Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of boost. Click here for the latest Boost documentation.

boost/intrusive/detail/utilities.hpp

/////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga  2006-2012
//
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/intrusive for documentation.
//
/////////////////////////////////////////////////////////////////////////////

#ifndef BOOST_INTRUSIVE_DETAIL_UTILITIES_HPP
#define BOOST_INTRUSIVE_DETAIL_UTILITIES_HPP

#include <boost/intrusive/detail/config_begin.hpp>
#include <boost/intrusive/pointer_traits.hpp>
#include <boost/intrusive/detail/parent_from_member.hpp>
#include <boost/intrusive/detail/ebo_functor_holder.hpp>
#include <boost/intrusive/link_mode.hpp>
#include <boost/intrusive/detail/mpl.hpp>
#include <boost/intrusive/detail/assert.hpp>
#include <boost/intrusive/detail/is_stateful_value_traits.hpp>
#include <boost/intrusive/pointer_traits.hpp>
#include <boost/cstdint.hpp>
#include <cstddef>
#include <climits>
#include <iterator>
#include <boost/cstdint.hpp>
#include <boost/static_assert.hpp>

namespace boost {
namespace intrusive {
namespace detail {

template <class T>
struct internal_member_value_traits
{
   template <class U> static detail::one test(...);
   template <class U> static detail::two test(typename U::member_value_traits* = 0);
   static const bool value = sizeof(test<T>(0)) == sizeof(detail::two);
};

template <class T>
struct internal_base_hook_bool
{
   template<bool Add>
   struct two_or_three {one _[2 + Add];};
   template <class U> static one test(...);
   template <class U> static two_or_three<U::boost_intrusive_tags::is_base_hook> test (int);
   static const std::size_t value = sizeof(test<T>(0));
};

template <class T>
struct internal_base_hook_bool_is_true
{
   static const bool value = internal_base_hook_bool<T>::value > sizeof(one)*2;
};

template <class T>
struct internal_any_hook_bool
{
   template<bool Add>
   struct two_or_three {one _[2 + Add];};
   template <class U> static one test(...);
   template <class U> static two_or_three<U::is_any_hook> test (int);
   static const std::size_t value = sizeof(test<T>(0));
};

template <class T>
struct internal_any_hook_bool_is_true
{
   static const bool value = internal_any_hook_bool<T>::value > sizeof(one)*2;
};


template <class T>
struct external_value_traits_bool
{
   template<bool Add>
   struct two_or_three {one _[2 + Add];};
   template <class U> static one test(...);
   template <class U> static two_or_three<U::external_value_traits> test (int);
   static const std::size_t value = sizeof(test<T>(0));
};

template <class T>
struct external_bucket_traits_bool
{
   template<bool Add>
   struct two_or_three {one _[2 + Add];};
   template <class U> static one test(...);
   template <class U> static two_or_three<U::external_bucket_traits> test (int);
   static const std::size_t value = sizeof(test<T>(0));
};

template <class T>
struct external_value_traits_is_true
{
   static const bool value = external_value_traits_bool<T>::value > sizeof(one)*2;
};

template<class Node, class Tag, link_mode_type LinkMode, int>
struct node_holder
   :  public Node
{};

template <class T>
inline T* to_raw_pointer(T* p)
{  return p; }

template <class Pointer>
inline typename boost::intrusive::pointer_traits<Pointer>::element_type*
to_raw_pointer(const Pointer &p)
{  return boost::intrusive::detail::to_raw_pointer(p.operator->());  }

//This functor compares a stored value
//and the one passed as an argument
template<class ConstReference>
class equal_to_value
{
   ConstReference t_;

   public:
   equal_to_value(ConstReference t)
      :  t_(t)
   {}

   bool operator()(ConstReference t)const
   {  return t_ == t;   }
};

class null_disposer
{
   public:
   template <class Pointer>
   void operator()(Pointer)
   {}
};

template<class NodeAlgorithms>
class init_disposer
{
   typedef typename NodeAlgorithms::node_ptr node_ptr;

   public:
   void operator()(const node_ptr & p)
   {  NodeAlgorithms::init(p);   }
};

template<bool ConstantSize, class SizeType>
struct size_holder
{
   static const bool constant_time_size = ConstantSize;
   typedef SizeType  size_type;

