Fix for SF getting stuck during search (issue #5023)

pb00067 · Disservin · commit c73f21df97e9 · 2025-11-30T21:58:34.000+01:00
Among several passed similar versions this is the simpliest one. Passed STC non-regression https://tests.stockfishchess.org/tests/view/691f3b4aacb6dbdf23d07d11 LLR: 2.93 (-2.94,2.94) <-1.75,0.25> Total: 126368 W: 32607 L: 32489 D: 61272 Ptnml(0-2): 408, 13974, 34298, 14100, 404 Passed LTC non-regression https://tests.stockfishchess.org/tests/view/69209712acb6dbdf23d0836a LLR: 2.94 (-2.94,2.94) <-1.75,0.25> Total: 114786 W: 29097 L: 28976 D: 56713 Ptnml(0-2): 53, 11841, 33488, 11954, 57 closes #6447 Bench: 2941767
diff --git a/src/search.cpp b/src/search.cpp
@@ -141,6 +141,16 @@ void update_all_stats(const Position& pos,
                       Move            TTMove,
                       int             moveCount);
 
+bool isShuffling(Move move, Stack* const ss, const Position& pos) {
+    if (type_of(pos.moved_piece(move)) == PAWN || pos.capture_stage(move)
+        || pos.rule50_count() < 10)
+        return false;
+    if (pos.state()->pliesFromNull <= 6 || ss->ply < 20)
+        return false;
+    return move.from_sq() == (ss - 2)->currentMove.to_sq()
+        && (ss - 2)->currentMove.from_sq() == (ss - 4)->currentMove.to_sq();
+}
+
 }  // namespace
 
 Search::Worker::Worker(SharedState&                    sharedState,
@@ -1114,7 +1124,7 @@ Value Search::Worker::search(
         // and lower extension margins scale well.
         if (!rootNode && move == ttData.move && !excludedMove && depth >= 6 + ss->ttPv
             && is_valid(ttData.value) && !is_decisive(ttData.value) && (ttData.bound & BOUND_LOWER)
-            && ttData.depth >= depth - 3)
+            && ttData.depth >= depth - 3 && !isShuffling(move, ss, pos))
         {
             Value singularBeta  = ttData.value - (53 + 75 * (ss->ttPv && !PvNode)) * depth / 60;
             Depth singularDepth = newDepth / 2;
