stl_uninitialized.h

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// Raw memory manipulators -*- C++ -*-
 
// Copyright (C) 2001-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */
 
/** @file bits/stl_uninitialized.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */
 
#ifndef _STL_UNINITIALIZED_H
#define _STL_UNINITIALIZED_H 1
 
#if __cplusplus >= 201103L
# include <type_traits>
# include <bits/ptr_traits.h>      // to_address
# include <bits/stl_pair.h>        // pair
# include <bits/stl_algobase.h>    // fill, fill_n
#endif
 
#include <bits/cpp_type_traits.h> // __is_pointer
#include <bits/stl_iterator_base_funcs.h> // distance, advance
#include <bits/stl_iterator.h>    // __niter_base
#include <ext/alloc_traits.h>     // __alloc_traits
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  /** @addtogroup memory
   *  @{
   */
 
  /// @cond undocumented
 
  template<typename _ForwardIterator, typename _Alloc = void>
    struct _UninitDestroyGuard
    {
      _GLIBCXX20_CONSTEXPR
      explicit
      _UninitDestroyGuard(_ForwardIterator& __first, _Alloc& __a)
      : _M_first(__first), _M_cur(__builtin_addressof(__first)), _M_alloc(__a)
      { }
 
      _GLIBCXX20_CONSTEXPR
      ~_UninitDestroyGuard()
      {
        if (__builtin_expect(_M_cur != 0, 0))
          std::_Destroy(_M_first, *_M_cur, _M_alloc);
      }
 
      _GLIBCXX20_CONSTEXPR
      void release() { _M_cur = 0; }
 
    private:
      _ForwardIterator const _M_first;
      _ForwardIterator* _M_cur;
      _Alloc& _M_alloc;
 
      _UninitDestroyGuard(const _UninitDestroyGuard&);
    };
 
  template<typename _ForwardIterator>
    struct _UninitDestroyGuard<_ForwardIterator, void>
    {
      _GLIBCXX20_CONSTEXPR
      explicit
      _UninitDestroyGuard(_ForwardIterator& __first)
      : _M_first(__first), _M_cur(__builtin_addressof(__first))
      { }
 
      _GLIBCXX20_CONSTEXPR
      ~_UninitDestroyGuard()
      {
        if (__builtin_expect(_M_cur != 0, 0))
#if __cplusplus == 201703L
          // std::uninitialized_{value,default}{,_n} can construct array types,
          // but std::_Destroy cannot handle them until C++20 (PR 120397).
          _S_destroy(_M_first, *_M_cur);
#else
          std::_Destroy(_M_first, *_M_cur);
#endif
      }
 
      _GLIBCXX20_CONSTEXPR
      void release() { _M_cur = 0; }
 
      _ForwardIterator const _M_first;
      _ForwardIterator* _M_cur;
 
    private:
      _UninitDestroyGuard(const _UninitDestroyGuard&);
 
#if __cplusplus == 201703L
      template<typename _Iter>
        static void
        _S_destroy(_Iter __first, _Iter __last)
        {
          using _ValT = typename iterator_traits<_Iter>::value_type;
          if constexpr (is_array<_ValT>::value)
            for (; __first != __last; ++__first)
              _S_destroy(*__first, *__first + extent<_ValT>::value);
          else
            std::_Destroy(__first, __last);
        }
#endif
    };
 
  // This is the default implementation of std::uninitialized_copy.
  // This can be used with C++20 iterators and non-common ranges.
  template<typename _InputIterator, typename _Sentinel,
           typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR
    _ForwardIterator
    __do_uninit_copy(_InputIterator __first, _Sentinel __last,
                     _ForwardIterator __result)
    {
      _UninitDestroyGuard<_ForwardIterator> __guard(__result);
      for (; __first != __last; ++__first, (void)++__result)
        std::_Construct(std::__addressof(*__result), *__first);
      __guard.release();
      return __result;
    }
 
#if __cplusplus < 201103L
 
  // True if we can unwrap _Iter to get a pointer by using std::__niter_base.
  template<typename _Iter,
           typename _Base = __decltype(std::__niter_base(*(_Iter*)0))>
    struct __unwrappable_niter
    { enum { __value = false }; };
 
  template<typename _Iter, typename _Tp>
    struct __unwrappable_niter<_Iter, _Tp*>
    { enum { __value = true }; };
 
  // Use template specialization for C++98 when 'if constexpr' can't be used.
  template<bool _CanMemcpy>
    struct __uninitialized_copy
    {
      template<typename _InputIterator, typename _ForwardIterator>
        static _ForwardIterator
        __uninit_copy(_InputIterator __first, _InputIterator __last,
                      _ForwardIterator __result)
        { return std::__do_uninit_copy(__first, __last, __result); }
    };
 
  template<>
    struct __uninitialized_copy<true>
    {
      // Overload for generic iterators.
      template<typename _InputIterator, typename _ForwardIterator>
        static _ForwardIterator
        __uninit_copy(_InputIterator __first, _InputIterator __last,
                      _ForwardIterator __result)
        {
          if (__unwrappable_niter<_InputIterator>::__value
                && __unwrappable_niter<_ForwardIterator>::__value)
            {
              __uninit_copy(std::__niter_base(__first),
                            std::__niter_base(__last),
                            std::__niter_base(__result));
              std::advance(__result, std::distance(__first, __last));
              return __result;
            }
          else
            return std::__do_uninit_copy(__first, __last, __result);
        }
 