   SizeType get_size() const
   {  return size_;  }

   void set_size(SizeType size)
   {  size_ = size; }

   void decrement()
   {  --size_; }

   void increment()
   {  ++size_; }

   SizeType size_;
};

template<class SizeType>
struct size_holder<false, SizeType>
{
   static const bool constant_time_size = false;
   typedef SizeType  size_type;

   size_type get_size() const
   {  return 0;  }

   void set_size(size_type)
   {}

   void decrement()
   {}

   void increment()
   {}
};

template<class KeyValueCompare, class Container>
struct key_nodeptr_comp
   :  private detail::ebo_functor_holder<KeyValueCompare>
{
   typedef typename Container::real_value_traits         real_value_traits;
   typedef typename Container::value_type                value_type;
   typedef typename real_value_traits::node_ptr          node_ptr;
   typedef typename real_value_traits::const_node_ptr    const_node_ptr;
   typedef detail::ebo_functor_holder<KeyValueCompare>   base_t;
   key_nodeptr_comp(KeyValueCompare kcomp, const Container *cont)
      :  base_t(kcomp), cont_(cont)
   {}

   template<class T>
   struct is_node_ptr
   {
      static const bool value = is_same<T, const_node_ptr>::value || is_same<T, node_ptr>::value;
   };

   template<class T>
   const value_type & key_forward
      (const T &node, typename enable_if_c<is_node_ptr<T>::value>::type * = 0) const
   {  return *cont_->get_real_value_traits().to_value_ptr(node);  }

   template<class T>
   const T & key_forward(const T &key, typename enable_if_c<!is_node_ptr<T>::value>::type* = 0) const
   {  return key;  }


   template<class KeyType, class KeyType2>
   bool operator()(const KeyType &key1, const KeyType2 &key2) const
   {  return base_t::get()(this->key_forward(key1), this->key_forward(key2));  }

   const Container *cont_;
};

template<class F, class Container>
struct node_cloner
   :  private detail::ebo_functor_holder<F>
{
   typedef typename Container::real_value_traits         real_value_traits;
   typedef typename Container::node_algorithms           node_algorithms;
   typedef typename real_value_traits::value_type        value_type;
   typedef typename real_value_traits::pointer           pointer;
   typedef typename real_value_traits::node_traits::node node;
   typedef typename real_value_traits::node_ptr          node_ptr;
   typedef typename real_value_traits::const_node_ptr    const_node_ptr;
   typedef detail::ebo_functor_holder<F>                 base_t;
   enum { safemode_or_autounlink  =
            (int)real_value_traits::link_mode == (int)auto_unlink   ||
            (int)real_value_traits::link_mode == (int)safe_link     };

   node_cloner(F f, const Container *cont)
      :  base_t(f), cont_(cont)
   {}

   node_ptr operator()(const node_ptr & p)
   {  return this->operator()(*p); }

   node_ptr operator()(const node &to_clone)
   {
      const value_type &v =
         *cont_->get_real_value_traits().to_value_ptr
            (pointer_traits<const_node_ptr>::pointer_to(to_clone));
      node_ptr n = cont_->get_real_value_traits().to_node_ptr(*base_t::get()(v));
      //Cloned node must be in default mode if the linking mode requires it
      if(safemode_or_autounlink)
         BOOST_INTRUSIVE_SAFE_HOOK_DEFAULT_ASSERT(node_algorithms::unique(n));
      return n;
   }

   const Container *cont_;
};

template<class F, class Container>
struct node_disposer
   :  private detail::ebo_functor_holder<F>
{
   typedef typename Container::real_value_traits   real_value_traits;
   typedef typename real_value_traits::node_ptr    node_ptr;
   typedef detail::ebo_functor_holder<F>           base_t;
   typedef typename Container::node_algorithms     node_algorithms;
   enum { safemode_or_autounlink  =
            (int)real_value_traits::link_mode == (int)auto_unlink   ||
            (int)real_value_traits::link_mode == (int)safe_link     };

   node_disposer(F f, const Container *cont)
      :  base_t(f), cont_(cont)
   {}

   void operator()(const node_ptr & p)
   {
      if(safemode_or_autounlink)
         node_algorithms::init(p);
      base_t::get()(cont_->get_real_value_traits().to_value_ptr(p));
   }
   const Container *cont_;
};

struct dummy_constptr
{
   dummy_constptr(const void *)
   {}

   const void *get_ptr() const
   {  return 0;  }
};

template<class VoidPointer>
struct constptr
{
   typedef typename boost::intrusive::pointer_traits<VoidPointer>::
      template rebind_pointer<const void>::type ConstVoidPtr;

   constptr(const void *ptr)
      :  const_void_ptr_(ptr)
   {}

   const void *get_ptr() const
   {  return boost::intrusive::detail::to_raw_pointer(const_void_ptr_);  }

