From 23494555411e120573a4f2b62e519aa9b1648204 Mon Sep 17 00:00:00 2001
From: Douglas Matos Gomes <dsmsgomes@gmail.com>
Date: Sun, 20 Nov 2022 23:21:40 -0300
Subject: [PATCH] Discourage '2-fold' repetition at root. Bench: 4294827

---
 src/search.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/search.cpp b/src/search.cpp
index fa87f1c3f0f..1d1f0735a15 100644
--- 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)
         {