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[EDIT] FILE: safe_iterator.h

// Safe iterator implementation  -*- C++ -*-

// Copyright (C) 2003-2018 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/>.

/** @file debug/safe_iterator.h
 *  This file is a GNU debug extension to the Standard C++ Library.
 */

#ifndef _GLIBCXX_DEBUG_SAFE_ITERATOR_H
#define _GLIBCXX_DEBUG_SAFE_ITERATOR_H 1

#include <debug/assertions.h>
#include <debug/macros.h>
#include <debug/functions.h>
#include <debug/safe_base.h>
#include <bits/stl_pair.h>
#include <ext/type_traits.h>

namespace __gnu_debug
{
  /** Helper struct to deal with sequence offering a before_begin
   *  iterator.
   **/
  template<typename _Sequence>
    struct _BeforeBeginHelper
    {
      template<typename _Iterator>
	static bool
	_S_Is(const _Safe_iterator<_Iterator, _Sequence>&)
	{ return false; }

template<typename _Iterator>
	static bool
	_S_Is_Beginnest(const _Safe_iterator<_Iterator, _Sequence>& __it)
	{ return __it.base() == __it._M_get_sequence()->_M_base().begin(); }
    };

/** Sequence traits giving the size of a container if possible. */
  template<typename _Sequence>
    struct _Sequence_traits
    {
      typedef _Distance_traits<typename _Sequence::iterator> _DistTraits;

static typename _DistTraits::__type
      _S_size(const _Sequence& __seq)
      { return std::make_pair(__seq.size(), __dp_exact); }
    };

/** \brief Safe iterator wrapper.
   *
   *  The class template %_Safe_iterator is a wrapper around an
   *  iterator that tracks the iterator's movement among sequences and
   *  checks that operations performed on the "safe" iterator are
   *  legal. In additional to the basic iterator operations (which are
   *  validated, and then passed to the underlying iterator),
   *  %_Safe_iterator has member functions for iterator invalidation,
   *  attaching/detaching the iterator from sequences, and querying
   *  the iterator's state.
   *
   *  Note that _Iterator must be the first base class so that it gets
   *  initialized before the iterator is being attached to the container's list
   *  of iterators and it is being detached before _Iterator get
   *  destroyed. Otherwise it would result in a data race.
   */
  template<typename _Iterator, typename _Sequence>
    class _Safe_iterator
    : private _Iterator,
      public _Safe_iterator_base
    {
      typedef _Iterator _Iter_base;
      typedef _Safe_iterator_base _Safe_base;
      typedef typename _Sequence::const_iterator _Const_iterator;

/// Determine if this is a constant iterator.
      bool
      _M_constant() const
      { return std::__are_same<_Const_iterator, _Safe_iterator>::__value; }

typedef std::iterator_traits<_Iterator> _Traits;

struct _Attach_single
      { };

_Safe_iterator(const _Iterator& __i, _Safe_sequence_base* __seq,
		     _Attach_single)
      _GLIBCXX_NOEXCEPT
      : _Iter_base(__i)
      { _M_attach_single(__seq); }

public:
      typedef _Iterator					iterator_type;
      typedef typename _Traits::iterator_category	iterator_category;
      typedef typename _Traits::value_type		value_type;
      typedef typename _Traits::difference_type		difference_type;
      typedef typename _Traits::reference		reference;
      typedef typename _Traits::pointer			pointer;

/// @post the iterator is singular and unattached
      _Safe_iterator() _GLIBCXX_NOEXCEPT : _Iter_base() { }

/**
       * @brief Safe iterator construction from an unsafe iterator and
       * its sequence.
       *
       * @pre @p seq is not NULL
       * @post this is not singular
       */
      _Safe_iterator(const _Iterator& __i, const _Safe_sequence_base* __seq)
      _GLIBCXX_NOEXCEPT
      : _Iter_base(__i), _Safe_base(__seq, _M_constant())
      {
	_GLIBCXX_DEBUG_VERIFY(!this->_M_singular(),
			      _M_message(__msg_init_singular)
			      ._M_iterator(*this, "this"));
      }

/**
       * @brief Copy construction.
       */
      _Safe_iterator(const _Safe_iterator& __x) _GLIBCXX_NOEXCEPT
      : _Iter_base(__x.base())
      {
	// _GLIBCXX_RESOLVE_LIB_DEFECTS
	// DR 408. Is vector<reverse_iterator<char*> > forbidden?
	_GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
			      || __x.base() == _Iterator(),
			      _M_message(__msg_init_copy_singular)
			      ._M_iterator(*this, "this")
			      ._M_iterator(__x, "other"));
	_M_attach(__x._M_sequence);
      }