   ConstVoidPtr const_void_ptr_;
};

template <class VoidPointer, bool store_ptr>
struct select_constptr
{
   typedef typename detail::if_c
      < store_ptr
      , constptr<VoidPointer>
      , dummy_constptr
      >::type type;
};

template<class T, bool Add>
struct add_const_if_c
{
   typedef typename detail::if_c
      < Add
      , typename detail::add_const<T>::type
      , T
      >::type type;
};

template <link_mode_type LinkMode>
struct link_dispatch
{};

template<class Hook>
void destructor_impl(Hook &hook, detail::link_dispatch<safe_link>)
{  //If this assertion raises, you might have destroyed an object
   //while it was still inserted in a container that is alive.
   //If so, remove the object from the container before destroying it.
   (void)hook; BOOST_INTRUSIVE_SAFE_HOOK_DESTRUCTOR_ASSERT(!hook.is_linked());
}

template<class Hook>
void destructor_impl(Hook &hook, detail::link_dispatch<auto_unlink>)
{  hook.unlink();  }

template<class Hook>
void destructor_impl(Hook &, detail::link_dispatch<normal_link>)
{}

template<class T, class NodeTraits, link_mode_type LinkMode, class Tag, int HookType>
struct base_hook_traits
{
   public:
   typedef detail::node_holder
      <typename NodeTraits::node, Tag, LinkMode, HookType>           node_holder;
   typedef typename NodeTraits::node                                 node;
   typedef NodeTraits                                                node_traits;
   typedef T                                                         value_type;
   typedef typename node_traits::node_ptr                            node_ptr;
   typedef typename node_traits::const_node_ptr                      const_node_ptr;
   typedef typename pointer_traits<node_ptr>::
      template rebind_pointer<T>::type                               pointer;
   typedef typename pointer_traits<node_ptr>::
      template rebind_pointer<const T>::type                         const_pointer;
   //typedef typename pointer_traits<pointer>::reference               reference;
   //typedef typename pointer_traits<const_pointer>::reference         const_reference;
   typedef T &                                                       reference;
   typedef const T &                                                 const_reference;
   typedef node_holder &                                             node_holder_reference;
   typedef const node_holder &                                       const_node_holder_reference;
   typedef node&                                                     node_reference;
   typedef const node &                                              const_node_reference;

   static const link_mode_type link_mode = LinkMode;

   static pointer to_value_ptr(const node_ptr & n)
   {
      return pointer_traits<pointer>::pointer_to
         (static_cast<reference>(static_cast<node_holder_reference>(*n)));
   }

   static const_pointer to_value_ptr(const const_node_ptr & n)
   {
      return pointer_traits<const_pointer>::pointer_to
         (static_cast<const_reference>(static_cast<const_node_holder_reference>(*n)));
   }

   static node_ptr to_node_ptr(reference value)
   {
      return pointer_traits<node_ptr>::pointer_to
         (static_cast<node_reference>(static_cast<node_holder_reference>(value)));
   }

   static const_node_ptr to_node_ptr(const_reference value)
   {
      return pointer_traits<const_node_ptr>::pointer_to
         (static_cast<const_node_reference>(static_cast<const_node_holder_reference>(value)));
   }
};

template<class T, class Hook, Hook T::* P>
struct member_hook_traits
{
   public:
   typedef Hook                                                      hook_type;
   typedef typename hook_type::boost_intrusive_tags::node_traits     node_traits;
   typedef typename node_traits::node                                node;
   typedef T                                                         value_type;
   typedef typename node_traits::node_ptr                            node_ptr;
   typedef typename node_traits::const_node_ptr                      const_node_ptr;
   typedef typename pointer_traits<node_ptr>::
      template rebind_pointer<T>::type                               pointer;
   typedef typename pointer_traits<node_ptr>::
      template rebind_pointer<const T>::type                         const_pointer;
   typedef T &                                                       reference;
   typedef const T &                                                 const_reference;
   typedef node&                                                     node_reference;
   typedef const node &                                              const_node_reference;
   typedef hook_type&                                                hook_reference;
   typedef const hook_type &                                         const_hook_reference;

   static const link_mode_type link_mode = Hook::boost_intrusive_tags::link_mode;

