Fixed search to return score for King of the Hill win/loss condition.

src/evaluate.cpp

@@ -699,9 +699,9 @@ namespace {
     score = pos.psq_score();
 
 #ifdef KOTH
+    // Possibly redundant static evaluator
     if (pos.is_koth())
     {
-        // TODO: Do we need or want both conditions here?
         if (pos.is_koth_win())
             return VALUE_MATE;
         if (pos.is_koth_loss())

src/movepick.cpp

@@ -302,14 +302,6 @@ void MovePicker::generate_next_stage() {
 template<>
 Move MovePicker::next_move<false>() {
 
-#ifdef KOTH
-  assert(!pos.is_koth_win());
-
-  // Best move can only be MOVE_NONE when searching on a lost KOTH position
-  if (pos.is_koth_loss())
-      return MOVE_NONE;
-#endif
-
   Move move;
 
   while (true)

src/position.cpp

@@ -539,6 +539,12 @@ bool Position::legal(Move m, Bitboard pinned) const {
   assert(color_of(moved_piece(m)) == us);
   assert(piece_on(king_square(us)) == make_piece(us, KING));
 
+#ifdef KOTH
+  // If the game is already won or lost, further moves are illegal
+  if (is_koth() && (is_koth_win() || is_koth_loss()))
+      return false;
+#endif
+
   // En passant captures are a tricky special case. Because they are rather
   // uncommon, we do it simply by testing whether the king is attacked after
   // the move is made.
@@ -583,6 +589,12 @@ bool Position::pseudo_legal(const Move m) const {
   Square to = to_sq(m);
   Piece pc = moved_piece(m);
 
+#ifdef KOTH
+  // If the game is already won or lost, further moves are illegal
+  if (is_koth() && (is_koth_win() || is_koth_loss()))
+      return false;
+#endif
+
   // Use a slower but simpler function for uncommon cases
   if (type_of(m) != NORMAL)
       return MoveList<LEGAL>(*this).contains(m);
@@ -719,10 +731,6 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
 
   assert(is_ok(m));
   assert(&newSt != st);
-#ifdef KOTH
-  assert(!is_koth_win());
-  assert(!is_koth_loss());
-#endif
 
   ++nodes;
   Key k = st->key;
@@ -1138,6 +1146,9 @@ Value Position::see(Move m) const {
 bool Position::is_draw() const {
 
   if (   !pieces(PAWN)
+#ifdef KOTH
+      && !is_koth()
+#endif
       && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
       return true;
 

src/search.cpp

@@ -481,6 +481,17 @@ namespace {
 
     if (!RootNode)
     {
+#ifdef KOTH
+        // Check for an instant win (King of the Hill)
+        if (pos.is_koth())
+        {
+            if (pos.is_koth_win())
+                return mate_in(ss->ply+1);
+            if (pos.is_koth_loss())
+                return mated_in(ss->ply);
+        }
+#endif
+
         // Step 2. Check for aborted search and immediate draw
         if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
             return ss->ply > MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
@@ -1065,6 +1076,17 @@ namespace {
     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;
 
+#ifdef KOTH
+    // Check for an instant win or loss (King of the Hill)
+    if (pos.is_koth())
+    {
+        if (pos.is_koth_win())
+            return mate_in(ss->ply+1);
+        if (pos.is_koth_loss())
+            return mated_in(ss->ply);
+    }
+#endif
+
     // Check for an instant draw or if the maximum ply has been reached
     if (pos.is_draw() || ss->ply > MAX_PLY)
         return ss->ply > MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];