From: Stéphane Nicolet <cassio@free.fr>
Date: Thu, 23 Sep 2021 09:20:03 +0000 (+0200)
Subject: Tweak doubly singular condition (Topo's patch)
X-Git-Url: https://git.sesse.net/?a=commitdiff_plain;ds=sidebyside;h=ff3fa0c664a5799e5531b0908018c59633d761bf;p=stockfish

Tweak doubly singular condition (Topo's patch)

This patch relax a little bit the condition for doubly singular moves
(ie moves that are so forced that we think that they deserve a local
double extension of the search). We lower the margin and allow up to
six such double extensions in the path between the root and the critical
node.

Original idea by Siad Daboul (@TopoIogist) in PR #3709

Tested with the previous commit:

passed STC:
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 33048 W: 8458 L: 8236 D: 16354
Ptnml(0-2): 120, 3701, 8660, 3923, 120
https://tests.stockfishchess.org/tests/view/614b24347bdc23e77ceb88fe

passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,3.50>
Total: 54176 W: 13712 L: 13406 D: 27058
Ptnml(0-2): 36, 5653, 15399, 5969, 31
https://tests.stockfishchess.org/tests/view/614b3b727bdc23e77ceb8911

closes https://github.com/official-stockfish/Stockfish/pull/3714

Bench: 5792377
---

diff --git a/src/search.cpp b/src/search.cpp
index 10a9027b..9b56bd2b 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1107,8 +1107,8 @@ moves_loop: // When in check, search starts here
 
               // Avoid search explosion by limiting the number of double extensions
               if (   !PvNode
-                  && value < singularBeta - 93
-                  && ss->doubleExtensions < 3)
+                  && value < singularBeta - 75
+                  && ss->doubleExtensions <= 6)
               {
                   extension = 2;
                   noLMRExtension = true;