Simplify multi-cut condition

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index ef691500e6425b651570b8c85fada80f4cf1c9ef..28049e87dcd8dd49a4f21242c88bf8ffa1d9a1bd 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -591,13 +591,13 @@ namespace {
     bool captureOrPromotion, doFullDepthSearch, moveCountPruning,
          ttCapture, singularQuietLMR, noLMRExtension;
     Piece movedPiece;
-    int moveCount, captureCount, quietCount;
+    int moveCount, captureCount, quietCount, bestMoveCount;
 
     // Step 1. Initialize node
     ss->inCheck        = pos.checkers();
     priorCapture       = pos.captured_piece();
     Color us           = pos.side_to_move();
-    moveCount          = captureCount = quietCount = ss->moveCount = 0;
+    moveCount          = bestMoveCount = captureCount = quietCount = ss->moveCount = 0;
     bestValue          = -VALUE_INFINITE;
     maxValue           = VALUE_INFINITE;
 
@@ -790,7 +790,6 @@ namespace {
     else
     {
         // In case of null move search use previous static eval with a different sign
-        // and addition of two tempos
         if ((ss-1)->currentMove != MOVE_NULL)
             ss->staticEval = eval = evaluate(pos);
         else
@@ -1124,18 +1123,9 @@ moves_loop: // When in check, search starts here
           else if (singularBeta >= beta)
               return singularBeta;
 
-          // If the eval of ttMove is greater than beta we try also if there is another
-          // move that pushes it over beta, if so the position also has probably multiple
-          // moves giving fail highs. We will then reduce the ttMove (negative extension).
+          // If the eval of ttMove is greater than beta, we reduce it (negative extension)
           else if (ttValue >= beta)
-          {
-              ss->excludedMove = move;
-              value = search<NonPV>(pos, ss, beta - 1, beta, (depth + 3) / 2, cutNode);
-              ss->excludedMove = MOVE_NONE;
-
-              if (value >= beta)
-                  extension = -2;
-          }
+              extension = -2;
       }
 
       // Capture extensions for PvNodes and cutNodes
@@ -1187,7 +1177,9 @@ moves_loop: // When in check, search starts here
       {
           Depth r = reduction(improving, depth, moveCount, rangeReduction > 2);
 
-          if (PvNode)
+          // Decrease reduction if on the PV (~2 Elo)
+          if (   PvNode
+              && bestMoveCount <= 3)
               r--;
 
           // Decrease reduction if the ttHit running average is large (~0 Elo)
@@ -1340,7 +1332,10 @@ moves_loop: // When in check, search starts here
                   update_pv(ss->pv, move, (ss+1)->pv);
 
               if (PvNode && value < beta) // Update alpha! Always alpha < beta
+              {
                   alpha = value;
+                  bestMoveCount++;
+              }
               else
               {
                   assert(value >= beta); // Fail high
@@ -1499,7 +1494,6 @@ moves_loop: // When in check, search starts here
         }
         else
             // In case of null move search use previous static eval with a different sign
-            // and addition of two tempos
             ss->staticEval = bestValue =
             (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
                                              : -(ss-1)->staticEval;