      // Overload for pointers.
      template<typename _Tp, typename _Up>
        static _Up*
        __uninit_copy(_Tp* __first, _Tp* __last, _Up* __result)
        {
          // Ensure that we don't successfully memcpy in cases that should be
          // ill-formed because is_constructible<_Up, _Tp&> is false.
          typedef __typeof__(static_cast<_Up>(*__first)) __check
            __attribute__((__unused__));
 
          const ptrdiff_t __n = __last - __first;
          if (__builtin_expect(__n > 0, true))
            {
              __builtin_memcpy(__result, __first, __n * sizeof(_Tp));
              __result += __n;
            }
          return __result;
        }
    };
#endif
  /// @endcond
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions"
#pragma GCC diagnostic ignored "-Wclass-memaccess"
  /**
   *  @brief Copies the range [first,last) into result.
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __result A forward iterator.
   *  @return   __result + (__last - __first)
   *
   *  Like std::copy, but does not require an initialized output range.
  */
  template<typename _InputIterator, typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    uninitialized_copy(_InputIterator __first, _InputIterator __last,
                       _ForwardIterator __result)
    {
      // We can use memcpy to copy the ranges under these conditions:
      //
      // _ForwardIterator and _InputIterator are both contiguous iterators,
      // so that we can turn them into pointers to pass to memcpy.
      // Before C++20 we can't detect all contiguous iterators, so we only
      // handle built-in pointers and __normal_iterator<T*, C> types.
      //
      // The value types of both iterators are trivially-copyable types,
      // so that memcpy is not undefined and can begin the lifetime of
      // new objects in the output range.
      //
      // Finally, memcpy from the source type, S, to the destination type, D,
      // must give the same value as initialization of D from S would give.
      // We require is_trivially_constructible<D, S> to be true, but that is
      // not sufficient. Some cases of trivial initialization are not just a
      // bitwise copy, even when sizeof(D) == sizeof(S),
      // e.g. bit_cast<unsigned>(1.0f) != 1u because the corresponding bits
      // of the value representations do not have the same meaning.
      // We cannot tell when this condition is true in general,
      // so we rely on the __memcpyable trait.
 
#if __cplusplus >= 201103L
      using _Dest = decltype(std::__niter_base(__result));
      using _Src = decltype(std::__miter_base(std::__niter_base(__first)));
      using _ValT = typename iterator_traits<_ForwardIterator>::value_type;
 
#if __glibcxx_raw_memory_algorithms >= 202411L // >= C++26
      if consteval {
        return std::__do_uninit_copy(__first, __last, __result);
      }
#endif
      if constexpr (!__is_trivially_constructible(_ValT, decltype(*__first)))
        return std::__do_uninit_copy(__first, __last, __result);
      else if constexpr (__memcpyable<_Dest, _Src>::__value)
        {
          ptrdiff_t __n = __last - __first;
          if (__n > 0) [[__likely__]]
            {
              using _ValT = typename remove_pointer<_Src>::type;
              __builtin_memcpy(std::__niter_base(__result),
                               std::__miter_base(std::__niter_base(__first)),
                               __n * sizeof(_ValT));
              __result += __n;
            }
          return __result;
        }
#if __cpp_lib_concepts
      else if constexpr (contiguous_iterator<_ForwardIterator>
                           && contiguous_iterator<_InputIterator>)
        {
          using _DestPtr = decltype(std::to_address(__result));
          using _SrcPtr = decltype(std::to_address(__first));
          if constexpr (__memcpyable<_DestPtr, _SrcPtr>::__value)
            {
              if (auto __n = __last - __first; __n > 0) [[likely]]
                {
                  void* __dest = std::to_address(__result);
                  const void* __src = std::to_address(__first);
                  size_t __nbytes = __n * sizeof(remove_pointer_t<_DestPtr>);
                  __builtin_memcpy(__dest, __src, __nbytes);
                  __result += __n;
                }
              return __result;
            }
          else
            return std::__do_uninit_copy(__first, __last, __result);
        }
#endif
      else
        return std::__do_uninit_copy(__first, __last, __result);
#else // C++98
      typedef typename iterator_traits<_InputIterator>::value_type
        _ValueType1;
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType2;
 
      const bool __can_memcpy
        = __memcpyable<_ValueType1*, _ValueType2*>::__value
            && __is_trivially_constructible(_ValueType2, __decltype(*__first));
 
      return __uninitialized_copy<__can_memcpy>::
               __uninit_copy(__first, __last, __result);
#endif
    }
#pragma GCC diagnostic pop
 
  /// @cond undocumented
 
  // This is the default implementation of std::uninitialized_fill.
  template<typename _ForwardIterator, typename _Tp>
    _GLIBCXX20_CONSTEXPR void
    __do_uninit_fill(_ForwardIterator __first, _ForwardIterator __last,
                     const _Tp& __x)
    {
      _UninitDestroyGuard<_ForwardIterator> __guard(__first);
      for (; __first != __last; ++__first)
        std::_Construct(std::__addressof(*__first), __x);
      __guard.release();
    }
 
#if __cplusplus < 201103L
  // Use template specialization for C++98 when 'if constexpr' can't be used.
  template<bool _CanMemset>
    struct __uninitialized_fill
    {
      template<typename _ForwardIterator, typename _Tp>
        static void
        __uninit_fill(_ForwardIterator __first, _ForwardIterator __last,
                      const _Tp& __x)
        { std::__do_uninit_fill(__first, __last, __x); }
    };
 
  template<>
    struct __uninitialized_fill<true>
    {
      // Overload for generic iterators.
      template<typename _ForwardIterator, typename _Tp>
        static void
        __uninit_fill(_ForwardIterator __first, _ForwardIterator __last,
                      const _Tp& __x)
        {
          if (__unwrappable_niter<_ForwardIterator>::__value)
            __uninit_fill(std::__niter_base(__first),
                          std::__niter_base(__last),
                          __x);
          else
            std::__do_uninit_fill(__first, __last, __x);
        }
 
      // Overload for pointers.
      template<typename _Up, typename _Tp>
        static void
        __uninit_fill(_Up* __first, _Up* __last, const _Tp& __x)
        {
          // Ensure that we don't successfully memset in cases that should be
          // ill-formed because is_constructible<_Up, const _Tp&> is false.
          typedef __typeof__(static_cast<_Up>(__x)) __check
            __attribute__((__unused__));
 
          if (__first != __last)
            __builtin_memset(__first, (unsigned char)__x, __last - __first);
        }
    };
#endif
  /// @endcond
 
  /**
   *  @brief Copies the value x into the range [first,last).
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @param  __x      The source value.
   *
   *  Like std::fill, but does not require an initialized output range.
  */
  template<typename _ForwardIterator,
           typename _Tp _GLIBCXX26_ALGO_DEF_VAL_T(_ForwardIterator)>
    _GLIBCXX26_CONSTEXPR
    inline void
    uninitialized_fill(_ForwardIterator __first, _ForwardIterator __last,
                       const _Tp& __x)
    {
      // We would like to use memset to optimize this loop when possible.
      // As for std::uninitialized_copy, the optimization requires
      // contiguous iterators and trivially copyable value types,
      // with the additional requirement that sizeof(_Tp) == 1 because
      // memset only writes single bytes.
 
