From 6b0563b1bd1d8c1afd8fb629fed0e790f7b61ce4 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Fri, 22 Jul 2022 10:14:46 +0200
Subject: [PATCH] Add 'Magic' type

---
 src/movegen/magic/magic.rs | 23 +++++++++++++++++++++++
 src/movegen/magic/mod.rs   |  2 ++
 src/movegen/mod.rs         |  4 ++++
 3 files changed, 29 insertions(+)
 create mode 100644 src/movegen/magic/magic.rs
 create mode 100644 src/movegen/magic/mod.rs

diff --git a/src/movegen/magic/magic.rs b/src/movegen/magic/magic.rs
new file mode 100644
index 0000000..0f328d5
--- /dev/null
+++ b/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
+    }
+}
diff --git a/src/movegen/magic/mod.rs b/src/movegen/magic/mod.rs
new file mode 100644
index 0000000..068c6e7
--- /dev/null
+++ b/src/movegen/magic/mod.rs
@@ -0,0 +1,2 @@
+pub mod magic;
+pub use magic::*;
diff --git a/src/movegen/mod.rs b/src/movegen/mod.rs
index 746011d..d379194 100644
--- a/src/movegen/mod.rs
+++ b/src/movegen/mod.rs
@@ -1,3 +1,7 @@
+// Magic bitboard
+pub mod magic;
+pub use magic::*;
+
 // Move generation implementation details
 mod bishop;
 mod king;