Add integer sequence

util.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdint.h>
+
 #include "../type/type.hpp"
 
 namespace util {
@@ -23,4 +25,80 @@ inline constexpr T &&forward(type::remove_reference_t<T> &&t) noexcept
 	return static_cast<T &&>(t);
 }
 
+template <typename T, T... Ints>
+struct integer_sequence {
+	using __type = integer_sequence;
+	using value_type = T;
+
+	static constexpr size_t size() noexcept
+	{
+		return sizeof...(Ints);
+	}
+};
+
+template <size_t... Ints>
+using index_sequence = integer_sequence<size_t, Ints...>;
+
+namespace detail {
+
+template <typename T, typename Seq1, typename Seq2>
+struct concat;
+
+template <typename T, T... Ints1, T... Ints2>
+struct concat<T, integer_sequence<T, Ints1...>, integer_sequence<T, Ints2...>>
+    : integer_sequence<T, Ints1..., (sizeof...(Ints1) + Ints2)...> {
+};
+
+// uint64_t because this must be able to hold all possible sizes and cannot be T, because then the specialization for 0
+// and 1 are not possible
+template <typename T, uint64_t N>
+struct gen_integer_sequence : detail::concat<T, typename gen_integer_sequence<T, N / 2>::__type,
+                                             typename gen_integer_sequence<T, N - N / 2>::__type> {
+};
+
+template <typename T>
+struct gen_integer_sequence<T, 0> : integer_sequence<T> {
+};
+
+template <typename T>
+struct gen_integer_sequence<T, 1> : integer_sequence<T, 0> {
+};
+
+} // namespace detail
+
+template <typename T, T N>
+struct make_integer_sequence : detail::gen_integer_sequence<T, N> {
+	static_assert(N >= 0, "Integer sequence cannot be negative");
+};
+
+template <size_t N>
+using make_index_sequence = make_integer_sequence<size_t, N>;
+
+template <typename... T>
+using index_sequence_for = make_index_sequence<sizeof...(T)>;
+
+// Not part of <utility>, but very useful
+
+namespace detail {
+
+template <typename T, T Offset, T... Ints>
+inline constexpr integer_sequence<T, (Offset + Ints)...> add_offset(integer_sequence<T, Ints...>)
+{
+	return {};
+}
+
+} // namespace detail
+
+template <typename T, T Offset, T N>
+inline constexpr auto make_offset_integer_sequence()
+{
+	return detail::add_offset<T, Offset>(make_integer_sequence<T, N>{});
+}
+
+template <size_t Offset, size_t N>
+inline constexpr auto make_offset_index_sequence()
+{
+	return make_offset_integer_sequence<size_t, Offset, N>();
+}
+
 } // namespace util