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Simplification of KPsK function 

Also the drawing criteria has been slightly loosened.
It now detects a draw if the king is ahead of all the
pawns and on the same file or the adjacent file.

bench: 7700683
sf_dd_base
Chris Caino 2013-10-15 00:20:34 +01:00 committed by Marco Costalba
parent 2bf18bfc63
commit 3cddb0c076
1 changed files with 8 additions and 18 deletions
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26
src/endgame.cpp
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@ -684,25 +684,15 @@ ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
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;
}