feat: move king to center in the endgame

1 files changed, 48 insertions, 1 deletions

diff --git a/src/grossmeister/evaluation.rs b/src/grossmeister/evaluation.rs
index 308f320..eb59b92 100644
--- a/src/grossmeister/evaluation.rs
+++ b/src/grossmeister/evaluation.rs
@@ -76,7 +76,24 @@ const KING_BONUS: [f32; 64] = [
      0.20,  0.10,  0.30, -0.20,  0.00,  0.10,  0.30,  0.20
 ];
 
+const KING_BONUS_ENGAME: [f32; 64] = [
+  //  A      B      C      D      E      F      G      H
+    -0.50, -0.40, -0.30, -0.20, -0.20, -0.30, -0.40, -0.50,
+    -0.30, -0.20, -0.10,  0.00,  0.00, -0.10, -0.20, -0.30,
+    -0.30, -0.10,  0.20,  0.30,  0.30,  0.20, -0.10, -0.30,
+    -0.30, -0.10,  0.30,  0.40,  0.40,  0.30, -0.10, -0.30,
+    -0.30, -0.10,  0.30,  0.40,  0.40,  0.30, -0.10, -0.30,
+    -0.30, -0.10,  0.20,  0.30,  0.30,  0.20, -0.10, -0.30,
+    -0.30, -0.30,  0.00,  0.00,  0.00,  0.00, -0.30, -0.30,
+    -0.50, -0.30, -0.30, -0.30, -0.30, -0.30, -0.30, -0.50
+];
+
 impl Grossmeister {
+    pub fn is_endgame(&self) -> bool {
+        // No queens on the board
+        self.board.piece_sets[Piece::Queen as usize].pop_count() == 0 &&
+        self.board.piece_sets[Piece::QueenBlack as usize].pop_count() == 0
+    }
     /// Evaluate a position relative to the current player
     pub fn evaluate(&self) -> f32 {
         let color = self.board.color();
@@ -99,6 +116,7 @@ impl Grossmeister {
 
     /// Count player pieces' material, giving bonus for pieces standing well
     pub fn material(&self, color: Color) -> f32 {
+        let is_endgame = self.is_endgame();
         let mut material = 0f32;
         for (piece_index, bitboard) in self.board.pieces_by_color(color).iter().enumerate() {
             let piece_type = Piece::from(piece_index);
@@ -108,7 +126,11 @@ impl Grossmeister {
                 Piece::Knight => KNIGHT_BONUS,
                 Piece::Bishop => BISHOP_BONUS,
                 Piece::Rook => ROOK_BONUS,
-                Piece::King => KING_BONUS,
+                Piece::King => if is_endgame {
+                    KING_BONUS_ENGAME
+                } else {
+                    KING_BONUS
+                },
                 Piece::Queen => QUEEN_BONUS,
                 _ => panic!("Unreachable")
             };
@@ -463,4 +485,29 @@ mod tests {
         assert_eq!(score1.abs(), score2.abs());
     }
 
+    #[test]
+    fn not_endgame() {
+        let board = Board::new();
+        let gm = Grossmeister::new(board);
+        let is_endgame = gm.is_endgame();
+        assert!(!is_endgame);
+    }
+
+    #[test]
+    fn is_endgame() {
+        let fen = String::from("8/1p6/p4k1K/6r1/8/8/8/8 w - - 10 49");
+        let board = Board::from_FEN(fen);
+        let gm = Grossmeister::new(board);
+        let is_endgame = gm.is_endgame();
+        assert!(is_endgame);
+    }
+
+    #[test]
+    fn is_endgame_no_queens() {
+        let fen = String::from("rnb1kbnr/pppppppp/8/8/8/8/PPPPPPPP/RNB1KBNR w KQkq - 0 1");
+        let board = Board::from_FEN(fen);
+        let gm = Grossmeister::new(board);
+        let is_endgame = gm.is_endgame();
+        assert!(is_endgame);
+    }
 }