Change multi-cut pruning condition

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index df777b3b170d48b25b0681e2502715678d46d515..f682da3ae6e8e9d6c92d709225871c168a3f9464 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -149,7 +149,7 @@ namespace {
 void Search::init() {
 
   for (int i = 1; i < MAX_MOVES; ++i)
-     Reductions[i] = int(22.9 * std::log(i));
+      Reductions[i] = int(22.9 * std::log(i));
 }
 
 
@@ -240,17 +240,13 @@ void MainThread::search() {
           minScore = std::min(minScore, th->rootMoves[0].score);
 
       // Vote according to score and depth, and select the best thread
-      int64_t bestVote = 0;
       for (Thread* th : Threads)
       {
           votes[th->rootMoves[0].pv[0]] +=
-               (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
+              (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
 
-          if (votes[th->rootMoves[0].pv[0]] > bestVote)
-          {
-              bestVote = votes[th->rootMoves[0].pv[0]];
+          if (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]])
               bestThread = th;
-          }
       }
   }
 
@@ -538,13 +534,13 @@ namespace {
     bool ttHit, ttPv, inCheck, givesCheck, improving;
     bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
     Piece movedPiece;
-    int moveCount, captureCount, quietCount;
+    int moveCount, captureCount, quietCount, singularLMR;
 
     // Step 1. Initialize node
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
     Color us = pos.side_to_move();
-    moveCount = captureCount = quietCount = ss->moveCount = 0;
+    moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0;
     bestValue = -VALUE_INFINITE;
     maxValue = VALUE_INFINITE;
 
@@ -589,10 +585,10 @@ namespace {
     // starts with statScore = 0. Later grandchildren start with the last calculated
     // statScore of the previous grandchild. This influences the reduction rules in
     // LMR which are based on the statScore of parent position.
-       if (rootNode)
-               (ss + 4)->statScore = 0;
-       else
-               (ss + 2)->statScore = 0;
+    if (rootNode)
+        (ss + 4)->statScore = 0;
+    else
+        (ss + 2)->statScore = 0;
 
     // Step 4. Transposition table lookup. We don't want the score of a partial
     // search to overwrite a previous full search TT value, so we use a different
@@ -850,7 +846,6 @@ moves_loop: // When in check, search starts from here
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
-    int singularExtensionLMRmultiplier = 0;
 
     // Step 12. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.
@@ -907,20 +902,22 @@ moves_loop: // When in check, search starts from here
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)
-              {
+          {
               extension = ONE_PLY;
-              singularExtensionLMRmultiplier++;
+              singularLMR++;
+
               if (value < singularBeta - std::min(3 * depth / ONE_PLY, 39))
-                 singularExtensionLMRmultiplier++;
-              }
+                  singularLMR++;
+          }
 
           // Multi-cut pruning
           // Our ttMove is assumed to fail high, and now we failed high also on a reduced
           // search without the ttMove. So we assume this expected Cut-node is not singular,
-          // that is multiple moves fail high, and we can prune the whole subtree by returning
-          // the hard beta bound.
-          else if (cutNode && singularBeta > beta)
-              return beta;
+          // that multiple moves fail high, and we can prune the whole subtree by returning
+          // a soft bound.
+          else if (   eval >= beta
+                   && singularBeta >= beta)
+              return singularBeta;
       }
 
       // Check extension (~2 Elo)
@@ -936,7 +933,7 @@ moves_loop: // When in check, search starts from here
       else if (   PvNode
                && pos.rule50_count() > 18
                && depth < 3 * ONE_PLY
-               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches
+               && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4)  // To avoid too many extensions
           extension = ONE_PLY;
 
       // Passed pawn extension
@@ -984,7 +981,7 @@ moves_loop: // When in check, search starts from here
               if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
                   continue;
           }
-          else if ((!givesCheck || !(pos.blockers_for_king(~us) & from_sq(move)))
+          else if ((!givesCheck || !extension)
                   && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo)
                   continue;
       }
@@ -1023,8 +1020,9 @@ moves_loop: // When in check, search starts from here
           // Decrease reduction if opponent's move count is high (~10 Elo)
           if ((ss-1)->moveCount > 15)
               r -= ONE_PLY;
+
           // Decrease reduction if move has been singularly extended
-          r -= singularExtensionLMRmultiplier * ONE_PLY;
+          r -= singularLMR * ONE_PLY;
 
           if (!captureOrPromotion)
           {
@@ -1060,7 +1058,7 @@ moves_loop: // When in check, search starts from here
               r -= ss->statScore / 20000 * ONE_PLY;
           }
 
-          Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY);
+          Depth d = clamp(newDepth - r, ONE_PLY, newDepth);
 
           value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
 
@@ -1366,6 +1364,7 @@ moves_loop: // When in check, search starts from here
 
       // Don't search moves with negative SEE values
       if (  (!inCheck || evasionPrunable)
+          && (!givesCheck || !(pos.blockers_for_king(~pos.side_to_move()) & from_sq(move)))
           && !pos.see_ge(move))
           continue;
 
@@ -1476,7 +1475,7 @@ moves_loop: // When in check, search starts from here
   void update_capture_stats(const Position& pos, Move move,
                             Move* captures, int captureCount, int bonus) {
 
-      CapturePieceToHistory& captureHistory =  pos.this_thread()->captureHistory;
+      CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
       Piece moved_piece = pos.moved_piece(move);
       PieceType captured = type_of(pos.piece_on(to_sq(move)));
 
@@ -1717,7 +1716,7 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
     }
     else
     {
-        // Assign the same rank to all moves
+        // Clean up if root_probe() and root_probe_wdl() have failed
         for (auto& m : rootMoves)
             m.tbRank = 0;
     }