Shuffle detection #2108

Bench: 3402947

diff --git a/src/search.cpp b/src/search.cpp
index f9fdc261b16c9185520fa79d7a0d02e0eccdf2a6..517499b543971798d432ab0856049ce11a8343a2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -606,6 +606,15 @@ namespace {
             : ttHit    ? tte->move() : MOVE_NONE;
     ttPv = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY);
 
+    // If position has been searched at higher depths and we are shuffling,
+    // return value_draw.
+    if (   pos.rule50_count() > 36 - 6 * (pos.count<ALL_PIECES>() > 14)
+        && ss->ply > 36 - 6 * (pos.count<ALL_PIECES>() > 14)
+        && ttHit
+        && tte->depth() > depth
+        && pos.count<PAWN>() > 0)
+           return VALUE_DRAW;
+
     // At non-PV nodes we check for an early TT cutoff
     if (  !PvNode
         && ttHit
@@ -927,6 +936,14 @@ moves_loop: // When in check, search starts from here
       else if (type_of(move) == CASTLING)
           extension = ONE_PLY;
 
+      // Shuffle extension
+      else if (   PvNode
+               && pos.rule50_count() > 18
+               && ss->ply > 18
+               && depth < 3 * ONE_PLY
+               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid infinite loops
+          extension = ONE_PLY;
+
       // Passed pawn extension
       else if (   move == ss->killers[0]
                && pos.advanced_pawn_push(move)