Simplify depth reduction in IID.

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 1bf855d5589212bc5aaafba6151f2cc2ea2d1c14..8415e24d7434200fae4a5998404fb1f4b6ef8f8a 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -834,8 +834,7 @@ namespace {
     if (    depth >= 8 * ONE_PLY
         && !ttMove)
     {
-        Depth d = 3 * depth / 4 - 2 * ONE_PLY;
-        search<NT>(pos, ss, alpha, beta, d, cutNode);
+        search<NT>(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode);
 
         tte = TT.probe(posKey, ttHit);
         ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
@@ -995,7 +994,14 @@ moves_loop: // When in check, search starts from here
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
           if (captureOrPromotion) // (~5 Elo)
+          {
+              //Increase reduction by comparing opponent's stat score
+              if (   (ss-1)->statScore >= 0 
+                  && thisThread->captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 0)
+                  r += ONE_PLY;
+                            
               r -= r ? ONE_PLY : DEPTH_ZERO;
+          }
           else
           {
               // Decrease reduction if opponent's move count is high (~5 Elo)