X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fposition.cpp;h=6a393ebb9b0730d5058a21c81ee622c71ec54225;hp=7c5ffdc5f6adcc905a2a98adb2e5b5cd60e1e4bc;hb=881a9dfb0a8fec3b1472791e2d98415e4a9a182a;hpb=9eccba776198c210563666787a9b5fe44b386fdc

diff --git a/src/position.cpp b/src/position.cpp
index 7c5ffdc5..6a393ebb 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -86,7 +86,7 @@ PieceType min_attacker<KING>(const Bitboard*, Square, Bitboard, Bitboard&, Bitbo
 
 /// operator<<(Position) returns an ASCII representation of the position
 
-std::ostream& operator<<(std::ostream& os, Position& pos) {
+std::ostream& operator<<(std::ostream& os, const Position& pos) {
 
   os << "\n +---+---+---+---+---+---+---+---+\n";
 
@@ -108,9 +108,12 @@ std::ostream& operator<<(std::ostream& os, Position& pos) {
   if (    int(Tablebases::MaxCardinality) >= popcount(pos.pieces())
       && !pos.can_castle(ANY_CASTLING))
   {
+      StateInfo st;
+      Position p;
+      p.set(pos.fen(), pos.is_chess960(), &st, pos.this_thread());
       Tablebases::ProbeState s1, s2;
-      Tablebases::WDLScore wdl = Tablebases::probe_wdl(pos, &s1);
-      int dtz = Tablebases::probe_dtz(pos, &s2);
+      Tablebases::WDLScore wdl = Tablebases::probe_wdl(p, &s1);
+      int dtz = Tablebases::probe_dtz(p, &s2);
       os << "\nTablebases WDL: " << std::setw(4) << wdl << " (" << s1 << ")"
          << "\nTablebases DTZ: " << std::setw(4) << dtz << " (" << s2 << ")";
   }
@@ -1076,25 +1079,30 @@ bool Position::see_ge(Move m, Value v) const {
 /// Position::is_draw() tests whether the position is drawn by 50-move rule
 /// or by repetition. It does not detect stalemates.
 
-bool Position::is_draw() const {
+bool Position::is_draw(int ply) const {
 
   if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
       return true;
 
-  int e = std::min(st->rule50, st->pliesFromNull);
+  int end = std::min(st->rule50, st->pliesFromNull);
 
-  if (e < 4)
+  if (end < 4)
     return false;
 
   StateInfo* stp = st->previous->previous;
+  int cnt = 0;
 
-  do {
+  for (int i = 4; i <= end; i += 2)
+  {
       stp = stp->previous->previous;
 
-      if (stp->key == st->key)
-          return true; // Draw at first repetition
-
-  } while ((e -= 2) >= 4);
+      // At root position ply is 1, so return a draw score if a position
+      // repeats once earlier but after or at the root, or repeats twice
+      // strictly before the root.
+      if (   stp->key == st->key
+          && ++cnt + (ply - i > 0) == 2)
+          return true;
+  }
 
   return false;
 }