X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=ae29a71aba07d0faa77847e7045a31f1ef92b58c;hp=c0d317b779234f4ae5cca323c221ffb5be8c4c93;hb=10d29add187fbc7ce20535a2beddc76e4a8ad0c2;hpb=cee6336515d5772370d061aa54cf3ec9f9a0d3c2

diff --git a/src/endgame.cpp b/src/endgame.cpp
index c0d317b7..ae29a71a 100644
--- a/src/endgame.cpp
+++ b/src/endgame.cpp
@@ -133,7 +133,7 @@ Value Endgame<KXK>::operator()(const Position& pos) const {
 
   // Stalemate detection with lone king
   if (    pos.side_to_move() == weakerSide
-      && !pos.in_check()
+      && !pos.checkers()
       && !MoveList<LEGAL>(pos).size()) {
     return VALUE_DRAW;
   }
@@ -471,6 +471,29 @@ ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
               return SCALE_FACTOR_DRAW;
       }
   }
+
+  // All pawns on same B or G file? Then potential draw
+  if (    (pawnFile == FILE_B || pawnFile == FILE_G)
+      && !(pos.pieces(PAWN) & ~file_bb(pawnFile))
+      && pos.non_pawn_material(weakerSide) == 0
+      && pos.piece_count(weakerSide, PAWN) >= 1)
+  {
+      // Get weaker pawn closest to opponent's queening square
+      Bitboard wkPawns = pos.pieces(weakerSide, PAWN);
+      Square weakerPawnSq = strongerSide == WHITE ? msb(wkPawns) : lsb(wkPawns);
+
+      Square strongerKingSq = pos.king_square(strongerSide);
+      Square weakerKingSq = pos.king_square(weakerSide);
+      Square bishopSq = pos.piece_list(strongerSide, BISHOP)[0];
+
+      // Draw if weaker pawn is on rank 7, bishop can't attack the pawn, and
+      // weaker king can stop opposing opponent's king from penetrating.
+      if (   relative_rank(strongerSide, weakerPawnSq) == RANK_7
+          && opposite_colors(bishopSq, weakerPawnSq)
+          && square_distance(weakerPawnSq, weakerKingSq) <= square_distance(weakerPawnSq, strongerKingSq))
+          return SCALE_FACTOR_DRAW;
+  }
+
   return SCALE_FACTOR_NONE;
 }