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

// Copyright (C) 2003, 2004, 2005, 2006, 2009, 2010, 2011
// 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/debug.h>
#include <debug/macros.h>
#include <debug/functions.h>
#include <debug/safe_base.h>
#include <bits/stl_pair.h>
#include <bits/stl_iterator_base_types.h> // for _Iter_base
#include <ext/type_traits.h>

namespace __gnu_debug
{
  /** Helper struct to deal with sequence offering a before_begin
   *  iterator.
   **/
  template <typename _Sequence>
    struct _BeforeBeginHelper
    {
      typedef typename _Sequence::const_iterator _It;
      typedef typename _It::iterator_type _BaseIt;

      static bool
      _M_Is(_BaseIt __it, const _Sequence* __seq)
      { return false; }
    };

  /** Iterators that derive from _Safe_iterator_base but that aren't
   *  _Safe_iterators can be determined singular or non-singular via
   *  _Safe_iterator_base.
   */
  inline bool 
  __check_singular_aux(const _Safe_iterator_base* __x)
  { return __x->_M_singular(); }

  /** \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.
   */
  template<typename _Iterator, typename _Sequence>
    class _Safe_iterator : public _Safe_iterator_base
    {
      typedef _Safe_iterator _Self;

      /** The precision to which we can calculate the distance between
       *  two iterators.
       */
      enum _Distance_precision
	{
	  __dp_equality, //< Can compare iterator equality, only
	  __dp_sign,     //< Can determine equality and ordering
	  __dp_exact     //< Can determine distance precisely
	};

      /// The underlying iterator
      _Iterator _M_current;

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

      typedef std::iterator_traits<_Iterator> _Traits;

    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() : _M_current() { }

      /**
       * @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 _Sequence* __seq)
      : _Safe_iterator_base(__seq, _M_constant()), _M_current(__i)
      {
	_GLIBCXX_DEBUG_VERIFY(! this->_M_singular(),
			      _M_message(__msg_init_singular)
			      ._M_iterator(*this, "this"));
      }

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

      /**
       *  @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)
	: _Safe_iterator_base(__x, _M_constant()), _M_current(__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"));
	}

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

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

      /**
       *  @brief Iterator dereference.
       *  @pre iterator is dereferenceable
       *  @todo Make this correct w.r.t. iterators that return proxies
       *  @todo Use addressof() instead of & operator
       */
      pointer
      operator->() const
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_dereferenceable(),
			      _M_message(__msg_bad_deref)
			      ._M_iterator(*this, "this"));
	return &*_M_current;
      }

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

      /**
       *  @brief Iterator postincrement
       *  @pre iterator is incrementable
       */
      _Safe_iterator
      operator++(int)
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
			      _M_message(__msg_bad_inc)
			      ._M_iterator(*this, "this"));
	_Safe_iterator __tmp(*this);
	++_M_current;
	return __tmp;
      }

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

      /**
       *  @brief Iterator postdecrement
       *  @pre iterator is decrementable
       */
      _Safe_iterator
      operator--(int)
      {
	_GLIBCXX_DEBUG_VERIFY(this->_M_decrementable(),
			      _M_message(__msg_bad_dec)
			      ._M_iterator(*this, "this"));
	_Safe_iterator __tmp(*this);
	--_M_current;
	return __tmp;
      }

      // ------ Random access iterator requirements ------
      reference
      operator[](const difference_type& __n) const
      {
	_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 _M_current[__n];
      }

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

      _Safe_iterator
      operator+(const difference_type& __n) const
      {
	_Safe_iterator __tmp(*this);
	__tmp += __n;
	return __tmp;
      }

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

      _Safe_iterator
      operator-(const difference_type& __n) const
      {
	_Safe_iterator __tmp(*this);
	__tmp -= __n;
	return __tmp;
      }

      // ------ Utilities ------
      /**
       * @brief Return the underlying iterator
       */
      _Iterator
      base() const { return _M_current; }

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

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

      /** Likewise, but not thread-safe. */
      void
      _M_attach_single(_Safe_sequence_base* __seq)
      {
	_Safe_iterator_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
      {
	_Self __it = *this;
	return __it._M_incrementable() && (++__it)._M_dereferenceable();
      }

      /// 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?
      template<typename _Other>
        bool
        _M_valid_range(const _Safe_iterator<_Other, _Sequence>& __rhs) const;

      // The sequence this iterator references.
      const _Sequence*
      _M_get_sequence() const
      { return static_cast<const _Sequence*>(_M_sequence); }

    /** Determine the distance between two iterators with some known
     *	precision.
    */
    template<typename _Iterator1, typename _Iterator2>
      static std::pair<difference_type, _Distance_precision>
      _M_get_distance(const _Iterator1& __lhs, const _Iterator2& __rhs)
      {
        typedef typename std::iterator_traits<_Iterator1>::iterator_category
	  _Category;
        return _M_get_distance(__lhs, __rhs, _Category());
      }

    template<typename _Iterator1, typename _Iterator2>
      static std::pair<difference_type, _Distance_precision>
      _M_get_distance(const _Iterator1& __lhs, const _Iterator2& __rhs,
		      std::random_access_iterator_tag)
      { return std::make_pair(__rhs - __lhs, __dp_exact); }

    template<typename _Iterator1, typename _Iterator2>
      static std::pair<difference_type, _Distance_precision>
      _M_get_distance(const _Iterator1& __lhs, const _Iterator2& __rhs,
		    std::forward_iterator_tag)
      { return std::make_pair(__lhs == __rhs? 0 : 1, __dp_equality); }

      /// 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>::_M_Is(base(), _M_get_sequence()); }
    };

  template<typename _IteratorL, typename _IteratorR, typename _Sequence>
    inline bool
    operator==(const _Safe_iterator<_IteratorL, _Sequence>& __lhs,
	       const _Safe_iterator<_IteratorR, _Sequence>& __rhs)
    {
      _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_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_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_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_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_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_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_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_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_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_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_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_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_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)
    { return __i + __n; }

  // Helper struct to detect random access safe iterators.
  template<typename _Iterator>
    struct __is_safe_random_iterator
    {
      enum { __value = 0 };
      typedef std::__false_type __type;
    };

  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>
    { };

  template<typename _Iterator>
    struct _Siter_base
    : std::_Iter_base<_Iterator, __is_safe_random_iterator<_Iterator>::__value>
    { };

  /** Helper function to extract base iterator of random access safe iterator
      in order to reduce performance impact of debug mode.  Limited to random
      access iterator because it is the only category for which it is possible
      to check for correct iterators order in the __valid_range function
      thanks to the < operator.
  */
  template<typename _Iterator>
    inline typename _Siter_base<_Iterator>::iterator_type
    __base(_Iterator __it)
    { return _Siter_base<_Iterator>::_S_base(__it); }
} // namespace __gnu_debug

#include <debug/safe_iterator.tcc>

#endif