Round up correctly when truncating max ancient storages

accounts-db/src/ancient_append_vecs.rs

@@ -195,6 +195,15 @@ impl AncientSlotInfos {
     /// The idea is that 'all_infos' is sorted from smallest capacity to largest,
     /// but that isn't required for this function to be 'correct'.
     fn truncate_to_max_storages(&mut self, tuning: &PackedAncientStorageTuning) {
+        fn div_round_up(x: u64, y: NonZeroU64) -> u64 {
+            debug_assert!(
+                x.checked_add(y.get()).is_some(),
+                "x + y overflowed! x: {x}, y: {y}",
+            );
+            // SAFETY: Since `y` is NonZero, subtracting 1 never wraps.
+            (x + (y.get() - 1)) / y
+        }
+
         // these indexes into 'all_infos' are useless once we truncate 'all_infos', so make sure they're cleared out to avoid any issues
         self.shrink_indexes.clear();
         let total_storages = self.all_infos.len();
@@ -203,7 +212,7 @@ impl AncientSlotInfos {
         for (i, info) in self.all_infos.iter().enumerate() {
             cumulative_bytes += info.alive_bytes;
             let ancient_storages_required =
-                (cumulative_bytes.0 / tuning.ideal_storage_size + 1) as usize;
+                div_round_up(cumulative_bytes.0, tuning.ideal_storage_size) as usize;
             let storages_remaining = total_storages - i - 1;
 
             // if the remaining uncombined storages and the # of resulting