   static node_ptr to_node_ptr(reference value)
   {
      return pointer_traits<node_ptr>::pointer_to
         (static_cast<node_reference>(static_cast<hook_reference>(value.*P)));
   }

   static const_node_ptr to_node_ptr(const_reference value)
   {
      return pointer_traits<const_node_ptr>::pointer_to
         (static_cast<const_node_reference>(static_cast<const_hook_reference>(value.*P)));
   }

   static pointer to_value_ptr(const node_ptr & n)
   {
      return pointer_traits<pointer>::pointer_to
         (*detail::parent_from_member<T, Hook>
            (static_cast<Hook*>(boost::intrusive::detail::to_raw_pointer(n)), P));
   }

   static const_pointer to_value_ptr(const const_node_ptr & n)
   {
      return pointer_traits<const_pointer>::pointer_to
         (*detail::parent_from_member<T, Hook>
            (static_cast<const Hook*>(boost::intrusive::detail::to_raw_pointer(n)), P));
   }
};

template<class Functor>
struct function_hook_traits
{
   public:
   typedef typename Functor::hook_type                               hook_type;
   typedef typename Functor::hook_ptr                                hook_ptr;
   typedef typename Functor::const_hook_ptr                          const_hook_ptr;
   typedef typename hook_type::boost_intrusive_tags::node_traits     node_traits;
   typedef typename node_traits::node                                node;
   typedef typename Functor::value_type                              value_type;
   typedef typename node_traits::node_ptr                            node_ptr;
   typedef typename node_traits::const_node_ptr                      const_node_ptr;
   typedef typename pointer_traits<node_ptr>::
      template rebind_pointer<value_type>::type                      pointer;
   typedef typename pointer_traits<node_ptr>::
      template rebind_pointer<const value_type>::type                const_pointer;
   typedef value_type &                                              reference;
   typedef const value_type &                                        const_reference;
   static const link_mode_type link_mode = hook_type::boost_intrusive_tags::link_mode;

   static node_ptr to_node_ptr(reference value)
   {  return static_cast<node*>(boost::intrusive::detail::to_raw_pointer(Functor::to_hook_ptr(value)));  }

   static const_node_ptr to_node_ptr(const_reference value)
   {  return static_cast<const node*>(boost::intrusive::detail::to_raw_pointer(Functor::to_hook_ptr(value)));  }

   static pointer to_value_ptr(const node_ptr & n)
   {  return Functor::to_value_ptr(to_hook_ptr(n));  }

   static const_pointer to_value_ptr(const const_node_ptr & n)
   {  return Functor::to_value_ptr(to_hook_ptr(n));  }

   private:
   static hook_ptr to_hook_ptr(const node_ptr & n)
   {  return hook_ptr(&*static_cast<hook_type*>(&*n));  }

   static const_hook_ptr to_hook_ptr(const const_node_ptr & n)
   {  return const_hook_ptr(&*static_cast<const hook_type*>(&*n));  }
};


//This function uses binary search to discover the
//highest set bit of the integer
inline std::size_t floor_log2 (std::size_t x)
{
   const std::size_t Bits = sizeof(std::size_t)*CHAR_BIT;
   const bool Size_t_Bits_Power_2= !(Bits & (Bits-1));
   BOOST_STATIC_ASSERT(Size_t_Bits_Power_2);

   std::size_t n = x;
   std::size_t log2 = 0;

   for(std::size_t shift = Bits >> 1; shift; shift >>= 1){
      std::size_t tmp = n >> shift;
      if (tmp)
         log2 += shift, n = tmp;
   }

   return log2;
}

inline float fast_log2 (float val)
{
   union caster_t
   {
      boost::uint32_t x;
      float val;
   } caster;

   caster.val = val;
   boost::uint32_t x = caster.x;
   const int log_2 = (int)(((x >> 23) & 255) - 128);
   x &= ~(255 << 23);
   x += 127 << 23;
   caster.x = x;
   val = caster.val;
   val = ((-1.0f/3.f) * val + 2.f) * val - (2.0f/3.f);

   return (val + log_2);
}

inline std::size_t ceil_log2 (std::size_t x)
{
   return ((x & (x-1))!= 0) + floor_log2(x);
}

template<class SizeType, std::size_t N>
struct numbits_eq
{
   static const bool value = sizeof(SizeType)*CHAR_BIT == N;
};

template<class SizeType, class Enabler = void >
struct sqrt2_pow_max;

template <class SizeType>
struct sqrt2_pow_max<SizeType, typename enable_if< numbits_eq<SizeType, 32> >::type>
{
   static const boost::uint32_t value = 0xb504f334;
   static const std::size_t pow   = 31;
};

template <class SizeType>
struct sqrt2_pow_max<SizeType, typename enable_if< numbits_eq<SizeType, 64> >::type>
{
   static const boost::uint64_t value = 0xb504f333f9de6484ull;
   static const std::size_t pow   = 63;
};

