}
-/// 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.
+/// Position::is_draw() tests whether the position is drawn by material, 50 moves
+/// rule or repetition. It does not detect stalemates.
+
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;
- int i = 4, e = std::min(st->rule50, st->pliesFromNull);
-
- if (i <= e)
+ StateInfo* stp = st;
+ for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
{
- StateInfo* stp = st->previous->previous;
-
- do {
- stp = stp->previous->previous;
-
- if (stp->key == st->key)
- return true; // Draw after first repetition
-
- i += 2;
+ stp = stp->previous->previous;
- } while (i <= e);
+ if (stp->key == st->key)
+ return true; // Draw at first repetition
}
return false;