Discourage '2-fold' repetition at root. Bench: 4294827

dsmsgms · Nov 21, 2022 · 2349455 · 2349455
1 parent d8f3209
commit 2349455
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/src/search.cpp b/src/search.cpp
@@ -1454,6 +1454,12 @@ namespace {
             (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
                                              : -(ss-1)->staticEval;
 
+        if (ss->ply >= 3) {
+            // Discourage "2-fold" repetition at root
+            Move ply1move = (ss-(ss->ply-1))->currentMove, ply3move = (ss-(ss->ply-3))->currentMove;
+            bestValue -= (ply3move == make_move(to_sq(ply1move), from_sq(ply1move)));
+        }
+
         // Stand pat. Return immediately if static value is at least beta
         if (bestValue >= beta)
         {