- if (!captureOrPromotion)
- {
- // Increase reduction if ttMove is a capture (~3 Elo)
- if (ttCapture)
- r++;
-
- // Increase reduction at root if failing high
- r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0;
-
- // Increase reduction for cut nodes (~10 Elo)
- if (cutNode)
- r += 2;
-
- ss->statScore = thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)]
- + (*contHist[1])[movedPiece][to_sq(move)]
- + (*contHist[3])[movedPiece][to_sq(move)]
- - 4741;
-
- // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= -89 && (ss-1)->statScore < -116)
- r--;
-
- else if ((ss-1)->statScore >= -112 && ss->statScore < -100)
- r++;
-
- // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- // If we are not in check use statScore, but if we are in check we use
- // the sum of main history and first continuation history with an offset.
- if (ss->inCheck)
- r -= (thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)] - 3833) / 16384;
- else
- r -= ss->statScore / 14790;
- }
+ // Increase reduction for cut nodes (~3 Elo)
+ if (cutNode && move != ss->killers[0])
+ r += 2;
+
+ // Increase reduction if ttMove is a capture (~3 Elo)
+ if (ttCapture)
+ r++;
+
+ ss->statScore = thisThread->mainHistory[us][from_to(move)]
+ + (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)]
+ - 4923;
+
+ // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
+ r -= ss->statScore / 14721;
+
+ // In general we want to cap the LMR depth search at newDepth. But if reductions
+ // are really negative and movecount is low, we allow this move to be searched
+ // deeper than the first move (this may lead to hidden double extensions).
+ int deeper = r >= -1 ? 0
+ : moveCount <= 3 ? 2
+ : moveCount <= 5 ? 1
+ : PvNode && depth > 6 ? 1
+ : 0;