Retire attackers_to(Square s, Color c)

Use the definition in the few places where is needed.

As a nice side effect there is also an optimization in
generate_evasions() where the bitboard of enemy pieces
is computed only once and out of a tight loop.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/movegen.cpp

@@ -254,12 +254,13 @@ MoveStack* generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pin
 
   // Generate evasions for king
   Bitboard b1 = pos.piece_attacks_from<KING>(ksq) & ~pos.pieces_of_color(us) & ~checkersAttacks;
+  Bitboard enemy = pos.pieces_of_color(them);
   while (b1)
   {
       to = pop_1st_bit(&b1);
       // Note that we can use attackers_to() only because we
       // have already removed slider checkers.
-      if (!pos.attackers_to(to, them))
+      if (!(pos.attackers_to(to) & enemy))
           (*mlist++).move = make_move(ksq, to);
   }
 
@@ -441,7 +442,7 @@ bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
       // is occupied or under attack.
       for (s = Min(from, g1); s <= Max(from, g1); s++)
           if (  (s != from && s != to && !pos.square_is_empty(s))
-              || pos.attackers_to(s, them))
+              ||(pos.attackers_to(s) & pos.pieces_of_color(them)))
               illegal = true;
 
       // Check if any of the squares between king and rook
@@ -472,7 +473,7 @@ bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
 
       for (s = Min(from, c1); s <= Max(from, c1); s++)
           if(  (s != from && s != to && !pos.square_is_empty(s))
-             || pos.attackers_to(s, them))
+             ||(pos.attackers_to(s) & pos.pieces_of_color(them)))
               illegal = true;
 
       for (s = Min(to, d1); s <= Max(to, d1); s++)
@@ -942,7 +943,7 @@ namespace {
         // It is a bit complicated to correctly handle Chess960
         for (s = Min(ksq, s1); s <= Max(ksq, s1); s++)
             if (  (s != ksq && s != rsq && pos.square_is_occupied(s))
-                || pos.attackers_to(s, them))
+                ||(pos.attackers_to(s) & pos.pieces_of_color(them)))
                 illegal = true;
 
         for (s = Min(rsq, s2); s <= Max(rsq, s2); s++)

src/position.cpp

@@ -452,7 +452,7 @@ bool Position::move_attacks_square(Move m, Square s) const {
 void Position::find_checkers() {
 
   Color us = side_to_move();
-  st->checkersBB = attackers_to(king_square(us), opposite_color(us));
+  st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
 }
 
 
@@ -509,7 +509,7 @@ bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
   // If the moving piece is a king, check whether the destination
   // square is attacked by the opponent.
   if (type_of_piece_on(from) == KING)
-      return !attackers_to(move_to(m), opposite_color(us));
+      return !(attackers_to(move_to(m)) & pieces_of_color(opposite_color(us)));
 
   // A non-king move is legal if and only if it is not pinned or it
   // is moving along the ray towards or away from the king.
@@ -864,7 +864,7 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
 
   // Update checkers bitboard, piece must be already moved
   if (ep | pm)
-      st->checkersBB = attackers_to(king_square(them), us);
+      st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
   else
   {
       st->checkersBB = EmptyBoardBB;
@@ -1041,7 +1041,7 @@ void Position::do_castle_move(Move m) {
   st->rule50 = 0;
 
   // Update checkers BB
-  st->checkersBB = attackers_to(king_square(them), us);
+  st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
 
   // Finish
   sideToMove = opposite_color(sideToMove);
@@ -1358,12 +1358,12 @@ int Position::see(Square from, Square to) const {
   while (true)
   {
       clear_bit(&occ, from);
-      attackers =  (rook_attacks_bb(to, occ)   & pieces(ROOK, QUEEN))
+      attackers =  (rook_attacks_bb(to, occ)       & pieces(ROOK, QUEEN))
-                 | (bishop_attacks_bb(to, occ) & pieces(BISHOP, QUEEN))
+                 | (bishop_attacks_bb(to, occ)     & pieces(BISHOP, QUEEN))
-                 | (piece_attacks_from<KNIGHT>(to)  & pieces(KNIGHT))
+                 | (piece_attacks_from<KNIGHT>(to) & pieces(KNIGHT))
-                 | (piece_attacks_from<KING>(to)    & pieces(KING))
+                 | (piece_attacks_from<KING>(to)   & pieces(KING))
-                 | (pawn_attacks_from(to, WHITE)    & pieces(PAWN, BLACK))
+                 | (pawn_attacks_from(to, WHITE)   & pieces(PAWN, BLACK))
-                 | (pawn_attacks_from(to, BLACK)    & pieces(PAWN, WHITE));
+                 | (pawn_attacks_from(to, BLACK)   & pieces(PAWN, WHITE));
 
       if (from != SQ_NONE)
           break;
@@ -1923,7 +1923,7 @@ bool Position::is_ok(int* failedStep) const {
       Color us = side_to_move();
       Color them = opposite_color(us);
       Square ksq = king_square(them);
-      if (attackers_to(ksq, us))
+      if (attackers_to(ksq) & pieces_of_color(us))
           return false;
   }
 

src/position.h

@@ -197,7 +197,6 @@ public:
 
   // Information about attacks to or from a given square
   Bitboard attackers_to(Square s) const;
-  Bitboard attackers_to(Square s, Color c) const;
   Bitboard piece_attacks_from(Piece p, Square s) const;
   Bitboard pawn_attacks_from(Square s, Color c) const;
   template<PieceType> Bitboard piece_attacks_from(Square s) const;
@@ -470,11 +469,6 @@ inline bool Position::is_check() const {
   return st->checkersBB != EmptyBoardBB;
 }
 
-inline Bitboard Position::attackers_to(Square s, Color c) const {
-
-  return attackers_to(s) & pieces_of_color(c);
-}
-
 inline bool Position::pawn_is_passed(Color c, Square s) const {
   return !(pieces(PAWN, opposite_color(c)) & passed_pawn_mask(c, s));
 }