From 9b90cd88f0ddd568e43161a0ada7daf02fc59c67 Mon Sep 17 00:00:00 2001
From: Stefan Geschwentner <stgeschwentner@gmail.com>
Date: Wed, 15 May 2024 04:10:58 +0200
Subject: [PATCH] Reduce more when improving and ttvalue is lower than alpha

More reduction if position is improving but value from TT doesn't
exceeds alpha but the tt move is excluded.

This idea is based on following LMR condition tuning
https://tests.stockfishchess.org/tests/view/66423a1bf9f4e8fc783cba37
by using only three of the four largest terms P[3], P[18] and P[12].

Passed STC:
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 27840 W: 7309 L: 7004 D: 13527
Ptnml(0-2): 85, 3219, 7018, 3502, 96
https://tests.stockfishchess.org/tests/view/6643dc1cbc537f56194508ba

Passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 191280 W: 48656 L: 48020 D: 94604
Ptnml(0-2): 78, 20979, 52903, 21589, 91
https://tests.stockfishchess.org/tests/view/6643e543bc537f5619451683

closes https://github.com/official-stockfish/Stockfish/pull/5245

Bench: 1430835
---
 src/search.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/search.cpp b/src/search.cpp
index 09a9cc92..2dadd0dc 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1134,6 +1134,9 @@ moves_loop:  // When in check, search starts here
         if (PvNode)
             r--;
 
+        if (improving && ttValue <= alpha && move != ttMove)
+            r++;
+
         // Increase reduction if next ply has a lot of fail high (~5 Elo)
         if ((ss + 1)->cutoffCnt > 3)
             r++;