From: Stéphane Nicolet <cassio@free.fr>
Date: Fri, 6 Nov 2020 18:20:27 +0000 (+0100)
Subject: Qsearch pruning: follow-up
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=392b529c3f52103ad47ad096b86103c17758cb4f

Qsearch pruning: follow-up

This is a follow-up of the recent qsearch pruning patch in
https://github.com/official-stockfish/Stockfish/commit/a260c9a8a24a2630a900efc3821000c3481b0c5d

We now use the same guard condition (testing that we already have a defense with
a score better  score than a TB loss) for all pruning heuristics in qsearch().
This allows some pruning when in check, but  in a controlled way to ensure that
no wrong mate scores appear.

Tested with Elo-gaining bounds:

STC:
LLR: 2.97 (-2.94,2.94) {-0.25,1.25}
Total: 22632 W: 2433 L: 2264 D: 17935
Ptnml(0-2): 98, 1744, 7487, 1865, 122
https://tests.stockfishchess.org/tests/view/5fa59405936c54e11ec99515

LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.25}
Total: 105432 W: 4965 L: 4648 D: 95819
Ptnml(0-2): 85, 4110, 44011, 4423, 87
https://tests.stockfishchess.org/tests/view/5fa5b609936c54e11ec9952a

closes https://github.com/official-stockfish/Stockfish/pull/3221

Bench: 3578092
---

diff --git a/src/search.cpp b/src/search.cpp
index 6e37fba1..b5b93bf0 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1525,7 +1525,7 @@ moves_loop: // When in check, search starts from here
       moveCount++;
 
       // Futility pruning
-      if (   !ss->inCheck
+      if (    bestValue > VALUE_TB_LOSS_IN_MAX_PLY
           && !givesCheck
           &&  futilityBase > -VALUE_KNOWN_WIN
           && !pos.advanced_pawn_push(move))
@@ -1552,7 +1552,7 @@ moves_loop: // When in check, search starts from here
       }
 
       // Do not search moves with negative SEE values
-      if (   !ss->inCheck
+      if (    bestValue > VALUE_TB_LOSS_IN_MAX_PLY
           && !(givesCheck && pos.is_discovery_check_on_king(~pos.side_to_move(), move))
           && !pos.see_ge(move))
           continue;