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Code Issues Releases Wiki Activity

Simpler stalemate check.

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Gary Linscott 2012-02-05 14:52:01 -05:00
parent 0347339970
commit b46bf2950f
1 changed files with 5 additions and 16 deletions
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21
src/endgame.cpp
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@ -22,6 +22,7 @@
#include "bitcount.h" #include "bitcount.h"
#include "endgame.h" #include "endgame.h"
#include "movegen.h"
using std::string; using std::string;
@ -82,21 +83,6 @@ namespace {
template<typename M> template<typename M>
void delete_endgame(const typename M::value_type& p) { delete p.second; } void delete_endgame(const typename M::value_type& p) { delete p.second; }
// Fast stalemate detection with lone king
bool is_kxk_stalemate(const Position &pos, const Color c) {
if ( pos.side_to_move() == c &&
!pos.in_check()) {
const Square from = pos.king_square(c);
Bitboard b = pos.attacks_from<KING>(from);
while (b) {
// Assume there are no pinned pieces, as it is a lone king
if (pos.pl_move_is_legal(make_move(from, pop_1st_bit(&b)), 0))
return false;
}
return true;
}
return false;
}
} // namespace } // namespace
@ -147,7 +133,10 @@ Value Endgame<KXK>::operator()(const Position& pos) const {
assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO); assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO); assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO);
if (is_kxk_stalemate(pos, weakerSide)) { // Stalemate detection with lone king
if ( pos.side_to_move() == weakerSide
&& !pos.in_check()
&& !MoveList<MV_LEGAL>(pos).size()) {
return VALUE_DRAW; return VALUE_DRAW;
} }