From 43e100ae06376d63461005422f26e5517db07c6d Mon Sep 17 00:00:00 2001
From: Nonlinear2 <131959792+Nonlinear2@users.noreply.github.com>
Date: Wed, 6 Nov 2024 21:35:59 +0100
Subject: [PATCH] Use cutnode as TT Cutoff Condition

At low enough depths, fail high with TT only when expected cutnode.

Passed STC:
https://tests.stockfishchess.org/tests/view/6726357b86d5ee47d953da8c
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 41184 W: 10873 L: 10551 D: 19760
Ptnml(0-2): 131, 4728, 10554, 5046, 133

Passed LTC:
https://tests.stockfishchess.org/tests/view/6727326a86d5ee47d953db30
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 270888 W: 69040 L: 68243 D: 133605
Ptnml(0-2): 180, 29385, 75485, 30246, 148

closes https://github.com/official-stockfish/Stockfish/pull/5670

Bench: 805776
---
 src/search.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index 2a2331cb..5fdfdeb2 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -636,7 +636,8 @@ Value Search::Worker::search(
     // At non-PV nodes we check for an early TT cutoff
     if (!PvNode && !excludedMove && ttData.depth > depth - (ttData.value <= beta)
         && ttData.value != VALUE_NONE  // Can happen when !ttHit or when access race in probe()
-        && (ttData.bound & (ttData.value >= beta ? BOUND_LOWER : BOUND_UPPER)))
+        && (ttData.bound & (ttData.value >= beta ? BOUND_LOWER : BOUND_UPPER))
+        && (cutNode == (ttData.value >= beta) || depth > 8))
     {
         // If ttMove is quiet, update move sorting heuristics on TT hit (~2 Elo)
         if (ttData.move && ttData.value >= beta)