feat: count the number of pawn islands

1 files changed, 12 insertions, 0 deletions

diff --git a/src/grossmeister/evaluation.rs b/src/grossmeister/evaluation.rs
index b7060ba..29c1128 100644
--- a/src/grossmeister/evaluation.rs
+++ b/src/grossmeister/evaluation.rs
@@ -162,6 +162,15 @@ impl Grossmeister {
         (behind_pawns & (king | king.west_one() | king.east_one())).pop_count() as f32
     }
 
+    /// Count the number of pawn islands of given color
+    pub fn pawn_islands(&self, color: Color) -> f32 {
+        let pawns = self.board.pieces_by_color(color)[Piece::Pawn as usize];
+        let fileset = pawns.nort_fill().sout_fill();
+        // Does not matter west/east, each island has both sides
+        let islands_west_files = fileset & !fileset.east_one();
+        islands_west_files.pop_count() as f32
+    }
+
     // Returns a value in [0, 240] representing how
     // much material is left in the game
     // Note: not related to actual material counting
@@ -230,15 +239,18 @@ impl Grossmeister {
         let material_advantage = self.material(color) - self.material(opponent_color);
         let mobility_advantage = self.mobility(color) - self.mobility(opponent_color);
         let pawn_shield_advantage = self.pawn_shield(color) - self.pawn_shield(opponent_color);
+        let pawn_islands_advantage = self.pawn_islands(opponent_color) - self.pawn_islands(color);
 
         let middlegame_eval =
             mobility_advantage * 0.05 +
             pawn_shield_advantage * 0.15 +
+            pawn_islands_advantage * 0.10 +
             (self.pst_bonus(color, false) - self.pst_bonus(opponent_color, false));
 
         let endgame_eval =
             mobility_advantage * 0.03 +
             pawn_shield_advantage * 0.20 +
+            pawn_islands_advantage * 0.15 +
             (self.pst_bonus(color, true) - self.pst_bonus(opponent_color, true));
 
         let phase = self.phase();