Revert "Revert "Shuffle detection #2064""

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 645b1f9cb0b80b6395717733e6b9b978a2565af0..95b14021c4e51bc7f7d8ad3d89686fd4ee8739c2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -607,6 +607,15 @@ 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
+        && ss->ply > 36
+        && depth < 3 * ONE_PLY
+        && 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
@@ -623,9 +632,8 @@ namespace {
                 if (!pos.capture_or_promotion(ttMove))
                     update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
 
-                // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
-                if (    ((ss-1)->moveCount == 1 || (ss-1)->currentMove == (ss-1)->killers[0])
-                     && !pos.captured_piece())
+                // Extra penalty for early quiet moves of the previous ply
+                if ((ss-1)->moveCount <= 2 && !pos.captured_piece())
                         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
             }
             // Penalty for a quiet ttMove that fails low
@@ -925,6 +933,10 @@ moves_loop: // When in check, search starts from here
                && (pos.blockers_for_king(~us) & from_sq(move) || pos.see_ge(move)))
           extension = ONE_PLY;
 
+      // Shuffle extension
+      else if(pos.rule50_count() > 14 && ss->ply > 14 && depth < 3 * ONE_PLY && PvNode)
+          extension = ONE_PLY;
+
       // Castling extension
       else if (type_of(move) == CASTLING)
           extension = ONE_PLY;
@@ -1227,8 +1239,7 @@ moves_loop: // When in check, search starts from here
 
     Thread* thisThread = pos.this_thread();
     (ss+1)->ply = ss->ply + 1;
-    ss->currentMove = bestMove = MOVE_NONE;
-    ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+    bestMove = MOVE_NONE;
     inCheck = pos.checkers();
     moveCount = 0;