}
#endif
+ // Map the square as if strongSide is white and strongSide's only pawn
+ // is on the left half of the board.
+ Square normalize(const Position& pos, Color strongSide, Square sq) {
+
+ assert(pos.count<PAWN>(strongSide) == 1);
+
+ if (file_of(pos.list<PAWN>(strongSide)[0]) >= FILE_E)
+ sq = Square(sq ^ 7); // Mirror SQ_H1 -> SQ_A1
+
+ if (strongSide == BLACK)
+ sq = ~sq;
+
+ return sq;
+ }
+
// 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
// and then let a Position object to do the work for us. Note that the
/// Mate with KX vs K. This function is used to evaluate positions with
-/// King and plenty of material vs a lone king. It simply gives the
+/// king and plenty of material vs a lone king. It simply gives the
/// attacking side a bonus for driving the defending king towards the edge
/// of the board, and for keeping the distance between the two kings small.
template<>
Square loserKSq = pos.king_square(weakSide);
Square bishopSq = pos.list<BISHOP>(strongSide)[0];
- // kbnk_mate_table() tries to drive toward corners A1 or H8,
- // if we have a bishop that cannot reach the above squares we
- // mirror the kings so to drive enemy toward corners A8 or H1.
+ // kbnk_mate_table() tries to drive toward corners A1 or H8, if we have a
+ // bishop that cannot reach the above squares we flip the kings in order
+ // to drive the enemy toward corners A8 or H1.
if (opposite_colors(bishopSq, SQ_A1))
{
- winnerKSq = mirror(winnerKSq);
- loserKSq = mirror(loserKSq);
+ winnerKSq = ~winnerKSq;
+ loserKSq = ~loserKSq;
}
Value result = VALUE_KNOWN_WIN
assert(verify_material(pos, strongSide, VALUE_ZERO, 1));
assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
- Square wksq = pos.king_square(strongSide);
- Square bksq = pos.king_square(weakSide);
- Square psq = pos.list<PAWN>(strongSide)[0];
- Color us = pos.side_to_move();
-
- if (strongSide == BLACK)
- {
- wksq = ~wksq;
- bksq = ~bksq;
- psq = ~psq;
- us = ~us;
- }
+ // Assume strongSide is white and the pawn is on files A-D
+ Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
+ Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
+ Square psq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
- if (file_of(psq) >= FILE_E)
- {
- wksq = mirror(wksq);
- bksq = mirror(bksq);
- psq = mirror(psq);
- }
+ Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
if (!Bitbases::probe_kpk(wksq, psq, bksq, us))
return VALUE_DRAW;
assert(verify_material(pos, strongSide, RookValueMg, 0));
assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
- Square wksq = pos.king_square(strongSide);
- Square bksq = pos.king_square(weakSide);
- Square rsq = pos.list<ROOK>(strongSide)[0];
- Square psq = pos.list<PAWN>(weakSide)[0];
-
- if (strongSide == BLACK)
- {
- wksq = ~wksq;
- bksq = ~bksq;
- rsq = ~rsq;
- psq = ~psq;
- }
+ Square wksq = relative_square(strongSide, pos.king_square(strongSide));
+ Square bksq = relative_square(strongSide, pos.king_square(weakSide));
+ Square rsq = relative_square(strongSide, pos.list<ROOK>(strongSide)[0]);
+ Square psq = relative_square(strongSide, pos.list<PAWN>(weakSide)[0]);
Square queeningSq = file_of(psq) | RANK_1;
Value result;
}
-/// KQ vs KP. In general, a win for the stronger side, however, there are a few
-/// important exceptions. Pawn on 7th rank, A,C,F or H file, with king next can
-/// be a draw, so we scale down to distance between kings only.
+/// KQ vs KP. In general, this is a win for the stronger side, but there are a
+/// few important exceptions. A pawn on 7th rank and on the A,C,F or H files
+/// with a king positioned next to it can be a draw, so in that case, we only
+/// use the distance between the kings.
template<>
Value Endgame<KQKP>::operator()(const Position& pos) const {
Square kingSq = pos.king_square(weakSide);
if ( opposite_colors(queeningSq, bishopSq)
- && abs(file_of(kingSq) - pawnFile) <= 1)
- {
- // The bishop has the wrong color, and the defending king is on the
- // file of the pawn(s) or the adjacent file. Find the rank of the
- // frontmost pawn.
