From 6d85f43e26cb8632337e67cea5ef88bab78121f3 Mon Sep 17 00:00:00 2001
From: cj5716 <125858804+cj5716@users.noreply.github.com>
Date: Sun, 10 Sep 2023 08:49:18 +0800
Subject: [PATCH] Simplify cutnode depth condition

With this patch, the depth condition for the cutnodes reduction is loosened from
tte->depth() >= depth + 3 to just tte->depth() >= depth.

Passed STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 101152 W: 25830 L: 25682 D: 49640
Ptnml(0-2): 312, 11788, 26258, 11876, 342
https://tests.stockfishchess.org/tests/view/64fd15635dab775b5359eaa6

Passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 82542 W: 20980 L: 20824 D: 40738
Ptnml(0-2): 42, 8795, 23440, 8953, 41
https://tests.stockfishchess.org/tests/view/64fda3545dab775b5359fbf1

closes https://github.com/official-stockfish/Stockfish/pull/4780

Bench: 1479029
---
 src/search.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index eefe5a3b..a745d3bf 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1131,7 +1131,7 @@ moves_loop: // When in check, search starts here
       // Decrease further on cutNodes. (~1 Elo)
       if (   ss->ttPv
           && !likelyFailLow)
-          r -= cutNode && tte->depth() >= depth + 3 ? 3 : 2;
+          r -= cutNode && tte->depth() >= depth ? 3 : 2;
 
       // Decrease reduction if opponent's move count is high (~1 Elo)
       if ((ss-1)->moveCount > 8)
-- 
2.39.2