}
#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
- // flip 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 = ~winnerKSq;
return strongSide == pos.side_to_move() ? result : -result;
}
-// Returns a square that will allow us to orient the board so that
-// strongSide is white and strongSide's only pawn is on the left
-// half of the board
-Square get_flip_sq(const Position& pos, Color strongSide) {
-
- assert(pos.count<PAWN>(strongSide) == 1);
-
- Square psq = pos.list<PAWN>(strongSide)[0];
-
- return (FILE_H * (file_of(psq) >= FILE_E)) | (RANK_8 * int(strongSide));
-}
-
-Square operator^(Square s, Square flip_sq) {
- assert(flip_sq == SQ_A1 || flip_sq == SQ_H1 || flip_sq == SQ_A8 || flip_sq == SQ_H8);
- return Square(int(s) ^ int(flip_sq));
-}
/// KP vs K. This endgame is evaluated with the help of a bitbase.
template<>
assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
// Assume strongSide is white and the pawn is on files A-D
- Square flip_sq = get_flip_sq(pos, strongSide);
-
- Square wksq = pos.king_square(strongSide) ^ flip_sq;
- Square bksq = pos.king_square(weakSide) ^ flip_sq;
- Square psq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
+ 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]);
Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
}
-/// 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 {
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
/// 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, weakSide, RookValueMg, 0));
// Assume strongSide is white and the pawn is on files A-D
- Square flip_sq = get_flip_sq(pos, strongSide);
-
- Square wksq = pos.king_square(strongSide) ^ flip_sq;
- Square bksq = pos.king_square(weakSide) ^ flip_sq;
- Square wrsq = pos.list<ROOK>(strongSide)[0] ^ flip_sq;
- Square wpsq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
- Square brsq = pos.list<ROOK>(weakSide)[0] ^ flip_sq;
+ 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);
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, weakSide, VALUE_ZERO, 0));
// Assume strongSide is white and the pawn is on files A-D
- Square flip_sq = get_flip_sq(pos, strongSide);
-
- Square pawnSq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
- Square weakKingSq = pos.king_square(weakSide) ^ flip_sq;
+ Square pawnSq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
+ Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide));
if (pawnSq == SQ_A7 && square_distance(SQ_A8, weakKingSq) <= 1)
return SCALE_FACTOR_DRAW;
assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
// Assume strongSide is white and the pawn is on files A-D
- Square flip_sq = get_flip_sq(pos, strongSide);
-
- Square wksq = pos.king_square(strongSide) ^ flip_sq;
- Square bksq = pos.king_square(weakSide) ^ flip_sq;
- Square psq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
+ 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]);
Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
projects / stockfish / blobdiff