Add move ordering heuristic MVV/LVA

src/search/negamax.rs

@@ -4,7 +4,7 @@ use crate::{
     movegen::r#move::Move,
 };
 
-use super::quiescence::quiescence;
+use super::{move_ordering::score_by_mvv_lva, quiescence::quiescence};
 
 pub fn negamax(
     game: &mut Game,
@@ -22,7 +22,10 @@ pub fn negamax(
     let (mut best_move, mut best_score, mate_score) = (None, MIN_SCORE, -MATE_SCORE + plies as i32);
     let mut legal_moves = 0;
 
-    for mv in game.board.pseudo_moves_all() {
+    let mut pseudo_legal_moves = game.board.pseudo_moves_all();
+    pseudo_legal_moves.sort_unstable_by_key(|mv| score_by_mvv_lva(&game.board, *mv));
+
+    for mv in pseudo_legal_moves {
         let move_parameters = MoveParameters::build(&game.board, &mv);
         game.board.make_move(&mv);
 
@@ -41,7 +44,7 @@ pub fn negamax(
         }
 
         if move_score >= beta {
-            return (Some(mv), beta);
+            return (best_move, beta);
         }
 
         alpha = alpha.max(move_score);
@@ -64,12 +67,22 @@ mod tests {
     use crate::movegen::r#move::Move;
     use crate::search::negamax::negamax;
 
-    const FEN_MATE_IN_1: &str = "8/8/8/8/8/4q1k1/8/5K2 b - - 0 1";
+    const FEN_MATE_IN_1: [&str; 2] = [
+        "8/8/8/8/8/4q1k1/8/5K2 b - - 0 1",
+        "8/8/8/8/8/4Q1K1/8/5k2 w - - 0 1",
+    ];
 
     #[test]
     fn test_negamax() -> Result<(), String> {
         init_attacks();
-        let mut game = from_fen(FEN_MATE_IN_1)?;
+        let mut game = from_fen(FEN_MATE_IN_1[0])?;
+
+        let e3f2 = Move::new(Square::E3, Square::F2);
+        let anointed_move = negamax(&mut game, MIN_SCORE, MAX_SCORE, 2, 0).0.unwrap();
+
+        assert_eq!(e3f2, anointed_move);
+
+        let mut game = from_fen(FEN_MATE_IN_1[1])?;
 
         let e3f2 = Move::new(Square::E3, Square::F2);
         let anointed_move = negamax(&mut game, MIN_SCORE, MAX_SCORE, 2, 0).0.unwrap();