Add naive bishop move generation

src/movegen/bishop.rs

@@ -0,0 +1,70 @@
+use crate::board::{Bitboard, Direction, Square};
+
+/// Compute a bishop's movement given a set of blockers that cannot be moved past.
+#[allow(unused)]
+pub fn bishop_moves(square: Square, blockers: Bitboard) -> Bitboard {
+    Direction::iter_bishop()
+        .map(|dir| dir.slide_board_with_blockers(square.into_bitboard(), blockers))
+        .fold(Bitboard::EMPTY, |lhs, rhs| lhs | rhs)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::board::{File, Rank};
+
+    #[test]
+    fn moves_lower_left_square() {
+        assert_eq!(
+            bishop_moves(Square::A1, Bitboard::EMPTY),
+            Bitboard::DIAGONAL - Square::A1
+        );
+        assert_eq!(
+            bishop_moves(Square::A1, Bitboard::ALL),
+            Square::B2.into_bitboard()
+        );
+        assert_eq!(
+            bishop_moves(Square::A1, Square::D4.into_bitboard()),
+            Square::B2 | Square::C3 | Square::D4
+        );
+        assert_eq!(
+            bishop_moves(Square::A1, File::D.into_bitboard()),
+            Square::B2 | Square::C3 | Square::D4
+        );
+    }
+
+    #[test]
+    fn moves_middle() {
+        let cross = Bitboard::DIAGONAL | Direction::South.move_board(Bitboard::ANTI_DIAGONAL);
+        assert_eq!(
+            bishop_moves(Square::D4, Bitboard::EMPTY),
+            cross - Square::D4
+        );
+        assert_eq!(
+            bishop_moves(Square::D4, Bitboard::ALL),
+            Square::C3 | Square::C5 | Square::E3 | Square::E5
+        );
+        assert_eq!(
+            bishop_moves(Square::D4, Rank::Fifth.into_bitboard()),
+            Square::A1
+                | Square::B2
+                | Square::C3
+                | Square::C5
+                | Square::E3
+                | Square::E5
+                | Square::F2
+                | Square::G1
+        );
+        assert_eq!(
+            bishop_moves(Square::D4, File::E.into_bitboard()),
+            Square::A1
+                | Square::A7
+                | Square::B2
+                | Square::B6
+                | Square::C3
+                | Square::C5
+                | Square::E3
+                | Square::E5
+        );
+    }
+}

src/movegen/mod.rs

@@ -1,3 +1,4 @@
 // Move generation implementation details
+mod bishop;
 mod king;
 mod knight;