// Tables used to drive a piece towards or away from another piece
const int PushClose[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
- const int PushAway [8] = { 0, 10, 14, 20, 30, 42, 58, 80 };
+ const int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 };
// Get the material key of a Position out of the given endgame key code
// like "KBPKN". The trick here is to first forge an ad-hoc fen string
add<KNPK>("KNPK");
add<KNPKB>("KNPKB");
add<KRPKR>("KRPKR");
+ add<KRPKB>("KRPKB");
add<KBPKB>("KBPKB");
add<KBPKN>("KBPKN");
add<KBPPKB>("KBPPKB");
return strongerSide == pos.side_to_move() ? result : -result;
}
+
+/// KBB vs KN. This is almost always a win. We try to push enemy king to a corner
+/// and away from his knight. For a reference of this difficult endgame see:
+/// en.wikipedia.org/wiki/Chess_endgame#Effect_of_tablebases_on_endgame_theory
+
template<>
Value Endgame<KBBKN>::operator()(const Position& pos) const {
assert(pos.count<KNIGHT>(weakerSide ) == 1);
assert(!pos.pieces(PAWN));
- Square wksq = pos.king_square(strongerSide);
- Square bksq = pos.king_square(weakerSide);
- Square nsq = pos.list<KNIGHT>(weakerSide)[0];
+ Square winnerKSq = pos.king_square(strongerSide);
+ Square loserKSq = pos.king_square(weakerSide);
+ Square knightSq = pos.list<KNIGHT>(weakerSide)[0];
- Value result = BishopValueEg
- + PushClose[square_distance(wksq, bksq)]
- + square_distance(bksq, nsq) * 32
- + (8 - popcount<Max15>(pos.attacks_from<KNIGHT>(nsq))) * 8;
+ Value result = VALUE_KNOWN_WIN
+ + PushToCorners[loserKSq]
+ + PushClose[square_distance(winnerKSq, loserKSq)]
+ + PushAway[square_distance(loserKSq, knightSq)];
return strongerSide == pos.side_to_move() ? result : -result;
}
Square weakerKingSq = pos.king_square(weakerSide);
Square bishopSq = pos.list<BISHOP>(strongerSide)[0];
- // Draw if weaker pawn is on rank 7, bishop can't attack the pawn, and
- // weaker king can stop opposing opponent's king from penetrating.
+ // Potential for a draw if our pawn is blocked on the 7th rank
+ // the bishop cannot attack it or they only have one pawn left
if ( relative_rank(strongerSide, weakerPawnSq) == RANK_7
- && opposite_colors(bishopSq, weakerPawnSq)
- && square_distance(weakerPawnSq, weakerKingSq) <= square_distance(weakerPawnSq, strongerKingSq))
- return SCALE_FACTOR_DRAW;
+ && (pos.pieces(strongerSide, PAWN) & (weakerPawnSq + pawn_push(weakerSide)))
+ && (opposite_colors(bishopSq, weakerPawnSq) || pos.count<PAWN>(strongerSide) == 1))
+ {
+ int strongerKingDist = square_distance(weakerPawnSq, strongerKingSq);
+ int weakerKingDist = square_distance(weakerPawnSq, weakerKingSq);
+
+ // Draw if the weak king is on it's back two ranks, within 2
+ // squares of the blocking pawn and the strong king is not
+ // closer. (I think this rule only fails in practically
+ // unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w
+ // and positions where qsearch will immediately correct the
+ // problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w)
+ if ( relative_rank(strongerSide, weakerKingSq) >= RANK_7
+ && weakerKingDist <= 2
+ && weakerKingDist <= strongerKingDist)
+ return SCALE_FACTOR_DRAW;
+ }
}
return SCALE_FACTOR_NONE;
return SCALE_FACTOR_NONE;
}
+template<>
+ScaleFactor Endgame<KRPKB>::operator()(const Position& pos) const {
+
+ assert(pos.non_pawn_material(strongerSide) == RookValueMg);
+ assert(pos.non_pawn_material(weakerSide) == BishopValueMg);
+ assert(pos.count<PAWN>(strongerSide) == 1);
+ assert(pos.count<PAWN>(weakerSide) == 0);
+
+ // Test for a rook pawn
+ if (pos.pieces(PAWN) & (FileABB | FileHBB))
+ {
+ Square ksq = pos.king_square(weakerSide);
+ Square bsq = pos.list<BISHOP>(weakerSide)[0];
+ Square psq = pos.list<PAWN>(strongerSide)[0];
+ Rank rk = relative_rank(strongerSide, psq);
+ Square push = pawn_push(strongerSide);
+
+ // If the pawn is on the 5th rank and the pawn (currently) is on
+ // the same color square as the bishop then there is a chance of
+ // a fortress. Depending on the king position give a moderate
+ // reduction or a stronger one if the defending king is near the
+ // corner but not trapped there.
+ if (rk == RANK_5 && !opposite_colors(bsq, psq))
+ {
+ int d = square_distance(psq + 3 * push, ksq);
+
+ if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongerSide) + 2 * push))
+ return ScaleFactor(24);
+ else
+ return ScaleFactor(48);
+ }
+
+ // When the pawn has moved to the 6th rank we can be fairly sure
+ // it's drawn if the bishop attacks the square in front of the
+ // pawn from a reasonable distance and the defending king is near
+ // the corner
+ if ( rk == RANK_6
+ && square_distance(psq + 2 * push, ksq) <= 1
+ && (PseudoAttacks[BISHOP][bsq] & (psq + push))
+ && file_distance(bsq, psq) >= 2)
+ return ScaleFactor(8);
+ }
+
+ return SCALE_FACTOR_NONE;
+}
/// K, rook and two pawns vs K, rook and one pawn. There is only a single
/// pattern: If the stronger side has no passed pawns and the defending king
Square bksq = pos.king_square(weakerSide);
// Does the stronger side have a passed pawn?
- if ( pos.pawn_is_passed(strongerSide, wpsq1)
- || pos.pawn_is_passed(strongerSide, wpsq2))
+ if (pos.pawn_passed(strongerSide, wpsq1) || pos.pawn_passed(strongerSide, wpsq2))
return SCALE_FACTOR_NONE;
Rank r = std::max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2));
projects / stockfish / blobdiff