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Improve ttPv reduction

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This patch allows a partial reduction decrease when a node is likely to
fail low, and increases the reduction decrease when a node has failed
high.

Passed STC:
https://tests.stockfishchess.org/tests/view/65a626e779aa8af82b9722bc
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 157824 W: 40332 L: 39835 D: 77657
Ptnml(0-2): 543, 18617, 40098, 19108, 546

Passed LTC:
https://tests.stockfishchess.org/tests/view/65a7290279aa8af82b97328a
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 57228 W: 14475 L: 14111 D: 28642
Ptnml(0-2): 34, 6278, 15633, 6628, 41

closes https://github.com/official-stockfish/Stockfish/pull/4994

Bench: 1364759
This commit is contained in:
Viren6 2024-01-17 14:45:59 +00:00 • committed by Disservin
parent 9a9702d668
commit c8bc2ce4fa
1 changed files with 4 additions and 8 deletions
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12
src/search.cpp
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@ -944,11 +944,6 @@ moves_loop: // When in check, search starts here
value = bestValue;
moveCountPruning = singularQuietLMR = false;
// Indicate PvNodes that will probably fail low if the node was searched
// at a depth equal to or greater than the current depth, and the result
// of this search was a fail low.
bool likelyFailLow = PvNode && ttMove && (tte->bound() & BOUND_UPPER) && tte->depth() >= depth;
// Step 13. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
while ((move = mp.next_move(moveCountPruning)) != Move::none())
@ -1153,9 +1148,10 @@ moves_loop: // When in check, search starts here
thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
pos.do_move(move, st, givesCheck);
// Decrease reduction if position is or has been on the PV (~4 Elo)
if (ss->ttPv && !likelyFailLow)
r -= 1 + (cutNode && tte->depth() >= depth) + (ttValue > alpha);
// Decrease reduction if position is or has been on the PV (~7 Elo)
if (ss->ttPv)
r -= !(tte->bound() == BOUND_UPPER && PvNode) + (cutNode && tte->depth() >= depth)
+ (ttValue > alpha) + (ttValue > beta && tte->depth() >= depth);
// Decrease reduction if opponent's move count is high (~1 Elo)
if ((ss - 1)->moveCount > 7)