Fix evasion pruning condition

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 7b4ba28618c537eb5804a67107008a150bb4d3a0..fff523c39e48e538099e3a169c7c9491c59154b5 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -87,7 +87,7 @@ namespace {
                Depth depth, bool mateThreat, int* moves, MovePicker* mp, int master, bool pvNode);
 
   private:
-    friend void poll(SearchStack ss[], int ply);
+    friend void poll();
 
     int ActiveThreads;
     volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
@@ -257,7 +257,7 @@ namespace {
   int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
   int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
   bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
-  bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
+  bool FirstRootMove, AbortSearch, Quit, AspirationFailLow, ZugDetection;
 
   // Log file
   bool UseLogFile;
@@ -294,7 +294,7 @@ namespace {
   Depth extension(const Position&, Move, bool, bool, bool, bool, bool, bool*);
   bool ok_to_do_nullmove(const Position& pos);
   bool ok_to_prune(const Position& pos, Move m, Move threat);
-  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
+  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove);
   Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
   void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
   void update_killers(Move m, SearchStack& ss);
@@ -302,7 +302,7 @@ namespace {
 
   int current_search_time();
   int nps();
-  void poll(SearchStack ss[], int ply);
+  void poll();
   void ponderhit();
   void wait_for_stop_or_ponderhit();
   void init_ss_array(SearchStack ss[]);
@@ -425,6 +425,7 @@ bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
   MultiPV                 = get_option_value_int("MultiPV");
   Chess960                = get_option_value_bool("UCI_Chess960");
   UseLogFile              = get_option_value_bool("Use Search Log");
+  ZugDetection            = get_option_value_bool("Zugzwang detection"); // To be removed after 1.7.1
 
   if (UseLogFile)
       LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
@@ -1299,7 +1300,7 @@ namespace {
     tte = TT.retrieve(posKey);
     ttMove = (tte ? tte->move() : MOVE_NONE);
 
-    if (tte && ok_to_use_TT(tte, depth, beta, ply))
+    if (tte && ok_to_use_TT(tte, depth, beta, ply, allowNullmove))
     {
         ss[ply].currentMove = ttMove; // Can be MOVE_NONE
         return value_from_tt(tte->value(), ply);
@@ -1379,13 +1380,18 @@ namespace {
             if (nullValue >= value_mate_in(PLY_MAX))
                 nullValue = beta;
 
-            if (depth < 6 * OnePly)
-                return nullValue;
+            // Do zugzwang verification search for high depths, don't store in TT
+            // if search was stopped.
+            if (   (   depth < 6 * OnePly
+                    || search(pos, ss, beta, depth-5*OnePly, ply, false, threadID) >= beta)
+                && !AbortSearch
+                && !TM.thread_should_stop(threadID))
+            {
+                assert(value_to_tt(nullValue, ply) == nullValue);
 
-            // Do zugzwang verification search
-            Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
-            if (v >= beta)
+                TT.store(posKey, nullValue, VALUE_TYPE_NS_LO, depth, MOVE_NONE);
                 return nullValue;
+            }
         } else {
             // The null move failed low, which means that we may be faced with
             // some kind of threat. If the previous move was reduced, check if
@@ -1620,7 +1626,7 @@ namespace {
     tte = TT.retrieve(pos.get_key());
     ttMove = (tte ? tte->move() : MOVE_NONE);
 
-    if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
+    if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply, true))
     {
         assert(tte->type() != VALUE_TYPE_EVAL);
 
@@ -1661,7 +1667,7 @@ namespace {
         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;
+    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,
@@ -1707,7 +1713,7 @@ namespace {
 
       // Detect blocking evasions that are candidate to be pruned
       evasionPrunable =   isCheck
-                       && bestValue != -VALUE_INFINITE
+                       && bestValue > value_mated_in(PLY_MAX)
                        && !pos.move_is_capture(move)
                        && pos.type_of_piece_on(move_from(move)) != KING
                        && !pos.can_castle(pos.side_to_move());
@@ -2046,7 +2052,7 @@ namespace {
         NodesSincePoll++;
         if (NodesSincePoll >= NodesBetweenPolls)
         {
-            poll(ss, ply);
+            poll();
             NodesSincePoll = 0;
         }
     }
@@ -2301,14 +2307,18 @@ namespace {
   }
 
 
-  // ok_to_use_TT() returns true if a transposition table score
-  // can be used at a given point in search.
+  // ok_to_use_TT() returns true if a transposition table score can be used at a
+  // given point in search. To avoid zugzwang issues TT cutoffs at the root node
+  // of a null move verification search are not allowed if the TT value was found
+  // by a null search, this is implemented testing allowNullmove and TT entry type.
 
-  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
+  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove) {
 
     Value v = value_from_tt(tte->value(), ply);
 
-    return   (   tte->depth() >= depth
+    return   (allowNullmove || !(tte->type() & VALUE_TYPE_NULL) || !ZugDetection)
+
+          && (   tte->depth() >= depth
               || v >= Max(value_mate_in(PLY_MAX), beta)
               || v < Min(value_mated_in(PLY_MAX), beta))
 
@@ -2409,7 +2419,7 @@ namespace {
   // looks at the time consumed so far and decides if it's time to abort the
   // search.
 
-  void poll(SearchStack ss[], int ply) {
+  void poll() {
 
     static int lastInfoTime;
     int t = current_search_time();
@@ -2764,7 +2774,7 @@ namespace {
         }
 
         // Wait until the thread has finished launching and is gone to sleep
-        while (threads[i].state != THREAD_SLEEPING);
+        while (threads[i].state != THREAD_SLEEPING) {}
     }
   }
 
@@ -2805,7 +2815,7 @@ namespace {
 
     SplitPoint* sp;
 
-    for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent);
+    for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
     return sp != NULL;
   }