Improve array KVO performance a bit

index_set.cpp

@@ -91,6 +91,15 @@ void IndexSet::insert_at(size_t index)
     do_add(pos, index);
 }
 
+void IndexSet::add_shifted(size_t index)
+{
+    auto it = m_ranges.begin();
+    for (auto end = m_ranges.end(); it != end && it->first <= index; ++it) {
+        index += it->second - it->first;
+    }
+    do_add(it, index);
+}
+
 size_t IndexSet::iterator::operator*() const
 {
     return m_data->first + m_offset;

index_set.hpp

@@ -48,6 +48,7 @@ public:
     void set(size_t len);
     // Insert an index at the given position, shifting existing indexes back
     void insert_at(size_t index);
+    void add_shifted(size_t index);
 
 private:
     using Range = std::pair<size_t, size_t>;

src/object-store/shared_realm.cpp

@@ -193,14 +193,7 @@ public:
         }
         else if (o->kind == kind) {
             if (kind == ColumnInfo::Kind::Remove) {
-                // Shift the index to compensate for already-removed indices
-                for (auto i : o->indices) {
-                    if (i <= index)
-                        ++index;
-                    else
-                        break;
-                }
-                o->indices.add(index);
+                o->indices.add_shifted(index);
             }
             else if (kind == ColumnInfo::Kind::Insert) {
                 o->indices.insert_at(index);