include/utility

// -*- C++ -*-
//===-------------------------- utility -----------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_UTILITY
#define _LIBCPP_UTILITY

/*
 utility synopsis

namespace std
{

template <class T>
 void
 swap(T& a, T& b);

namespace rel_ops
{
 template<class T> bool operator!=(const T&, const T&);
 template<class T> bool operator> (const T&, const T&);
 template<class T> bool operator<=(const T&, const T&);
 template<class T> bool operator>=(const T&, const T&);
}

template<class T>
void
swap(T& a, T& b) noexcept(is_nothrow_move_constructible<T>::value &&
 is_nothrow_move_assignable<T>::value);

template <class T, size_t N>
void
swap(T (&a)[N], T (&b)[N]) noexcept(noexcept(swap(*a, *b)));

template <class T> T&& forward(typename remove_reference<T>::type& t) noexcept; // constexpr in C++14
template <class T> T&& forward(typename remove_reference<T>::type&& t) noexcept; // constexpr in C++14

template <class T> typename remove_reference<T>::type&& move(T&&) noexcept; // constexpr in C++14

template <class T>
 typename conditional
 <
 !is_nothrow_move_constructible<T>::value && is_copy_constructible<T>::value,
 const T&,
 T&&
 >::type
 move_if_noexcept(T& x) noexcept; // constexpr in C++14

template <class T> constexpr add_const<T>_t& as_const(T& t) noexcept; // C++17
template <class T> void as_const(const T&&) = delete; // C++17

template <class T> typename add_rvalue_reference<T>::type declval() noexcept;

template <class T1, class T2>
struct pair
{
 typedef T1 first_type;
 typedef T2 second_type;

 T1 first;
 T2 second;

 pair(const pair&) = default;
 pair(pair&&) = default;
 constexpr pair();
 pair(const T1& x, const T2& y); // constexpr in C++14
 template <class U, class V> pair(U&& x, V&& y); // constexpr in C++14
 template <class U, class V> pair(const pair<U, V>& p); // constexpr in C++14
 template <class U, class V> pair(pair<U, V>&& p); // constexpr in C++14
 template <class... Args1, class... Args2>
 pair(piecewise_construct_t, tuple<Args1...> first_args,
 tuple<Args2...> second_args);

 template <class U, class V> pair& operator=(const pair<U, V>& p);
 pair& operator=(pair&& p) noexcept(is_nothrow_move_assignable<T1>::value &&
 is_nothrow_move_assignable<T2>::value);
 template <class U, class V> pair& operator=(pair<U, V>&& p);

 void swap(pair& p) noexcept(noexcept(swap(first, p.first)) &&
 noexcept(swap(second, p.second)));
};

template <class T1, class T2> bool operator==(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
template <class T1, class T2> bool operator!=(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
template <class T1, class T2> bool operator< (const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
template <class T1, class T2> bool operator> (const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
template <class T1, class T2> bool operator>=(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
template <class T1, class T2> bool operator<=(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14

template <class T1, class T2> pair<V1, V2> make_pair(T1&&, T2&&); // constexpr in C++14
template <class T1, class T2>
void
swap(pair<T1, T2>& x, pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));

struct piecewise_construct_t { };
constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();

template <class T> class tuple_size;
template <size_t I, class T> class tuple_element;

template <class T1, class T2> struct tuple_size<pair<T1, T2> >;
template <class T1, class T2> struct tuple_element<0, pair<T1, T2> >;
template <class T1, class T2> struct tuple_element<1, pair<T1, T2> >;

template<size_t I, class T1, class T2>
 typename tuple_element<I, pair<T1, T2> >::type&
 get(pair<T1, T2>&) noexcept; // constexpr in C++14

template<size_t I, class T1, class T2>
 const typename const tuple_element<I, pair<T1, T2> >::type&
 get(const pair<T1, T2>&) noexcept; // constexpr in C++14

template<size_t I, class T1, class T2>
 typename tuple_element<I, pair<T1, T2> >::type&&
 get(pair<T1, T2>&&) noexcept; // constexpr in C++14

template<class T1, class T2>
 constexpr T1& get(pair<T1, T2>&) noexcept; // C++14

template<size_t I, class T1, class T2>
 constexpr T1 const& get(pair<T1, T2> const &) noexcept; // C++14

template<size_t I, class T1, class T2>
 constexpr T1&& get(pair<T1, T2>&&) noexcept; // C++14

