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Sometimes do a reduced search if LMR is skipped

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If the node doesn't go through LMR and r is too big,
reduce search depth by one ply.

STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 664888 W: 176375 L: 175169 D: 313344
Ptnml(0-2): 1965, 73754, 179851, 74858, 2016
https://tests.stockfishchess.org/tests/view/6399414c93ed41c57ede8fb8

LTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 150784 W: 40553 L: 40031 D: 70200
Ptnml(0-2): 76, 14668, 45387, 15180, 81
https://tests.stockfishchess.org/tests/view/639dee6e11c576d919dc2b38

closes https://github.com/official-stockfish/Stockfish/pull/4290

Bench: 3727508
This commit is contained in:
Alfredo Menezes 2022-12-19 16:07:09 -03:00 • committed by Joost VandeVondele
parent 61ea1534ff
commit c2d507005c
1 changed files with 48 additions and 48 deletions
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24
src/search.cpp
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@ -1120,16 +1120,6 @@ moves_loop: // When in check, search starts here
// Step 16. Make the move
pos.do_move(move, st, givesCheck);
// Step 17. Late moves reduction / extension (LMR, ~98 Elo)
// We use various heuristics for the sons of a node after the first son has
// been searched. In general we would like to reduce them, but there are many
// cases where we extend a son if it has good chances to be "interesting".
if ( depth >= 2
&& moveCount > 1 + (PvNode && ss->ply <= 1)
&& ( !ss->ttPv
|| !capture
|| (cutNode && (ss-1)->moveCount > 1)))
{
Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
// Decrease reduction if position is or has been on the PV
@ -1176,6 +1166,16 @@ moves_loop: // When in check, search starts here
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
r -= ss->statScore / (13000 + 4152 * (depth > 7 && depth < 19));
// Step 17. Late moves reduction / extension (LMR, ~98 Elo)
// We use various heuristics for the sons of a node after the first son has
// been searched. In general we would like to reduce them, but there are many
// cases where we extend a son if it has good chances to be "interesting".
if ( depth >= 2
&& moveCount > 1 + (PvNode && ss->ply <= 1)
&& ( !ss->ttPv
|| !capture
|| (cutNode && (ss-1)->moveCount > 1)))
{
// In general we want to cap the LMR depth search at newDepth, but when
// reduction is negative, we allow this move a limited search extension
// beyond the first move depth. This may lead to hidden double extensions.
@ -1209,10 +1209,10 @@ moves_loop: // When in check, search starts here
}
}
// Step 18. Full depth search when LMR is skipped
// Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
else if (!PvNode || moveCount > 1)
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 4), !cutNode);
}
// For PV nodes only, do a full PV search on the first move or after a fail