feat: apply null move heuristic

1 files changed, 22 insertions, 3 deletions

diff --git a/src/board/engine.rs b/src/board/engine.rs
index 7f2fef3..ee5be65 100644
--- a/src/board/engine.rs
+++ b/src/board/engine.rs
@@ -371,13 +371,32 @@ impl Board {
             None => {},
         }
 
-        let mut moves = self.generate_pseudolegal_moves(color);
-        moves = self.order_moves(moves, parent_killers.to_vec());
-
         if depth_left == 0 {
             return (self.quiscence(alpha, beta), principal_variation);
         }
 
+        // Try a Null Move heuristic
+        if !is_in_check && depth_left >= 3 {
+            let reduction = 3;
+             // Apply Null Move
+            self.ply += 1;
+            self.hash ^= self.zobrist_seed[780];
+
+            let (mut score, ..) = self.negamax_search(-beta, -alpha, (depth_left as i8 - 1 - reduction).max(0) as u8, &mut Vec::new(), deadline);
+            score *= -1.;
+
+            // Undo Null Move
+            self.ply -= 1;
+            self.hash ^= self.zobrist_seed[780];
+
+            if score >= beta {
+                return (beta, principal_variation);
+            }
+        }
+
+        let mut moves = self.generate_pseudolegal_moves(color);
+        moves = self.order_moves(moves, parent_killers.to_vec());
+
         let mut should_pv_search = true; // = !should_apply_LMR
         let mut legal_move_found = false;
         for mov in moves {