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Negative extension on cutNodes based on depth

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This patch was inspired by candirufish original attempt at negative extensions
here that failed yellow: https://tests.stockfishchess.org/tests/view/6486529065ffe077ca124f32

I tested some variations of the idea and tuned a depth condition for
a modified version of it here https://tests.stockfishchess.org/tests/view/648db80a91c58631ce31fe00
after noticing abnormal scaling (ie many passed STC but not LTC)
After some small tweaks I got the final version here

Passed STC:
LLR: 2.98 (-2.94,2.94) <0.00,2.00>
Total: 122208 W: 32776 L: 32350 D: 57082
Ptnml(0-2): 310, 13250, 33553, 13686, 305
https://tests.stockfishchess.org/tests/view/64997934dc7002ce609d01e3

Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 145092 W: 39617 L: 39115 D: 66360
Ptnml(0-2): 54, 13691, 44552, 14197, 52
https://tests.stockfishchess.org/tests/view/649a1c5ddc7002ce609d0bff

closes https://github.com/official-stockfish/Stockfish/pull/4644

Bench: 2637784
This commit is contained in:
cj5716 2023-06-26 19:40:22 +08:00 • committed by Joost VandeVondele
parent e355c70594
commit e551964ef6
1 changed files with 4 additions and 0 deletions
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4
src/search.cpp
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@ -1097,6 +1097,10 @@ moves_loop: // When in check, search starts here
else if (ttValue >= beta) else if (ttValue >= beta)
extension = -2 - !PvNode; extension = -2 - !PvNode;
// If we are on a cutNode, reduce it based on depth (negative extension) (~1 Elo)
else if (cutNode)
extension = depth > 8 && depth < 17 ? -3 : -1;
// If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo) // If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo)
else if (ttValue <= value) else if (ttValue <= value)
extension = -1; extension = -1;