Sprout/sprout/index_tuple/integer_range.hpp

#ifndef SPROUT_INDEX_TUPLE_INTEGER_RANGE_HPP
#define SPROUT_INDEX_TUPLE_INTEGER_RANGE_HPP

#include <type_traits>
#include <sprout/config.hpp>
#include <sprout/index_tuple/integer_seq.hpp>
#include <sprout/index_tuple/detail/make_indexes_helper.hpp>

namespace sprout {
	namespace detail {
		template<typename T, T First, T Last>
		struct integer_range_default_step
			: public std::integral_constant<typename std::make_signed<T>::type, (First <= Last ? 1 : -1)>
		{};
	}	// namespace detail

	namespace detail {
		template<typename T, typename Seq, T Next>
		struct integer_range_next_even;
		template<typename T, T... Is, T Next>
		struct integer_range_next_even<T, sprout::integer_seq<T, Is...>, Next>
			: public sprout::integer_seq<T, Is..., (Is + Next)...>
		{};

		template<typename T, typename Seq, T Next, T Tail>
		struct integer_range_next_odd;
		template<typename T, T... Is, T Next, T Tail>
		struct integer_range_next_odd<T, sprout::integer_seq<T, Is...>, Next, Tail>
			 : public sprout::integer_seq<T, Is..., (Is + Next)..., Tail>
		{};

		template<typename T, T First, typename std::make_signed<T>::type Step, typename std::make_unsigned<T>::type N, typename Enable = void>
		struct integer_range_impl;
		template<typename T, T First, typename std::make_signed<T>::type Step, typename std::make_unsigned<T>::type N>
		struct integer_range_impl<
			T, First, Step, N,
			typename std::enable_if<(N == 0)>::type
		>
			: public sprout::integer_seq<T>
		{};
		template<typename T, T First, typename std::make_signed<T>::type Step, typename std::make_unsigned<T>::type N>
		struct integer_range_impl<
			T, First, Step, N,
			typename std::enable_if<(N == 1)>::type
		>
			: public sprout::integer_seq<T, First>
		{};
		template<typename T, T First, typename std::make_signed<T>::type Step, typename std::make_unsigned<T>::type N>
		struct integer_range_impl<
			T, First, Step, N,
			typename std::enable_if<(N > 1 && N % 2 == 0)>::type
		>
			: public sprout::detail::integer_range_next_even<
				T, typename sprout::detail::integer_range_impl<T, First, Step, N / 2>::type,
				N / 2 * Step
			>
		{};
		template<typename T, T First, typename std::make_signed<T>::type Step, typename std::make_unsigned<T>::type N>
		struct integer_range_impl<
			T, First, Step, N,
			typename std::enable_if<(N > 1 && N % 2 == 1)>::type
		>
			: public sprout::detail::integer_range_next_odd<
				T, typename sprout::detail::integer_range_impl<T, First, Step, N / 2>::type,
				N / 2 * Step, First + (N - 1) * Step
			>
		{};
		template<typename T, T First, T Last, typename std::make_signed<T>::type Step, typename Enable = void>
		struct integer_range {};
		template<typename T, T First, T Last, typename std::make_signed<T>::type Step>
		struct integer_range<
			T, First, Last, Step,
			typename std::enable_if<((First < Last && Step > 0) || (First > Last && Step < 0) || (First == Last))>::type
		>
			: public sprout::detail::integer_range_impl<
				T, First, Step,
				(static_cast<typename std::make_signed<T>::type>(Last - First) + (Step > 0 ? Step - 1 : Step + 1)) / Step
			>
		{};
	}	// namespace detail
	//
	// integer_range
	//
	template<
		typename T, T First, T Last,
		typename std::make_signed<T>::type Step = sprout::detail::integer_range_default_step<T, First, Last>::value
	>
	struct integer_range
		: public sprout::detail::make_indexes_helper<
			sprout::detail::integer_range<T, First, Last, Step>
		>
	{
		static_assert(
			(First < Last && Step > 0) || (First > Last && Step < 0) || (First == Last),
			"(First < Last && Step > 0) || (First > Last && Step < 0) || (First == Last)"
			);
	};
}	// namespace sprout

#endif	// #ifndef SPROUT_INDEX_TUPLE_INTEGER_RANGE_HPP