Simplify away improvement term in null move search

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 740ad71efee01461cc40b5992c757f2caa4db81e..656558f87c472821f20898965dd0be30e8d47a1e 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -779,10 +779,11 @@ namespace {
         && (ss-1)->statScore < 17329
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 21 * depth - improvement / 13 + 258
+        &&  ss->staticEval >= beta - 21 * depth + 258
         && !excludedMove
         &&  pos.non_pawn_material(us)
-        && (ss->ply >= thisThread->nmpMinPly))
+        &&  ss->ply >= thisThread->nmpMinPly
+        &&  beta > VALUE_TB_LOSS_IN_MAX_PLY)
     {
         assert(eval - beta >= 0);
 
@@ -1097,6 +1098,10 @@ moves_loop: // When in check, search starts here
               else if (ttValue >= beta)
                   extension = -2 - !PvNode;
 
+              // If we are on a cutNode, reduce it based on depth (negative extension) (~1 Elo)
+              else if (cutNode)
+                  extension = depth > 8 && depth < 17 ? -3 : -1;
+
               // If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo)
               else if (ttValue <= value)
                   extension = -1;