- Square pawnSq = frontmost_sq(strongSide, pawns);
-
- // If the defending king has distance 1 to the promotion square or
- // is placed somewhere in front of the pawn, it's a draw.
- if ( square_distance(kingSq, queeningSq) <= 1
- || relative_rank(weakSide, kingSq) <= relative_rank(weakSide, pawnSq))
- return SCALE_FACTOR_DRAW;
- }
+ && square_distance(queeningSq, kingSq) <= 1)
+ return SCALE_FACTOR_DRAW;
}
- // All pawns on same B or G file? Then potential draw
+ // If all the pawns are on the same B or G file, then it's potentially a draw
if ( (pawnFile == FILE_B || pawnFile == FILE_G)
&& !(pos.pieces(PAWN) & ~file_bb(pawnFile))
&& pos.non_pawn_material(weakSide) == 0
&& pos.count<PAWN>(weakSide) >= 1)
{
- // Get weakSide pawn that is closest to home rank
+ // Get weakSide pawn that is closest to the home rank
Square weakPawnSq = backmost_sq(weakSide, pos.pieces(weakSide, PAWN));
Square strongKingSq = pos.king_square(strongSide);
Square weakKingSq = pos.king_square(weakSide);
Square bishopSq = pos.list<BISHOP>(strongSide)[0];
- // Potential for a draw if our pawn is blocked on the 7th rank
+ // There's 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(strongSide, weakPawnSq) == RANK_7
&& (pos.pieces(strongSide, PAWN) & (weakPawnSq + pawn_push(weakSide)))
int strongKingDist = square_distance(weakPawnSq, strongKingSq);
int weakKingDist = square_distance(weakPawnSq, weakKingSq);
- // Draw if the weak king is on it's back two ranks, within 2
+ // It's a draw if the weak king is on its 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
if ( relative_rank(weakSide, kingSq) <= RANK_2
&& relative_rank(weakSide, pos.king_square(strongSide)) >= RANK_4
- && (pos.pieces(weakSide, ROOK) & rank_bb(relative_rank(weakSide, RANK_3)))
- && (pos.pieces(weakSide, PAWN) & rank_bb(relative_rank(weakSide, RANK_2)))
- && (pos.attacks_from<KING>(kingSq) & pos.pieces(weakSide, PAWN))
- && (pos.attacks_from<PAWN>(rsq, strongSide) & pos.pieces(weakSide, PAWN)))
+ && relative_rank(weakSide, rsq) == RANK_3
+ && ( pos.pieces(weakSide, PAWN)
+ & pos.attacks_from<KING>(kingSq)
+ & pos.attacks_from<PAWN>(rsq, strongSide)))
return SCALE_FACTOR_DRAW;
return SCALE_FACTOR_NONE;
/// probably be a good idea to add more knowledge in the future.
///
/// It would also be nice to rewrite the actual code for this function,
-/// which is mostly copied from Glaurung 1.x, and not very pretty.
+/// which is mostly copied from Glaurung 1.x, and isn't very pretty.
template<>
ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
assert(verify_material(pos, strongSide, RookValueMg, 1));
assert(verify_material(pos, weakSide, RookValueMg, 0));
- Square wksq = pos.king_square(strongSide);
- Square bksq = pos.king_square(weakSide);
- Square wrsq = pos.list<ROOK>(strongSide)[0];
- Square wpsq = pos.list<PAWN>(strongSide)[0];
- Square brsq = pos.list<ROOK>(weakSide)[0];
-
- // Orient the board in such a way that the stronger side is white, and the
- // pawn is on the left half of the board.
- if (strongSide == BLACK)
- {
- wksq = ~wksq;
- wrsq = ~wrsq;
- wpsq = ~wpsq;
- bksq = ~bksq;
- brsq = ~brsq;
- }
-
- if (file_of(wpsq) > FILE_D)
- {
- wksq = mirror(wksq);
- wrsq = mirror(wrsq);
- wpsq = mirror(wpsq);
- bksq = mirror(bksq);
- brsq = mirror(brsq);
- }
+ // Assume strongSide is white and the pawn is on files A-D
+ Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
+ Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
+ Square wrsq = normalize(pos, strongSide, pos.list<ROOK>(strongSide)[0]);
+ Square wpsq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
+ Square brsq = normalize(pos, strongSide, pos.list<ROOK>(weakSide)[0]);
File f = file_of(wpsq);
Rank r = rank_of(wpsq);
Square ksq = pos.king_square(weakSide);
Bitboard pawns = pos.pieces(strongSide, PAWN);
+ Square psq = pos.list<PAWN>(strongSide)[0];
+
+ // If all pawns are ahead of the king, all pawns are on a single
+ // rook file and the king is within one file of the pawns then draw.
