility_move_count(improving, depth)
- (singularBound == BOUND_UPPER && singularValue < alpha - 50);
// Reduced depth of the next LMR search
int lmrDepth = newDepth - r;
@ -1058,8 +1063,9 @@ moves_loop: // When in check, search starts here
Depth singularDepth = newDepth / 2;
ss->excludedMove = move;
value =
value = singularValue =
search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
singularBound = singularValue >= singularBeta ? BOUND_LOWER : BOUND_UPPER;
ss->excludedMove = Move::none();
if (value < singularBeta)