// Returns floor(pow(sqrt(2), x * 2 + 1)).
// Defined for X from 0 up to the number of bits in size_t minus 1.
inline std::size_t sqrt2_pow_2xplus1 (std::size_t x)
{
   const std::size_t value = (std::size_t)sqrt2_pow_max<std::size_t>::value;
   const std::size_t pow   = (std::size_t)sqrt2_pow_max<std::size_t>::pow;
   return (value >> (pow - x)) + 1;
}

template<class Container, class Disposer>
class exception_disposer
{
   Container *cont_;
   Disposer  &disp_;

   exception_disposer(const exception_disposer&);
   exception_disposer &operator=(const exception_disposer&);

   public:
   exception_disposer(Container &cont, Disposer &disp)
      :  cont_(&cont), disp_(disp)
   {}

   void release()
   {  cont_ = 0;  }

   ~exception_disposer()
   {
      if(cont_){
         cont_->clear_and_dispose(disp_);
      }
   }
};

template<class Container, class Disposer, class SizeType>
class exception_array_disposer
{
   Container *cont_;
   Disposer  &disp_;
   SizeType  &constructed_;

   exception_array_disposer(const exception_array_disposer&);
   exception_array_disposer &operator=(const exception_array_disposer&);

   public:

   exception_array_disposer
      (Container &cont, Disposer &disp, SizeType &constructed)
      :  cont_(&cont), disp_(disp), constructed_(constructed)
   {}

   void release()
   {  cont_ = 0;  }

   ~exception_array_disposer()
   {
      SizeType n = constructed_;
      if(cont_){
         while(n--){
            cont_[n].clear_and_dispose(disp_);
         }
      }
   }
};

template<class ValueTraits, bool ExternalValueTraits>
struct store_cont_ptr_on_it_impl
{
   static const bool value = is_stateful_value_traits<ValueTraits>::value;
};

template<class ValueTraits>
struct  store_cont_ptr_on_it_impl<ValueTraits, true>
{
   static const bool value = true;
};

template <class Container>
struct store_cont_ptr_on_it
{
   typedef typename Container::value_traits value_traits;
   static const bool value = store_cont_ptr_on_it_impl
      <value_traits, external_value_traits_is_true<value_traits>::value>::value;
};

template<class Container, bool IsConst>
struct node_to_value
   :  public detail::select_constptr
      < typename pointer_traits
            <typename Container::pointer>::template rebind_pointer<void>::type
      , detail::store_cont_ptr_on_it<Container>::value
      >::type
{
   static const bool store_container_ptr =
      detail::store_cont_ptr_on_it<Container>::value;

   typedef typename Container::real_value_traits         real_value_traits;
   typedef typename real_value_traits::value_type        value_type;
   typedef typename detail::select_constptr
      < typename pointer_traits
            <typename Container::pointer>::template rebind_pointer<void>::type
      , store_container_ptr >::type                      Base;
   typedef typename real_value_traits::node_traits::node node;
   typedef typename detail::add_const_if_c
         <value_type, IsConst>::type                  vtype;
   typedef typename detail::add_const_if_c
         <node, IsConst>::type                        ntype;
   typedef typename pointer_traits
      <typename Container::pointer>::template rebind_pointer<ntype>::type npointer;

   node_to_value(const Container *cont)
      :  Base(cont)
   {}

   typedef vtype &                                 result_type;
   typedef ntype &                                 first_argument_type;

   const Container *get_container() const
   {
      if(store_container_ptr)
         return static_cast<const Container*>(Base::get_ptr());
      else
         return 0;
   }

   const real_value_traits *get_real_value_traits() const
   {
      if(store_container_ptr)
         return &this->get_container()->get_real_value_traits();
      else
         return 0;
   }

   result_type operator()(first_argument_type arg) const
   {
      return *(this->get_real_value_traits()->to_value_ptr
         (pointer_traits<npointer>::pointer_to(arg)));
   }
};

