Remove an useless condition in equal SEE pruning

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 6d05405b6f79c9ad002824bbafd0777b132f000b..f35f6b6cf91293bb5b43c1d8ef58df75bf7f8211 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -209,10 +209,6 @@ namespace {
   // Minimum depth for use of singular extension
   const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
 
-  // If the TT move is at least SingularExtensionMargin better than the
-  // remaining ones we will extend it.
-  const Value SingularExtensionMargin = Value(0x20);
-
   // Step 12. Futility pruning
 
   // Futility margin for quiescence search
@@ -306,7 +302,7 @@ namespace {
 
   int current_search_time();
   std::string value_to_uci(Value v);
-  int nps(const Position& pos);
+  std::string speed_to_uci(int64_t nodes);
   void poll(const Position& pos);
   void wait_for_stop_or_ponderhit();
 
@@ -558,14 +554,14 @@ bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[
   Move bestMove = id_loop(pos, searchMoves, &ponderMove);
 
   // Print final search statistics
-  cout << "info nodes " << pos.nodes_searched()
-       << " nps " << nps(pos)
-       << " time " << current_search_time() << endl;
+  cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
 
   if (UseLogFile)
   {
+      int t = current_search_time();
+
       LogFile << "Nodes: "          << pos.nodes_searched()
-              << "\nNodes/second: " << nps(pos)
+              << "\nNodes/second: " << (t > 0 ? int(pos.nodes_searched() * 1000 / t) : 0)
               << "\nBest move: "    << move_to_san(pos, bestMove);
 
       StateInfo st;
@@ -1028,9 +1024,7 @@ split_point_start: // At split points actual search starts from here
           if (SendSearchedNodes)
           {
               SendSearchedNodes = false;
-              cout << "info nodes " << nodes
-                   << " nps " << nps(pos)
-                   << " time " << current_search_time() << endl;
+              cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
           }
 
           if (current_search_time() >= 1000)
@@ -1057,7 +1051,7 @@ split_point_start: // At split points actual search starts from here
 
           if (abs(ttValue) < VALUE_KNOWN_WIN)
           {
-              Value b = ttValue - SingularExtensionMargin;
+              Value b = ttValue - depth;
               ss->excludedMove = move;
               ss->skipNullMove = true;
               Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
@@ -1433,6 +1427,12 @@ split_point_start: // At split points actual search starts from here
                   bestValue = futilityValue;
               continue;
           }
+
+          // Prune moves with negative or equal SEE
+          if (   futilityBase < beta
+              && depth < DEPTH_ZERO
+              && pos.see(move) <= 0)
+              continue;
       }
 
       // Detect non-capture evasions that are candidate to be pruned
@@ -1858,6 +1858,14 @@ split_point_start: // At split points actual search starts from here
         H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
   }
 
+  // current_search_time() returns the number of milliseconds which have passed
+  // since the beginning of the current search.
+
+  int current_search_time() {
+
+    return get_system_time() - SearchStartTime;
+  }
+
 
   // value_to_uci() converts a value to a string suitable for use with the UCI
   // protocol specifications:
@@ -1879,21 +1887,19 @@ split_point_start: // At split points actual search starts from here
   }
 
 
-  // current_search_time() returns the number of milliseconds which have passed
-  // since the beginning of the current search.
-
-  int current_search_time() {
+  // speed_to_uci() returns a string with time stats of current search suitable
+  // to be sent to UCI gui.
 
-    return get_system_time() - SearchStartTime;
-  }
+  std::string speed_to_uci(int64_t nodes) {
 
+    std::stringstream s;
+    int t = current_search_time();
 
-  // nps() computes the current nodes/second count
-
-  int nps(const Position& pos) {
+    s << " nodes " << nodes
+      << " nps "   << (t > 0 ? int(nodes * 1000 / t) : 0)
+      << " time "  << t;
 
-    int t = current_search_time();
-    return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
+    return s.str();
   }
 
 
@@ -2538,9 +2544,7 @@ split_point_start: // At split points actual search starts from here
       << " multipv " << pvLine + 1
       << " score " << value_to_uci(pv_score)
       << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
-      << " time "  << current_search_time()
-      << " nodes " << pos.nodes_searched()
-      << " nps "   << nps(pos)
+      << speed_to_uci(pos.nodes_searched())
       << " pv "    << l.str();
 
     return s.str();