Stat score initialization: grandchildren

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 23608f7a379570ff72d27a42816ead695e82e7f5..3874852b1bbcac48a34ea38812b79b047a283d5d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -108,6 +108,13 @@ namespace {
   void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
   void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus);
 
+  inline bool gives_check(const Position& pos, Move move) {
+    Color us = pos.side_to_move();
+    return  type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us))
+          ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
+          : pos.gives_check(move);
+  }
+
   // perft() is our utility to verify move generation. All the leaf nodes up
   // to the given depth are generated and counted, and the sum is returned.
   template<bool Root>
@@ -507,7 +514,6 @@ namespace {
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
     moveCount = captureCount = quietCount = ss->moveCount = 0;
-    ss->statScore = 0;
     bestValue = -VALUE_INFINITE;
     maxValue = VALUE_INFINITE;
 
@@ -547,6 +553,13 @@ namespace {
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
 
+    // Initialize statScore to zero for the grandchildren of the current position.
+    // So statScore is shared between all grandchildren and only the first grandchild
+    // 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;
+
     // 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
     // position key in case of an excluded move.
@@ -742,7 +755,18 @@ namespace {
                 assert(depth >= 5 * ONE_PLY);
 
                 pos.do_move(move, st);
-                value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+
+                // Perform a preliminary search at depth 1 to verify that the move holds.
+                // We will only do this search if the depth is not 5, thus avoiding two
+                // searches at depth 1 in a row.
+                if (depth != 5 * ONE_PLY)
+                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, ONE_PLY, !cutNode, true);
+
+                // If the first search was skipped or was performed and held, perform
+                // the regular search.
+                if (depth == 5 * ONE_PLY || value >= rbeta)
+                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+
                 pos.undo_move(move);
                 if (value >= rbeta)
                     return value;
@@ -758,6 +782,7 @@ namespace {
         search<NT>(pos, ss, alpha, beta, d, cutNode, true);
 
         tte = TT.probe(posKey, ttHit);
+        ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
         ttMove = ttHit ? tte->move() : MOVE_NONE;
     }
 
@@ -811,10 +836,7 @@ moves_loop: // When in check, search starts from here
       extension = DEPTH_ZERO;
       captureOrPromotion = pos.capture_or_promotion(move);
       movedPiece = pos.moved_piece(move);
-
-      givesCheck =  type_of(move) == NORMAL && !pos.discovered_check_candidates()
-                  ? pos.check_squares(type_of(movedPiece)) & to_sq(move)
-                  : pos.gives_check(move);
+      givesCheck = gives_check(pos, move);
 
       moveCountPruning =   depth < 16 * ONE_PLY
                         && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
@@ -1164,8 +1186,8 @@ moves_loop: // When in check, search starts from here
     // Transposition table lookup
     posKey = pos.key();
     tte = TT.probe(posKey, ttHit);
-    ttMove = ttHit ? tte->move() : MOVE_NONE;
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
+    ttMove = ttHit ? tte->move() : MOVE_NONE;
 
     if (  !PvNode
         && ttHit
@@ -1226,9 +1248,7 @@ moves_loop: // When in check, search starts from here
     {
       assert(is_ok(move));
 
-      givesCheck =  type_of(move) == NORMAL && !pos.discovered_check_candidates()
-                  ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
-                  : pos.gives_check(move);
+      givesCheck = gives_check(pos, move);
 
       moveCount++;