// C++14

template<class T, T... I>
struct integer_sequence
{
 typedef T value_type;

 static constexpr size_t size() noexcept;
};

template<size_t... I>
 using index_sequence = integer_sequence<size_t, I...>;

template<class T, T N>
 using make_integer_sequence = integer_sequence<T, 0, 1, ..., N-1>;
template<size_t N>
 using make_index_sequence = make_integer_sequence<size_t, N>;

template<class... T>
 using index_sequence_for = make_index_sequence<sizeof...(T)>;

template<class T, class U=T> 
 T exchange(T& obj, U&& new_value);
} // std

*/

#include <__config>
#include <__tuple>
#include <type_traits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

namespace rel_ops
{

template<class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator!=(const _Tp& __x, const _Tp& __y)
{
 return !(__x == __y);
}

template<class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator> (const _Tp& __x, const _Tp& __y)
{
 return __y < __x;
}

template<class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator<=(const _Tp& __x, const _Tp& __y)
{
 return !(__y < __x);
}

template<class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator>=(const _Tp& __x, const _Tp& __y)
{
 return !(__x < __y);
}

} // rel_ops

// swap_ranges

// forward
template<class _Tp, size_t _Np>
inline _LIBCPP_INLINE_VISIBILITY
void swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value);

template <class _ForwardIterator1, class _ForwardIterator2>
inline _LIBCPP_INLINE_VISIBILITY
_ForwardIterator2
swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2)
{
 for(; __first1 != __last1; ++__first1, (void) ++__first2)
 swap(*__first1, *__first2);
 return __first2;
}

template<class _Tp, size_t _Np>
inline _LIBCPP_INLINE_VISIBILITY
void
swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
{
 _VSTD::swap_ranges(__a, __a + _Np, __b);
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
typename conditional
<
 !is_nothrow_move_constructible<_Tp>::value && is_copy_constructible<_Tp>::value,
 const _Tp&,
 _Tp&&
>::type
#else // _LIBCPP_HAS_NO_RVALUE_REFERENCES
const _Tp&
#endif
move_if_noexcept(_Tp& __x) _NOEXCEPT
{
 return _VSTD::move(__x);
}

#if _LIBCPP_STD_VER > 14
template <class _Tp> constexpr add_const_t<_Tp>& as_const(_Tp& __t) noexcept { return __t; }
template <class _Tp> void as_const(const _Tp&&) = delete;
#endif

struct _LIBCPP_TYPE_VIS_ONLY piecewise_construct_t { };
#if defined(_LIBCPP_HAS_NO_CONSTEXPR) || defined(_LIBCPP_BUILDING_UTILITY)
extern const piecewise_construct_t piecewise_construct;// = piecewise_construct_t();
#else
constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
#endif

template <class _T1, class _T2>
struct _LIBCPP_TYPE_VIS_ONLY pair
{
 typedef _T1 first_type;
 typedef _T2 second_type;

 _T1 first;
 _T2 second;

 // pair(const pair&) = default;
 // pair(pair&&) = default;

 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR pair() : first(), second() {}

 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 pair(const _T1& __x, const _T2& __y)
 : first(__x), second(__y) {}

 template<class _U1, class _U2>
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 pair(const pair<_U1, _U2>& __p
#ifndef _LIBCPP_HAS_NO_ADVANCED_SFINAE
 ,typename enable_if<is_convertible<const _U1&, _T1>::value &&
 is_convertible<const _U2&, _T2>::value>::type* = 0
#endif
 )
 : first(__p.first), second(__p.second) {}

#if !defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && _LIBCPP_TRIVIAL_PAIR_COPY_CTOR
 _LIBCPP_INLINE_VISIBILITY
 pair(const pair& __p) = default;
#elif !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) || !_LIBCPP_TRIVIAL_PAIR_COPY_CTOR
 _LIBCPP_INLINE_VISIBILITY
 pair(const pair& __p)
 _NOEXCEPT_(is_nothrow_copy_constructible<first_type>::value &&
 is_nothrow_copy_constructible<second_type>::value)
 : first(__p.first),
 second(__p.second)
 {
 }
#endif

 _LIBCPP_INLINE_VISIBILITY
 pair& operator=(const pair& __p)
 _NOEXCEPT_(is_nothrow_copy_assignable<first_type>::value &&
 is_nothrow_copy_assignable<second_type>::value)
 {
 first = __p.first;
 second = __p.second;
 return *this;
 }