      // FIXME: We could additionally enable this for 1-byte enums.
      // Maybe any 1-byte Val if is_trivially_constructible<Val, const T&>?
 
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType;
 
#if __cplusplus >= 201103L
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions"
#pragma GCC diagnostic ignored "-Wclass-memaccess"
#if __glibcxx_raw_memory_algorithms >= 202411L // >= C++26
      if consteval {
        return std::__do_uninit_fill(__first, __last, __x);
      }
#endif
      if constexpr (__is_byte<_ValueType>::__value)
        if constexpr (is_same<_ValueType, _Tp>::value
                        || is_integral<_Tp>::value)
          {
            using _BasePtr = decltype(std::__niter_base(__first));
            if constexpr (is_pointer<_BasePtr>::value)
              {
                void* __dest = std::__niter_base(__first);
                ptrdiff_t __n = __last - __first;
                if (__n > 0) [[__likely__]]
                  __builtin_memset(__dest, (unsigned char)__x, __n);
                return;
              }
#if __cpp_lib_concepts
            else if constexpr (contiguous_iterator<_ForwardIterator>)
              {
                auto __dest = std::to_address(__first);
                auto __n = __last - __first;
                if (__n > 0) [[__likely__]]
                  __builtin_memset(__dest, (unsigned char)__x, __n);
                return;
              }
#endif
          }
      std::__do_uninit_fill(__first, __last, __x);
#pragma GCC diagnostic pop
#else // C++98
      const bool __can_memset = __is_byte<_ValueType>::__value
                                  && __is_integer<_Tp>::__value;
 
      __uninitialized_fill<__can_memset>::__uninit_fill(__first, __last, __x);
#endif
    }
 
  /// @cond undocumented
 
  // This is the default implementation of std::uninitialized_fill_n.
  template<typename _ForwardIterator, typename _Size, typename _Tp>
    _GLIBCXX20_CONSTEXPR
    _ForwardIterator
    __do_uninit_fill_n(_ForwardIterator __first, _Size __n, const _Tp& __x)
    {
      _UninitDestroyGuard<_ForwardIterator> __guard(__first);
#if __cplusplus >= 201103L
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions"
      if constexpr (is_integral<_Size>::value)
        // Loop will never terminate if __n is negative.
        __glibcxx_assert(__n >= 0);
      else if constexpr (is_floating_point<_Size>::value)
        // Loop will never terminate if __n is not an integer.
        __glibcxx_assert(__n >= 0 && static_cast<size_t>(__n) == __n);
#pragma GCC diagnostic pop
#endif
      for (; __n--; ++__first)
        std::_Construct(std::__addressof(*__first), __x);
      __guard.release();
      return __first;
    }
 
#if __cplusplus < 201103L
  // Use template specialization for C++98 when 'if constexpr' can't be used.
  template<bool _CanMemset>
    struct __uninitialized_fill_n
    {
      template<typename _ForwardIterator, typename _Size, typename _Tp>
        static _ForwardIterator
        __uninit_fill_n(_ForwardIterator __first, _Size __n,
                        const _Tp& __x)
        { return std::__do_uninit_fill_n(__first, __n, __x); }
    };
 
  template<>
    struct __uninitialized_fill_n<true>
    {
      // Overload for generic iterators.
      template<typename _ForwardIterator, typename _Size, typename _Tp>
        static _ForwardIterator
        __uninit_fill_n(_ForwardIterator __first, _Size __n,
                        const _Tp& __x)
        {
          if (__unwrappable_niter<_ForwardIterator>::__value)
            {
              _ForwardIterator __last = __first;
              std::advance(__last, __n);
              __uninitialized_fill<true>::__uninit_fill(__first, __last, __x);
              return __last;
            }
          else
            return std::__do_uninit_fill_n(__first, __n, __x);
        }
    };
#endif
  /// @endcond
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions"
#pragma GCC diagnostic ignored "-Wclass-memaccess"
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // DR 1339. uninitialized_fill_n should return the end of its range
  /**
   *  @brief Copies the value x into the range [first,first+n).
   *  @param  __first  A forward iterator.
   *  @param  __n      The number of copies to make.
   *  @param  __x      The source value.
   *  @return   __first + __n.
   *
   *  Like std::fill_n, but does not require an initialized output range.
  */
  template<typename _ForwardIterator, typename _Size,
           typename _Tp _GLIBCXX26_ALGO_DEF_VAL_T(_ForwardIterator)>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    uninitialized_fill_n(_ForwardIterator __first, _Size __n, const _Tp& __x)
    {
      // See uninitialized_fill conditions. We also require _Size to be
      // an integer. The standard only requires _Size to be decrementable
      // and contextually convertible to bool, so don't assume first+n works.
 
      // FIXME: We could additionally enable this for 1-byte enums.
 
