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Detect drawish KQKP endings

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Based off of the rules from the wikipedia page,
here: http://en.wikipedia.org/wiki/Queen_versus_pawn_endgame.

bench does not change: 5312693 but patch is real, has been
tested on specific positions.
This commit is contained in:
Gary Linscott
2012-10-27 22:27:19 -04:00
committed by Marco Costalba
parent b3d030294b
commit cee6336515
2 changed files with 35 additions and 2 deletions
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36
src/endgame.cpp
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@@ -95,6 +95,7 @@ Endgames::Endgames() {
add<KRKP>("KRKP");
add<KRKB>("KRKB");
add<KRKN>("KRKN");
add<KQKP>("KQKP");
add<KQKR>("KQKR");
add<KBBKN>("KBBKN");
@@ -169,12 +170,12 @@ Value Endgame<KBNK>::operator()(const Position& pos) const {
Square winnerKSq = pos.king_square(strongerSide);
Square loserKSq = pos.king_square(weakerSide);
Square bishopSquare = pos.piece_list(strongerSide, BISHOP)[0];
Square bishopSq = pos.piece_list(strongerSide, BISHOP)[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.
if (opposite_colors(bishopSquare, SQ_A1))
if (opposite_colors(bishopSq, SQ_A1))
{
winnerKSq = mirror(winnerKSq);
loserKSq = mirror(loserKSq);
@@ -326,6 +327,37 @@ Value Endgame<KRKN>::operator()(const Position& pos) const {
}
/// 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.
template<>
Value Endgame<KQKP>::operator()(const Position& pos) const {
assert(pos.non_pawn_material(strongerSide) == QueenValueMg);
assert(pos.piece_count(strongerSide, PAWN) == 0);
assert(pos.non_pawn_material(weakerSide) == 0);
assert(pos.piece_count(weakerSide, PAWN) == 1);
Square winnerKSq = pos.king_square(strongerSide);
Square loserKSq = pos.king_square(weakerSide);
Square pawnSq = pos.piece_list(weakerSide, PAWN)[0];
Value result = QueenValueEg
- PawnValueEg
+ DistanceBonus[square_distance(winnerKSq, loserKSq)];
if ( square_distance(loserKSq, pawnSq) == 1
&& relative_rank(weakerSide, pawnSq) == RANK_7)
{
File f = file_of(pawnSq);
if (f == FILE_A || f == FILE_C || f == FILE_F || f == FILE_H)
result = Value(DistanceBonus[square_distance(winnerKSq, loserKSq)]);
}
return strongerSide == pos.side_to_move() ? result : -result;
}
/// KQ vs KR. This is almost identical to KX vs K: We give the attacking
/// king a bonus for having the kings close together, and for forcing the
/// defending king towards the edge. If we also take care to avoid null move