Reduce more if multiple moves exceed alpha

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index df4af54a5eebb54308ce6d849f461f4feacf47da..73fc8a55fef18d57212ff4bf0deaf7a87ffa846f 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -80,7 +80,7 @@ namespace {
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return d > 14 ? 73 : 6 * d * d + 229 * d - 215;
+    return std::min((6 * d + 229) * d - 215 , 2000);
   }
 
   // Add a small random component to draw evaluations to avoid 3-fold blindness
@@ -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
@@ -1187,7 +1186,9 @@ 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 +1341,10 @@ 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 +1503,6 @@ 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;
@@ -1709,8 +1712,8 @@ moves_loop: // When in check, search starts here
     PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
 
     bonus1 = stat_bonus(depth + 1);
-    bonus2 = bestValue > beta + PawnValueMg ? bonus1                                 // larger bonus
-                                            : std::min(bonus1, stat_bonus(depth));   // smaller bonus
+    bonus2 = bestValue > beta + PawnValueMg ? bonus1               // larger bonus
+                                            : stat_bonus(depth);   // smaller bonus
 
     if (!pos.capture_or_promotion(bestMove))
     {