add MoveGen::has_legal_moves and use it in Board.status

src/board.rs

@@ -155,16 +155,14 @@ impl Board {
     /// ```
     #[inline]
     pub fn status(&self) -> BoardStatus {
-        let moves = MoveGen::new_legal(&self).len();
-        match moves {
-            0 => {
-                if self.checkers == EMPTY {
-                    BoardStatus::Stalemate
-                } else {
-                    BoardStatus::Checkmate
-                }
+        if MoveGen::has_legal_moves(&self) {
+            BoardStatus::Ongoing
+        } else {
+            if self.checkers == EMPTY {
+                BoardStatus::Stalemate
+            } else {
+                BoardStatus::Checkmate
             }
-            _ => BoardStatus::Ongoing,
         }
     }
 

src/movegen/movegen.rs

@@ -118,6 +118,45 @@ impl MoveGen {
         movelist
     }
 
+    /// Check whether the board has any legal moves or not
+    #[inline(always)]
+    pub fn has_legal_moves(board: &Board) -> bool {
+        let checkers = *board.checkers();
+        let mask = !board.color_combined(board.side_to_move());
+        let mut movelist = NoDrop::new(ArrayVec::<[SquareAndBitBoard; 18]>::new());
+
+        let legal_fns = if checkers == EMPTY {
+            [
+                PawnType::legals::<NotInCheckType>  ,
+                KnightType::legals::<NotInCheckType>,
+                BishopType::legals::<NotInCheckType>,
+                RookType::legals::<NotInCheckType>  ,
+                QueenType::legals::<NotInCheckType> ,
+                KingType::legals::<NotInCheckType>  ,
+            ]
+        } else if checkers.popcnt() == 1 {
+            [
+                PawnType::legals::<InCheckType>  ,
+                KnightType::legals::<InCheckType>,
+                BishopType::legals::<InCheckType>,
+                RookType::legals::<InCheckType>  ,
+                QueenType::legals::<InCheckType> ,
+                KingType::legals::<InCheckType>  ,
+            ]
+        } else {
+            KingType::legals::<InCheckType>(&mut movelist, &board, mask);
+            return movelist.len() != 0
+        };
+
+        for f in legal_fns {
+            f(&mut movelist, &board, mask);
+            if movelist.len() != 0 { return true }
+            movelist.clear();
+        }
+
+        return false
+    }
+
     /// Create a new `MoveGen` structure, only generating legal moves
     #[inline(always)]
     pub fn new_legal(board: &Board) -> MoveGen {