From 645b636dfa83648b1b5fdd79d9616e78c2316a0d Mon Sep 17 00:00:00 2001
From: Stefan Geschwentner <git config --global user.email>
Date: Sat, 6 Jun 2026 10:05:50 +0200
Subject: [PATCH] Tweak best move history updates.

If not at an PV node, scale history bonus for the found best move up proportionally to the count of the other moves searched.

Passed STC:
LLR: 2.96 (-2.94,2.94) <0.00,2.00>
Total: 219712 W: 56104 L: 55525 D: 108083
Ptnml(0-2): 565, 25482, 57188, 26051, 570
https://tests.stockfishchess.org/tests/view/6a1306fb818cacc1db0ac5b7

Passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 53988 W: 13851 L: 13498 D: 26639
Ptnml(0-2): 22, 5779, 15051, 6108, 34
https://tests.stockfishchess.org/tests/view/6a1b557e818cacc1db0ad0b8

closes https://github.com/official-stockfish/Stockfish/pull/6871

Bench: 2935474
---
 src/search.cpp | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 12169dede..959792e42 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -144,7 +144,8 @@ void update_all_stats(const Position& pos,
                       SearchedList&   quietsSearched,
                       SearchedList&   capturesSearched,
                       Depth           depth,
-                      Move            ttMove);
+                      Move            ttMove,
+                      bool            PvNode);
 
 bool is_shuffling(Move move, Stack* const ss, const Position& pos) {
     if (pos.capture_stage(move) || pos.rule50_count() < 10)
@@ -1477,7 +1478,7 @@ moves_loop:  // When in check, search starts here
     else if (bestMove)
     {
         update_all_stats(pos, ss, *this, bestMove, prevSq, quietsSearched, capturesSearched, depth,
-                         ttData.move);
+                         ttData.move, PvNode);
         if (!PvNode)
             ttMoveHistory << (bestMove == ttData.move ? 792 : -779);
     }
@@ -1871,7 +1872,8 @@ void update_all_stats(const Position& pos,
                       SearchedList&   quietsSearched,
                       SearchedList&   capturesSearched,
                       Depth           depth,
-                      Move            ttMove) {
+                      Move            ttMove,
+                      bool            PvNode) {
 
     CapturePieceToHistory& captureHistory = workerThread.captureHistory;
     Piece                  movedPiece     = pos.moved_piece(bestMove);
@@ -1881,6 +1883,11 @@ void update_all_stats(const Position& pos,
       std::min(134 * depth - 79, 1572) + 382 * (bestMove == ttMove) + (ss - 1)->statScore / 30;
     int malus = std::min(1005 * depth - 205, 2218);
 
+    if (!PvNode)
+        // Important: don't remove the cast to a 64-bit number else the multiplication
+        // can overflow on 32-bit platforms which would change the bench signature
+        bonus += bonus * uint64_t(quietsSearched.size() + capturesSearched.size()) / 256;
+
     if (!pos.capture_stage(bestMove))
     {
         update_quiet_histories(pos, ss, workerThread, bestMove, bonus * 824 / 1024);