//This is not standard, but should work with all compilers
union max_align
{
   char        char_;
   short       short_;
   int         int_;
   long        long_;
   #ifdef BOOST_HAS_LONG_LONG
   long long   long_long_;
   #endif
   float       float_;
   double      double_;
   long double long_double_;
   void *      void_ptr_;
};

template<class T, std::size_t N>
class array_initializer
{
   public:
   template<class CommonInitializer>
   array_initializer(const CommonInitializer &init)
   {
      char *init_buf = (char*)rawbuf;
      std::size_t i = 0;
      try{
         for(; i != N; ++i){
            new(init_buf)T(init);
            init_buf += sizeof(T);
         }
      }
      catch(...){
         while(i--){
            init_buf -= sizeof(T);
            ((T*)init_buf)->~T();
         }
         throw;
      }
   }

   operator T* ()
   {  return (T*)(rawbuf);  }

   operator const T*() const
   {  return (const T*)(rawbuf);  }

   ~array_initializer()
   {
      char *init_buf = (char*)rawbuf + N*sizeof(T);
      for(std::size_t i = 0; i != N; ++i){
         init_buf -= sizeof(T);
         ((T*)init_buf)->~T();
      }
   }

   private:
   detail::max_align rawbuf[(N*sizeof(T)-1)/sizeof(detail::max_align)+1];
};




template<class It>
class reverse_iterator
	: public std::iterator<
		typename std::iterator_traits<It>::iterator_category,
		typename std::iterator_traits<It>::value_type,
		typename std::iterator_traits<It>::difference_type,
		typename std::iterator_traits<It>::pointer,
		typename std::iterator_traits<It>::reference>
{
   public:
	typedef typename std::iterator_traits<It>::pointer pointer;
	typedef typename std::iterator_traits<It>::reference reference;
 	typedef typename std::iterator_traits<It>::difference_type difference_type;
	typedef It iterator_type;

	reverse_iterator(){}

	explicit reverse_iterator(It r)
		: m_current(r)
   {}

	template<class OtherIt>
	reverse_iterator(const reverse_iterator<OtherIt>& r)
	   : m_current(r.base())
	{}

	It base() const
   {  return m_current;  }

	reference operator*() const
   {  It temp(m_current);   --temp; return *temp; }

	pointer operator->() const
   {  It temp(m_current);   --temp; return temp.operator->(); }

	reference operator[](difference_type off) const
	{  return this->m_current[-off];  }

	reverse_iterator& operator++()
   {  --m_current;   return *this;   }

	reverse_iterator operator++(int)
	{
		reverse_iterator temp = *this;
		--m_current;
		return temp;
	}

	reverse_iterator& operator--()
	{
	   ++m_current;
		return *this;
   }

	reverse_iterator operator--(int)
	{
	   reverse_iterator temp(*this);
	   ++m_current;
	   return temp;
	}

	friend bool operator==(const reverse_iterator& l, const reverse_iterator& r)
	{  return l.m_current == r.m_current;  }

	friend bool operator!=(const reverse_iterator& l, const reverse_iterator& r)
	{  return l.m_current != r.m_current;  }

	friend bool operator<(const reverse_iterator& l, const reverse_iterator& r)
	{  return l.m_current < r.m_current;  }

	friend bool operator<=(const reverse_iterator& l, const reverse_iterator& r)
	{  return l.m_current <= r.m_current;  }

	friend bool operator>(const reverse_iterator& l, const reverse_iterator& r)
	{  return l.m_current > r.m_current;  }

	friend bool operator>=(const reverse_iterator& l, const reverse_iterator& r)
	{  return l.m_current >= r.m_current;  }

	reverse_iterator& operator+=(difference_type off)
	{  m_current -= off; return *this;  }

	friend reverse_iterator operator+(const reverse_iterator & l, difference_type off)
	{
      reverse_iterator tmp(l.m_current);
      tmp.m_current -= off;
      return tmp;
   }

	reverse_iterator& operator-=(difference_type off)
	{  m_current += off; return *this;  }

	friend reverse_iterator operator-(const reverse_iterator & l, difference_type off)
	{
      reverse_iterator tmp(l.m_current);
      tmp.m_current += off;
      return tmp;
   }

	friend difference_type operator-(const reverse_iterator& l, const reverse_iterator& r)
	{  return r.m_current - l.m_current;  }

   private:
	It m_current;	// the wrapped iterator
};

} //namespace detail
} //namespace intrusive
} //namespace boost

#include <boost/intrusive/detail/config_end.hpp>

#endif //BOOST_INTRUSIVE_DETAIL_UTILITIES_HPP