From d97e7d646e721b691b01069b77bac0c59b60b76f Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Fri, 22 Jul 2022 18:50:44 +0200
Subject: [PATCH] Move 'Magic' into 'seer::movegen::magic'

---
 src/movegen/magic/magic.rs         | 21 ---------------------
 src/movegen/magic/mod.rs           | 23 +++++++++++++++++++++--
 src/movegen/wizardry/generation.rs | 24 ++++++++++++------------
 3 files changed, 33 insertions(+), 35 deletions(-)
 delete mode 100644 src/movegen/magic/magic.rs

diff --git a/src/movegen/magic/magic.rs b/src/movegen/magic/magic.rs
deleted file mode 100644
index f59bde2..0000000
--- a/src/movegen/magic/magic.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-use crate::board::Bitboard;
-
-/// A type representing the magic board indexing a given [Square].
-pub struct Magic {
-    /// Magic number.
-    pub(crate) magic: u64,
-    /// Base offset into the magic square table.
-    pub(crate) offset: usize,
-    /// Mask to apply to the blocker board before applying the magic.
-    pub(crate) mask: Bitboard,
-    /// Length of the resulting mask after applying the magic.
-    pub(crate) shift: u8,
-}
-
-impl Magic {
-    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
index 068c6e7..251a5d9 100644
--- a/src/movegen/magic/mod.rs
+++ b/src/movegen/magic/mod.rs
@@ -1,2 +1,21 @@
-pub mod magic;
-pub use magic::*;
+use crate::board::Bitboard;
+
+/// A type representing the magic board indexing a given [crate::board::Square].
+pub struct Magic {
+    /// Magic number.
+    pub(crate) magic: u64,
+    /// Base offset into the magic square table.
+    pub(crate) offset: usize,
+    /// Mask to apply to the blocker board before applying the magic.
+    pub(crate) mask: Bitboard,
+    /// Length of the resulting mask after applying the magic.
+    pub(crate) shift: u8,
+}
+
+impl Magic {
+    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/wizardry/generation.rs b/src/movegen/wizardry/generation.rs
index 48e80e1..ee75d57 100644
--- a/src/movegen/wizardry/generation.rs
+++ b/src/movegen/wizardry/generation.rs
@@ -22,42 +22,42 @@ fn generate_magics(
     mask_fn: impl Fn(Square) -> Bitboard,
     moves_fn: impl Fn(Square, Bitboard) -> Bitboard,
 ) -> MagicGenerationType {
-    let mut offset = 0;
-
     let mut magics = Vec::new();
     let mut boards = Vec::new();
 
     for square in Square::iter() {
         let mask = mask_fn(square);
         let mut candidate: Magic;
-        let potential_occupancy: Vec<_> = mask.iter_power_set().collect();
-        let moves_len = potential_occupancy.len();
+
+        let occupancy_to_moves: Vec<_> = mask
+            .iter_power_set()
+            .map(|occupancy| (occupancy, moves_fn(square, occupancy)))
+            .collect();
 
         'candidate_search: loop {
             candidate = Magic {
                 magic: magic_candidate(rng),
-                offset,
+                offset: 0,
                 mask,
                 shift: (64 - mask.count()) as u8,
             };
-            let mut candidate_moves = Vec::new();
-            candidate_moves.resize(moves_len, Bitboard::EMPTY);
+            let mut candidate_moves = vec![Bitboard::EMPTY; occupancy_to_moves.len()];
 
-            for occupancy in potential_occupancy.iter().cloned() {
+            for (occupancy, moves) in occupancy_to_moves.iter().cloned() {
                 let index = candidate.get_index(occupancy);
-                let moves = moves_fn(square, occupancy);
+                // Non-constructive collision, try with another candidate
                 if candidate_moves[index] != Bitboard::EMPTY && candidate_moves[index] != moves {
                     continue 'candidate_search;
                 }
                 candidate_moves[index] = moves;
             }
 
+            // We have filled all candidate boards, record the correct offset and add the moves
+            candidate.offset = boards.len();
             boards.append(&mut candidate_moves);
+            magics.push(candidate);
             break;
         }
-
-        magics.push(candidate);
-        offset += moves_len;
     }
 
     (magics, boards)