Add naive knight move generation

src/movegen/knight.rs

@@ -0,0 +1,184 @@
+use crate::board::{Bitboard, Direction, Square};
+
+/// Compute a knight's movement.
+#[allow(unused)]
+pub fn knight_moves(square: Square) -> Bitboard {
+    let board = square.into_bitboard();
+
+    Direction::iter_knight()
+        .map(|dir| dir.move_board(board))
+        .fold(Bitboard::EMPTY, |lhs, rhs| lhs | rhs)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn moves_first_rank() {
+        assert_eq!(knight_moves(Square::A1), Square::B3 | Square::C2);
+        assert_eq!(
+            knight_moves(Square::B1),
+            Square::A3 | Square::C3 | Square::D2
+        );
+        assert_eq!(
+            knight_moves(Square::C1),
+            Square::A2 | Square::B3 | Square::D3 | Square::E2
+        );
+        assert_eq!(
+            knight_moves(Square::D1),
+            Square::B2 | Square::C3 | Square::E3 | Square::F2
+        );
+        assert_eq!(
+            knight_moves(Square::E1),
+            Square::C2 | Square::D3 | Square::F3 | Square::G2
+        );
+        assert_eq!(
+            knight_moves(Square::F1),
+            Square::D2 | Square::E3 | Square::G3 | Square::H2
+        );
+        assert_eq!(
+            knight_moves(Square::G1),
+            Square::E2 | Square::F3 | Square::H3
+        );
+        assert_eq!(knight_moves(Square::H1), Square::F2 | Square::G3);
+    }
+
+    #[test]
+    fn moves_last_rank() {
+        assert_eq!(knight_moves(Square::A8), Square::B6 | Square::C7);
+        assert_eq!(
+            knight_moves(Square::B8),
+            Square::A6 | Square::C6 | Square::D7
+        );
+        assert_eq!(
+            knight_moves(Square::C8),
+            Square::A7 | Square::B6 | Square::D6 | Square::E7
+        );
+        assert_eq!(
+            knight_moves(Square::D8),
+            Square::B7 | Square::C6 | Square::E6 | Square::F7
+        );
+        assert_eq!(
+            knight_moves(Square::E8),
+            Square::C7 | Square::D6 | Square::F6 | Square::G7
+        );
+        assert_eq!(
+            knight_moves(Square::F8),
+            Square::D7 | Square::E6 | Square::G6 | Square::H7
+        );
+        assert_eq!(
+            knight_moves(Square::G8),
+            Square::E7 | Square::F6 | Square::H6
+        );
+        assert_eq!(knight_moves(Square::H8), Square::F7 | Square::G6);
+    }
+
+    #[test]
+    fn moves_first_file() {
+        assert_eq!(knight_moves(Square::A1), Square::B3 | Square::C2);
+        assert_eq!(
+            knight_moves(Square::A2),
+            Square::B4 | Square::C1 | Square::C3
+        );
+        assert_eq!(
+            knight_moves(Square::A3),
+            Square::B1 | Square::B5 | Square::C2 | Square::C4
+        );
+        assert_eq!(
+            knight_moves(Square::A4),
+            Square::B2 | Square::B6 | Square::C3 | Square::C5
+        );
+        assert_eq!(
+            knight_moves(Square::A5),
+            Square::B3 | Square::B7 | Square::C4 | Square::C6
+        );
+        assert_eq!(
+            knight_moves(Square::A6),
+            Square::B4 | Square::B8 | Square::C5 | Square::C7
+        );
+        assert_eq!(
+            knight_moves(Square::A7),
+            Square::B5 | Square::C6 | Square::C8
+        );
+        assert_eq!(knight_moves(Square::A8), Square::B6 | Square::C7);
+    }
+
+    #[test]
+    fn moves_last_file() {
+        assert_eq!(knight_moves(Square::H1), Square::G3 | Square::F2);
+        assert_eq!(
+            knight_moves(Square::H2),
+            Square::G4 | Square::F1 | Square::F3
+        );
+        assert_eq!(
+            knight_moves(Square::H3),
+            Square::G1 | Square::G5 | Square::F2 | Square::F4
+        );
+        assert_eq!(
+            knight_moves(Square::H4),
+            Square::G2 | Square::G6 | Square::F3 | Square::F5
+        );
+        assert_eq!(
+            knight_moves(Square::H5),
+            Square::G3 | Square::G7 | Square::F4 | Square::F6
+        );
+        assert_eq!(
+            knight_moves(Square::H6),
+            Square::G4 | Square::G8 | Square::F5 | Square::F7
+        );
+        assert_eq!(
+            knight_moves(Square::H7),
+            Square::G5 | Square::F6 | Square::F8
+        );
+        assert_eq!(knight_moves(Square::H8), Square::G6 | Square::F7);
+    }
+
+    #[test]
+    fn moves_middle() {
+        assert_eq!(
+            knight_moves(Square::D4),
+            Square::B3
+                | Square::B5
+                | Square::C2
+                | Square::C6
+                | Square::E2
+                | Square::E6
+                | Square::F3
+                | Square::F5
+        );
+        assert_eq!(
+            knight_moves(Square::D5),
+            Square::B4
+                | Square::B6
+                | Square::C3
+                | Square::C7
+                | Square::E3
+                | Square::E7
+                | Square::F4
+                | Square::F6
+        );
+        assert_eq!(
+            knight_moves(Square::E4),
+            Square::C3
+                | Square::C5
+                | Square::D2
+                | Square::D6
+                | Square::F2
+                | Square::F6
+                | Square::G3
+                | Square::G5
+        );
+        assert_eq!(
+            knight_moves(Square::E5),
+            Square::C4
+                | Square::C6
+                | Square::D3
+                | Square::D7
+                | Square::F3
+                | Square::F7
+                | Square::G4
+                | Square::G6
+        );
+    }
+}

src/movegen/mod.rs

@@ -1,2 +1,3 @@
 // Move generation implementation details
 mod king;
+mod knight;