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

 template <class _U1, class _U2,
 class = typename enable_if<is_convertible<_U1, first_type>::value &&
 is_convertible<_U2, second_type>::value>::type>
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 pair(_U1&& __u1, _U2&& __u2)
 : first(_VSTD::forward<_U1>(__u1)),
 second(_VSTD::forward<_U2>(__u2))
 {}

 template<class _U1, class _U2>
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 pair(pair<_U1, _U2>&& __p,
 typename enable_if<is_convertible<_U1, _T1>::value &&
 is_convertible<_U2, _T2>::value>::type* = 0)
 : first(_VSTD::forward<_U1>(__p.first)),
 second(_VSTD::forward<_U2>(__p.second)) {}

#ifndef _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS
 _LIBCPP_INLINE_VISIBILITY
 pair(pair&& __p) = default;
#else
 _LIBCPP_INLINE_VISIBILITY
 pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value &&
 is_nothrow_move_constructible<second_type>::value)
 : first(_VSTD::forward<first_type>(__p.first)),
 second(_VSTD::forward<second_type>(__p.second))
 {
 }
#endif

 _LIBCPP_INLINE_VISIBILITY
 pair&
 operator=(pair&& __p) _NOEXCEPT_(is_nothrow_move_assignable<first_type>::value &&
 is_nothrow_move_assignable<second_type>::value)
 {
 first = _VSTD::forward<first_type>(__p.first);
 second = _VSTD::forward<second_type>(__p.second);
 return *this;
 }

#ifndef _LIBCPP_HAS_NO_VARIADICS

 template<class _Tuple,
 class = typename enable_if<__tuple_convertible<_Tuple, pair>::value>::type>
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 pair(_Tuple&& __p)
 : first(_VSTD::forward<typename tuple_element<0,
 typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<0>(__p))),
 second(_VSTD::forward<typename tuple_element<1,
 typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<1>(__p)))
 {}



 template <class... _Args1, class... _Args2>
 _LIBCPP_INLINE_VISIBILITY
 pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
 tuple<_Args2...> __second_args)
 : pair(__pc, __first_args, __second_args,
 typename __make_tuple_indices<sizeof...(_Args1)>::type(),
 typename __make_tuple_indices<sizeof...(_Args2) >::type())
 {}

 template <class _Tuple,
 class = typename enable_if<__tuple_assignable<_Tuple, pair>::value>::type>
 _LIBCPP_INLINE_VISIBILITY
 pair&
 operator=(_Tuple&& __p)
 {
 typedef typename __make_tuple_types<_Tuple>::type _TupleRef;
 typedef typename tuple_element<0, _TupleRef>::type _U0;
 typedef typename tuple_element<1, _TupleRef>::type _U1;
 first = _VSTD::forward<_U0>(_VSTD::get<0>(__p));
 second = _VSTD::forward<_U1>(_VSTD::get<1>(__p));
 return *this;
 }

#endif // _LIBCPP_HAS_NO_VARIADICS

#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 _LIBCPP_INLINE_VISIBILITY
 void
 swap(pair& __p) _NOEXCEPT_(__is_nothrow_swappable<first_type>::value &&
 __is_nothrow_swappable<second_type>::value)
 {
 using _VSTD::swap;
 swap(first, __p.first);
 swap(second, __p.second);
 }
private:

#ifndef _LIBCPP_HAS_NO_VARIADICS
 template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
 _LIBCPP_INLINE_VISIBILITY
 pair(piecewise_construct_t,
 tuple<_Args1...>& __first_args, tuple<_Args2...>& __second_args,
 __tuple_indices<_I1...>, __tuple_indices<_I2...>);
#endif // _LIBCPP_HAS_NO_VARIADICS
};

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool
operator==(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
{
 return __x.first == __y.first && __x.second == __y.second;
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool
operator!=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
{
 return !(__x == __y);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool
operator< (const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
{
 return __x.first < __y.first || (!(__y.first < __x.first) && __x.second < __y.second);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool
operator> (const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
{
 return __y < __x;
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool
operator>=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
{
 return !(__x < __y);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool
operator<=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
{
 return !(__y < __x);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
typename enable_if
<
 __is_swappable<_T1>::value &&
 __is_swappable<_T2>::value,
 void
>::type
swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
 _NOEXCEPT_((__is_nothrow_swappable<_T1>::value &&
 __is_nothrow_swappable<_T2>::value))
{
 __x.swap(__y);
}

