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Do more reductions at Pv nodes with low delta

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This patch increases reduction for PvNodes that have their delta (difference between beta and alpha) significantly reduced compared to what it was at root.

passed STC
https://tests.stockfishchess.org/tests/view/617f9063af49befdeee40226
LLR: 2.94 (-2.94,2.94) <0.00,2.50>
Total: 220840 W: 55752 L: 55150 D: 109938
Ptnml(0-2): 583, 24982, 58712, 25536, 607

passed LTC
https://tests.stockfishchess.org/tests/view/61815de959e71df00dcc42ed
LLR: 2.95 (-2.94,2.94) <0.50,3.00>
Total: 79000 W: 19937 L: 19562 D: 39501
Ptnml(0-2): 36, 8190, 22674, 8563, 37

closes https://github.com/official-stockfish/Stockfish/pull/3774

bench: 6717808
This commit is contained in:
Michael Chaly 2021-11-04 18:35:01 +03:00 • committed by Joost VandeVondele
parent 11c6cf720d
commit c2b9134c6e
2 changed files with 7 additions and 0 deletions
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6
src/search.cpp
View file

@ -625,6 +625,8 @@ namespace {
if (alpha >= beta)
return alpha;
}
else
thisThread->rootDelta = beta - alpha;
assert(0 <= ss->ply && ss->ply < MAX_PLY);
@ -1167,6 +1169,10 @@ moves_loop: // When in check, search starts here
&& bestMoveCount <= 3)
r--;
// Increases reduction for PvNodes that have small window
if (PvNode && beta - alpha < thisThread->rootDelta / 4)
r++;
// Decrease reduction if position is or has been on the PV
// and node is not likely to fail low. (~3 Elo)
if ( ss->ttPv

1
src/thread.h
View file

@ -72,6 +72,7 @@ public:
StateInfo rootState;
Search::RootMoves rootMoves;
Depth rootDepth, completedDepth;
Value rootDelta;
CounterMoveHistory counterMoves;
ButterflyHistory mainHistory;
LowPlyHistory lowPlyHistory;