If near beta generate checks at -OnePly

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 43fb7067a4692a0ca8915c68316215125e109261..0c6cf8becbea5abd01e4918d2d3e4e60a317e6d4 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -23,6 +23,7 @@
 ////
 
 #include <cassert>
+#include <cmath>
 #include <cstring>
 #include <fstream>
 #include <iostream>
@@ -192,9 +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;
 
@@ -235,6 +233,10 @@ namespace {
   bool UseLogFile;
   std::ofstream LogFile;
 
+  // Natural logarithmic lookup table and its getter function
+  double lnArray[512];
+  inline double ln(int i) { return lnArray[i]; }
+
   // MP related variables
   int ActiveThreads = 1;
   Depth MinimumSplitDepth;
@@ -319,13 +321,6 @@ namespace {
 //// Functions
 ////
 
-//FIXME: HACK
-static double lnArray[512];
-
-inline double ln(int i)
-{
-    return lnArray[i];
-}
 
 /// perft() is our utility to verify move generation is bug free. All the legal
 /// moves up to given depth are generated and counted and the sum returned.
@@ -428,8 +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");
@@ -559,20 +552,18 @@ bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
 /// and initializes the split point stack and the global locks and condition
 /// objects.
 
-#include <cmath> //FIXME: HACK
-
 void init_threads() {
 
-  // FIXME: HACK!!
-  for (int i = 0; i < 512; i++)
-    lnArray[i] = log(double(i));
-
   volatile int i;
 
 #if !defined(_MSC_VER)
   pthread_t pthread[1];
 #endif
 
+  // Init our logarithmic lookup table
+  for (i = 0; i < 512; i++)
+      lnArray[i] = log(double(i)); // log() returns base-e logarithm
+
   for (i = 0; i < THREAD_MAX; i++)
       Threads[i].activeSplitPoints = 0;
 
@@ -1696,10 +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;