LMR for captures not cracking alpha

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 517499b543971798d432ab0856049ce11a8343a2..bafc374ba29993ab05b62c8ec95729990a7fbbb8 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
@@ -606,15 +610,6 @@ namespace {
             : ttHit    ? tte->move() : MOVE_NONE;
     ttPv = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY);
 
-    // If position has been searched at higher depths and we are shuffling,
-    // return value_draw.
-    if (   pos.rule50_count() > 36 - 6 * (pos.count<ALL_PIECES>() > 14)
-        && ss->ply > 36 - 6 * (pos.count<ALL_PIECES>() > 14)
-        && ttHit
-        && tte->depth() > depth
-        && pos.count<PAWN>() > 0)
-           return VALUE_DRAW;
-
     // At non-PV nodes we check for an early TT cutoff
     if (  !PvNode
         && ttHit
@@ -903,7 +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
@@ -939,9 +934,8 @@ moves_loop: // When in check, search starts from here
       // Shuffle extension
       else if (   PvNode
                && pos.rule50_count() > 18
-               && ss->ply > 18
                && depth < 3 * ONE_PLY
-               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid infinite loops
+               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches
           extension = ONE_PLY;
 
       // Passed pawn extension
@@ -1014,7 +1008,9 @@ moves_loop: // When in check, search starts from here
       // re-searched at full depth.
       if (    depth >= 3 * ONE_PLY
           &&  moveCount > 1
-          && (!captureOrPromotion || moveCountPruning))
+          && (  !captureOrPromotion
+              || moveCountPruning
+              || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha))
       {
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
@@ -1211,8 +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) {