X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=5cca911bdaf266ee3affa144368912c4af622064;hp=0e65d19ff3c9f5d8da2d9fd7887ceb2bb42ec3e5;hb=c23cd4d90aa91504a5a3ec3ce896d1e35e34c494;hpb=94bb1964f6b5b4b9abca0bde03367d071922f449

diff --git a/src/search.cpp b/src/search.cpp
index 0e65d19f..5cca911b 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -257,7 +257,7 @@ namespace {
   int SearchStartTime, MaxNodes, MaxDepth, MaxSearchTime;
   int AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
   bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
-  bool FirstRootMove, AbortSearch, Quit, AspirationFailLow, ZugDetection;
+  bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
 
   // 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 allowNullmove);
+  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
   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);
@@ -425,7 +425,6 @@ 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);
@@ -1300,7 +1299,7 @@ namespace {
     tte = TT.retrieve(posKey);
     ttMove = (tte ? tte->move() : MOVE_NONE);
 
-    if (tte && ok_to_use_TT(tte, depth, beta, ply, allowNullmove))
+    if (tte && ok_to_use_TT(tte, depth, beta, ply))
     {
         ss[ply].currentMove = ttMove; // Can be MOVE_NONE
         return value_from_tt(tte->value(), ply);
@@ -1380,18 +1379,13 @@ namespace {
             if (nullValue >= value_mate_in(PLY_MAX))
                 nullValue = beta;
 
-            // 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);
+            if (depth < 6 * OnePly)
+                return nullValue;
 
-                TT.store(posKey, nullValue, VALUE_TYPE_NS_LO, depth, MOVE_NONE);
+            // Do zugzwang verification search
+            Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
+            if (v >= beta)
                 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
@@ -1626,7 +1620,7 @@ namespace {
     tte = TT.retrieve(pos.get_key());
     ttMove = (tte ? tte->move() : MOVE_NONE);
 
-    if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply, true))
+    if (!pvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
     {
         assert(tte->type() != VALUE_TYPE_EVAL);
 
@@ -2307,18 +2301,14 @@ namespace {
   }
 
 
-  // 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.
+  // ok_to_use_TT() returns true if a transposition table score
+  // can be used at a given point in search.
 
-  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply, bool allowNullmove) {
+  bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
 
     Value v = value_from_tt(tte->value(), ply);
 
-    return   (allowNullmove || !(tte->type() & VALUE_TYPE_NULL) || !ZugDetection)
-
-          && (   tte->depth() >= depth
+    return   (   tte->depth() >= depth
               || v >= Max(value_mate_in(PLY_MAX), beta)
               || v < Min(value_mated_in(PLY_MAX), beta))