KQKP, // KQ vs KP
KQKR, // KQ vs KR
KBBKN, // KBB vs KN
- KmmKm, // K and one or two minors vs K and zero or one minor
+ KmmKm, // K and two minors vs K and one or two minors
// Scaling functions
return e;
}
- // Draw by insufficient material (trivial draws like KK, KBK and KNK)
- if ( !pos.pieces(PAWN)
- && pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) <= BishopValueMg)
- {
- e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
- return e;
- }
-
- // Minor piece endgame with at least one minor piece per side and
- // no pawns. Note that the case KmmK is already handled by KXK.
if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
{
+ // Minor piece endgame with at least one minor piece per side and
+ // no pawns. Note that the case KmmK is already handled by KXK.
assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
}
}
- // No pawns makes it difficult to win, even with a material advantage
+ // No pawns makes it difficult to win, even with a material advantage. This
+ // catches some trivial draws like KK, KBK and KNK
if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
{
e->factor[WHITE] = (uint8_t)
}
-/// Position::is_draw() tests whether the position is drawn by 50 moves rule
-/// or by repetition. It does not detect stalemates.
-
+/// Position::is_draw() tests whether the position is drawn by material,
+/// repetition, or the 50 moves rule. It does not detect stalemates, this
+/// must be done by the search.
bool Position::is_draw() const {
+ // Draw by material?
+ if ( !pieces(PAWN)
+ && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
+ return true;
+
+ // Draw by the 50 moves rule?
if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
return true;