- // If the pawn is supported by a friendly pawn, increase bonus.
- b2 = pos.pawns(us) & neighboring_files_bb(s);
- if(b2 & rank_bb(s))
- ebonus += Value(r * 20);
- else if(pos.pawn_attacks(them, s) & b2)
- ebonus += Value(r * 12);
-
- // If the other side has only a king, check whether the pawn is
- // unstoppable:
- if(pos.non_pawn_material(them) == Value(0)) {
- Square qsq;
- int d;
-
- qsq = relative_square(us, make_square(square_file(s), RANK_8));
- d = square_distance(s, qsq) - square_distance(theirKingSq, qsq)
- + ((us == pos.side_to_move())? 0 : 1);
-
- if(d < 0) {
- int mtg = RANK_8 - relative_rank(us, s);
- int blockerCount =
- count_1s_max_15(squares_in_front_of(us,s)&pos.occupied_squares());
- mtg += blockerCount;
- d += blockerCount;
- if(d < 0) {
- hasUnstoppable[us] = true;
- movesToGo[us] = Min(movesToGo[us], mtg);
+ // Adjust bonus based on kings proximity
+ ebonus -= Value(square_distance(pos.king_square(Us), blockSq) * 3 * tr);
+ ebonus -= Value(square_distance(pos.king_square(Us), blockSq + pawn_push(Us)) * 1 * tr);
+ ebonus += Value(square_distance(pos.king_square(Them), blockSq) * 6 * tr);
+
+ // If the pawn is free to advance, increase bonus
+ if (pos.square_is_empty(blockSq))
+ {
+ squaresToQueen = squares_in_front_of(Us, s);
+ defendedSquares = squaresToQueen & ei.attacked_by(Us);
+
+ // There are no enemy pawns in the pawn's path
+ assert(!(squaresToQueen & pos.pieces(PAWN, Them)));
+
+ // If there is an enemy rook or queen attacking the pawn from behind,
+ // add all X-ray attacks by the rook or queen. Otherwise consider only
+ // the squares in the pawn's path attacked or occupied by the enemy.
+ if ( (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them))
+ && (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them) & pos.attacks_from<QUEEN>(s)))
+ unsafeSquares = squaresToQueen;
+ else
+ unsafeSquares = squaresToQueen & (ei.attacked_by(Them) | pos.pieces_of_color(Them));
+
+ // If there aren't enemy attacks or pieces along the path to queen give
+ // huge bonus. Even bigger if we protect the pawn's path.
+ if (!unsafeSquares)
+ ebonus += Value(tr * (squaresToQueen == defendedSquares ? 17 : 15));
+ else
+ // OK, there are enemy attacks or pieces (but not pawns). Are those
+ // squares which are attacked by the enemy also attacked by us ?
+ // If yes, big bonus (but smaller than when there are no enemy attacks),
+ // if no, somewhat smaller bonus.
+ ebonus += Value(tr * ((unsafeSquares & defendedSquares) == unsafeSquares ? 13 : 8));
+
+ // At last, add a small bonus when there are no *friendly* pieces
+ // in the pawn's path.
+ if (!(squaresToQueen & pos.pieces_of_color(Us)))
+ ebonus += Value(tr);