From 757ae2ff53714b975066cd9eb3b518611bc06b11 Mon Sep 17 00:00:00 2001
From: Muzhen Gaming <61100393+XInTheDark@users.noreply.github.com>
Date: Sat, 25 Nov 2023 22:16:56 +0800
Subject: [PATCH] Simplify move history reduction

Recent VLTC search tuning has suggested that the depth limit can be increased
by a lot. This patch simplifies away the depth-based bonus from statScore
reduction, making the divisor a constant.

Passed STC:
https://tests.stockfishchess.org/tests/view/656201f5136acbc573549791
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 91520 W: 23130 L: 22967 D: 45423
Ptnml(0-2): 282, 10947, 23141, 11106, 284

Passed LTC:
https://tests.stockfishchess.org/tests/view/6562b43a136acbc57354a581
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 352902 W: 86796 L: 86917 D: 179189
Ptnml(0-2): 190, 40227, 95741, 40100, 193

closes https://github.com/official-stockfish/Stockfish/pull/4886

Bench: 1297179
---
 src/search.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index 55be43b3..6580f520 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1165,7 +1165,7 @@ moves_loop:  // When in check, search starts here
                       + (*contHist[3])[movedPiece][to_sq(move)] - 3848;
 
         // Decrease/increase reduction for moves with a good/bad history (~25 Elo)
-        r -= ss->statScore / (10216 + 3855 * (depth > 5 && depth < 23));
+        r -= ss->statScore / 14200;
 
         // Step 17. Late moves reduction / extension (LMR, ~117 Elo)
         // We use various heuristics for the sons of a node after the first son has
-- 
2.39.2