From 2717bfd67bdedc7c29bbc80dccfdae2aa2be4960 Mon Sep 17 00:00:00 2001
From: Andrew Grant <andrew.github@grantnet.us>
Date: Tue, 1 Oct 2024 22:44:24 -0400
Subject: [PATCH] Fix bug with wrong tt entry write during exit unwind

Bench 1173651
---
 src/search.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/search.cpp b/src/search.cpp
index a206cddab3d..909413e23ef 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -895,6 +895,11 @@ Value Search::Worker::search(
 
             pos.undo_move(move);
 
+            // If a stop occurred, the return value of the search cannot be trusted, and we
+            // must return immediately without updating any histories nor the transposition table.
+            if (threads.stop.load(std::memory_order_relaxed))
+                return VALUE_ZERO;
+
             if (value >= probCutBeta)
             {
                 thisThread->captureHistory[movedPiece][move.to_sq()][type_of(captured)]