#if __cplusplus >= 201103L
      /**
       * @brief Move construction.
       * @post __x is singular and unattached
       */
      _Safe_iterator(_Safe_iterator&& __x) noexcept
      : _Iter_base()
      {
	_GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
			      || __x.base() == _Iterator(),
			      _M_message(__msg_init_copy_singular)
			      ._M_iterator(*this, "this")
			      ._M_iterator(__x, "other"));
	_Safe_sequence_base* __seq = __x._M_sequence;
	__x._M_detach();
	std::swap(base(), __x.base());
	_M_attach(__seq);
      }
#endif

/**
       *  @brief Converting constructor from a mutable iterator to a
       *  constant iterator.
      */
      template<typename _MutableIterator>
	_Safe_iterator(
	  const _Safe_iterator<_MutableIterator,
	  typename __gnu_cxx::__enable_if<(std::__are_same<_MutableIterator,
		      typename _Sequence::iterator::iterator_type>::__value),
		   _Sequence>::__type>& __x) _GLIBCXX_NOEXCEPT
	: _Iter_base(__x.base())
	{
	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
	  // DR 408. Is vector<reverse_iterator<char*> > forbidden?
	  _GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
				|| __x.base() == _Iterator(),
				_M_message(__msg_init_const_singular)
				._M_iterator(*this, "this")
				._M_iterator(__x, "other"));
	  _M_attach(__x._M_sequence);
	}

/**
       * @brief Copy assignment.
       */
      _Safe_iterator&
      operator=(const _Safe_iterator& __x) _GLIBCXX_NOEXCEPT
      {
	// _GLIBCXX_RESOLVE_LIB_DEFECTS
	// DR 408. Is vector<reverse_iterator<char*> > forbidden?
	_GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
			      || __x.base() == _Iterator(),
			      _M_message(__msg_copy_singular)
			      ._M_iterator(*this, "this")
			      ._M_iterator(__x, "other"));

if (this->_M_sequence && this->_M_sequence == __x._M_sequence)
	  {
	    __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	    base() = __x.base();
	    _M_version = __x._M_sequence->_M_version;
	  }
	else
	  {
	    _M_detach();
	    base() = __x.base();
	    _M_attach(__x._M_sequence);
	  }

return *this;
      }

#if __cplusplus >= 201103L
      /**
       * @brief Move assignment.
       * @post __x is singular and unattached
       */
      _Safe_iterator&
      operator=(_Safe_iterator&& __x) noexcept
      {
	_GLIBCXX_DEBUG_VERIFY(this != &__x,
			      _M_message(__msg_self_move_assign)
			      ._M_iterator(*this, "this"));
	_GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
			      || __x.base() == _Iterator(),
			      _M_message(__msg_copy_singular)
			      ._M_iterator(*this, "this")
			      ._M_iterator(__x, "other"));

__x._M_detach();
	__x.base() = _Iterator();
	return *this;
      }
#endif

/**
       *  @brief Iterator dereference.
       *  @pre iterator is dereferenceable
       */
      reference
      operator*() const _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_dereferenceable(),
			      _M_message(__msg_bad_deref)
			      ._M_iterator(*this, "this"));
	return *base();
      }

/**
       *  @brief Iterator dereference.
       *  @pre iterator is dereferenceable
       */
      pointer
      operator->() const _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_dereferenceable(),
			      _M_message(__msg_bad_deref)
			      ._M_iterator(*this, "this"));
	return base().operator->();
      }

// ------ Input iterator requirements ------
      /**
       *  @brief Iterator preincrement
       *  @pre iterator is incrementable
       */
      _Safe_iterator&
      operator++() _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
			      _M_message(__msg_bad_inc)
			      ._M_iterator(*this, "this"));
	__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	++base();
	return *this;
      }

/**
       *  @brief Iterator postincrement
       *  @pre iterator is incrementable
       */
      _Safe_iterator
      operator++(int) _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
			      _M_message(__msg_bad_inc)
			      ._M_iterator(*this, "this"));
	__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	return _Safe_iterator(base()++, this->_M_sequence, _Attach_single());
      }

// ------ Bidirectional iterator requirements ------
      /**
       *  @brief Iterator predecrement
       *  @pre iterator is decrementable
       */
      _Safe_iterator&
      operator--() _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_decrementable(),
			      _M_message(__msg_bad_dec)
			      ._M_iterator(*this, "this"));
	__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	--base();
	return *this;
      }

