do not change cursed wins to draws (take 2)

src/position.cpp

@@ -1187,11 +1187,12 @@ bool Position::is_draw(int ply) const {
     if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
         return true;
 
-    // Return a draw score if a position repeats once earlier but strictly
-    // after the root, or repeats twice before or at the root.
-    return st->repetition && st->repetition < ply;
+    return is_repetition(ply);
 }
 
+// Return a draw score if a position repeats once earlier but strictly
+// after the root, or repeats twice before or at the root.
+bool Position::is_repetition(int ply) const { return st->repetition && st->repetition < ply; }
 
 // Tests whether there has been at least one repetition
 // of positions since the last capture or pawn move.

src/position.h

@@ -163,6 +163,7 @@ class Position {
     int   game_ply() const;
     bool  is_chess960() const;
     bool  is_draw(int ply) const;
+    bool  is_repetition(int ply) const;
     bool  upcoming_repetition(int ply) const;
     bool  has_repeated() const;
     int   rule50_count() const;

src/search.cpp

@@ -1952,6 +1952,7 @@ void syzygy_extend_pv(const OptionsMap&         options,
 
     auto t_start      = std::chrono::steady_clock::now();
     int  moveOverhead = int(options["Move Overhead"]);
+    bool rule50       = bool(options["Syzygy50MoveRule"]);
 
     // Do not use more than moveOverhead / 2 time, if time management is active
     auto time_abort = [&t_start, &moveOverhead, &limits]() -> bool {
@@ -1989,7 +1990,7 @@ void syzygy_extend_pv(const OptionsMap&         options,
         pos.do_move(pvMove, st);
 
         // Do not allow for repetitions or drawing moves along the PV in TB regime
-        if (config.rootInTB && pos.is_draw(ply))
+        if (config.rootInTB && ((rule50 && pos.is_draw(ply)) || pos.is_repetition(ply)))
         {
             pos.undo_move(pvMove);
             ply--;
@@ -2008,7 +2009,7 @@ void syzygy_extend_pv(const OptionsMap&         options,
     // Step 2, now extend the PV to mate, as if the user explored syzygy-tables.info
     // using top ranked moves (minimal DTZ), which gives optimal mates only for simple
     // endgames e.g. KRvK.
-    while (!pos.is_draw(0))
+    while (!(rule50 && pos.is_draw(0)))
     {
         if (time_abort())
             break;
@@ -2051,7 +2052,7 @@ void syzygy_extend_pv(const OptionsMap&         options,
         pos.do_move(pvMove, st);
     }
 
-    // Finding a draw in this function is an exceptional case, that cannot happen
+    // Finding a draw in this function is an exceptional case, that cannot happen when rule50 is false or
     // during engine game play, since we have a winning score, and play correctly
     // with TB support. However, it can be that a position is draw due to the 50 move
     // rule if it has been been reached on the board with a non-optimal 50 move counter

src/syzygy/tbprobe.cpp

@@ -1620,7 +1620,7 @@ bool Tablebases::root_probe(Position&          pos,
             WDLScore wdl = -probe_wdl(pos, &result);
             dtz          = dtz_before_zeroing(wdl);
         }
-        else if (pos.is_draw(1))
+        else if ((rule50 && pos.is_draw(1)) || pos.is_repetition(1))
         {
             // In case a root move leads to a draw by repetition or 50-move rule,
             // we set dtz to zero. Note: since we are only 1 ply from the root,