From 849750dc80b07a1de6212b02761ba5408f116364 Mon Sep 17 00:00:00 2001
From: Morten Lohne <lohnemorten@gmail.com>
Date: Mon, 29 Jul 2024 18:36:30 +0200
Subject: [PATCH] Optimize group building by using pre-computed neighbor
 bitboards

---
 src/position/mod.rs   | 19 ++++++++-----------
 src/position/utils.rs |  4 ++++
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/src/position/mod.rs b/src/position/mod.rs
index c7a6e1b..19c413b 100644
--- a/src/position/mod.rs
+++ b/src/position/mod.rs
@@ -1827,28 +1827,25 @@ impl<const S: usize> pgn_traits::PgnPosition for Position<S> {
 }
 
 pub(crate) fn connected_components_graph<const S: usize>(
-    road_pieces: BitBoard,
+    mut road_pieces: BitBoard,
     components: &mut AbstractBoard<u8, S>,
     id: &mut u8,
 ) {
-    for square in square::squares_iterator::<S>() {
-        if components[square] == 0 && road_pieces.get_square(square) {
-            connect_component(road_pieces, components, square, *id);
-            *id += 1;
-        }
+    while let Some(square) = road_pieces.occupied_square() {
+        connect_component(&mut road_pieces, components, square, *id);
+        *id += 1;
     }
 }
 
 fn connect_component<const S: usize>(
-    road_pieces: BitBoard,
+    road_pieces: &mut BitBoard,
     components: &mut AbstractBoard<u8, S>,
     square: Square<S>,
     id: u8,
 ) {
     components[square] = id;
-    for neighbour in square.neighbors() {
-        if road_pieces.get_square(neighbour) && components[neighbour] == 0 {
-            connect_component(road_pieces, components, neighbour, id);
-        }
+    *road_pieces = road_pieces.clear_square(square);
+    while let Some(neighbor) = (square.neighbors_bitboard() & *road_pieces).occupied_square() {
+        connect_component(road_pieces, components, neighbor, id);
     }
 }
diff --git a/src/position/utils.rs b/src/position/utils.rs
index ebc7781..c3cd011 100644
--- a/src/position/utils.rs
+++ b/src/position/utils.rs
@@ -610,6 +610,10 @@ impl<const S: usize> Square<S> {
             .map(|(_, neighbor)| neighbor)
     }
 
+    pub(crate) fn neighbors_bitboard(self) -> BitBoard {
+        lookup_neighbor_table::<S>(self)
+    }
+
     pub fn directions(self) -> impl Iterator<Item = Direction> {
         lookup_neighbor_array_table::<S>(self)
             .into_iter()