/**
       *  @brief Iterator postdecrement
       *  @pre iterator is decrementable
       */
      _Safe_iterator
      operator--(int) _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_decrementable(),
			      _M_message(__msg_bad_dec)
			      ._M_iterator(*this, "this"));
	__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	return _Safe_iterator(base()--, this->_M_sequence, _Attach_single());
      }

// ------ Random access iterator requirements ------
      reference
      operator[](const difference_type& __n) const _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(__n)
			      && this->_M_can_advance(__n+1),
			      _M_message(__msg_iter_subscript_oob)
			      ._M_iterator(*this)._M_integer(__n));
	return base()[__n];
      }

_Safe_iterator&
      operator+=(const difference_type& __n) _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(__n),
			      _M_message(__msg_advance_oob)
			      ._M_iterator(*this)._M_integer(__n));
	__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	base() += __n;
	return *this;
      }

_Safe_iterator
      operator+(const difference_type& __n) const _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(__n),
			      _M_message(__msg_advance_oob)
			      ._M_iterator(*this)._M_integer(__n));
	return _Safe_iterator(base() + __n, this->_M_sequence);
      }

_Safe_iterator&
      operator-=(const difference_type& __n) _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(-__n),
			      _M_message(__msg_retreat_oob)
			      ._M_iterator(*this)._M_integer(__n));
	__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
	base() -= __n;
	return *this;
      }

_Safe_iterator
      operator-(const difference_type& __n) const _GLIBCXX_NOEXCEPT
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(-__n),
			      _M_message(__msg_retreat_oob)
			      ._M_iterator(*this)._M_integer(__n));
	return _Safe_iterator(base() - __n, this->_M_sequence);
      }

// ------ Utilities ------
      /**
       * @brief Return the underlying iterator
       */
      _Iterator&
      base() _GLIBCXX_NOEXCEPT { return *this; }

const _Iterator&
      base() const _GLIBCXX_NOEXCEPT { return *this; }

/**
       * @brief Conversion to underlying non-debug iterator to allow
       * better interaction with non-debug containers.
       */
      operator _Iterator() const _GLIBCXX_NOEXCEPT { return *this; }

/** Attach iterator to the given sequence. */
      void
      _M_attach(_Safe_sequence_base* __seq)
      { _Safe_base::_M_attach(__seq, _M_constant()); }

/** Likewise, but not thread-safe. */
      void
      _M_attach_single(_Safe_sequence_base* __seq)
      { _Safe_base::_M_attach_single(__seq, _M_constant()); }

/// Is the iterator dereferenceable?
      bool
      _M_dereferenceable() const
      { return !this->_M_singular() && !_M_is_end() && !_M_is_before_begin(); }

/// Is the iterator before a dereferenceable one?
      bool
      _M_before_dereferenceable() const
      {
	if (this->_M_incrementable())
	{
	  _Iterator __base = base();
	  return ++__base != _M_get_sequence()->_M_base().end();
	}
	return false;
      }

/// Is the iterator incrementable?
      bool
      _M_incrementable() const
      { return !this->_M_singular() && !_M_is_end(); }

// Is the iterator decrementable?
      bool
      _M_decrementable() const { return !_M_singular() && !_M_is_begin(); }

// Can we advance the iterator @p __n steps (@p __n may be negative)
      bool
      _M_can_advance(const difference_type& __n) const;

// Is the iterator range [*this, __rhs) valid?
      bool
      _M_valid_range(const _Safe_iterator& __rhs,
		     std::pair<difference_type, _Distance_precision>& __dist,
		     bool __check_dereferenceable = true) const;

// The sequence this iterator references.
      typename
      __gnu_cxx::__conditional_type<std::__are_same<_Const_iterator,
						    _Safe_iterator>::__value,
				    const _Sequence*,
				    _Sequence*>::__type
      _M_get_sequence() const
      { return static_cast<_Sequence*>(_M_sequence); }

/// Is this iterator equal to the sequence's begin() iterator?
      bool
      _M_is_begin() const
      { return base() == _M_get_sequence()->_M_base().begin(); }

/// Is this iterator equal to the sequence's end() iterator?
      bool
      _M_is_end() const
      { return base() == _M_get_sequence()->_M_base().end(); }

/// Is this iterator equal to the sequence's before_begin() iterator if
      /// any?
      bool
      _M_is_before_begin() const
      { return _BeforeBeginHelper<_Sequence>::_S_Is(*this); }

