- // 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);
+ assert(pos.piece_on(s) == piece_of_color_and_type(us, PAWN));
+ assert(pos.pawn_is_passed(us, s));
+
+ int r = int(relative_rank(us, s) - RANK_2);
+ int tr = Max(0, r * (r - 1));
+ Square blockSq = s + pawn_push(us);
+
+ // Base bonus based on rank
+ Value mbonus = Value(20 * tr);
+ Value ebonus = Value(10 + r * r * 10);
+
+ // Adjust bonus based on king proximity
+ if (tr != 0)
+ {
+ ebonus -= Value(square_distance(ourKingSq, blockSq) * 3 * tr);
+ ebonus -= Value(square_distance(ourKingSq, blockSq + pawn_push(us)) * 1 * tr);
+ ebonus += Value(square_distance(theirKingSq, blockSq) * 6 * tr);
+
+ // If the pawn is free to advance, increase bonus
+ if (pos.square_is_empty(blockSq))
+ {
+ b2 = squares_in_front_of(us, s);
+ b3 = b2 & ei.attacked_by(them);
+ b4 = b2 & ei.attacked_by(us);
+
+ // If there is an enemy rook or queen attacking the pawn from behind,
+ // add all X-ray attacks by the rook or queen.
+ if ( bit_is_set(ei.attacked_by(them,ROOK) | ei.attacked_by(them,QUEEN),s)
+ && (squares_behind(us, s) & pos.rooks_and_queens(them)))
+ b3 = b2;
+
+ if ((b2 & pos.pieces_of_color(them)) == EmptyBoardBB)
+ {
+ // There are no enemy pieces in the pawn's path! Are any of the
+ // squares in the pawn's path attacked by the enemy?
+ if (b3 == EmptyBoardBB)
+ // No enemy attacks, huge bonus!
+ ebonus += Value(tr * (b2 == b4 ? 17 : 15));
+ else
+ // OK, there are enemy attacks. 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 * ((b3 & b4) == b3 ? 13 : 8));
+ }
+ else
+ {
+ // There are some enemy pieces in the pawn's path. While this is
+ // sad, we still assign a moderate bonus if all squares in the path
+ // which are either occupied by or attacked by enemy pieces are
+ // also attacked by us.
+ if (((b3 | (b2 & pos.pieces_of_color(them))) & ~b4) == EmptyBoardBB)
+ ebonus += Value(tr * 6);
+ }
+ // At last, add a small bonus when there are no *friendly* pieces
+ // in the pawn's path.
+ if ((b2 & pos.pieces_of_color(us)) == EmptyBoardBB)
+ ebonus += Value(tr);
+ }