diff --git a/include/fast_io_dsal/impl/deque.h b/include/fast_io_dsal/impl/deque.h
index 24a2ef43..4fd47cbc 100644
--- a/include/fast_io_dsal/impl/deque.h
+++ b/include/fast_io_dsal/impl/deque.h
@@ -358,7 +358,7 @@ inline constexpr ::std::ptrdiff_t deque_iter_difference_common(::fast_io::contai
 {
 	::std::ptrdiff_t controllerdiff{a.controller_ptr - b.controller_ptr};
 	constexpr ::std::ptrdiff_t blocksizedf{static_cast<::std::ptrdiff_t>(::fast_io::containers::details::deque_block_size<sizeof(T)>)};
-	return controllerdiff * blocksizedf + (a.curr_ptr - b.begin_ptr) + (b.begin_ptr - b.curr_ptr);
+	return controllerdiff * blocksizedf + (a.curr_ptr - a.begin_ptr) + (b.begin_ptr - b.curr_ptr);
 }
 
 template <typename T>
@@ -366,7 +366,7 @@ inline constexpr ::std::size_t deque_iter_difference_unsigned_common(::fast_io::
 {
 	::std::size_t controllerdiff{a.controller_ptr - b.controller_ptr};
 	constexpr ::std::size_t blocksizedf{::fast_io::containers::details::deque_block_size<sizeof(T)>};
-	return controllerdiff * blocksizedf + static_cast<::std::size_t>((a.curr_ptr - b.begin_ptr) + (b.begin_ptr - b.curr_ptr));
+	return controllerdiff * blocksizedf + static_cast<::std::size_t>((a.curr_ptr - a.begin_ptr) + (b.begin_ptr - b.curr_ptr));
 }
 
 template <typename T, bool isconst1, bool isconst2>
@@ -1776,8 +1776,8 @@ class deque FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE
 		requires ::std::constructible_from<value_type, ::std::ranges::range_value_t<R>>
 	inline constexpr insert_range_result insert_range_impl(size_type pos, R &&rg, size_type old_size) noexcept(::std::is_nothrow_constructible_v<value_type, ::std::ranges::range_value_t<R>>)
 	{
-		size_type const halfold_size{old_size >> 1u};
 #if 0
+		size_type const halfold_size{old_size >> 1u};
 		if constexpr(::std::ranges::sized_range<R>)
 		{
 			size_type const rgsize{::std::ranges::size(rg)};
@@ -1785,31 +1785,13 @@ class deque FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE
 		else
 #endif
 		{
-			size_type retpos;
-			iterator retit, rotfirst, rotmid, rotlast;
-			if (pos < halfold_size)
-			{
-				this->prepend_range(rg);
-				size_type const new_size{this->size()};
-				size_type const inserted{new_size - old_size};
-				auto bg{this->begin()};
-				size_type newpos{pos + inserted};
-				rotfirst = bg;
-				rotmid = bg + inserted;
-				retpos = newpos;
-				retit = rotlast = bg + newpos;
-			}
-			else
-			{
-				this->append_range(rg);
-				auto bg{this->begin()};
-				rotfirst = retit = bg + pos;
-				rotmid = bg + old_size;
-				rotlast = this->end();
-				retpos = pos;
-			}
+			this->append_range(rg);
+			auto bg{this->begin()};
+			iterator rotfirst = bg + pos;
+			iterator rotmid = bg + old_size;
+			iterator rotlast = this->end();
 			::fast_io::containers::rotate_for_fast_io_deque(rotfirst, rotmid, rotlast);
-			return {retpos, retit};
+			return {pos, rotfirst};
 		}
 	}
 
@@ -1845,18 +1827,28 @@ class deque FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE
 			this->push_back(e);
 		}
 	}
-
+#if 0
+private:
 	template <::std::ranges::range R>
 		requires ::std::constructible_from<value_type, ::std::ranges::range_value_t<R>>
-	inline constexpr void prepend_range(R &&rg) noexcept(::std::is_nothrow_constructible_v<value_type, ::std::ranges::range_value_t<R>>)
+	inline constexpr size_type prepend_range_impl(R &&rg) noexcept(::std::is_nothrow_constructible_v<value_type, ::std::ranges::range_value_t<R>>)
 	{
-		// To do: cleanup code
+		size_type const old_size{this->size()};
 		for (auto &e : rg)
 		{
 			this->push_front(e);
 		}
+		return this->size() - old_size;
 	}
-
+public:
+	template <::std::ranges::range R>
+		requires ::std::constructible_from<value_type, ::std::ranges::range_value_t<R>>
+	inline constexpr void prepend_range(R &&rg) noexcept(::std::is_nothrow_constructible_v<value_type, ::std::ranges::range_value_t<R>>)
+	{
+		// To do: cleanup code
+		this->prepend_range_impl(::std::forward<R>(rg));
+	}
+#endif
 
 	inline constexpr ~deque()
 	{
diff --git a/tests/0026.container/0003.deque/insert_range.cc b/tests/0026.container/0003.deque/insert_range.cc
index ee3569f4..2052e088 100644
--- a/tests/0026.container/0003.deque/insert_range.cc
+++ b/tests/0026.container/0003.deque/insert_range.cc
@@ -196,16 +196,16 @@ inline void test_insert_range_index()
 	}
 
 	// Helper to compare dq and ref
-	auto check_equal = [&](auto const &msg) {
+	auto check_equal = [&](auto const &msg, ::std::source_location src = ::std::source_location::current()) {
 		if (dq.size() != ref.size())
 		{
-			::fast_io::io::panicln("ERROR: size mismatch: ", msg);
+			::fast_io::io::panicln(src, "\tERROR: size mismatch: ", msg);
 		}
 		for (::std::size_t i{}; i != dq.size(); ++i)
 		{
 			if (dq[i] != ref[i])
 			{
-				::fast_io::io::panicln("ERROR: value mismatch at index ", i, " : ", msg);
+				::fast_io::io::panicln(src, "\tERROR: value mismatch at index ", i, "\tdq[i]=", dq[i], "\tref[i]=", ref[i], " : ", msg);
 			}
 		}
 	};
@@ -257,7 +257,7 @@ inline void test_insert_range_index()
 int main()
 {
 	test_iterator_ops();
-#if 0
-    test_insert_range_index();
+#if 1
+	test_insert_range_index();
 #endif
 }
\ No newline at end of file