From 28f8663f3947e716fefe392a463060dc12e39849 Mon Sep 17 00:00:00 2001
From: Viren6 <94880762+Viren6@users.noreply.github.com>
Date: Tue, 2 Jan 2024 02:54:45 +0000
Subject: [PATCH] Modify ttPV reduction

This patch modifies ttPV reduction by reducing 1 more unless ttValue is above alpha.

Inspired from @pb00068 https://tests.stockfishchess.org/tests/view/658060796a3b4f6202215f1f

Passed STC:
https://tests.stockfishchess.org/tests/view/6591867679aa8af82b958328
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 37856 W: 9727 L: 9407 D: 18722
Ptnml(0-2): 99, 4444, 9568, 4672, 145

Passed LTC:
https://tests.stockfishchess.org/tests/view/6591d9b679aa8af82b958a6c
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 128256 W: 32152 L: 31639 D: 64465
Ptnml(0-2): 64, 14364, 34772, 14851, 77

closes https://github.com/official-stockfish/Stockfish/pull/4957

Bench: 1176235
---
 src/search.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index 3553065f..aae3625a 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1152,7 +1152,7 @@ moves_loop:  // When in check, search starts here
 
         // Decrease reduction if position is or has been on the PV (~4 Elo)
         if (ss->ttPv && !likelyFailLow)
-            r -= cutNode && tte->depth() >= depth ? 3 : 2;
+            r -= 1 + (cutNode && tte->depth() >= depth) + (ttValue > alpha);
 
         // Decrease reduction if opponent's move count is high (~1 Elo)
         if ((ss - 1)->moveCount > 7)