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType;
 
#if __cplusplus >= 201103L
#if __glibcxx_raw_memory_algorithms >= 202411L // >= C++26
      if consteval {
        return std::__do_uninit_fill_n(__first, __n, __x);
      }
#endif
      if constexpr (__is_byte<_ValueType>::__value)
        if constexpr (is_integral<_Tp>::value)
          if constexpr (is_integral<_Size>::value)
            {
              using _BasePtr = decltype(std::__niter_base(__first));
              if constexpr (is_pointer<_BasePtr>::value)
                {
                  void* __dest = std::__niter_base(__first);
                  if (__n > 0) [[__likely__]]
                    {
                      __builtin_memset(__dest, (unsigned char)__x, __n);
                      __first += __n;
                    }
                  return __first;
                }
#if __cpp_lib_concepts
              else if constexpr (contiguous_iterator<_ForwardIterator>)
                {
                  auto __dest = std::to_address(__first);
                  if (__n > 0) [[__likely__]]
                    {
                      __builtin_memset(__dest, (unsigned char)__x, __n);
                      __first += __n;
                    }
                  return __first;
                }
#endif
            }
      return std::__do_uninit_fill_n(__first, __n, __x);
#else // C++98
      const bool __can_memset = __is_byte<_ValueType>::__value
                                  && __is_integer<_Tp>::__value
                                  && __is_integer<_Size>::__value;
 
      return __uninitialized_fill_n<__can_memset>::
        __uninit_fill_n(__first, __n, __x);
#endif
    }
#pragma GCC diagnostic pop
 
  /// @cond undocumented
 
  // Extensions: versions of uninitialized_copy, uninitialized_fill,
  //  and uninitialized_fill_n that take an allocator parameter.
  //  We dispatch back to the standard versions when we're given the
  //  default allocator.  For nondefault allocators we do not use
  //  any of the POD optimizations.
 
  template<typename _InputIterator, typename _Sentinel,
           typename _ForwardIterator, typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    _ForwardIterator
    __uninitialized_copy_a(_InputIterator __first, _Sentinel __last,
                           _ForwardIterator __result, _Allocator& __alloc)
    {
      _UninitDestroyGuard<_ForwardIterator, _Allocator>
        __guard(__result, __alloc);
 
      typedef __gnu_cxx::__alloc_traits<_Allocator> __traits;
      for (; __first != __last; ++__first, (void)++__result)
        __traits::construct(__alloc, std::__addressof(*__result), *__first);
      __guard.release();
      return __result;
    }
 
#if _GLIBCXX_HOSTED
  template<typename _InputIterator, typename _Sentinel,
           typename _ForwardIterator, typename _Tp>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_copy_a(_InputIterator __first, _Sentinel __last,
                           _ForwardIterator __result, allocator<_Tp>&)
    {
#ifdef __cpp_lib_is_constant_evaluated
      if (std::is_constant_evaluated())
        return std::__do_uninit_copy(std::move(__first), __last, __result);
#endif
 
#ifdef __glibcxx_ranges
      if constexpr (!is_same_v<_InputIterator, _Sentinel>)
        {
          // Convert to a common range if possible, to benefit from memcpy
          // optimizations that std::uninitialized_copy might use.
          if constexpr (sized_sentinel_for<_Sentinel, _InputIterator>
                          && random_access_iterator<_InputIterator>)
            return std::uninitialized_copy(__first,
                                           __first + (__last - __first),
                                           __result);
          else // Just use default implementation.
            return std::__do_uninit_copy(std::move(__first), __last, __result);
        }
      else
        return std::uninitialized_copy(std::move(__first), __last, __result);
#else
      return std::uninitialized_copy(__first, __last, __result);
#endif
    }
#endif
 
#if __cplusplus >= 201103L
  template<typename _ITp, typename _IRef, typename _IPtr, typename _OTp,
           typename _Tp>
    _GLIBCXX26_CONSTEXPR
    _GLIBCXX_STD_C::_Deque_iterator<_OTp, _OTp&, _OTp*>
    __uninitialized_copy_a(
      _GLIBCXX_STD_C::_Deque_iterator<_ITp, _IRef, _IPtr> __first,
      _GLIBCXX_STD_C::_Deque_iterator<_ITp, _IRef, _IPtr> __last,
      _GLIBCXX_STD_C::_Deque_iterator<_OTp, _OTp&, _OTp*> __result,
      allocator<_Tp>&);
 
  template<typename _Iter, typename _OTp, typename _Tp>
    _GLIBCXX26_CONSTEXPR
    __enable_if_t<__is_random_access_iter<_Iter>::value,
                  _GLIBCXX_STD_C::_Deque_iterator<_OTp, _OTp&, _OTp*>>
    __uninitialized_copy_a(_Iter __first, _Iter __last,
      _GLIBCXX_STD_C::_Deque_iterator<_OTp, _OTp&, _OTp*> __result,
      allocator<_Tp>&);
 
  template<typename _ITp, typename _IRef, typename _IPtr, typename _OTp,
           typename _Tp>
    _GLIBCXX26_CONSTEXPR
    _GLIBCXX_STD_C::_Deque_iterator<_OTp, _OTp&, _OTp*>
    __uninitialized_move_a(
      _GLIBCXX_STD_C::_Deque_iterator<_ITp, _IRef, _IPtr> __first,
      _GLIBCXX_STD_C::_Deque_iterator<_ITp, _IRef, _IPtr> __last,
      _GLIBCXX_STD_C::_Deque_iterator<_OTp, _OTp&, _OTp*> __result,
      allocator<_Tp>&);
#endif
 
  template<typename _InputIterator, typename _ForwardIterator,
           typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_move_a(_InputIterator __first, _InputIterator __last,
                           _ForwardIterator __result, _Allocator& __alloc)
    {
      return std::__uninitialized_copy_a(_GLIBCXX_MAKE_MOVE_ITERATOR(__first),
                                         _GLIBCXX_MAKE_MOVE_ITERATOR(__last),
                                         __result, __alloc);
    }
 
  template<typename _InputIterator, typename _ForwardIterator,
           typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_move_if_noexcept_a(_InputIterator __first,
                                       _InputIterator __last,
                                       _ForwardIterator __result,
                                       _Allocator& __alloc)
    {
      return std::__uninitialized_copy_a
        (_GLIBCXX_MAKE_MOVE_IF_NOEXCEPT_ITERATOR(__first),
         _GLIBCXX_MAKE_MOVE_IF_NOEXCEPT_ITERATOR(__last), __result, __alloc);
    }
 
  template<typename _ForwardIterator, typename _Tp, typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    void
    __uninitialized_fill_a(_ForwardIterator __first, _ForwardIterator __last,
                           const _Tp& __x, _Allocator& __alloc)
    {
      _UninitDestroyGuard<_ForwardIterator, _Allocator>
        __guard(__first, __alloc);
 
      typedef __gnu_cxx::__alloc_traits<_Allocator> __traits;
      for (; __first != __last; ++__first)
        __traits::construct(__alloc, std::__addressof(*__first), __x);
 
      __guard.release();
    }
 
#if _GLIBCXX_HOSTED
  template<typename _ForwardIterator, typename _Tp, typename _Tp2>
    _GLIBCXX20_CONSTEXPR
    inline void
    __uninitialized_fill_a(_ForwardIterator __first, _ForwardIterator __last,
                           const _Tp& __x, allocator<_Tp2>&)
    {
#ifdef __cpp_lib_is_constant_evaluated
      if (std::is_constant_evaluated())
        return std::__do_uninit_fill(__first, __last, __x);
#endif
      std::uninitialized_fill(__first, __last, __x);
    }
#endif
 
  template<typename _ForwardIterator, typename _Size, typename _Tp,
           typename _Allocator>
     _GLIBCXX20_CONSTEXPR
    _ForwardIterator
    __uninitialized_fill_n_a(_ForwardIterator __first, _Size __n,
                             const _Tp& __x, _Allocator& __alloc)
    {
      _UninitDestroyGuard<_ForwardIterator, _Allocator>
        __guard(__first, __alloc);
      typedef __gnu_cxx::__alloc_traits<_Allocator> __traits;
      for (; __n > 0; --__n, (void) ++__first)
        __traits::construct(__alloc, std::__addressof(*__first), __x);
      __guard.release();
      return __first;
    }
 
#if _GLIBCXX_HOSTED
  template<typename _ForwardIterator, typename _Size, typename _Tp,
           typename _Tp2>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_fill_n_a(_ForwardIterator __first, _Size __n,
                             const _Tp& __x, allocator<_Tp2>&)
    {
#ifdef __cpp_lib_is_constant_evaluated
      if (std::is_constant_evaluated())
        return std::__do_uninit_fill_n(__first, __n, __x);
#endif
      return std::uninitialized_fill_n(__first, __n, __x);
    }
#endif
 
  // Extensions: __uninitialized_copy_move, __uninitialized_move_copy,
  // __uninitialized_fill_move, __uninitialized_move_fill.
  // All of these algorithms take a user-supplied allocator, which is used
  // for construction and destruction.
 
  // __uninitialized_copy_move
  // Copies [first1, last1) into [result, result + (last1 - first1)), and
  //  move [first2, last2) into
  //  [result, result + (last1 - first1) + (last2 - first2)).
  template<typename _InputIterator1, typename _InputIterator2,
           typename _ForwardIterator, typename _Allocator>
    inline _ForwardIterator
    __uninitialized_copy_move(_InputIterator1 __first1,
                              _InputIterator1 __last1,
                              _InputIterator2 __first2,
                              _InputIterator2 __last2,
                              _ForwardIterator __result,
                              _Allocator& __alloc)
    {
      _ForwardIterator __mid = std::__uninitialized_copy_a(__first1, __last1,
                                                           __result, __alloc);
      _UninitDestroyGuard<_ForwardIterator, _Allocator> __guard(__result,
                                                                __alloc);
      __result = __mid; // Everything up to __mid is now guarded.
      __result = std::__uninitialized_move_a(__first2, __last2, __mid, __alloc);
      __guard.release();
      return __result;
    }
 
  // __uninitialized_move_copy
  // Moves [first1, last1) into [result, result + (last1 - first1)), and
  //  copies [first2, last2) into
  //  [result, result + (last1 - first1) + (last2 - first2)).
  template<typename _InputIterator1, typename _InputIterator2,
           typename _ForwardIterator, typename _Allocator>
    inline _ForwardIterator
    __uninitialized_move_copy(_InputIterator1 __first1,
                              _InputIterator1 __last1,
                              _InputIterator2 __first2,
                              _InputIterator2 __last2,
                              _ForwardIterator __result,
                              _Allocator& __alloc)
    {
      _ForwardIterator __mid = std::__uninitialized_move_a(__first1, __last1,
                                                           __result, __alloc);
      _UninitDestroyGuard<_ForwardIterator, _Allocator> __guard(__result,
                                                                __alloc);
      __result = __mid; // Everything up to __mid is now guarded.
      __result = std::__uninitialized_copy_a(__first2, __last2, __mid, __alloc);
      __guard.release();
      return __result;
    }
 
  // __uninitialized_fill_move
  // Fills [result, mid) with x, and moves [first, last) into
  //  [mid, mid + (last - first)).
  template<typename _ForwardIterator, typename _Tp, typename _InputIterator,
           typename _Allocator>
    inline _ForwardIterator
    __uninitialized_fill_move(_ForwardIterator __result, _ForwardIterator __mid,
                              const _Tp& __x, _InputIterator __first,
                              _InputIterator __last, _Allocator& __alloc)
    {
      std::__uninitialized_fill_a(__result, __mid, __x, __alloc);
      _UninitDestroyGuard<_ForwardIterator, _Allocator> __guard(__result,
                                                                __alloc);
      __result = __mid; // Everything up to __mid is now guarded.
      __result = std::__uninitialized_move_a(__first, __last, __mid, __alloc);
      __guard.release();
      return __result;
    }
 
  // __uninitialized_move_fill
  // Moves [first1, last1) into [first2, first2 + (last1 - first1)), and
  //  fills [first2 + (last1 - first1), last2) with x.
  template<typename _InputIterator, typename _ForwardIterator, typename _Tp,
           typename _Allocator>
    inline void
    __uninitialized_move_fill(_InputIterator __first1, _InputIterator __last1,
                              _ForwardIterator __first2,
                              _ForwardIterator __last2, const _Tp& __x,
                              _Allocator& __alloc)
    {
      _ForwardIterator __mid2 = std::__uninitialized_move_a(__first1, __last1,
                                                            __first2,
                                                            __alloc);
      _UninitDestroyGuard<_ForwardIterator, _Allocator> __guard(__first2,
                                                                __alloc);
      __first2 = __mid2; // Everything up to __mid2 is now guarded.
      std::__uninitialized_fill_a(__mid2, __last2, __x, __alloc);
      __guard.release();
    }
 
  /// @endcond
 
#if __cplusplus >= 201103L
  /// @cond undocumented
 
  // Extensions: __uninitialized_default, __uninitialized_default_n,
  // __uninitialized_default_a, __uninitialized_default_n_a.
 
  template<bool _TrivialValueType>
    struct __uninitialized_default_1
    {
      template<typename _ForwardIterator>
        _GLIBCXX26_CONSTEXPR
        static void
        __uninit_default(_ForwardIterator __first, _ForwardIterator __last)
        {
          _UninitDestroyGuard<_ForwardIterator> __guard(__first);
          for (; __first != __last; ++__first)
            std::_Construct(std::addressof(*__first));
          __guard.release();
        }
    };
 
  template<>
    struct __uninitialized_default_1<true>
    {
      template<typename _ForwardIterator>
        _GLIBCXX26_CONSTEXPR
        static void
        __uninit_default(_ForwardIterator __first, _ForwardIterator __last)
        {
          if (__first == __last)
            return;
 
          typename iterator_traits<_ForwardIterator>::value_type* __val
            = std::addressof(*__first);
          std::_Construct(__val);
          if (++__first != __last)
            std::fill(__first, __last, *__val);
        }
    };
 
  template<bool _TrivialValueType>
    struct __uninitialized_default_n_1
    {
      template<typename _ForwardIterator, typename _Size>
        _GLIBCXX20_CONSTEXPR
        static _ForwardIterator
        __uninit_default_n(_ForwardIterator __first, _Size __n)
        {
          _UninitDestroyGuard<_ForwardIterator> __guard(__first);
          for (; __n > 0; --__n, (void) ++__first)
            std::_Construct(std::addressof(*__first));
          __guard.release();
          return __first;
        }
    };
 
  template<>
    struct __uninitialized_default_n_1<true>
    {
      template<typename _ForwardIterator, typename _Size>
        _GLIBCXX20_CONSTEXPR
        static _ForwardIterator
        __uninit_default_n(_ForwardIterator __first, _Size __n)
        {
          if (__n > 0)
            {
              typename iterator_traits<_ForwardIterator>::value_type* __val
                = std::addressof(*__first);
              std::_Construct(__val);
              ++__first;
              __first = std::fill_n(__first, __n - 1, *__val);
            }
          return __first;
        }
    };
 
  // __uninitialized_default
  // Fills [first, last) with value-initialized value_types.
  template<typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR
    inline void
    __uninitialized_default(_ForwardIterator __first,
                            _ForwardIterator __last)
    {
#ifdef __cpp_lib_is_constant_evaluated
      if (std::is_constant_evaluated())
        return __uninitialized_default_1<false>::
                 __uninit_default(__first, __last);
#endif
 
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType;
      // trivial types can have deleted assignment
      const bool __assignable = is_copy_assignable<_ValueType>::value;
 
      std::__uninitialized_default_1<__is_trivial(_ValueType)
                                     && __assignable>::
        __uninit_default(__first, __last);
    }
 
  // __uninitialized_default_n
  // Fills [first, first + n) with value-initialized value_types.
  template<typename _ForwardIterator, typename _Size>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_default_n(_ForwardIterator __first, _Size __n)
    {
#ifdef __cpp_lib_is_constant_evaluated
      if (std::is_constant_evaluated())
        return __uninitialized_default_n_1<false>::
                 __uninit_default_n(__first, __n);
#endif
 
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType;
      // See uninitialized_fill_n for the conditions for using std::fill_n.
      constexpr bool __can_fill
        = __and_<is_integral<_Size>, is_copy_assignable<_ValueType>>::value;
 
      return __uninitialized_default_n_1<__is_trivial(_ValueType)
                                         && __can_fill>::
        __uninit_default_n(__first, __n);
    }
 
 
  // __uninitialized_default_a
  // Fills [first, last) with value_types constructed by the allocator
  // alloc, with no arguments passed to the construct call.
  template<typename _ForwardIterator, typename _Allocator>
    _GLIBCXX20_CONSTEXPR void
    __uninitialized_default_a(_ForwardIterator __first,
                              _ForwardIterator __last,
                              _Allocator& __alloc)
    {
      _UninitDestroyGuard<_ForwardIterator, _Allocator> __guard(__first,
                                                                __alloc);
      typedef __gnu_cxx::__alloc_traits<_Allocator> __traits;
      for (; __first != __last; ++__first)
        __traits::construct(__alloc, std::addressof(*__first));
      __guard.release();
    }
 
#if _GLIBCXX_HOSTED
  template<typename _ForwardIterator, typename _Tp>
    inline _GLIBCXX20_CONSTEXPR void
    __uninitialized_default_a(_ForwardIterator __first,
                              _ForwardIterator __last,
                              allocator<_Tp>&)
    { std::__uninitialized_default(__first, __last); }
#endif
 
  // __uninitialized_default_n_a
  // Fills [first, first + n) with value_types constructed by the allocator
  // alloc, with no arguments passed to the construct call.
  template<typename _ForwardIterator, typename _Size, typename _Allocator>
    _GLIBCXX20_CONSTEXPR _ForwardIterator
    __uninitialized_default_n_a(_ForwardIterator __first, _Size __n,
                                _Allocator& __alloc)
    {
      _UninitDestroyGuard<_ForwardIterator, _Allocator> __guard(__first,
                                                                __alloc);
      typedef __gnu_cxx::__alloc_traits<_Allocator> __traits;
      for (; __n > 0; --__n, (void) ++__first)
        __traits::construct(__alloc, std::addressof(*__first));
      __guard.release();
      return __first;
    }
 
