// Evaluate passed pawns. We evaluate passed pawns for both sides at once,
// because we need to know which side promotes first in positions where
- // both sides have an unstoppable passed pawn.
+ // both sides have an unstoppable passed pawn. To be called after all attacks
+ // are computed, included king.
if (ei.pi->passed_pawns())
evaluate_passed_pawns(pos, ei);
// evaluate_passed_pawns() evaluates the passed pawns of the given color
template<Color Us>
- void evaluate_passed_pawns_of_color(const Position& pos, int movesToGo[], EvalInfo& ei) {
+ void evaluate_passed_pawns_of_color(const Position& pos, int movesToGo[], Square pawnToGo[], EvalInfo& ei) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
// 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.pieces(ROOK, QUEEN, Them)))
+ if ( (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them))
+ && (squares_behind(Us, s) & pos.pieces(ROOK, QUEEN, Them) & pos.attacks_from<QUEEN>(s)))
b3 = b2;
// Are any of the squares in the pawn's path attacked or occupied by the enemy?
int blockerCount = count_1s_max_15(squares_in_front_of(Us,s) & pos.occupied_squares());
mtg += blockerCount;
d += blockerCount;
- if (d < 0)
- movesToGo[Us] = movesToGo[Us] ? Min(movesToGo[Us], mtg) : mtg;
+ if (d < 0 && (!movesToGo[Us] || movesToGo[Us] > mtg))
+ {
+ movesToGo[Us] = mtg;
+ pawnToGo[Us] = s;
+ }
}
}
void evaluate_passed_pawns(const Position& pos, EvalInfo& ei) {
int movesToGo[2] = {0, 0};
+ Square pawnToGo[2] = {SQ_NONE, SQ_NONE};
// Evaluate pawns for each color
- evaluate_passed_pawns_of_color<WHITE>(pos, movesToGo, ei);
- evaluate_passed_pawns_of_color<BLACK>(pos, movesToGo, ei);
-
- // Does either side have an unstoppable passed pawn?
- if (movesToGo[WHITE] && !movesToGo[BLACK])
- ei.egValue += UnstoppablePawnValue - Value(0x40 * movesToGo[WHITE]);
- else if (movesToGo[BLACK] && !movesToGo[WHITE])
- ei.egValue -= UnstoppablePawnValue - Value(0x40 * movesToGo[BLACK]);
- else if (movesToGo[BLACK] && movesToGo[WHITE])
+ evaluate_passed_pawns_of_color<WHITE>(pos, movesToGo, pawnToGo, ei);
+ evaluate_passed_pawns_of_color<BLACK>(pos, movesToGo, pawnToGo, ei);
+
+ // Neither side has an unstoppable passed pawn?
+ if (!(movesToGo[WHITE] | movesToGo[BLACK]))
+ return;
+
+ // Does only one side have an unstoppable passed pawn?
+ if (!movesToGo[WHITE] || !movesToGo[BLACK])
{
- // Both sides have unstoppable pawns! Try to find out who queens
+ Color winnerSide = movesToGo[WHITE] ? WHITE : BLACK;
+ ei.egValue += Sign[winnerSide] * (UnstoppablePawnValue - Value(0x40 * movesToGo[winnerSide]));
+ }
+ else
+ { // Both sides have unstoppable pawns! Try to find out who queens
// first. We begin by transforming 'movesToGo' to the number of
// plies until the pawn queens for both sides.
movesToGo[WHITE] *= 2;
movesToGo[BLACK] *= 2;
movesToGo[pos.side_to_move()]--;
- // If one side queens at least three plies before the other, that
- // side wins.
- if (movesToGo[WHITE] <= movesToGo[BLACK] - 3)
- ei.egValue += UnstoppablePawnValue - Value(0x40 * (movesToGo[WHITE]/2));
- else if (movesToGo[BLACK] <= movesToGo[WHITE] - 3)
- ei.egValue -= UnstoppablePawnValue - Value(0x40 * (movesToGo[BLACK]/2));
-
- // We could also add some rules about the situation when one side
- // queens exactly one ply before the other: Does the first queen
- // check the opponent's king, or attack the opponent's queening square?
- // This is slightly tricky to get right, because it is possible that
- // the opponent's king has moved somewhere before the first pawn queens.
+ Color winnerSide = movesToGo[WHITE] < movesToGo[BLACK] ? WHITE : BLACK;
+ Color loserSide = opposite_color(winnerSide);
+
+ // If one side queens at least three plies before the other, that side wins
+ if (movesToGo[winnerSide] <= movesToGo[loserSide] - 3)
+ ei.egValue += Sign[winnerSide] * (UnstoppablePawnValue - Value(0x40 * (movesToGo[winnerSide]/2)));
+
+ // If one side queens one ply before the other and checks the king or attacks
+ // the undefended opponent's queening square, that side wins. To avoid cases
+ // where the opponent's king could move somewhere before first pawn queens we
+ // consider only free paths to queen for both pawns.
+ else if ( !(squares_in_front_of(WHITE, pawnToGo[WHITE]) & pos.occupied_squares())
+ && !(squares_in_front_of(BLACK, pawnToGo[BLACK]) & pos.occupied_squares()))
+ {
+ assert(movesToGo[loserSide] - movesToGo[winnerSide] == 1);
+
+ Square winnerQSq = relative_square(winnerSide, make_square(square_file(pawnToGo[winnerSide]), RANK_8));
+ Square loserQSq = relative_square(loserSide, make_square(square_file(pawnToGo[loserSide]), RANK_8));
+
+ Bitboard b = pos.attacks_from<QUEEN>(winnerQSq);
+
+ if ( (b & pos.pieces(KING, loserSide))
+ ||(bit_is_set(b, loserQSq) && !bit_is_set(ei.attacked_by(loserSide), loserQSq)))
+ ei.egValue += Sign[winnerSide] * (UnstoppablePawnValue - Value(0x40 * (movesToGo[winnerSide]/2)));
+ }
}
}
projects / stockfish / blobdiff