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Refine SEE threshold for capture pruning.

Browse source 
eloDoc suggests that this part of search is worth ~18 Elo.
This patch refines the depth dependence of the SEE threshold.

passed STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 21398 W: 4474 L: 4245 D: 12679
http://tests.stockfishchess.org/tests/view/5abfb0630ebc591a560aae07

passed LTC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 9028 W: 1439 L: 1285 D: 6304
http://tests.stockfishchess.org/tests/view/5abfbff30ebc591a560aae11

Closes https://github.com/official-stockfish/Stockfish/pull/1527

Bench: 6036915
This commit is contained in:
Joost VandeVondele 2018-03-31 23:10:24 +02:00 • committed by Stéphane Nicolet
parent d5e3e7d207
commit f2681232e5
1 changed files with 11 additions and 1 deletions
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12
src/search.cpp
View file

@ -72,6 +72,16 @@ namespace {
return Value((175 - 50 * improving) * d / ONE_PLY);
}
// Margin for pruning capturing moves: almost linear in depth
constexpr int CapturePruneMargin[] = { 0,
1 * PawnValueEg * 1055 / 1000,
2 * PawnValueEg * 1042 / 1000,
3 * PawnValueEg * 963 / 1000,
4 * PawnValueEg * 1038 / 1000,
5 * PawnValueEg * 950 / 1000,
6 * PawnValueEg * 930 / 1000
};
// Futility and reductions lookup tables, initialized at startup
int FutilityMoveCounts[2][16]; // [improving][depth]
int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
@ -919,7 +929,7 @@ moves_loop: // When in check, search starts from here
}
else if ( depth < 7 * ONE_PLY
&& !extension
&& !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
&& !pos.see_ge(move, -Value(CapturePruneMargin[depth / ONE_PLY])))
continue;
}