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Capping stat bonus at 2000

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This patch updates the stat_bonus() function (used in the history tables to
help move ordering), keeping the same quadratic for small depths but changing
the values for depth >= 9:

The old bonus formula was increasing from zero at depth 1 to 4100 at depth 14,
then used the strange, small value of 73 for all depths >= 15.

The new bonus formula increases from 0 at depth 1 to 2000 at depth 8, then
keeps 2000 for all depths >= 8.

passed STC:
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 169624 W: 42875 L: 42454 D: 84295
Ptnml(0-2): 585, 19340, 44557, 19729, 601
https://tests.stockfishchess.org/tests/view/615bd69e9d256038a969b97c

passed LTC:
LLR: 3.07 (-2.94,2.94) <0.50,3.50>
Total: 37336 W: 9456 L: 9191 D: 18689
Ptnml(0-2): 20, 3810, 10747, 4067, 24
https://tests.stockfishchess.org/tests/view/615c75d99d256038a969b9b2

closes https://github.com/official-stockfish/Stockfish/pull/3731

Bench: 6261865
This commit is contained in:
Stéphane Nicolet 2021-10-04 20:37:26 +02:00
parent 329bdbd9cf
commit 54a989930e
1 changed files with 3 additions and 3 deletions
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6
src/search.cpp
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@ -80,7 +80,7 @@ namespace {
// History and stats update bonus, based on depth // History and stats update bonus, based on depth
int stat_bonus(Depth d) { int stat_bonus(Depth d) {
return d > 14 ? 73 : 6 * d * d + 229 * d - 215; return std::min((6 * d + 229) * d - 215 , 2000);
} }
// Add a small random component to draw evaluations to avoid 3-fold blindness // Add a small random component to draw evaluations to avoid 3-fold blindness
@ -1709,8 +1709,8 @@ moves_loop: // When in check, search starts here
PieceType captured = type_of(pos.piece_on(to_sq(bestMove))); PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
bonus1 = stat_bonus(depth + 1); bonus1 = stat_bonus(depth + 1);
bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
: std::min(bonus1, stat_bonus(depth)); // smaller bonus : stat_bonus(depth); // smaller bonus
if (!pos.capture_or_promotion(bestMove)) if (!pos.capture_or_promotion(bestMove))
{ {