/// Is this iterator equal to the sequence's before_begin() iterator if
      /// any or begin() otherwise?
      bool
      _M_is_beginnest() const
      { return _BeforeBeginHelper<_Sequence>::_S_Is_Beginnest(*this); }
    };

template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator==(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	       const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_compare_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_compare_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() == __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
    inline bool
    operator==(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	       const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_compare_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_compare_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() == __rhs.base();
    }

template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator!=(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	       const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_compare_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_compare_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() != __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
    inline bool
    operator!=(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	       const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_compare_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_compare_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() != __rhs.base();
    }

template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator<(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	      const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() < __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
    inline bool
    operator<(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	      const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() < __rhs.base();
    }

template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator<=(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	       const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() <= __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
    inline bool
    operator<=(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	       const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() <= __rhs.base();
    }

template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator>(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	      const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() > __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
    inline bool
    operator>(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	      const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() > __rhs.base();
    }

template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator>=(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	       const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() >= __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
    inline bool
    operator>=(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	       const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_iter_order_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_order_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() >= __rhs.base();
    }

// _GLIBCXX_RESOLVE_LIB_DEFECTS
  // According to the resolution of DR179 not only the various comparison
  // operators but also operator- must accept mixed iterator/const_iterator
  // parameters.
  template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline typename _Safe_iterator<_IteratorL, _Sequence>::difference_type
    operator-(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	      const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
    {
      _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			    _M_message(__msg_distance_bad)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			    _M_message(__msg_distance_different)
			    ._M_iterator(__lhs, "lhs")
			    ._M_iterator(__rhs, "rhs"));
      return __lhs.base() - __rhs.base();
    }

template<typename _Iterator, typename _Sequence>
     inline typename _Safe_iterator<_Iterator, _Sequence>::difference_type
     operator-(const _Safe_iterator<_Iterator, _Sequence>& __lhs,
	       const _Safe_iterator<_Iterator, _Sequence>& __rhs)
    _GLIBCXX_NOEXCEPT
     {
       _GLIBCXX_DEBUG_VERIFY(! __lhs._M_singular() && ! __rhs._M_singular(),
			     _M_message(__msg_distance_bad)
			     ._M_iterator(__lhs, "lhs")
			     ._M_iterator(__rhs, "rhs"));
       _GLIBCXX_DEBUG_VERIFY(__lhs._M_can_compare(__rhs),
			     _M_message(__msg_distance_different)
			     ._M_iterator(__lhs, "lhs")
			     ._M_iterator(__rhs, "rhs"));
       return __lhs.base() - __rhs.base();
     }

template<typename _Iterator, typename _Sequence>
    inline _Safe_iterator<_Iterator, _Sequence>
    operator+(typename _Safe_iterator<_Iterator,_Sequence>::difference_type __n,
	      const _Safe_iterator<_Iterator, _Sequence>& __i) _GLIBCXX_NOEXCEPT
    { return __i + __n; }

/** Safe iterators know if they are dereferenceable. */
  template<typename _Iterator, typename _Sequence>
    inline bool
    __check_dereferenceable(const _Safe_iterator<_Iterator, _Sequence>& __x)
    { return __x._M_dereferenceable(); }

/** Safe iterators know how to check if they form a valid range. */
  template<typename _Iterator, typename _Sequence>
    inline bool
    __valid_range(const _Safe_iterator<_Iterator, _Sequence>& __first,
		  const _Safe_iterator<_Iterator, _Sequence>& __last,
		  typename _Distance_traits<_Iterator>::__type& __dist)
    { return __first._M_valid_range(__last, __dist); }

/** Safe iterators can help to get better distance knowledge. */
  template<typename _Iterator, typename _Sequence>
    inline typename _Distance_traits<_Iterator>::__type
    __get_distance(const _Safe_iterator<_Iterator, _Sequence>& __first,
		   const _Safe_iterator<_Iterator, _Sequence>& __last,
		   std::random_access_iterator_tag)
    { return std::make_pair(__last.base() - __first.base(), __dp_exact); }

template<typename _Iterator, typename _Sequence>
    inline typename _Distance_traits<_Iterator>::__type
    __get_distance(const _Safe_iterator<_Iterator, _Sequence>& __first,
		   const _Safe_iterator<_Iterator, _Sequence>& __last,
		   std::input_iterator_tag)
    {
      typedef typename _Distance_traits<_Iterator>::__type _Diff;
      typedef _Sequence_traits<_Sequence> _SeqTraits;

