feat: add bonus table for passers

1 files changed, 55 insertions, 1 deletions

diff --git a/src/grossmeister/evaluation.rs b/src/grossmeister/evaluation.rs
index eb59b92..572fa63 100644
--- a/src/grossmeister/evaluation.rs
+++ b/src/grossmeister/evaluation.rs
@@ -16,6 +16,18 @@ const PAWN_BONUS: [f32; 64] = [
      0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00
 ];
 
+const PAWN_PASSER_BONUS: [f32; 64] = [
+  //  A      B      C      D      E      F      G      H
+     0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,
+     2.00,  2.00,  2.00,  2.00,  2.00,  2.00,  2.00,  2.00,
+     1.50,  1.50,  1.50,  1.50,  1.50,  1.50,  1.50,  1.50,
+     1.00,  1.00,  1.00,  1.00,  1.00,  1.00,  1.00,  1.00,
+     0.70,  0.70,  0.70,  0.70,  0.70,  0.70,  0.70,  0.70,
+     0.50,  0.50,  0.50,  0.50,  0.50,  0.50,  0.50,  0.50,
+     0.20,  0.20,  0.20,  0.20,  0.20,  0.20,  0.20,  0.20,
+     0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,  0.00,
+];
+
 const KNIGHT_BONUS: [f32; 64] = [
   //  A      B      C      D      E      F      G      H
     -0.50, -0.40, -0.30, -0.30, -0.30, -0.30, -0.40, -0.50,
@@ -94,6 +106,25 @@ impl Grossmeister {
         self.board.piece_sets[Piece::Queen as usize].pop_count() == 0 &&
         self.board.piece_sets[Piece::QueenBlack as usize].pop_count() == 0
     }
+
+    pub fn passer_mask(&self, color: Color) -> Bitboard {
+        let black_pawns = self.board.piece_sets[Piece::PawnBlack as usize];
+        let white_pawns = self.board.piece_sets[Piece::Pawn as usize];
+
+        match color {
+            Color::Black => {
+                let mut front_fill = white_pawns.nort_fill().nort_one();
+                front_fill |= front_fill.east_one() | front_fill.west_one();
+                black_pawns & !front_fill
+            }
+            Color::White => {
+                let mut front_fill = black_pawns.sout_fill().sout_one();
+                front_fill |= front_fill.east_one() | front_fill.west_one();
+                white_pawns & !front_fill
+            }
+        }
+    }
+
     /// Evaluate a position relative to the current player
     pub fn evaluate(&self) -> f32 {
         let color = self.board.color();
@@ -117,12 +148,18 @@ 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 passer_mask = self.passer_mask(color);
+
         let mut material = 0f32;
         for (piece_index, bitboard) in self.board.pieces_by_color(color).iter().enumerate() {
             let piece_type = Piece::from(piece_index);
 
             let bonus_table = match piece_type {
-                Piece::Pawn => PAWN_BONUS,
+                Piece::Pawn => if bitboard & passer_mask != 0 {
+                    PAWN_PASSER_BONUS
+                } else {
+                    PAWN_BONUS
+                }
                 Piece::Knight => KNIGHT_BONUS,
                 Piece::Bishop => BISHOP_BONUS,
                 Piece::Rook => ROOK_BONUS,
@@ -510,4 +547,21 @@ mod tests {
         let is_endgame = gm.is_endgame();
         assert!(is_endgame);
     }
+
+    #[test]
+    fn passer() {
+        let fen = String::from("rnbqkbnr/ppp3pp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
+        let board = Board::from_FEN(fen);
+        let gm = Grossmeister::new(board);
+        let mask = gm.passer_mask(Color::White);
+        assert_eq!(mask, Square::E2.to_bitboard());
+    }
+
+    #[test]
+    fn no_passer() {
+        let board = Board::new();
+        let gm = Grossmeister::new(board);
+        let mask = gm.passer_mask(Color::White);
+        assert_eq!(mask, 0);
+    }
 }