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _Tp> class _LIBCPP_TYPE_VIS_ONLY reference_wrapper;

template <class _Tp>
struct __make_pair_return_impl
{
 typedef _Tp type;
};

template <class _Tp>
struct __make_pair_return_impl<reference_wrapper<_Tp>>
{
 typedef _Tp& type;
};

template <class _Tp>
struct __make_pair_return
{
 typedef typename __make_pair_return_impl<typename decay<_Tp>::type>::type type;
};

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
pair<typename __make_pair_return<_T1>::type, typename __make_pair_return<_T2>::type>
make_pair(_T1&& __t1, _T2&& __t2)
{
 return pair<typename __make_pair_return<_T1>::type, typename __make_pair_return<_T2>::type>
 (_VSTD::forward<_T1>(__t1), _VSTD::forward<_T2>(__t2));
}

#else // _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
pair<_T1,_T2>
make_pair(_T1 __x, _T2 __y)
{
 return pair<_T1, _T2>(__x, __y);
}

#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _T1, class _T2>
 class _LIBCPP_TYPE_VIS_ONLY tuple_size<pair<_T1, _T2> >
 : public integral_constant<size_t, 2> {};

template <class _T1, class _T2>
class _LIBCPP_TYPE_VIS_ONLY tuple_element<0, pair<_T1, _T2> >
{
public:
 typedef _T1 type;
};

template <class _T1, class _T2>
class _LIBCPP_TYPE_VIS_ONLY tuple_element<1, pair<_T1, _T2> >
{
public:
 typedef _T2 type;
};

template <size_t _Ip> struct __get_pair;

template <>
struct __get_pair<0>
{
 template <class _T1, class _T2>
 static
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _T1&
 get(pair<_T1, _T2>& __p) _NOEXCEPT {return __p.first;}

 template <class _T1, class _T2>
 static
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 const _T1&
 get(const pair<_T1, _T2>& __p) _NOEXCEPT {return __p.first;}

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

 template <class _T1, class _T2>
 static
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _T1&&
 get(pair<_T1, _T2>&& __p) _NOEXCEPT {return _VSTD::forward<_T1>(__p.first);}

#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
};

template <>
struct __get_pair<1>
{
 template <class _T1, class _T2>
 static
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _T2&
 get(pair<_T1, _T2>& __p) _NOEXCEPT {return __p.second;}

 template <class _T1, class _T2>
 static
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 const _T2&
 get(const pair<_T1, _T2>& __p) _NOEXCEPT {return __p.second;}

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

 template <class _T1, class _T2>
 static
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _T2&&
 get(pair<_T1, _T2>&& __p) _NOEXCEPT {return _VSTD::forward<_T2>(__p.second);}

#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
};

template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
typename tuple_element<_Ip, pair<_T1, _T2> >::type&
get(pair<_T1, _T2>& __p) _NOEXCEPT
{
 return __get_pair<_Ip>::get(__p);
}

template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
const typename tuple_element<_Ip, pair<_T1, _T2> >::type&
get(const pair<_T1, _T2>& __p) _NOEXCEPT
{
 return __get_pair<_Ip>::get(__p);
}

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <size_t _Ip, class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
get(pair<_T1, _T2>&& __p) _NOEXCEPT
{
 return __get_pair<_Ip>::get(_VSTD::move(__p));
}

#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES

#if _LIBCPP_STD_VER > 11
template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
constexpr _T1 & get(pair<_T1, _T2>& __p) _NOEXCEPT
{
 return __get_pair<0>::get(__p);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
constexpr _T1 const & get(pair<_T1, _T2> const& __p) _NOEXCEPT
{
 return __get_pair<0>::get(__p);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
constexpr _T1 && get(pair<_T1, _T2>&& __p) _NOEXCEPT
{
 return __get_pair<0>::get(_VSTD::move(__p));
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
constexpr _T1 & get(pair<_T2, _T1>& __p) _NOEXCEPT
{
 return __get_pair<1>::get(__p);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
constexpr _T1 const & get(pair<_T2, _T1> const& __p) _NOEXCEPT
{
 return __get_pair<1>::get(__p);
}

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
constexpr _T1 && get(pair<_T2, _T1>&& __p) _NOEXCEPT
{
 return __get_pair<1>::get(_VSTD::move(__p));
}

