From b280d2f06553e8c8d98379fe547f3b995cc56d59 Mon Sep 17 00:00:00 2001
From: Michael Chaly <Vizvezdenec@gmail.com>
Date: Thu, 30 May 2024 19:27:12 +0300
Subject: [PATCH] Allow tt cutoffs for shallower depths in certain conditions

Current master allows tt cutoffs only when depth
from tt is strictly greater than current node
depth. This patch also allows them when it's equal
and if tt value is lower or equal to beta.

Passed STC:
https://tests.stockfishchess.org/tests/view/66578e2e6b0e318cefa8d447
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 26592 W: 6944 L: 6645 D: 13003
Ptnml(0-2): 67, 3039, 6795, 3318, 77

Passed LTC:
https://tests.stockfishchess.org/tests/view/6657f46b6b0e318cefa8d7e9
LLR: 2.96 (-2.94,2.94) <0.50,2.50>
Total: 142572 W: 36315 L: 35776 D: 70481
Ptnml(0-2): 70, 15666, 39288, 16179, 83

closes https://github.com/official-stockfish/Stockfish/pull/5314

Bench: 1368486
---
 src/search.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index d72dbfa1..638af546 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -618,7 +618,7 @@ Value Search::Worker::search(
         ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
 
     // At non-PV nodes we check for an early TT cutoff
-    if (!PvNode && !excludedMove && tte->depth() > depth
+    if (!PvNode && !excludedMove && tte->depth() > depth - (ttValue <= beta)
         && ttValue != VALUE_NONE  // Possible in case of TT access race or if !ttHit
         && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
     {