Add move ordering heuristic MVV/LVA

src/search/move_ordering.rs

@@ -0,0 +1,42 @@
+use crate::{board::board::Board, movegen::r#move::Move};
+
+// Rows: Aggressors (P, N, B, R, Q, K)
+// Columns: Victims (K, Q, R, B, N, P)
+const MVV_LVA: [[usize; 6]; 6] = [
+    [30, 29, 28, 27, 26, 00],
+    [25, 24, 23, 22, 21, 00],
+    [20, 19, 18, 17, 16, 00],
+    [15, 14, 13, 12, 11, 00],
+    [10, 09, 08, 07, 06, 00],
+    [05, 04, 03, 02, 01, 00],
+];
+
+pub fn score_by_mvv_lva(board: &Board, mv: Move) -> usize {
+    match (board.piece_type_at(mv.src), board.piece_type_at(mv.dst)) {
+        (Some(aggressor), Some(victim)) => MVV_LVA[aggressor.idx()][victim.idx()],
+        _ => 0,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        board::{board::PieceType, fen::from_fen, square::Square},
+        movegen::r#move::{Move, MoveType},
+        search::move_ordering::{score_by_mvv_lva, MVV_LVA},
+    };
+
+    const FEN: &'static str = "1r2k2r/2P1pq1p/2npb3/1p3ppP/p3P3/P2B1Q2/1P1PNPP1/R3K2R w KQk g6 0 1";
+
+    #[test]
+    fn test_score_by_mvv_lva() -> Result<(), String> {
+        let game = from_fen(FEN)?;
+        let f3f5 = Move::new_with_type(Square::F3, Square::F5, MoveType::Capture);
+        let actual = score_by_mvv_lva(&game.board, f3f5);
+        let expected = MVV_LVA[PieceType::Queen.idx()][PieceType::Pawn.idx()];
+
+        assert_eq!(expected, actual);
+
+        Ok(())
+    }
+}