From 6a6e32dfc80488dfdcd6c23e601063b47729e890 Mon Sep 17 00:00:00 2001
From: FauziAkram <fauzi.dabat@hotmail.com>
Date: Sat, 1 Apr 2023 15:22:53 +0300
Subject: [PATCH] Decrease Depth more for positions not in TT.

If the position is not in TT, decrease depth by 2
or by 4 if the TT entry for the current position was hit
and the stored depth is greater than or equal to the current depth.

Many thanks to Vizvezdenec as the main idea was his.

Passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 70664 W: 18995 L: 18639 D: 33030
Ptnml(0-2): 228, 7712, 19090, 8080, 222
https://tests.stockfishchess.org/tests/view/64258a8bdb43ab2ba6f9b682

Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 85040 W: 23227 L: 22836 D: 38977
Ptnml(0-2): 26, 8115, 25867, 8466, 46
https://tests.stockfishchess.org/tests/view/64262057db43ab2ba6f9d0e7

closes https://github.com/official-stockfish/Stockfish/pull/4482

bench: 4380438
---
 src/search.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 3136046d..46cca50f 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -899,11 +899,11 @@ namespace {
         Eval::NNUE::hint_common_parent_position(pos);
     }
 
-    // Step 11. If the position is not in TT, decrease depth by 3.
+    // Step 11. If the position is not in TT, decrease depth by 2 (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
     // Use qsearch if depth is equal or below zero (~9 Elo)
     if (    PvNode
         && !ttMove)
-        depth -= 3;
+        depth -= 2 + 2 * (ss->ttHit &&  tte->depth() >= depth);
 
     if (depth <= 0)
         return qsearch<PV>(pos, ss, alpha, beta);