Replace calls to rem_euclid with unknown denominator with simple &

agb/src/display/tiled/infinite_scrolled_map.rs

@@ -63,8 +63,8 @@ impl<'a> InfiniteScrolledMap<'a> {
 
         let offset = self.current_pos - (x_start * 8, y_start * 8).into();
         let offset_scroll = (
-            offset.x.rem_euclid(self.map.size().width() as i32 * 8) as u16,
+            self.map.size().rem_euclid_width(offset.x) as u16,
-            offset.y.rem_euclid(self.map.size().height() as i32 * 8) as u16,
+            self.map.size().rem_euclid_height(offset.y) as u16,
         )
             .into();
 
@@ -179,8 +179,8 @@ impl<'a> InfiniteScrolledMap<'a> {
             self.map.set_tile(
                 vram,
                 (
-                    (tile_x - self.offset.x).rem_euclid(size.width() as i32) as u16,
+                    size.rem_euclid_width(tile_x - self.offset.x) as u16,
-                    (tile_y - self.offset.y).rem_euclid(size.height() as i32) as u16,
+                    size.rem_euclid_height(tile_y - self.offset.y) as u16,
                 )
                     .into(),
                 tileset,
@@ -190,8 +190,8 @@ impl<'a> InfiniteScrolledMap<'a> {
 
         let current_scroll = self.map.scroll_pos();
         let new_scroll = (
-            (current_scroll.x as i32 + difference.x).rem_euclid(size.width() as i32 * 8) as u16,
+            size.rem_euclid_width(current_scroll.x as i32 + difference.x) as u16,
-            (current_scroll.y as i32 + difference.y).rem_euclid(size.height() as i32 * 8) as u16,
+            size.rem_euclid_height(current_scroll.y as i32 + difference.y) as u16,
         )
             .into();
 

agb/src/display/tiled/mod.rs

@@ -47,6 +47,14 @@ impl RegularBackgroundSize {
     pub(crate) fn num_tiles(&self) -> usize {
         (self.width() * self.height()) as usize
     }
+
+    pub(crate) fn rem_euclid_width(&self, x: i32) -> u32 {
+        (x as u32) & (self.width() - 1)
+    }
+
+    pub(crate) fn rem_euclid_height(&self, y: i32) -> u32 {
+        (y as u32) & (self.height() - 1)
+    }
 }
 
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
@@ -88,3 +96,31 @@ impl TileSetting {
         self.0 & !((1 << 10) - 1)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test_case]
+    fn rem_euclid_width_works(_gba: &mut crate::Gba) {
+        use RegularBackgroundSize::*;
+
+        let sizes = [
+            Background32x32,
+            Background32x64,
+            Background64x32,
+            Background64x64,
+        ];
+
+        for size in sizes.iter() {
+            let width = size.width() as i32;
+
+            assert_eq!(size.rem_euclid_width(8), 8);
+            assert_eq!(size.rem_euclid_width(3 + width), 3);
+            assert_eq!(size.rem_euclid_width(7 + width * 9), 7);
+
+            assert_eq!(size.rem_euclid_width(-8), size.width() - 8);
+            assert_eq!(size.rem_euclid_width(-17 - width * 8), size.width() - 17);
+        }
+    }
+}