From: Marco Costalba <mcostalba@gmail.com>
Date: Mon, 28 Jan 2013 16:24:01 +0000 (+0100)
Subject: Revert "Extend full 3 fold detection to PvNodes"
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=58c9fbacc787cc3b654244c071169057e6895c91

Revert "Extend full 3 fold detection to PvNodes"
---

diff --git a/src/position.cpp b/src/position.cpp
index 4045a25d..310e46e3 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1363,31 +1363,36 @@ Value Position::compute_non_pawn_material(Color c) const {
 /// Position::is_draw() tests whether the position is drawn by material,
 /// repetition, or the 50 moves rule. It does not detect stalemates, this
 /// must be done by the search.
-template<bool CheckRepetition, bool CheckThreeFold>
+template<bool SkipRepetition>
 bool Position::is_draw() const {
 
+  // Draw by material?
   if (   !pieces(PAWN)
       && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
       return true;
 
+  // Draw by the 50 moves rule?
   if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
       return true;
 
-  if (CheckRepetition)
+  // Draw by repetition?
+  if (!SkipRepetition)
   {
-      int i = 4, e = std::min(st->rule50, st->pliesFromNull), cnt;
+      int i = 4, e = std::min(st->rule50, st->pliesFromNull);
 
       if (i <= e)
       {
           StateInfo* stp = st->previous->previous;
 
-          for (cnt = 0; i <= e; i += 2)
-          {
+          do {
               stp = stp->previous->previous;
 
-              if (stp->key == st->key && (!CheckThreeFold || ++cnt >= 2))
+              if (stp->key == st->key)
                   return true;
-          }
+
+              i += 2;
+
+          } while (i <= e);
       }
   }
 
@@ -1395,9 +1400,8 @@ bool Position::is_draw() const {
 }
 
 // Explicit template instantiations
-template bool Position::is_draw<true,  true>() const;
-template bool Position::is_draw<true, false>() const;
-template bool Position::is_draw<false,false>() const;
+template bool Position::is_draw<false>() const;
+template bool Position::is_draw<true>() const;
 
 
 /// Position::flip() flips position with the white and black sides reversed. This
diff --git a/src/position.h b/src/position.h
index 8b475dd9..579b5308 100644
--- a/src/position.h
+++ b/src/position.h
@@ -179,7 +179,7 @@ public:
   Thread* this_thread() const;
   int64_t nodes_searched() const;
   void set_nodes_searched(int64_t n);
-  template<bool CheckRepetition, bool CheckThreeFold> bool is_draw() const;
+  template<bool SkipRepetition> bool is_draw() const;
 
   // Position consistency check, for debugging
   bool pos_is_ok(int* failedStep = NULL) const;
diff --git a/src/search.cpp b/src/search.cpp
index 15c3b15a..cb7b30b8 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -534,7 +534,7 @@ namespace {
     if (!RootNode)
     {
         // Step 2. Check for aborted search and immediate draw
-        if (Signals.stop || pos.is_draw<true, PvNode>() || ss->ply > MAX_PLY)
+        if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
             return DrawValue[pos.side_to_move()];
 
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
@@ -1109,7 +1109,7 @@ split_point_start: // At split points actual search starts from here
     ss->ply = (ss-1)->ply + 1;
 
     // Check for an instant draw or maximum ply reached
-    if (pos.is_draw<false, false>() || ss->ply > MAX_PLY)
+    if (pos.is_draw<true>() || ss->ply > MAX_PLY)
         return DrawValue[pos.side_to_move()];
 
     // Transposition table lookup. At PV nodes, we don't use the TT for
@@ -1516,7 +1516,7 @@ void RootMove::extract_pv_from_tt(Position& pos) {
            && pos.is_pseudo_legal(m = tte->move()) // Local copy, TT could change
            && pos.pl_move_is_legal(m, pos.pinned_pieces())
            && ply < MAX_PLY
-           && (!pos.is_draw<true, true>() || ply < 2));
+           && (!pos.is_draw<false>() || ply < 2));
 
   pv.push_back(MOVE_NONE); // Must be zero-terminating