Less LMR at root

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index f9fdc261b16c9185520fa79d7a0d02e0eccdf2a6..866444a8388e29236d50ec4a609a59f11f45df74 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -18,6 +18,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <algorithm>
 #include <cassert>
 #include <cmath>
 #include <cstring>   // For std::memset
@@ -593,7 +594,10 @@ namespace {
     // starts with statScore = 0. Later grandchildren start with the last calculated
     // statScore of the previous grandchild. This influences the reduction rules in
     // LMR which are based on the statScore of parent position.
-    (ss+2)->statScore = 0;
+       if (rootNode)
+               (ss + 4)->statScore = 0;
+       else
+               (ss + 2)->statScore = 0;
 
     // Step 4. Transposition table lookup. We don't want the score of a partial
     // search to overwrite a previous full search TT value, so we use a different
@@ -894,7 +898,7 @@ moves_loop: // When in check, search starts from here
           &&  move == ttMove
           && !rootNode
           && !excludedMove // Avoid recursive singular search
-      /*  &&  ttValue != VALUE_NONE Already implicit in the next condition */
+       /* &&  ttValue != VALUE_NONE Already implicit in the next condition */
           &&  abs(ttValue) < VALUE_KNOWN_WIN
           && (tte->bound() & BOUND_LOWER)
           &&  tte->depth() >= depth - 3 * ONE_PLY
@@ -927,6 +931,13 @@ moves_loop: // When in check, search starts from here
       else if (type_of(move) == CASTLING)
           extension = ONE_PLY;
 
+      // Shuffle extension
+      else if (   PvNode
+               && pos.rule50_count() > 18
+               && depth < 3 * ONE_PLY
+               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches
+          extension = ONE_PLY;
+
       // Passed pawn extension
       else if (   move == ss->killers[0]
                && pos.advanced_pawn_push(move)
@@ -996,8 +1007,10 @@ moves_loop: // When in check, search starts from here
       // Step 16. Reduced depth search (LMR). If the move fails high it will be
       // re-searched at full depth.
       if (    depth >= 3 * ONE_PLY
-          &&  moveCount > 1
-          && (!captureOrPromotion || moveCountPruning))
+          &&  moveCount > 1 + 3 * rootNode
+          && (  !captureOrPromotion
+              || moveCountPruning
+              || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha))
       {
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
@@ -1194,8 +1207,8 @@ moves_loop: // When in check, search starts from here
   }
 
 
-  // qsearch() is the quiescence search function, which is called by the main
-  // search function with depth zero, or recursively with depth less than ONE_PLY.
+  // qsearch() is the quiescence search function, which is called by the main search
+  // function with zero depth, or recursively with further decreasing depth per call.
   template <NodeType NT>
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {