stl_bvector.h

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// vector<bool> specialization -*- 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) 1996-1999
 * 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_bvector.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{vector}
 */
 
#ifndef _STL_BVECTOR_H
#define _STL_BVECTOR_H 1
 
#ifndef _GLIBCXX_ALWAYS_INLINE
#define _GLIBCXX_ALWAYS_INLINE inline __attribute__((__always_inline__))
#endif
 
#if __cplusplus >= 201103L
#include <initializer_list>
#include <bits/functional_hash.h>
#endif
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  typedef unsigned long _Bit_type;
  enum { _S_word_bit = int(__CHAR_BIT__ * sizeof(_Bit_type)) };
 
  __attribute__((__nonnull__))
  _GLIBCXX20_CONSTEXPR
  void
  __fill_bvector_n(_Bit_type*, size_t, bool) _GLIBCXX_NOEXCEPT;
 
_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
  struct _Bit_reference
  {
  private:
    template<typename, typename> friend class vector;
    friend struct _Bit_iterator;
    friend struct _Bit_const_iterator;
 
    _GLIBCXX20_CONSTEXPR
    _Bit_reference() _GLIBCXX_NOEXCEPT : _M_p(0), _M_mask(0) { }
 
    _Bit_type * _M_p;
    _Bit_type _M_mask;
 
    _GLIBCXX20_CONSTEXPR
    _Bit_reference(_Bit_type * __x, _Bit_type __y)
    : _M_p(__x), _M_mask(__y) { }
 
  public:
#if __cplusplus >= 201103L
    _Bit_reference(const _Bit_reference&) = default;
#endif
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    operator bool() const _GLIBCXX_NOEXCEPT
    { return !!(*_M_p & _M_mask); }
 
    _GLIBCXX20_CONSTEXPR
    _Bit_reference&
    operator=(bool __x) _GLIBCXX_NOEXCEPT
    {
      if (__x)
        *_M_p |= _M_mask;
      else
        *_M_p &= ~_M_mask;
      return *this;
    }
 
#if __glibcxx_ranges_zip // >= C++23
    constexpr const _Bit_reference&
    operator=(bool __x) const noexcept
    {
      if (__x)
        *_M_p |= _M_mask;
      else
        *_M_p &= ~_M_mask;
      return *this;
    }
#endif // C++23
 
    _GLIBCXX20_CONSTEXPR
    _Bit_reference&
    operator=(const _Bit_reference& __x) _GLIBCXX_NOEXCEPT
    { return *this = bool(__x); }
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    bool
    operator==(const _Bit_reference& __x) const
    { return bool(*this) == bool(__x); }
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    bool
    operator<(const _Bit_reference& __x) const
    { return !bool(*this) && bool(__x); }
 
    _GLIBCXX20_CONSTEXPR
    void
    flip() _GLIBCXX_NOEXCEPT
    { *_M_p ^= _M_mask; }
 
#if __cplusplus >= 201103L
    // _GLIBCXX_RESOLVE_LIB_DEFECTS
    // 3638. vector<bool>::swap(reference, reference) is useless
 
    _GLIBCXX20_CONSTEXPR
    friend void
    swap(_Bit_reference __x, _Bit_reference __y) noexcept
    {
      bool __tmp = __x;
      __x = __y;
      __y = __tmp;
    }
 
    _GLIBCXX20_CONSTEXPR
    friend void
    swap(_Bit_reference __x, bool& __y) noexcept
    {
      bool __tmp = __x;
      __x = __y;
      __y = __tmp;
    }
 
    _GLIBCXX20_CONSTEXPR
    friend void
    swap(bool& __x, _Bit_reference __y) noexcept
    {
      bool __tmp = __x;
      __x = __y;
      __y = __tmp;
    }
#endif
  };
 
// Ignore warnings about std::iterator.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  struct _Bit_iterator_base
  : public std::iterator<std::random_access_iterator_tag, bool>
  {
    _Bit_type * _M_p;
    unsigned int _M_offset;
 
    _GLIBCXX20_CONSTEXPR _GLIBCXX_ALWAYS_INLINE
    void
    _M_assume_normalized() const
    {
#if __has_attribute(__assume__) && !defined(_GLIBCXX_CLANG)
      unsigned int __ofst = _M_offset;
      __attribute__ ((__assume__ (__ofst < unsigned(_S_word_bit))));
#endif
    }
 
    _GLIBCXX20_CONSTEXPR
    _Bit_iterator_base(_Bit_type * __x, unsigned int __y)
    : _M_p(__x), _M_offset(__y) { }
 
    _GLIBCXX20_CONSTEXPR
    void
    _M_bump_up()
    {
      _M_assume_normalized();
      if (_M_offset++ == int(_S_word_bit) - 1)
        {
          _M_offset = 0;
          ++_M_p;
        }
    }
 
    _GLIBCXX20_CONSTEXPR
    void
    _M_bump_down()
    {
      _M_assume_normalized();
      if (_M_offset-- == 0)
        {
          _M_offset = int(_S_word_bit) - 1;
          --_M_p;
        }
    }
 
    _GLIBCXX20_CONSTEXPR
    void
    _M_incr(ptrdiff_t __i)
    {
      _M_assume_normalized();
      difference_type __n = __i + _M_offset;
      _M_p += __n / int(_S_word_bit);
      __n = __n % int(_S_word_bit);
      if (__n < 0)
        {
          __n += int(_S_word_bit);
          --_M_p;
        }
      _M_offset = static_cast<unsigned int>(__n);
    }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR bool
    operator==(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    {
      __x._M_assume_normalized();
      __y._M_assume_normalized();
      return __x._M_p == __y._M_p && __x._M_offset == __y._M_offset;
    }
 
#if __cpp_lib_three_way_comparison
    [[nodiscard]]
    friend constexpr strong_ordering
    operator<=>(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    noexcept
    {
      __x._M_assume_normalized();
      __y._M_assume_normalized();
      if (const auto __cmp = __x._M_p <=> __y._M_p; __cmp != 0)
        return __cmp;
      return __x._M_offset <=> __y._M_offset;
    }
#else
    _GLIBCXX_NODISCARD
    friend bool
    operator<(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    {
      __x._M_assume_normalized();
      __y._M_assume_normalized();
      return __x._M_p < __y._M_p
            || (__x._M_p == __y._M_p && __x._M_offset < __y._M_offset);
    }
 
    _GLIBCXX_NODISCARD
    friend bool
    operator!=(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    { return !(__x == __y); }
 
    _GLIBCXX_NODISCARD
    friend bool
    operator>(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    { return __y < __x; }
 
    _GLIBCXX_NODISCARD
    friend bool
    operator<=(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    { return !(__y < __x); }
 
    _GLIBCXX_NODISCARD
    friend bool
    operator>=(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    { return !(__x < __y); }
#endif // three-way comparison
 
    friend _GLIBCXX20_CONSTEXPR ptrdiff_t
    operator-(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
    {
      __x._M_assume_normalized();
      __y._M_assume_normalized();
      return (int(_S_word_bit) * (__x._M_p - __y._M_p)
              + __x._M_offset - __y._M_offset);
    }
  };
#pragma GCC diagnostic pop
 
  struct _Bit_iterator : public _Bit_iterator_base
  {
    typedef _Bit_reference  reference;
#if __cplusplus > 201703L
    typedef void            pointer;
#else
    typedef _Bit_reference* pointer;
#endif
    typedef _Bit_iterator   iterator;
 
    _GLIBCXX20_CONSTEXPR
    _Bit_iterator() : _Bit_iterator_base(0, 0) { }
 
    _GLIBCXX20_CONSTEXPR
    _Bit_iterator(_Bit_type * __x, unsigned int __y)
    : _Bit_iterator_base(__x, __y) { }
 
    _GLIBCXX20_CONSTEXPR
    iterator
    _M_const_cast() const
    { return *this; }
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    reference
    operator*() const
    {
      _M_assume_normalized();
      return reference(_M_p, 1UL << _M_offset);
    }
 
    _GLIBCXX20_CONSTEXPR
    iterator&
    operator++()
    {
      _M_bump_up();
      return *this;
    }
 
    _GLIBCXX20_CONSTEXPR
    iterator
    operator++(int)
    {
      iterator __tmp = *this;
      _M_bump_up();
      return __tmp;
    }
 
    _GLIBCXX20_CONSTEXPR
    iterator&
    operator--()
    {
      _M_bump_down();
      return *this;
    }
 
    _GLIBCXX20_CONSTEXPR
    iterator
    operator--(int)
    {
      iterator __tmp = *this;
      _M_bump_down();
      return __tmp;
    }
 
    _GLIBCXX20_CONSTEXPR
    iterator&
    operator+=(difference_type __i)
    {
      _M_incr(__i);
      return *this;
    }
 
    _GLIBCXX20_CONSTEXPR
    iterator&
    operator-=(difference_type __i)
    {
      *this += -__i;
      return *this;
    }
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    reference
    operator[](difference_type __i) const
    { return *(*this + __i); }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR iterator
    operator+(const iterator& __x, difference_type __n)
    {
      iterator __tmp = __x;
      __tmp += __n;
      return __tmp;
    }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR iterator
    operator+(difference_type __n, const iterator& __x)
    { return __x + __n; }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR iterator
    operator-(const iterator& __x, difference_type __n)
    {
      iterator __tmp = __x;
      __tmp -= __n;
      return __tmp;
    }
  };
 
  struct _Bit_const_iterator : public _Bit_iterator_base
  {
    typedef bool                 reference;
    typedef bool                 const_reference;
#if __cplusplus > 201703L
    typedef void            pointer;
#else
    typedef const bool*          pointer;
#endif
    typedef _Bit_const_iterator  const_iterator;
 
    _GLIBCXX20_CONSTEXPR
    _Bit_const_iterator() : _Bit_iterator_base(0, 0) { }
 
    _GLIBCXX20_CONSTEXPR
    _Bit_const_iterator(_Bit_type * __x, unsigned int __y)
    : _Bit_iterator_base(__x, __y) { }
 
    _GLIBCXX20_CONSTEXPR
    _Bit_const_iterator(const _Bit_iterator& __x)
    : _Bit_iterator_base(__x._M_p, __x._M_offset) { }
 
    _GLIBCXX20_CONSTEXPR
    _Bit_iterator
    _M_const_cast() const
    { return _Bit_iterator(_M_p, _M_offset); }
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    const_reference
    operator*() const
    {
      _M_assume_normalized();
      return _Bit_reference(_M_p, 1UL << _M_offset);
    }
 
    _GLIBCXX20_CONSTEXPR
    const_iterator&
    operator++()
    {
      _M_bump_up();
      return *this;
    }
 
    _GLIBCXX20_CONSTEXPR
    const_iterator
    operator++(int)
    {
      const_iterator __tmp = *this;
      _M_bump_up();
      return __tmp;
    }
 
    _GLIBCXX20_CONSTEXPR
    const_iterator&
    operator--()
    {
      _M_bump_down();
      return *this;
    }
 
    _GLIBCXX20_CONSTEXPR
    const_iterator
    operator--(int)
    {
      const_iterator __tmp = *this;
      _M_bump_down();
      return __tmp;
    }
 
    _GLIBCXX20_CONSTEXPR
    const_iterator&
    operator+=(difference_type __i)
    {
      _M_incr(__i);
      return *this;
    }
 
    _GLIBCXX20_CONSTEXPR
    const_iterator&
    operator-=(difference_type __i)
    {
      *this += -__i;
      return *this;
    }
 
    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
    const_reference
    operator[](difference_type __i) const
    { return *(*this + __i); }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR const_iterator
    operator+(const const_iterator& __x, difference_type __n)
    {
      const_iterator __tmp = __x;
      __tmp += __n;
      return __tmp;
    }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR const_iterator
    operator-(const const_iterator& __x, difference_type __n)
    {
      const_iterator __tmp = __x;
      __tmp -= __n;
      return __tmp;
    }
 
    _GLIBCXX_NODISCARD
    friend _GLIBCXX20_CONSTEXPR const_iterator
    operator+(difference_type __n, const const_iterator& __x)
    { return __x + __n; }
  };
 
  template<typename _Alloc>
    struct _Bvector_base
    {
      typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template
        rebind<_Bit_type>::other _Bit_alloc_type;
      typedef typename __gnu_cxx::__alloc_traits<_Bit_alloc_type>
        _Bit_alloc_traits;
      typedef typename _Bit_alloc_traits::pointer _Bit_pointer;
 
      struct _Bvector_impl_data
      {
#if !_GLIBCXX_INLINE_VERSION
        _Bit_iterator   _M_start;
#else
        // We don't need the offset field for the start, it's always zero.
        struct {
          _Bit_type* _M_p;
          // Allow assignment from iterators (assume offset is zero):
          _GLIBCXX20_CONSTEXPR
          void operator=(_Bit_iterator __it) { _M_p = __it._M_p; }
        } _M_start;
#endif
        _Bit_iterator   _M_finish;
        _Bit_pointer    _M_end_of_storage;
 
        _GLIBCXX20_CONSTEXPR
        _Bvector_impl_data() _GLIBCXX_NOEXCEPT
        : _M_start(), _M_finish(), _M_end_of_storage()
        { }
 
#if __cplusplus >= 201103L
        _Bvector_impl_data(const _Bvector_impl_data&) = default;
 
        _Bvector_impl_data&
        operator=(const _Bvector_impl_data&) = default;
 
        _GLIBCXX20_CONSTEXPR
        _Bvector_impl_data(_Bvector_impl_data&& __x) noexcept
        : _Bvector_impl_data(__x)
        { __x._M_reset(); }
 
        _GLIBCXX20_CONSTEXPR
        void
        _M_move_data(_Bvector_impl_data&& __x) noexcept
        {
          *this = __x;
          __x._M_reset();
        }
#endif
 
        _GLIBCXX20_CONSTEXPR
        void
        _M_reset() _GLIBCXX_NOEXCEPT
        { *this = _Bvector_impl_data(); }
 
        _GLIBCXX20_CONSTEXPR
        void
        _M_swap_data(_Bvector_impl_data& __x) _GLIBCXX_NOEXCEPT
        {
          // Do not use std::swap(_M_start, __x._M_start), etc as it loses
          // information used by TBAA.
          std::swap(*this, __x);
        }
      };
 
      struct _Bvector_impl
        : public _Bit_alloc_type, public _Bvector_impl_data
      {
        _GLIBCXX20_CONSTEXPR
        _Bvector_impl() _GLIBCXX_NOEXCEPT_IF(
          is_nothrow_default_constructible<_Bit_alloc_type>::value)
#if __cpp_concepts && __glibcxx_type_trait_variable_templates
        requires is_default_constructible_v<_Bit_alloc_type>
#endif
        : _Bit_alloc_type()
        { }
 
        _GLIBCXX20_CONSTEXPR
        _Bvector_impl(const _Bit_alloc_type& __a) _GLIBCXX_NOEXCEPT
        : _Bit_alloc_type(__a)
        { }
 
#if __cplusplus >= 201103L
        // Not defaulted, to enforce noexcept(true) even when
        // !is_nothrow_move_constructible<_Bit_alloc_type>.
        _GLIBCXX20_CONSTEXPR
        _Bvector_impl(_Bvector_impl&& __x) noexcept
        : _Bit_alloc_type(std::move(__x)), _Bvector_impl_data(std::move(__x))
        { }
 
        _GLIBCXX20_CONSTEXPR
        _Bvector_impl(_Bit_alloc_type&& __a, _Bvector_impl&& __x) noexcept
        : _Bit_alloc_type(std::move(__a)), _Bvector_impl_data(std::move(__x))
        { }
#endif
 
        _GLIBCXX20_CONSTEXPR
        _Bit_type*
        _M_end_addr() const _GLIBCXX_NOEXCEPT
        {
          if (this->_M_end_of_storage)
            return std::__addressof(this->_M_end_of_storage[-1]) + 1;
          return 0;
        }
      };
 
    public:
      typedef _Alloc allocator_type;
 
      _GLIBCXX20_CONSTEXPR
      _Bit_alloc_type&
      _M_get_Bit_allocator() _GLIBCXX_NOEXCEPT
      { return this->_M_impl; }
 
      _GLIBCXX20_CONSTEXPR
      const _Bit_alloc_type&
      _M_get_Bit_allocator() const _GLIBCXX_NOEXCEPT
      { return this->_M_impl; }
 
      _GLIBCXX20_CONSTEXPR
      allocator_type
      get_allocator() const _GLIBCXX_NOEXCEPT
      { return allocator_type(_M_get_Bit_allocator()); }
 
#if __cplusplus >= 201103L
      _Bvector_base() = default;
#else
      _Bvector_base() { }
#endif
 
      _GLIBCXX20_CONSTEXPR
      _Bvector_base(const allocator_type& __a)
      : _M_impl(_Bit_alloc_type(__a)) { }
 
#if __cplusplus >= 201103L
      _Bvector_base(_Bvector_base&&) = default;
 
      _GLIBCXX20_CONSTEXPR
      _Bvector_base(_Bvector_base&& __x, const allocator_type& __a) noexcept
      : _M_impl(_Bit_alloc_type(__a), std::move(__x._M_impl))
      { }
#endif
 
      _GLIBCXX20_CONSTEXPR
      ~_Bvector_base()
      { this->_M_deallocate(); }
 
    protected:
      _Bvector_impl _M_impl;
 
      _GLIBCXX20_CONSTEXPR
      _Bit_pointer
      _M_allocate(size_t __n)
      {
        _Bit_pointer __p = _Bit_alloc_traits::allocate(_M_impl, _S_nword(__n));
#if __cpp_lib_is_constant_evaluated && __cpp_constexpr_dynamic_alloc
        if (std::is_constant_evaluated())
          {
            __n = _S_nword(__n);
            for (size_t __i = 0; __i < __n; ++__i)
              std::construct_at(std::to_address(__p) + __i);
          }
#endif
        return __p;
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_deallocate()
      {
        if (_M_impl._M_start._M_p)
          {
            const size_t __n = _M_impl._M_end_addr() - _M_impl._M_start._M_p;
            _Bit_alloc_traits::deallocate(_M_impl,
                                          _M_impl._M_end_of_storage - __n,
                                          __n);
            _M_impl._M_reset();
          }
      }
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      void
      _M_move_data(_Bvector_base&& __x) noexcept
      { _M_impl._M_move_data(std::move(__x._M_impl)); }
#endif
 
      _GLIBCXX_CONSTEXPR
      static size_t
      _S_nword(size_t __n)
      { return (__n + int(_S_word_bit) - 1) / int(_S_word_bit); }
    };
 
  /**
   *  @brief  A specialization of vector for booleans which offers fixed time
   *  access to individual elements in any order.
   *
   *  @ingroup sequences
   *  @headerfile vector
   *  @since C++98
   *
   *  @tparam _Alloc  Allocator type.
   *
   *  Note that vector<bool> does not actually meet the requirements for being
   *  a container.  This is because the reference and pointer types are not
   *  really references and pointers to bool.  See DR96 for details.  @see
   *  vector for function documentation.
   *
   *  In some terminology a %vector can be described as a dynamic
   *  C-style array, it offers fast and efficient access to individual
   *  elements in any order and saves the user from worrying about
   *  memory and size allocation.  Subscripting ( @c [] ) access is
   *  also provided as with C-style arrays.
  */
  template<typename _Alloc>
    class vector<bool, _Alloc> : protected _Bvector_base<_Alloc>
    {
      typedef _Bvector_base<_Alloc>                     _Base;
      typedef typename _Base::_Bit_pointer              _Bit_pointer;
      typedef typename _Base::_Bit_alloc_traits         _Bit_alloc_traits;
 
#if __cplusplus >= 201103L
      friend struct std::hash<vector>;
# if __cplusplus > 201703L // || defined __STRICT_ANSI__
      static_assert(is_same<typename _Alloc::value_type, bool>::value,
          "std::vector must have the same value_type as its allocator");
# endif
#endif
 
    public:
      typedef bool                                      value_type;
      typedef size_t                                    size_type;
      typedef ptrdiff_t                                 difference_type;
      typedef _Bit_reference                            reference;
      typedef bool                                      const_reference;
      typedef _Bit_reference*                           pointer;
      typedef const bool*                               const_pointer;
      typedef _Bit_iterator                             iterator;
      typedef _Bit_const_iterator                       const_iterator;
      typedef std::reverse_iterator<const_iterator>     const_reverse_iterator;
      typedef std::reverse_iterator<iterator>           reverse_iterator;
      typedef _Alloc                                    allocator_type;
 
      _GLIBCXX20_CONSTEXPR
      allocator_type
      get_allocator() const
      { return _Base::get_allocator(); }
 
    protected:
      using _Base::_M_allocate;
      using _Base::_M_deallocate;
      using _Base::_S_nword;
      using _Base::_M_get_Bit_allocator;
 
    public:
#if __cplusplus >= 201103L
      vector() = default;
#else
      vector() { }
#endif
 
      _GLIBCXX20_CONSTEXPR
      explicit
      vector(const allocator_type& __a) _GLIBCXX_NOEXCEPT
      : _Base(__a) { }
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      explicit
      vector(size_type __n, const allocator_type& __a = allocator_type())
      : vector(__n, false, __a)
      { }
 
      _GLIBCXX20_CONSTEXPR
      vector(size_type __n, const bool& __value,
             const allocator_type& __a = allocator_type())
#else
      explicit
      vector(size_type __n, const bool& __value = bool(),
             const allocator_type& __a = allocator_type())
#endif
      : _Base(__a)
      {
        _M_initialize(__n);
        _M_initialize_value(__value);
      }
 
      _GLIBCXX20_CONSTEXPR
      vector(const vector& __x)
      : _Base(_Bit_alloc_traits::_S_select_on_copy(__x._M_get_Bit_allocator()))
      {
        const_iterator __xbegin = __x.begin(), __xend = __x.end();
        _M_initialize(__x.size());
        _M_copy_aligned(__xbegin, __xend, begin());
      }
 
#if __cplusplus >= 201103L
      vector(vector&&) = default;
 
    private:
      _GLIBCXX20_CONSTEXPR
      vector(vector&& __x, const allocator_type& __a, true_type) noexcept
      : _Base(std::move(__x), __a)
      { }
 
      _GLIBCXX20_CONSTEXPR
      vector(vector&& __x, const allocator_type& __a, false_type)
      : _Base(__a)
      {
        if (__x.get_allocator() == __a)
          this->_M_move_data(std::move(__x));
        else
          {
            _M_initialize(__x.size());
            _M_copy_aligned(__x.begin(), __x.end(), begin());
            __x.clear();
          }
      }
 
    public:
      _GLIBCXX20_CONSTEXPR
      vector(vector&& __x, const __type_identity_t<allocator_type>& __a)
      noexcept(_Bit_alloc_traits::_S_always_equal())
      : vector(std::move(__x), __a,
               typename _Bit_alloc_traits::is_always_equal{})
      { }
 
      _GLIBCXX20_CONSTEXPR
      vector(const vector& __x, const __type_identity_t<allocator_type>& __a)
      : _Base(__a)
      {
        _M_initialize(__x.size());
        _M_copy_aligned(__x.begin(), __x.end(), begin());
      }
 
      _GLIBCXX20_CONSTEXPR
      vector(initializer_list<bool> __l,
             const allocator_type& __a = allocator_type())
      : _Base(__a)
      {
        _M_initialize_range(__l.begin(), __l.end(),
                            random_access_iterator_tag());
      }
#endif
 
#if __cplusplus >= 201103L
      template<typename _InputIterator,
               typename = std::_RequireInputIter<_InputIterator>>
        _GLIBCXX20_CONSTEXPR
        vector(_InputIterator __first, _InputIterator __last,
               const allocator_type& __a = allocator_type())
        : _Base(__a)
        {
          _M_initialize_range(__first, __last,
                              std::__iterator_category(__first));
        }
#else
      template<typename _InputIterator>
        vector(_InputIterator __first, _InputIterator __last,
               const allocator_type& __a = allocator_type())
        : _Base(__a)
        {
          // Check whether it's an integral type. If so, it's not an iterator.
          typedef typename std::__is_integer<_InputIterator>::__type _Integral;
          _M_initialize_dispatch(__first, __last, _Integral());
        }
#endif
 
#if __glibcxx_containers_ranges // C++ >= 23
      /**
       * @brief Construct a vector from a range.
       * @param __rg A range of values that are convertible to `value_type`.
       * @since C++23
       */
      template<__detail::__container_compatible_range<bool> _Rg>
        constexpr
        vector(from_range_t, _Rg&& __rg, const _Alloc& __a = _Alloc())
        : _Base(__a)
        {
          if constexpr (ranges::forward_range<_Rg> || ranges::sized_range<_Rg>)
            {
              _M_initialize(size_type(ranges::distance(__rg)));
              ranges::copy(__rg, begin());
            }
          else
            {
              auto __first = ranges::begin(__rg);
              const auto __last = ranges::end(__rg);
              for (; __first != __last; ++__first)
                emplace_back(*__first);
            }
        }
#endif
 
      _GLIBCXX20_CONSTEXPR
      ~vector() _GLIBCXX_NOEXCEPT { }
 
      _GLIBCXX20_CONSTEXPR
      vector&
      operator=(const vector& __x)
      {
        if (&__x == this)
          return *this;
#if __cplusplus >= 201103L
        if (_Bit_alloc_traits::_S_propagate_on_copy_assign())
          {
            if (this->_M_get_Bit_allocator() != __x._M_get_Bit_allocator())
              {
                this->_M_deallocate();
                std::__alloc_on_copy(_M_get_Bit_allocator(),
                                     __x._M_get_Bit_allocator());
                _M_initialize(__x.size());
              }
            else
              std::__alloc_on_copy(_M_get_Bit_allocator(),
                                   __x._M_get_Bit_allocator());
          }
#endif
        if (__x.size() > capacity())
          {
            this->_M_deallocate();
            _M_initialize(__x.size());
          }
        this->_M_impl._M_finish = _M_copy_aligned(__x.begin(), __x.end(),
                                                  begin());
        return *this;
      }
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      vector&
      operator=(vector&& __x) noexcept(_Bit_alloc_traits::_S_nothrow_move())
      {
        if (_Bit_alloc_traits::_S_propagate_on_move_assign()
            || this->_M_get_Bit_allocator() == __x._M_get_Bit_allocator())
          {
            this->_M_deallocate();
            this->_M_move_data(std::move(__x));
            std::__alloc_on_move(_M_get_Bit_allocator(),
                                 __x._M_get_Bit_allocator());
          }
        else
          {
            if (__x.size() > capacity())
              {
                this->_M_deallocate();
                _M_initialize(__x.size());
              }
            this->_M_impl._M_finish = _M_copy_aligned(__x.begin(), __x.end(),
                                                      begin());
            __x.clear();
          }
        return *this;
      }
 
      _GLIBCXX20_CONSTEXPR
      vector&
      operator=(initializer_list<bool> __l)
      {
        this->assign(__l.begin(), __l.end());
        return *this;
      }
#endif
 
      // assign(), a generalized assignment member function.  Two
      // versions: one that takes a count, and one that takes a range.
      // The range version is a member template, so we dispatch on whether
      // or not the type is an integer.
      _GLIBCXX20_CONSTEXPR
      void
      assign(size_type __n, const bool& __x)
      { _M_fill_assign(__n, __x); }
 
#if __cplusplus >= 201103L
      template<typename _InputIterator,
               typename = std::_RequireInputIter<_InputIterator>>
        _GLIBCXX20_CONSTEXPR
        void
        assign(_InputIterator __first, _InputIterator __last)
        { _M_assign_aux(__first, __last, std::__iterator_category(__first)); }
#else
      template<typename _InputIterator>
        void
        assign(_InputIterator __first, _InputIterator __last)
        {
          // Check whether it's an integral type. If so, it's not an iterator.
          typedef typename std::__is_integer<_InputIterator>::__type _Integral;
          _M_assign_dispatch(__first, __last, _Integral());
        }
#endif
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      void
      assign(initializer_list<bool> __l)
      { _M_assign_aux(__l.begin(), __l.end(), random_access_iterator_tag()); }
#endif
 
#if __glibcxx_containers_ranges // C++ >= 23
      /**
       * @brief Assign a range to the vector.
       * @param __rg A range of values that are convertible to `value_type`.
       * @pre `__rg` and `*this` do not overlap.
       * @since C++23
       */
      template<__detail::__container_compatible_range<bool> _Rg>
        constexpr void
        assign_range(_Rg&& __rg)
        {
          static_assert(assignable_from<bool&, ranges::range_reference_t<_Rg>>);
          if constexpr (ranges::forward_range<_Rg> || ranges::sized_range<_Rg>)
            {
              if (auto __n = size_type(ranges::distance(__rg)))
                {
                  reserve(__n);
                  this->_M_impl._M_finish
                      = ranges::copy(std::forward<_Rg>(__rg), begin()).out;
                }
              else
                clear();
            }
          else
            {
              clear();
              auto __first = ranges::begin(__rg);
              const auto __last = ranges::end(__rg);
              for (; __first != __last; ++__first)
                emplace_back(*__first);
            }
        }
#endif
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      iterator
      begin() _GLIBCXX_NOEXCEPT
      { return iterator(this->_M_impl._M_start._M_p, 0); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_iterator
      begin() const _GLIBCXX_NOEXCEPT
      { return const_iterator(this->_M_impl._M_start._M_p, 0); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      iterator
      end() _GLIBCXX_NOEXCEPT
      { return this->_M_impl._M_finish; }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_iterator
      end() const _GLIBCXX_NOEXCEPT
      { return this->_M_impl._M_finish; }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      reverse_iterator
      rbegin() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(end()); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_reverse_iterator
      rbegin() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(end()); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      reverse_iterator
      rend() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(begin()); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_reverse_iterator
      rend() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(begin()); }
 
#if __cplusplus >= 201103L
      [[__nodiscard__]] _GLIBCXX20_CONSTEXPR
      const_iterator
      cbegin() const noexcept
      { return const_iterator(this->_M_impl._M_start._M_p, 0); }
 
      [[__nodiscard__]] _GLIBCXX20_CONSTEXPR
      const_iterator
      cend() const noexcept
      { return this->_M_impl._M_finish; }
 
      [[__nodiscard__]] _GLIBCXX20_CONSTEXPR
      const_reverse_iterator
      crbegin() const noexcept
      { return const_reverse_iterator(end()); }
 
      [[__nodiscard__]] _GLIBCXX20_CONSTEXPR
      const_reverse_iterator
      crend() const noexcept
      { return const_reverse_iterator(begin()); }
#endif
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      size_type
      size() const _GLIBCXX_NOEXCEPT
      { return size_type(end() - begin()); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      size_type
      max_size() const _GLIBCXX_NOEXCEPT
      {
        const size_type __isize =
          __gnu_cxx::__numeric_traits<difference_type>::__max
          - int(_S_word_bit) + 1;
        const size_type __asize
          = _Bit_alloc_traits::max_size(_M_get_Bit_allocator());
        return (__asize <= __isize / int(_S_word_bit)
                ? __asize * int(_S_word_bit) : __isize);
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      size_type
      capacity() const _GLIBCXX_NOEXCEPT
      { return size_type(const_iterator(this->_M_impl._M_end_addr(), 0)
                         - begin()); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      bool
      empty() const _GLIBCXX_NOEXCEPT
      { return begin() == end(); }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      reference
      operator[](size_type __n)
      {
        __glibcxx_requires_subscript(__n);
        return _Bit_reference (this->_M_impl._M_start._M_p
                               + __n / int(_S_word_bit),
                               1UL << __n % int(_S_word_bit));
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_reference
      operator[](size_type __n) const
      {
        __glibcxx_requires_subscript(__n);
        return _Bit_reference (this->_M_impl._M_start._M_p
                               + __n / int(_S_word_bit),
                               1UL << __n % int(_S_word_bit));
      }
 
    protected:
      _GLIBCXX20_CONSTEXPR
      void
      _M_range_check(size_type __n) const
      {
        if (__n >= this->size())
          __throw_out_of_range_fmt(__N("vector<bool>::_M_range_check: __n "
                                       "(which is %zu) >= this->size() "
                                       "(which is %zu)"),
                                   __n, this->size());
      }
 
    public:
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      reference
      at(size_type __n)
      {
        _M_range_check(__n);
        return (*this)[__n];
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_reference
      at(size_type __n) const
      {
        _M_range_check(__n);
        return (*this)[__n];
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      reserve(size_type __n)
      {
        if (__n > max_size())
          __throw_length_error(__N("vector::reserve"));
        if (capacity() < __n)
          _M_reallocate(__n);
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      reference
      front()
      {
        __glibcxx_requires_nonempty();
        return *begin();
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_reference
      front() const
      {
        __glibcxx_requires_nonempty();
        return *begin();
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      reference
      back()
      {
        __glibcxx_requires_nonempty();
        return *(end() - 1);
      }
 
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
      const_reference
      back() const
      {
        __glibcxx_requires_nonempty();
        return *(end() - 1);
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      push_back(bool __x)
      {
        if (this->_M_impl._M_finish._M_p != this->_M_impl._M_end_addr())
          *this->_M_impl._M_finish++ = __x;
        else
          _M_insert_aux(end(), __x);
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      swap(vector& __x) _GLIBCXX_NOEXCEPT
      {
#if __cplusplus >= 201103L
        __glibcxx_assert(_Bit_alloc_traits::propagate_on_container_swap::value
                         || _M_get_Bit_allocator() == __x._M_get_Bit_allocator());
#endif
        this->_M_impl._M_swap_data(__x._M_impl);
        _Bit_alloc_traits::_S_on_swap(_M_get_Bit_allocator(),
                                      __x._M_get_Bit_allocator());
      }
 
      // [23.2.5]/1, third-to-last entry in synopsis listing
      _GLIBCXX26_DEPRECATED_SUGGEST("swap' invoked via ADL or 'std::ranges::swap")
      _GLIBCXX20_CONSTEXPR
      static void
      swap(reference __x, reference __y) _GLIBCXX_NOEXCEPT
      {
        bool __tmp = __x;
        __x = __y;
        __y = __tmp;
      }
 
      _GLIBCXX20_CONSTEXPR
      iterator
#if __cplusplus >= 201103L
      insert(const_iterator __position, const bool& __x)
#else
      insert(iterator __position, const bool& __x)
#endif
      {
        const difference_type __n = __position - begin();
        if (this->_M_impl._M_finish._M_p != this->_M_impl._M_end_addr()
            && __position == end())
          *this->_M_impl._M_finish++ = __x;
        else
          _M_insert_aux(__position._M_const_cast(), __x);
        return begin() + __n;
      }
 
#if _GLIBCXX_USE_DEPRECATED
      _GLIBCXX_DEPRECATED_SUGGEST("insert(position, false)")
      iterator
      insert(const_iterator __position)
      { return this->insert(__position._M_const_cast(), false); }
#endif
 
#if __cplusplus >= 201103L
      template<typename _InputIterator,
               typename = std::_RequireInputIter<_InputIterator>>
        _GLIBCXX20_CONSTEXPR
        iterator
        insert(const_iterator __position,
               _InputIterator __first, _InputIterator __last)
        {
          difference_type __offset = __position - cbegin();
          _M_insert_range(__position._M_const_cast(),
                          __first, __last,
                          std::__iterator_category(__first));
          return begin() + __offset;
        }
#else
      template<typename _InputIterator>
        void
        insert(iterator __position,
               _InputIterator __first, _InputIterator __last)
        {
          // Check whether it's an integral type. If so, it's not an iterator.
          typedef typename std::__is_integer<_InputIterator>::__type _Integral;
          _M_insert_dispatch(__position, __first, __last, _Integral());
        }
#endif
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      iterator
      insert(const_iterator __position, size_type __n, const bool& __x)
      {
        difference_type __offset = __position - cbegin();
        _M_fill_insert(__position._M_const_cast(), __n, __x);
        return begin() + __offset;
      }
#else
      void
      insert(iterator __position, size_type __n, const bool& __x)
      { _M_fill_insert(__position, __n, __x); }
#endif
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      iterator
      insert(const_iterator __p, initializer_list<bool> __l)
      { return this->insert(__p, __l.begin(), __l.end()); }
#endif
 
#if __glibcxx_containers_ranges // C++ >= 23
      /**
       * @brief Insert a range into the vector.
       * @param __rg A range of values that are convertible to `bool`.
       * @return An iterator that points to the first new element inserted,
       *         or to `__pos` if `__rg` is an empty range.
       * @pre `__rg` and `*this` do not overlap.
       * @since C++23
       */
      template<__detail::__container_compatible_range<bool> _Rg>
        constexpr iterator
        insert_range(const_iterator __pos, _Rg&& __rg)
        {
          if constexpr (ranges::forward_range<_Rg> || ranges::sized_range<_Rg>)
            {
              if (auto __n = size_type(ranges::distance(__rg)))
                {
                  if (capacity() - size() >= __n)
                    {
                      std::copy_backward(__pos._M_const_cast(), end(),
                                         this->_M_impl._M_finish
                                           + difference_type(__n));
                      ranges::copy(__rg, __pos._M_const_cast());
                      this->_M_impl._M_finish += difference_type(__n);
                      return __pos._M_const_cast();
                    }
                  else
                    {
                      const size_type __len =
                        _M_check_len(__n, "vector<bool>::insert_range");
                      const iterator __begin = begin(), __end = end();
                      _Bit_pointer __q = this->_M_allocate(__len);
                      iterator __start(std::__addressof(*__q), 0);
                      iterator __i = _M_copy_aligned(__begin,
                                                     __pos._M_const_cast(),
                                                     __start);
                      iterator __j = ranges::copy(__rg, __i).out;
                      iterator __finish = std::copy(__pos._M_const_cast(),
                                                    __end, __j);
                      this->_M_deallocate();
                      this->_M_impl._M_end_of_storage = __q + _S_nword(__len);
                      this->_M_impl._M_start = __start;
                      this->_M_impl._M_finish = __finish;
                      return __i;
                    }
                }
              else
                return __pos._M_const_cast();
            }
          else
            return insert_range(__pos,
                                vector(from_range, __rg, get_allocator()));
        }
 
      /**
       * @brief Append a range at the end of the vector.
       * @since C++23
       */
      template<__detail::__container_compatible_range<bool> _Rg>
        constexpr void
        append_range(_Rg&& __rg)
        {
          // N.B. __rg may overlap with *this, so we must copy from __rg before
          // existing elements or iterators referring to *this are invalidated.
          // e.g. in v.append_range(views::concat(v, foo)) rg overlaps v.
          if constexpr (ranges::forward_range<_Rg> || ranges::sized_range<_Rg>)
            {
              const auto __n = size_type(ranges::distance(__rg));
 
              // If there is no existing storage, there are no iterators that
              // can be referring to our storage, so it's safe to allocate now.
              if (capacity() == 0)
                reserve(__n);
 
              const auto __sz = size();
              const auto __capacity = capacity();
              if ((__capacity - __sz) >= __n)
                {
                  this->_M_impl._M_finish
                      = ranges::copy(std::forward<_Rg>(__rg), end()).out;
                  return;
                }
 
              vector __tmp(get_allocator());
              __tmp.reserve(_M_check_len(__n, "vector::append_range"));
              __tmp._M_impl._M_finish
                   = _M_copy_aligned(cbegin(), cend(), __tmp.begin());
              __tmp._M_impl._M_finish
                   = ranges::copy(std::forward<_Rg>(__rg), __tmp.end()).out;
              swap(__tmp);
            }
          else
            {
              auto __first = ranges::begin(__rg);
              const auto __last = ranges::end(__rg);
 
              // Fill up to the end of current capacity.
              for (auto __free = capacity() - size();
                   __first != __last && __free > 0;
                   ++__first, (void) --__free)
                emplace_back(*__first);
 
              if (__first == __last)
                return;
 
              // Copy the rest of the range to a new vector.
              ranges::subrange __rest(std::move(__first), __last);
              vector __tmp(from_range, __rest, get_allocator());
              insert(end(), __tmp.begin(), __tmp.end());
            }
        }
#endif // containers_ranges
 
      _GLIBCXX20_CONSTEXPR
      void
      pop_back()
      { --this->_M_impl._M_finish; }
 
      _GLIBCXX20_CONSTEXPR
      iterator
#if __cplusplus >= 201103L
      erase(const_iterator __position)
#else
      erase(iterator __position)
#endif
      { return _M_erase(__position._M_const_cast()); }
 
      _GLIBCXX20_CONSTEXPR
      iterator
#if __cplusplus >= 201103L
      erase(const_iterator __first, const_iterator __last)
#else
      erase(iterator __first, iterator __last)
#endif
      { return _M_erase(__first._M_const_cast(), __last._M_const_cast()); }
 
      _GLIBCXX20_CONSTEXPR
      void
      resize(size_type __new_size, bool __x = bool())
      {
        if (__new_size < size())
          _M_erase_at_end(begin() + difference_type(__new_size));
        else
          insert(end(), __new_size - size(), __x);
      }
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      void
      shrink_to_fit()
      { _M_shrink_to_fit(); }
#endif
 
      _GLIBCXX20_CONSTEXPR
      void
      flip() _GLIBCXX_NOEXCEPT
      {
        _Bit_type * const __end = this->_M_impl._M_end_addr();
        for (_Bit_type * __p = this->_M_impl._M_start._M_p; __p != __end; ++__p)
          *__p = ~*__p;
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      clear() _GLIBCXX_NOEXCEPT
      { _M_erase_at_end(begin()); }
 
#if __cplusplus >= 201103L
      template<typename... _Args>
#if __cplusplus > 201402L
        _GLIBCXX20_CONSTEXPR
        reference
#else
        void
#endif
        emplace_back(_Args&&... __args)
        {
          push_back(bool(std::forward<_Args>(__args)...));
#if __cplusplus > 201402L
          return back();
#endif
        }
 
      template<typename... _Args>
        _GLIBCXX20_CONSTEXPR
        iterator
        emplace(const_iterator __pos, _Args&&... __args)
        { return insert(__pos, bool(std::forward<_Args>(__args)...)); }
#endif
 
    protected:
      // Precondition: __first._M_offset == 0 && __result._M_offset == 0.
      _GLIBCXX20_CONSTEXPR
      iterator
      _M_copy_aligned(const_iterator __first, const_iterator __last,
                      iterator __result)
      {
        _Bit_type* __q = std::copy(__first._M_p, __last._M_p, __result._M_p);
        return std::copy(const_iterator(__last._M_p, 0), __last,
                         iterator(__q, 0));
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_initialize(size_type __n)
      {
        if (__n)
          {
            _Bit_pointer __q = this->_M_allocate(__n);
            this->_M_impl._M_end_of_storage = __q + _S_nword(__n);
            iterator __start = iterator(std::__addressof(*__q), 0);
            this->_M_impl._M_start = __start;
            this->_M_impl._M_finish = __start + difference_type(__n);
          }
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_initialize_value(bool __x) _GLIBCXX_NOEXCEPT
      {
        if (_Bit_type* __p = this->_M_impl._M_start._M_p)
          __fill_bvector_n(__p, this->_M_impl._M_end_addr() - __p, __x);
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_reallocate(size_type __n);
 
#if __cplusplus >= 201103L
      _GLIBCXX20_CONSTEXPR
      bool
      _M_shrink_to_fit();
#endif
 
#if __cplusplus < 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<typename _Integer>
        void
        _M_initialize_dispatch(_Integer __n, _Integer __x, __true_type)
        {
          _M_initialize(static_cast<size_type>(__n));
          _M_initialize_value(__x);
        }
 
      template<typename _InputIterator>
        void
        _M_initialize_dispatch(_InputIterator __first, _InputIterator __last,
                               __false_type)
        { _M_initialize_range(__first, __last,
                              std::__iterator_category(__first)); }
#endif
 
      template<typename _InputIterator>
        _GLIBCXX20_CONSTEXPR
        void
        _M_initialize_range(_InputIterator __first, _InputIterator __last,
                            std::input_iterator_tag)
        {
          for (; __first != __last; ++__first)
            push_back(*__first);
        }
 
      template<typename _ForwardIterator>
        _GLIBCXX20_CONSTEXPR
        void
        _M_initialize_range(_ForwardIterator __first, _ForwardIterator __last,
                            std::forward_iterator_tag)
        {
          const size_type __n = std::distance(__first, __last);
          _M_initialize(__n);
          std::copy(__first, __last, begin());
        }
 
#if __cplusplus < 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<typename _Integer>
        void
        _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
        { _M_fill_assign(__n, __val); }
 
      template<class _InputIterator>
        void
        _M_assign_dispatch(_InputIterator __first, _InputIterator __last,
                           __false_type)
        { _M_assign_aux(__first, __last, std::__iterator_category(__first)); }
#endif
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_fill_assign(size_t __n, bool __x)
      {
        if (__n > size())
          {
            _M_initialize_value(__x);
            insert(end(), __n - size(), __x);
          }
        else
          {
            _M_erase_at_end(begin() + __n);
            _M_initialize_value(__x);
          }
      }
 
      template<typename _InputIterator>
        _GLIBCXX20_CONSTEXPR
        void
        _M_assign_aux(_InputIterator __first, _InputIterator __last,
                      std::input_iterator_tag)
        {
          iterator __cur = begin();
          for (; __first != __last && __cur != end(); ++__cur, (void)++__first)
            *__cur = *__first;
          if (__first == __last)
            _M_erase_at_end(__cur);
          else
            insert(end(), __first, __last);
        }
 
      template<typename _ForwardIterator>
        _GLIBCXX20_CONSTEXPR
        void
        _M_assign_aux(_ForwardIterator __first, _ForwardIterator __last,
                      std::forward_iterator_tag)
        {
          const size_type __len = std::distance(__first, __last);
          if (__len < size())
            _M_erase_at_end(std::copy(__first, __last, begin()));
          else
            {
              _ForwardIterator __mid = __first;
              std::advance(__mid, size());
              std::copy(__first, __mid, begin());
              insert(end(), __mid, __last);
            }
        }
 
#if __cplusplus < 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<typename _Integer>
        void
        _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x,
                           __true_type)
        { _M_fill_insert(__pos, __n, __x); }
 
      template<typename _InputIterator>
        void
        _M_insert_dispatch(iterator __pos,
                           _InputIterator __first, _InputIterator __last,
                           __false_type)
        { _M_insert_range(__pos, __first, __last,
                          std::__iterator_category(__first)); }
#endif
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_fill_insert(iterator __position, size_type __n, bool __x);
 
      template<typename _InputIterator>
        _GLIBCXX20_CONSTEXPR
        void
        _M_insert_range(iterator __pos, _InputIterator __first,
                        _InputIterator __last, std::input_iterator_tag)
        {
          for (; __first != __last; ++__first)
            {
              __pos = insert(__pos, *__first);
              ++__pos;
            }
        }
 
      template<typename _ForwardIterator>
        _GLIBCXX20_CONSTEXPR
        void
        _M_insert_range(iterator __position, _ForwardIterator __first,
                        _ForwardIterator __last, std::forward_iterator_tag);
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_insert_aux(iterator __position, bool __x);
 
      _GLIBCXX20_CONSTEXPR
      size_type
      _M_check_len(size_type __n, const char* __s) const
      {
        if (max_size() - size() < __n)
          __throw_length_error(__N(__s));
 
        const size_type __len = size() + std::max(size(), __n);
        return (__len < size() || __len > max_size()) ? max_size() : __len;
      }
 
      _GLIBCXX20_CONSTEXPR
      void
      _M_erase_at_end(iterator __pos)
      { this->_M_impl._M_finish = __pos; }
 
      _GLIBCXX20_CONSTEXPR
      iterator
      _M_erase(iterator __pos);
 
      _GLIBCXX20_CONSTEXPR
      iterator
      _M_erase(iterator __first, iterator __last);
 
    protected:
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // DR 464. Suggestion for new member functions in standard containers.
      // N.B. DR 464 says nothing about vector<bool> but we need something
      // here due to the using-declaration in __gnu_debug::vector.
      // vector class.
#if __cplusplus >= 201103L
      void data() = delete;
#else
      void data() { }
#endif
    };
 
_GLIBCXX_END_NAMESPACE_CONTAINER
 
  // Fill a partial word.
  _GLIBCXX20_CONSTEXPR
  inline void
  __fill_bvector(_Bit_type* __v, unsigned int __first, unsigned int __last,
                 bool __x) _GLIBCXX_NOEXCEPT
  {
    const _Bit_type __fmask = ~0ul << __first;
    const _Bit_type __lmask = ~0ul >> (_S_word_bit - __last);
    const _Bit_type __mask = __fmask & __lmask;
 
    if (__x)
      *__v |= __mask;
    else
      *__v &= ~__mask;
  }
 
  // Fill N full words, as if using memset, but usable in constant expressions.
  __attribute__((__nonnull__))
  _GLIBCXX20_CONSTEXPR
  inline void
  __fill_bvector_n(_Bit_type* __p, size_t __n, bool __x) _GLIBCXX_NOEXCEPT
  {
#if __cpp_lib_is_constant_evaluated
    if (std::is_constant_evaluated())
    {
      for (size_t __i = 0; __i < __n; ++__i)
        __p[__i] = __x ? ~0ul : 0ul;
      return;
    }
#endif
    __builtin_memset(__p, __x ? ~0 : 0, __n * sizeof(_Bit_type));
  }
 
 
  _GLIBCXX20_CONSTEXPR
  inline void
  __fill_a1(_GLIBCXX_STD_C::_Bit_iterator __first,
            _GLIBCXX_STD_C::_Bit_iterator __last, const bool& __x)
  {
    if (__first._M_p != __last._M_p)
      {
        _Bit_type* __first_p = __first._M_p;
        if (__first._M_offset != 0)
          __fill_bvector(__first_p++, __first._M_offset, _S_word_bit, __x);
 
        __fill_bvector_n(__first_p, __last._M_p - __first_p, __x);
 
        if (__last._M_offset != 0)
          __fill_bvector(__last._M_p, 0, __last._M_offset, __x);
      }
    else if (__first._M_offset != __last._M_offset)
      __fill_bvector(__first._M_p, __first._M_offset, __last._M_offset, __x);
  }
 
#if __cplusplus >= 201103L
  // DR 1182.
  /// std::hash specialization for vector<bool>.
  template<typename _Alloc>
    struct hash<_GLIBCXX_STD_C::vector<bool, _Alloc>>
    : public __hash_base<size_t, _GLIBCXX_STD_C::vector<bool, _Alloc>>
    {
      size_t
      operator()(const _GLIBCXX_STD_C::vector<bool, _Alloc>&) const noexcept;
    };
#endif // C++11
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
 
#endif