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Add KBPKP endgame

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It is a draw if pawns are on G or B files, weaker pawn is
on rank 7 and bishop can't attack the pawn.

No functional change (because it is very rare and does not appear in bench)
This commit is contained in:
Gary Linscott 2013-02-03 15:42:51 -05:00 • committed by Marco Costalba
parent 14c2c1395b
commit c67fb8ef04
1 changed files with 23 additions and 0 deletions
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23
src/endgame.cpp
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@ -471,6 +471,29 @@ ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
return SCALE_FACTOR_DRAW; return SCALE_FACTOR_DRAW;
} }
} }
// All pawns on same B or G file? Then potential draw
if ( (pawnFile == FILE_B || pawnFile == FILE_G)
&& !(pos.pieces(PAWN) & ~file_bb(pawnFile))
&& pos.non_pawn_material(weakerSide) == 0
&& pos.piece_count(weakerSide, PAWN) >= 1)
{
// Get weaker pawn closest to opponent's queening square
Bitboard wkPawns = pos.pieces(weakerSide, PAWN);
Square weakerPawnSq = strongerSide == WHITE ? msb(wkPawns) : lsb(wkPawns);
Square strongerKingSq = pos.king_square(strongerSide);
Square weakerKingSq = pos.king_square(weakerSide);
Square bishopSq = pos.piece_list(strongerSide, BISHOP)[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.
if ( relative_rank(strongerSide, weakerPawnSq) == RANK_7
&& opposite_colors(bishopSq, weakerPawnSq)
&& square_distance(weakerPawnSq, weakerKingSq) <= square_distance(weakerPawnSq, strongerKingSq))
return SCALE_FACTOR_DRAW;
}
return SCALE_FACTOR_NONE; return SCALE_FACTOR_NONE;
} }