X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fposition.cpp;h=a51383f0d4eed8c2c9c08d318a6f422c743102a1;hp=4045a25d96f454182b9de283b593d0b0d48c53c1;hb=ea4e22be1da1ccbf316d27f2eb3b14d0e13388e4;hpb=483c98a69e8c6836c655d92a150d70fbe780341f

diff --git a/src/position.cpp b/src/position.cpp
index 4045a25d..a51383f0 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -278,11 +278,11 @@ void Position::set(const string& fenStr, bool isChess960, Thread* th) {
   }
 
   // 5-6. Halfmove clock and fullmove number
-  ss >> std::skipws >> st->rule50 >> startPosPly;
+  ss >> std::skipws >> st->rule50 >> gamePly;
 
   // Convert from fullmove starting from 1 to ply starting from 0,
   // handle also common incorrect FEN with fullmove = 0.
-  startPosPly = std::max(2 * (startPosPly - 1), 0) + int(sideToMove == BLACK);
+  gamePly = std::max(2 * (gamePly - 1), 0) + int(sideToMove == BLACK);
 
   st->key = compute_key();
   st->pawnKey = compute_pawn_key();
@@ -373,7 +373,7 @@ const string Position::fen() const {
       ss << '-';
 
   ss << (ep_square() == SQ_NONE ? " - " : " " + square_to_string(ep_square()) + " ")
-      << st->rule50 << " " << 1 + (startPosPly - int(sideToMove == BLACK)) / 2;
+      << st->rule50 << " " << 1 + (gamePly - int(sideToMove == BLACK)) / 2;
 
   return ss.str();
 }
@@ -735,8 +735,9 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   // Update side to move
   k ^= Zobrist::side;
 
-  // Increment the 50 moves rule draw counter. Resetting it to zero in the
-  // case of a capture or a pawn move is taken care of later.
+  // Increment ply counters.In particular rule50 will be later reset it to zero
+  // in case of a capture or a pawn move.
+  gamePly++;
   st->rule50++;
   st->pliesFromNull++;
 
@@ -802,7 +803,7 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
       // Update piece list, move the last piece at index[capsq] position and
       // shrink the list.
       //
-      // WARNING: This is a not revresible operation. When we will reinsert the
+      // WARNING: This is a not reversible operation. When we will reinsert the
       // captured piece in undo_move() we will put it at the end of the list and
       // not in its original place, it means index[] and pieceList[] are not
       // guaranteed to be invariant to a do_move() + undo_move() sequence.
@@ -1054,6 +1055,7 @@ void Position::undo_move(Move m) {
 
   // Finally point our state pointer back to the previous state
   st = st->previous;
+  gamePly--;
 
   assert(pos_is_ok());
 }
@@ -1363,31 +1365,36 @@ 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 +1402,8 @@ 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
@@ -1413,7 +1419,7 @@ void Position::flip() {
   thisThread = pos.this_thread();
   nodes = pos.nodes_searched();
   chess960 = pos.is_chess960();
-  startPosPly = pos.startpos_ply_counter();
+  gamePly = pos.game_ply();
 
   for (Square s = SQ_A1; s <= SQ_H8; s++)
       if (!pos.is_empty(s))