if (__first.base() == __last.base())
	return std::make_pair(0, __dp_exact);

if (__first._M_is_before_begin())
	{
	  if (__last._M_is_begin())
	    return std::make_pair(1, __dp_exact);

return std::make_pair(1, __dp_sign);
	}

if (__first._M_is_begin())
	{
	  if (__last._M_is_before_begin())
	    return std::make_pair(-1, __dp_exact);

if (__last._M_is_end())
	    return _SeqTraits::_S_size(*__first._M_get_sequence());

return std::make_pair(1, __dp_sign);
	}

if (__first._M_is_end())
	{
	  if (__last._M_is_before_begin())
	    return std::make_pair(-1, __dp_exact);

if (__last._M_is_begin())
	    {
	      _Diff __diff = _SeqTraits::_S_size(*__first._M_get_sequence());
	      return std::make_pair(-__diff.first, __diff.second);
	    }

return std::make_pair(-1, __dp_sign);
	}

if (__last._M_is_before_begin() || __last._M_is_begin())
	return std::make_pair(-1, __dp_sign);

if (__last._M_is_end())
	return std::make_pair(1, __dp_sign);

return std::make_pair(1, __dp_equality);
    }

// Get distance from sequence begin to specified iterator.
  template<typename _Iterator, typename _Sequence>
    inline typename _Distance_traits<_Iterator>::__type
    __get_distance_from_begin(const _Safe_iterator<_Iterator, _Sequence>& __it)
    {
      typedef _Sequence_traits<_Sequence> _SeqTraits;

// No need to consider before_begin as this function is only used in
      // _M_can_advance which won't be used for forward_list iterators.
      if (__it._M_is_begin())
	return std::make_pair(0, __dp_exact);

if (__it._M_is_end())
	return _SeqTraits::_S_size(*__it._M_get_sequence());

typename _Distance_traits<_Iterator>::__type __res
	= __get_distance(__it._M_get_sequence()->_M_base().begin(), __it.base());

if (__res.second == __dp_equality)
	return std::make_pair(1, __dp_sign);

return __res;
    }

// Get distance from specified iterator to sequence end.
  template<typename _Iterator, typename _Sequence>
    inline typename _Distance_traits<_Iterator>::__type
    __get_distance_to_end(const _Safe_iterator<_Iterator, _Sequence>& __it)
    {
      typedef _Sequence_traits<_Sequence> _SeqTraits;

// No need to consider before_begin as this function is only used in
      // _M_can_advance which won't be used for forward_list iterators.
      if (__it._M_is_begin())
	return _SeqTraits::_S_size(*__it._M_get_sequence());

if (__it._M_is_end())
	return std::make_pair(0, __dp_exact);

typename _Distance_traits<_Iterator>::__type __res
	= __get_distance(__it.base(), __it._M_get_sequence()->_M_base().end());

if (__res.second == __dp_equality)
	return std::make_pair(1, __dp_sign);

return __res;
    }

#if __cplusplus < 201103L
  template<typename _Iterator, typename _Sequence>
    struct __is_safe_random_iterator<_Safe_iterator<_Iterator, _Sequence> >
    : std::__are_same<std::random_access_iterator_tag,
                      typename std::iterator_traits<_Iterator>::
		      iterator_category>
    { };
#else
  template<typename _Iterator, typename _Sequence>
    _Iterator
    __base(const _Safe_iterator<_Iterator, _Sequence>& __it,
	   std::random_access_iterator_tag)
    { return __it.base(); }

template<typename _Iterator, typename _Sequence>
    const _Safe_iterator<_Iterator, _Sequence>&
    __base(const _Safe_iterator<_Iterator, _Sequence>& __it,
	   std::input_iterator_tag)
    { return __it; }

template<typename _Iterator, typename _Sequence>
    auto
    __base(const _Safe_iterator<_Iterator, _Sequence>& __it)
    -> decltype(__base(__it, std::__iterator_category(__it)))
    { return __base(__it, std::__iterator_category(__it)); }
#endif

#if __cplusplus < 201103L
  template<typename _Iterator, typename _Sequence>
    struct _Unsafe_type<_Safe_iterator<_Iterator, _Sequence> >
    { typedef _Iterator _Type; };
#endif

template<typename _Iterator, typename _Sequence>
    inline _Iterator
    __unsafe(const _Safe_iterator<_Iterator, _Sequence>& __it)
    { return __it.base(); }

} // namespace __gnu_debug

#include <debug/safe_iterator.tcc>

#endif

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