From 30fdbf43283eb0d2f8e5ca325877d3e514758804 Mon Sep 17 00:00:00 2001
From: Michael Chaly <Vizvezdenec@gmail.com>
Date: Fri, 10 Sep 2021 11:38:50 +0300
Subject: [PATCH] Decrease depth for cutnodes with no tt move

By analogy to existing logic of decreasing depth for PvNodes w/o tt move
do the same for cutNodes.

Passed STC
https://tests.stockfishchess.org/tests/view/613abf5a689039fce12e1155
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 90336 W: 23108 L: 22804 D: 44424
Ptnml(0-2): 286, 10316, 23642, 10656, 268

Passed LTC
https://tests.stockfishchess.org/tests/view/613ae330689039fce12e1172
LLR: 2.94 (-2.94,2.94) <0.50,3.50>
Total: 37736 W: 9607 L: 9346 D: 18783
Ptnml(0-2): 21, 3917, 10730, 4180, 20

closes https://github.com/official-stockfish/Stockfish/pull/3697

bench 5891181
---
 src/search.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index ed5dd6c2..a4b17d9d 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -903,12 +903,17 @@ namespace {
          ss->ttPv = ttPv;
     }
 
-    // Step 10. If the position is not in TT, decrease depth by 2
+    // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type
     if (   PvNode
         && depth >= 6
         && !ttMove)
         depth -= 2;
 
+    if (   cutNode
+        && depth >= 9
+        && !ttMove)
+        depth--;
+
 moves_loop: // When in check, search starts here
 
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
-- 
2.39.2