+ if ( !(pawns & ~in_front_bb(weakSide, rank_of(ksq)))
+ && !((pawns & ~FileABB) && (pawns & ~FileHBB))
+ && file_distance(ksq, psq) <= 1)
+ return SCALE_FACTOR_DRAW;
- // Are all pawns on the 'a' file?
- if (!(pawns & ~FileABB))
- {
- // Does the defending king block the pawns?
- if ( square_distance(ksq, relative_square(strongSide, SQ_A8)) <= 1
- || ( file_of(ksq) == FILE_A
- && !(in_front_bb(strongSide, rank_of(ksq)) & pawns)))
- return SCALE_FACTOR_DRAW;
- }
- // Are all pawns on the 'h' file?
- else if (!(pawns & ~FileHBB))
- {
- // Does the defending king block the pawns?
- if ( square_distance(ksq, relative_square(strongSide, SQ_H8)) <= 1
- || ( file_of(ksq) == FILE_H
- && !(in_front_bb(strongSide, rank_of(ksq)) & pawns)))
- return SCALE_FACTOR_DRAW;
- }
return SCALE_FACTOR_NONE;
}
switch (file_distance(psq1, psq2))
{
case 0:
- // Both pawns are on the same file. Easy draw if defender firmly controls
- // some square in the frontmost pawn's path.
+ // Both pawns are on the same file. It's an easy draw if the defender firmly
+ // controls some square in the frontmost pawn's path.
if ( file_of(ksq) == file_of(blockSq1)
&& relative_rank(strongSide, ksq) >= relative_rank(strongSide, blockSq1)
&& opposite_colors(ksq, wbsq))
return SCALE_FACTOR_NONE;
case 1:
- // Pawns on adjacent files. Draw if defender firmly controls the square
- // in front of the frontmost pawn's path, and the square diagonally behind
- // this square on the file of the other pawn.
+ // Pawns on adjacent files. It's a draw if the defender firmly controls the
+ // square in front of the frontmost pawn's path, and the square diagonally
+ // behind this square on the file of the other pawn.
if ( ksq == blockSq1
&& opposite_colors(ksq, wbsq)
&& ( bbsq == blockSq2
assert(verify_material(pos, strongSide, KnightValueMg, 1));
assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
- Square pawnSq = pos.list<PAWN>(strongSide)[0];
- Square weakKingSq = pos.king_square(weakSide);
-
- if ( pawnSq == relative_square(strongSide, SQ_A7)
- && square_distance(weakKingSq, relative_square(strongSide, SQ_A8)) <= 1)
- return SCALE_FACTOR_DRAW;
+ // Assume strongSide is white and the pawn is on files A-D
+ Square pawnSq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
+ Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide));
- if ( pawnSq == relative_square(strongSide, SQ_H7)
- && square_distance(weakKingSq, relative_square(strongSide, SQ_H8)) <= 1)
+ if (pawnSq == SQ_A7 && square_distance(SQ_A8, weakKingSq) <= 1)
return SCALE_FACTOR_DRAW;
return SCALE_FACTOR_NONE;
assert(verify_material(pos, strongSide, VALUE_ZERO, 1));
assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
- Square wksq = pos.king_square(strongSide);
- Square bksq = pos.king_square(weakSide);
- Square psq = pos.list<PAWN>(strongSide)[0];
- Color us = pos.side_to_move();
+ // Assume strongSide is white and the pawn is on files A-D
+ Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
+ Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
+ Square psq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
- if (strongSide == BLACK)
- {
- wksq = ~wksq;
- bksq = ~bksq;
- psq = ~psq;
- us = ~us;
- }
-
- if (file_of(psq) >= FILE_E)
- {
- wksq = mirror(wksq);
- bksq = mirror(bksq);
- psq = mirror(psq);
- }
+ Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
// If the pawn has advanced to the fifth rank or further, and is not a
// rook pawn, it's too dangerous to assume that it's at least a draw.
projects / stockfish / blobdiff