Add 'Magic' type

src/movegen/magic/magic.rs

@@ -0,0 +1,23 @@
+use crate::board::Bitboard;
+
+/// A type representing the magic board indexing a given [Square].
+#[allow(unused)] // FIXME: remove once used
+pub struct Magic {
+    /// Magic number.
+    magic: u64,
+    /// Base offset into the magic square table.
+    offset: usize,
+    /// Mask to apply to the blocker board before applying the magic.
+    mask: Bitboard,
+    /// Length of the resulting mask after applying the magic.
+    shift: u8,
+}
+
+impl Magic {
+    #[allow(unused)] // FIXME: remove once used
+    pub fn get_index(&self, blockers: Bitboard) -> usize {
+        let relevant_occupancy = (blockers & self.mask).0;
+        let base_index = ((relevant_occupancy.wrapping_mul(self.magic)) >> self.shift) as usize;
+        base_index + self.offset
+    }
+}