#if _GLIBCXX_HOSTED
  // __uninitialized_default_n_a specialization for std::allocator,
  // which ignores the allocator and value-initializes the elements.
  template<typename _ForwardIterator, typename _Size, typename _Tp>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_default_n_a(_ForwardIterator __first, _Size __n,
                                allocator<_Tp>&)
    { return std::__uninitialized_default_n(__first, __n); }
#endif
 
  template<bool _TrivialValueType>
    struct __uninitialized_default_novalue_1
    {
      template<typename _ForwardIterator>
        _GLIBCXX26_CONSTEXPR
        static void
        __uninit_default_novalue(_ForwardIterator __first,
                                 _ForwardIterator __last)
        {
          _UninitDestroyGuard<_ForwardIterator> __guard(__first);
          for (; __first != __last; ++__first)
            std::_Construct_novalue(std::addressof(*__first));
          __guard.release();
        }
    };
 
  template<>
    struct __uninitialized_default_novalue_1<true>
    {
      template<typename _ForwardIterator>
        _GLIBCXX26_CONSTEXPR
        static void
        __uninit_default_novalue(_ForwardIterator, _ForwardIterator)
        {
        }
    };
 
  template<bool _TrivialValueType>
    struct __uninitialized_default_novalue_n_1
    {
      template<typename _ForwardIterator, typename _Size>
        _GLIBCXX26_CONSTEXPR
        static _ForwardIterator
        __uninit_default_novalue_n(_ForwardIterator __first, _Size __n)
        {
          _UninitDestroyGuard<_ForwardIterator> __guard(__first);
          for (; __n > 0; --__n, (void) ++__first)
            std::_Construct_novalue(std::addressof(*__first));
          __guard.release();
          return __first;
        }
    };
 
  template<>
    struct __uninitialized_default_novalue_n_1<true>
    {
      template<typename _ForwardIterator, typename _Size>
        _GLIBCXX26_CONSTEXPR
        static _ForwardIterator
        __uninit_default_novalue_n(_ForwardIterator __first, _Size __n)
        { return std::next(__first, __n); }
    };
 
  // __uninitialized_default_novalue
  // Fills [first, last) with default-initialized value_types.
  template<typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline void
    __uninitialized_default_novalue(_ForwardIterator __first,
                                    _ForwardIterator __last)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType;
 
      std::__uninitialized_default_novalue_1<
        is_trivially_default_constructible<_ValueType>::value>::
        __uninit_default_novalue(__first, __last);
    }
 
  // __uninitialized_default_novalue_n
  // Fills [first, first + n) with default-initialized value_types.
  template<typename _ForwardIterator, typename _Size>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_default_novalue_n(_ForwardIterator __first, _Size __n)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType;
 
      return __uninitialized_default_novalue_n_1<
        is_trivially_default_constructible<_ValueType>::value>::
        __uninit_default_novalue_n(__first, __n);
    }
 
  template<typename _InputIterator, typename _Size,
           typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    _ForwardIterator
    __uninitialized_copy_n(_InputIterator __first, _Size __n,
                           _ForwardIterator __result, input_iterator_tag)
    {
      _UninitDestroyGuard<_ForwardIterator> __guard(__result);
      for (; __n > 0; --__n, (void) ++__first, ++__result)
        std::_Construct(std::addressof(*__result), *__first);
      __guard.release();
      return __result;
    }
 
  template<typename _RandomAccessIterator, typename _Size,
           typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    __uninitialized_copy_n(_RandomAccessIterator __first, _Size __n,
                           _ForwardIterator __result,
                           random_access_iterator_tag)
    { return std::uninitialized_copy(__first, __first + __n, __result); }
 
  template<typename _InputIterator, typename _Size,
           typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    pair<_InputIterator, _ForwardIterator>
    __uninitialized_copy_n_pair(_InputIterator __first, _Size __n,
                                _ForwardIterator __result, input_iterator_tag)
    {
      _UninitDestroyGuard<_ForwardIterator> __guard(__result);
      for (; __n > 0; --__n, (void) ++__first, ++__result)
        std::_Construct(std::addressof(*__result), *__first);
      __guard.release();
      return {__first, __result};
    }
 
  template<typename _RandomAccessIterator, typename _Size,
           typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline pair<_RandomAccessIterator, _ForwardIterator>
    __uninitialized_copy_n_pair(_RandomAccessIterator __first, _Size __n,
                           _ForwardIterator __result,
                           random_access_iterator_tag)
    {
      auto __second_res = uninitialized_copy(__first, __first + __n, __result);
      auto __first_res = std::next(__first, __n);
      return {__first_res, __second_res};
    }
 
  /// @endcond
 
  /**
   *  @brief Copies the range [first,first+n) into result.
   *  @param  __first  An input iterator.
   *  @param  __n      The number of elements to copy.
   *  @param  __result An output iterator.
   *  @return  __result + __n
   *  @since C++11
   *
   *  Like copy_n(), but does not require an initialized output range.
  */
  template<typename _InputIterator, typename _Size, typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    uninitialized_copy_n(_InputIterator __first, _Size __n,
                         _ForwardIterator __result)
    { return std::__uninitialized_copy_n(__first, __n, __result,
                                         std::__iter_concept_or_category(__first)); }
 
  /// @cond undocumented
  template<typename _InputIterator, typename _Size, typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline pair<_InputIterator, _ForwardIterator>
    __uninitialized_copy_n_pair(_InputIterator __first, _Size __n,
                              _ForwardIterator __result)
    {
      return
        std::__uninitialized_copy_n_pair(__first, __n, __result,
                                         std::__iter_concept_or_category(__first));
    }
  /// @endcond
#endif
 
#ifdef __glibcxx_raw_memory_algorithms // C++ >= 17
  /**
   *  @brief Default-initializes objects in the range [first,last).
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @since C++17
  */
  template <typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline void
    uninitialized_default_construct(_ForwardIterator __first,
                                    _ForwardIterator __last)
    {
      std::__uninitialized_default_novalue(__first, __last);
    }
 
