If near beta generate checks at -OnePly

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 2c4d5ece2eb237f861890d7ac4add6c1c8c273ed..0c6cf8becbea5abd01e4918d2d3e4e60a317e6d4 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -193,9 +193,6 @@ namespace {
 
   /// Variables initialized by UCI options
 
-  // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
-  int LMRPVMoves, LMRNonPVMoves;
-
   // Depth limit for use of dynamic threat detection
   Depth ThreatDepth;
 
@@ -426,8 +423,6 @@ bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
   MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
   MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
 
-  LMRPVMoves    = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
-  LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
   ThreatDepth   = get_option_value_int("Threat Depth") * OnePly;
 
   Chess960 = get_option_value_bool("UCI_Chess960");
@@ -566,7 +561,7 @@ void init_threads() {
 #endif
 
   // Init our logarithmic lookup table
-  for (int i = 0; i < 512; i++)
+  for (i = 0; i < 512; i++)
       lnArray[i] = log(double(i)); // log() returns base-e logarithm
 
   for (i = 0; i < THREAD_MAX; i++)
@@ -1692,10 +1687,14 @@ namespace {
     if (bestValue > alpha)
         alpha = bestValue;
 
+    // If we are near beta then try to get a cutoff pushing checks a bit further
+    bool deepChecks = depth == -OnePly && staticValue >= beta - PawnValueMidgame / 8;
+
     // Initialize a MovePicker object for the current position, and prepare
-    // to search the moves.  Because the depth is <= 0 here, only captures,
-    // queen promotions and checks (only if depth == 0) will be generated.
-    MovePicker mp = MovePicker(pos, ttMove, depth, H);
+    // to search the moves. Because the depth is <= 0 here, only captures,
+    // queen promotions and checks (only if depth == 0 or depth == -OnePly
+    // and we are near beta) will be generated.
+    MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
     CheckInfo ci(pos);
     enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
     futilityBase = staticValue + FutilityMarginQS + ei.futilityMargin;