#endif

#if _LIBCPP_STD_VER > 11

template<class _Tp, _Tp... _Ip>
struct _LIBCPP_TYPE_VIS_ONLY integer_sequence
{
 typedef _Tp value_type;
 static_assert( is_integral<_Tp>::value,
 "std::integer_sequence can only be instantiated with an integral type" );
 static
 _LIBCPP_INLINE_VISIBILITY
 constexpr
 size_t
 size() noexcept { return sizeof...(_Ip); }
};

template<size_t... _Ip>
 using index_sequence = integer_sequence<size_t, _Ip...>;

namespace __detail {

template<typename _Tp, size_t ..._Extra> struct __repeat;
template<typename _Tp, _Tp ..._Np, size_t ..._Extra> struct __repeat<integer_sequence<_Tp, _Np...>, _Extra...> {
 typedef integer_sequence<_Tp,
 _Np...,
 sizeof...(_Np) + _Np...,
 2 * sizeof...(_Np) + _Np...,
 3 * sizeof...(_Np) + _Np...,
 4 * sizeof...(_Np) + _Np...,
 5 * sizeof...(_Np) + _Np...,
 6 * sizeof...(_Np) + _Np...,
 7 * sizeof...(_Np) + _Np...,
 _Extra...> type;
};

template<size_t _Np> struct __parity;
template<size_t _Np> struct __make : __parity<_Np % 8>::template __pmake<_Np> {};

template<> struct __make<0> { typedef integer_sequence<size_t> type; };
template<> struct __make<1> { typedef integer_sequence<size_t, 0> type; };
template<> struct __make<2> { typedef integer_sequence<size_t, 0, 1> type; };
template<> struct __make<3> { typedef integer_sequence<size_t, 0, 1, 2> type; };
template<> struct __make<4> { typedef integer_sequence<size_t, 0, 1, 2, 3> type; };
template<> struct __make<5> { typedef integer_sequence<size_t, 0, 1, 2, 3, 4> type; };
template<> struct __make<6> { typedef integer_sequence<size_t, 0, 1, 2, 3, 4, 5> type; };
template<> struct __make<7> { typedef integer_sequence<size_t, 0, 1, 2, 3, 4, 5, 6> type; };

template<> struct __parity<0> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type> {}; };
template<> struct __parity<1> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 1> {}; };
template<> struct __parity<2> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 2, _Np - 1> {}; };
template<> struct __parity<3> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 3, _Np - 2, _Np - 1> {}; };
template<> struct __parity<4> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
template<> struct __parity<5> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 5, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
template<> struct __parity<6> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 6, _Np - 5, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
template<> struct __parity<7> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 7, _Np - 6, _Np - 5, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };

template<typename _Tp, typename _Up> struct __convert {
 template<typename> struct __result;
 template<_Tp ..._Np> struct __result<integer_sequence<_Tp, _Np...> > { typedef integer_sequence<_Up, _Np...> type; };
};
template<typename _Tp> struct __convert<_Tp, _Tp> { template<typename _Up> struct __result { typedef _Up type; }; };

}

template<typename _Tp, _Tp _Np> using __make_integer_sequence_unchecked =
 typename __detail::__convert<size_t, _Tp>::template __result<typename __detail::__make<_Np>::type>::type;

template <class _Tp, _Tp _Ep>
struct __make_integer_sequence
{
 static_assert(is_integral<_Tp>::value,
 "std::make_integer_sequence can only be instantiated with an integral type" );
 static_assert(0 <= _Ep, "std::make_integer_sequence input shall not be negative");
 typedef __make_integer_sequence_unchecked<_Tp, _Ep> type;
};

template<class _Tp, _Tp _Np>
 using make_integer_sequence = typename __make_integer_sequence<_Tp, _Np>::type;

template<size_t _Np>
 using make_index_sequence = make_integer_sequence<size_t, _Np>;

template<class... _Tp>
 using index_sequence_for = make_index_sequence<sizeof...(_Tp)>;
 
#endif // _LIBCPP_STD_VER > 11

#if _LIBCPP_STD_VER > 11
template<class _T1, class _T2 = _T1>
inline _LIBCPP_INLINE_VISIBILITY
_T1 exchange(_T1& __obj, _T2 && __new_value)
{
 _T1 __old_value = _VSTD::move(__obj);
 __obj = _VSTD::forward<_T2>(__new_value);
 return __old_value;
} 
#endif // _LIBCPP_STD_VER > 11

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_UTILITY