  /**
   *  @brief Default-initializes objects in the range [first,first+count).
   *  @param  __first  A forward iterator.
   *  @param  __count  The number of objects to construct.
   *  @return   __first + __count
   *  @since C++17
  */
  template <typename _ForwardIterator, typename _Size>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    uninitialized_default_construct_n(_ForwardIterator __first, _Size __count)
    {
      return std::__uninitialized_default_novalue_n(__first, __count);
    }
 
  /**
   *  @brief Value-initializes objects in the range [first,last).
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @since C++17
  */
  template <typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline void
    uninitialized_value_construct(_ForwardIterator __first,
                                  _ForwardIterator __last)
    {
      return std::__uninitialized_default(__first, __last);
    }
 
  /**
   *  @brief Value-initializes objects in the range [first,first+count).
   *  @param  __first  A forward iterator.
   *  @param  __count  The number of objects to construct.
   *  @return   __result + __count
   *  @since C++17
  */
  template <typename _ForwardIterator, typename _Size>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    uninitialized_value_construct_n(_ForwardIterator __first, _Size __count)
    {
      return std::__uninitialized_default_n(__first, __count);
    }
 
  /**
   *  @brief Move-construct from the range [first,last) into result.
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __result An output iterator.
   *  @return   __result + (__first - __last)
   *  @since C++17
  */
  template <typename _InputIterator, typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline _ForwardIterator
    uninitialized_move(_InputIterator __first, _InputIterator __last,
                       _ForwardIterator __result)
    {
      return std::uninitialized_copy(std::make_move_iterator(__first),
                                     std::make_move_iterator(__last),
                                     __result);
    }
 
  /**
   *  @brief Move-construct from the range [first,first+count) into result.
   *  @param  __first  An input iterator.
   *  @param  __count  The number of objects to initialize.
   *  @param  __result An output iterator.
   *  @return  __result + __count
   *  @since C++17
  */
  template <typename _InputIterator, typename _Size, typename _ForwardIterator>
    _GLIBCXX26_CONSTEXPR
    inline pair<_InputIterator, _ForwardIterator>
    uninitialized_move_n(_InputIterator __first, _Size __count,
                         _ForwardIterator __result)
    {
      auto __res
        = std::__uninitialized_copy_n_pair(std::make_move_iterator(__first),
                                           __count, __result);
      return {__res.first.base(), __res.second};
    }
#endif // __glibcxx_raw_memory_algorithms
 
#if __cplusplus >= 201103L
  /// @cond undocumented
 
  template<typename _Tp, typename _Up, typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    inline void
    __relocate_object_a(_Tp* __restrict __dest, _Up* __restrict __orig,
                        _Allocator& __alloc)
    noexcept(noexcept(std::allocator_traits<_Allocator>::construct(__alloc,
                         __dest, std::move(*__orig)))
             && noexcept(std::allocator_traits<_Allocator>::destroy(
                            __alloc, std::addressof(*__orig))))
    {
      typedef std::allocator_traits<_Allocator> __traits;
      __traits::construct(__alloc, __dest, std::move(*__orig));
      __traits::destroy(__alloc, std::addressof(*__orig));
    }
 
  // This class may be specialized for specific types.
  // Also known as is_trivially_relocatable.
  template<typename _Tp, typename = void>
    struct __is_bitwise_relocatable
    : __bool_constant<__is_trivial(_Tp)>
    { };
 
  template <typename _InputIterator, typename _ForwardIterator,
            typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __relocate_a_1(_InputIterator __first, _InputIterator __last,
                   _ForwardIterator __result, _Allocator& __alloc)
    noexcept(noexcept(std::__relocate_object_a(std::addressof(*__result),
                                               std::addressof(*__first),
                                               __alloc)))
    {
      typedef typename iterator_traits<_InputIterator>::value_type
        _ValueType;
      typedef typename iterator_traits<_ForwardIterator>::value_type
        _ValueType2;
      static_assert(std::is_same<_ValueType, _ValueType2>::value,
          "relocation is only possible for values of the same type");
      _ForwardIterator __cur = __result;
      for (; __first != __last; ++__first, (void)++__cur)
        std::__relocate_object_a(std::addressof(*__cur),
                                 std::addressof(*__first), __alloc);
      return __cur;
    }
 
#if _GLIBCXX_HOSTED
  template <typename _Tp, typename _Up>
    _GLIBCXX20_CONSTEXPR
    inline __enable_if_t<std::__is_bitwise_relocatable<_Tp>::value, _Tp*>
    __relocate_a_1(_Tp* __first, _Tp* __last,
                   _Tp* __result,
                   [[__maybe_unused__]] allocator<_Up>& __alloc) noexcept
    {
      ptrdiff_t __count = __last - __first;
      if (__count > 0)
        {
#ifdef __cpp_lib_is_constant_evaluated
          if (std::is_constant_evaluated())
            {
              // Can't use memcpy. Wrap the pointer so that __relocate_a_1
              // resolves to the non-trivial overload above.
              __gnu_cxx::__normal_iterator<_Tp*, void> __out(__result);
              __out = std::__relocate_a_1(__first, __last, __out, __alloc);
              return __out.base();
            }
#endif
          __builtin_memcpy(__result, __first, __count * sizeof(_Tp));
        }
      return __result + __count;
    }
#endif
 
  template <typename _InputIterator, typename _ForwardIterator,
            typename _Allocator>
    _GLIBCXX20_CONSTEXPR
    inline _ForwardIterator
    __relocate_a(_InputIterator __first, _InputIterator __last,
                 _ForwardIterator __result, _Allocator& __alloc)
    noexcept(noexcept(__relocate_a_1(std::__niter_base(__first),
                                     std::__niter_base(__last),
                                     std::__niter_base(__result), __alloc)))
    {
      return std::__relocate_a_1(std::__niter_base(__first),
                                 std::__niter_base(__last),
                                 std::__niter_base(__result), __alloc);
    }
 
  /// @endcond
#endif // C++11
 
  /// @} group memory
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
 
#endif /* _STL_UNINITIALIZED_H */