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Introduce Triple Extensions

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This replaces singularquietLMR with triple instead of double extending non-capture ttmoves that have value far below singularBeta. This threshold value is initially set to 200, there is scope for more scaling by reducing it as occured with double extensions.

Passed STC:
https://tests.stockfishchess.org/tests/view/65b683b8c865510db0274074
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 222912 W: 58141 L: 57535 D: 107236
Ptnml(0-2): 1063, 26244, 56154, 27014, 981

Passed LTC:
https://tests.stockfishchess.org/tests/view/65bae6d4c865510db0278eb5
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 66306 W: 16825 L: 16440 D: 33041
Ptnml(0-2): 40, 7374, 17952, 7735, 52

closes https://github.com/official-stockfish/Stockfish/pull/5027

bench 1394701
This commit is contained in:
Viren6 2024-02-01 18:48:45 +00:00 • committed by Joost VandeVondele
parent 56b342f9b2
commit f2b6b5cfc9
1 changed files with 6 additions and 11 deletions
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17
src/search.cpp
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@ -522,7 +522,7 @@ Value Search::Worker::search(
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
bool givesCheck, improving, priorCapture, singularQuietLMR;
bool givesCheck, improving, priorCapture;
bool capture, moveCountPruning, ttCapture;
Piece movedPiece;
int moveCount, captureCount, quietCount;
@ -900,7 +900,7 @@ moves_loop: // When in check, search starts here
contHist, &thisThread->pawnHistory, countermove, ss->killers);
value = bestValue;
moveCountPruning = singularQuietLMR = false;
moveCountPruning = false;
// Step 13. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
@ -1034,13 +1034,12 @@ moves_loop: // When in check, search starts here
if (value < singularBeta)
{
extension = 1;
singularQuietLMR = !ttCapture;
extension = 1;
// Avoid search explosion by limiting the number of double extensions
if (!PvNode && value < singularBeta - 2 && ss->doubleExtensions <= 12)
if (!PvNode && value < singularBeta - 2 && ss->doubleExtensions <= 15)
{
extension = 2;
extension = 2 + (value < singularBeta - 200 && !ttCapture);
depth += depth < 15;
}
}
@ -1091,7 +1090,7 @@ moves_loop: // When in check, search starts here
// Add extension to new depth
newDepth += extension;
ss->doubleExtensions = (ss - 1)->doubleExtensions + (extension == 2);
ss->doubleExtensions = (ss - 1)->doubleExtensions + (extension >= 2);
// Speculative prefetch as early as possible
prefetch(tt.first_entry(pos.key_after(move)));
@ -1125,10 +1124,6 @@ moves_loop: // When in check, search starts here
if (PvNode && tte->bound() != BOUND_UPPER)
r--;
// Decrease reduction if a quiet ttMove has been singularly extended (~1 Elo)
if (singularQuietLMR)
r--;
// Increase reduction on repetition (~1 Elo)
if (move == (ss - 4)->currentMove && pos.has_repeated())
r += 2;