Fix small bug in move_attacks_square()

[stockfish] / src / position.cpp

diff --git a/src/position.cpp b/src/position.cpp
index abde14593bbf833914be4651387e867770262744..12485fbb780fb64026e359bc97cdd271ea9c2599 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -349,7 +349,6 @@ void Position::print(Move move) const {
 /// king) pieces for the given color. Or, when template parameter FindPinned is
 /// false, the function return the pieces of the given color candidate for a
 /// discovery check against the enemy king.
-
 template<bool FindPinned>
 Bitboard Position::hidden_checkers() const {
 
@@ -373,26 +372,12 @@ Bitboard Position::hidden_checkers() const {
   return result;
 }
 
+// Explicit template instantiations
+template Bitboard Position::hidden_checkers<true>() const;
+template Bitboard Position::hidden_checkers<false>() const;
 
-/// Position:pinned_pieces() returns a bitboard of all pinned (against the
-/// king) pieces for the side to move.
-
-Bitboard Position::pinned_pieces() const {
-
-  return hidden_checkers<true>();
-}
-
-
-/// Position:discovered_check_candidates() returns a bitboard containing all
-/// pieces for the side to move which are candidates for giving a discovered
-/// check.
-
-Bitboard Position::discovered_check_candidates() const {
 
-  return hidden_checkers<false>();
-}
-
-/// Position::attackers_to() computes a bitboard of all pieces which attacks a
+/// Position::attackers_to() computes a bitboard of all pieces which attack a
 /// given square. Slider attacks use occ bitboard as occupancy.
 
 Bitboard Position::attackers_to(Square s, Bitboard occ) const {
@@ -405,6 +390,7 @@ Bitboard Position::attackers_to(Square s, Bitboard occ) const {
         | (attacks_from<KING>(s)        & pieces(KING));
 }
 
+
 /// Position::attacks_from() computes a bitboard of all attacks of a given piece
 /// put in a given square. Slider attacks use occ bitboard as occupancy.
 
@@ -431,22 +417,25 @@ bool Position::move_attacks_square(Move m, Square s) const {
   assert(square_is_ok(s));
 
   Bitboard occ, xray;
-  Square f = move_from(m), t = move_to(m);
+  Square from = move_from(m);
+  Square to = move_to(m);
+  Piece piece = piece_on(from);
+
+  assert(!square_is_empty(from));
 
-  assert(!square_is_empty(f));
+  // Update occupancy as if the piece is moving
+  occ = occupied_squares();
+  do_move_bb(&occ, make_move_bb(from, to));
 
-  if (bit_is_set(attacks_from(piece_on(f), t), s))
+  // The piece moved in 'to' attacks the square 's' ?
+  if (bit_is_set(attacks_from(piece, to, occ), s))
       return true;
 
-  // Move the piece and scan for X-ray attacks behind it
-  occ = occupied_squares();
-  do_move_bb(&occ, make_move_bb(f, t));
-  xray = ( (rook_attacks_bb(s, occ)   & pieces(ROOK, QUEEN))
-          |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
-         & pieces(color_of(piece_on(f)));
+  // Scan for possible X-ray attackers behind the moved piece
+  xray = (rook_attacks_bb(s, occ)   & pieces(ROOK, QUEEN, color_of(piece)))
+        |(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN, color_of(piece)));
 
-  // If we have attacks we need to verify that are caused by our move
-  // and are not already existent ones.
+  // Verify attackers are triggered by our move and not already existing
   return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
 }
 
@@ -503,8 +492,8 @@ bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
 
 
 /// Position::move_is_legal() takes a random move and tests whether the move
-/// is legal. This version is not very fast and should be used only
-/// in non time-critical paths.
+/// is legal. This version is not very fast and should be used only in non
+/// time-critical paths.
 
 bool Position::move_is_legal(const Move m) const {