Adjust reductions based on current node delta and root delta

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 2abfbaf2f3dd35d6f0fb414a03fa13b327bcca90..8a4db35185921776e4288e02e83c8744c2c35db7 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -69,9 +69,9 @@ namespace {
   // Reductions lookup table, initialized at startup
   int Reductions[MAX_MOVES]; // [depth or moveNumber]
 
-  Depth reduction(bool i, Depth d, int mn, bool rangeReduction) {
+  Depth reduction(bool i, Depth d, int mn, bool rangeReduction, Value delta, Value rootDelta) {
     int r = Reductions[d] * Reductions[mn];
-    return (r + 534) / 1024 + (!i && r > 904) + rangeReduction;
+    return (r + 1358 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 904) + rangeReduction;
   }
 
   constexpr int futility_move_count(bool improving, Depth depth) {
@@ -1015,6 +1015,8 @@ moves_loop: // When in check, search starts here
       // Calculate new depth for this move
       newDepth = depth - 1;
 
+      Value delta = beta - alpha;
+
       // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding.
       if (  !rootNode
           && pos.non_pawn_material(us)
@@ -1024,7 +1026,7 @@ moves_loop: // When in check, search starts here
           moveCountPruning = moveCount >= futility_move_count(improving, depth);
 
           // Reduced depth of the next LMR search
-          int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0);
+          int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2, delta, thisThread->rootDelta), 0);
 
           if (   captureOrPromotion
               || givesCheck)
@@ -1052,8 +1054,6 @@ moves_loop: // When in check, search starts here
 
               history += thisThread->mainHistory[us][from_to(move)];
 
-              lmrDepth = std::max(0, lmrDepth - (beta - alpha < thisThread->rootDelta / 4));
-
               // Futility pruning: parent node (~5 Elo)
               if (   !ss->inCheck
                   && lmrDepth < 8
@@ -1161,12 +1161,11 @@ moves_loop: // When in check, search starts here
               || !captureOrPromotion
               || (cutNode && (ss-1)->moveCount > 1)))
       {
-          Depth r = reduction(improving, depth, moveCount, rangeReduction > 2);
+          Depth r = reduction(improving, depth, moveCount, rangeReduction > 2, delta, thisThread->rootDelta);
 
           // Decrease reduction at some PvNodes (~2 Elo)
           if (   PvNode
-              && bestMoveCount <= 3
-              && beta - alpha >= thisThread->rootDelta / 4)
+              && bestMoveCount <= 3)
               r--;
 
           // Decrease reduction if position is or has been on the PV
@@ -1175,10 +1174,6 @@ moves_loop: // When in check, search starts here
               && !likelyFailLow)
               r -= 2;
 
-          // Increase reduction at non-PV nodes (~3 Elo)
-          if (!PvNode)
-              r++;
-
           // Decrease reduction if opponent's move count is high (~1 Elo)
           if ((ss-1)->moveCount > 13)
               r--;