Boost C++ Libraries 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 to view this page for the latest version.


// (C) Copyright Ion Gaztanaga  2007-2008
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
// See for documentation.


#include <boost/intrusive/detail/mpl.hpp> //ls_zeros
#include <boost/intrusive/detail/assert.hpp> //BOOST_INTRUSIVE_INVARIANT_ASSERT

namespace boost {
namespace intrusive {

//!This trait class is used to know if a pointer
//!can embed extra bits of information if
//!it's going to be used to point to objects
//!with an alignment of "Alignment" bytes.
template<class VoidPointer, std::size_t Alignment>
struct max_pointer_plus_bits
   static const std::size_t value = 0;

//!This is a specialization for raw pointers.
//!Raw pointers can embed extra bits in the lower bits
//!if the alignment is multiple of 2pow(NumBits).
template<std::size_t Alignment>
struct max_pointer_plus_bits<void*, Alignment>
   static const std::size_t value = detail::ls_zeros<Alignment>::value;

//!This is class that is supposed to have static methods
//!to embed extra bits of information in a pointer.
//!This is a declaration and there is no default implementation,
//!because operations to embed the bits change with every pointer type.
//!An implementation that detects that a pointer type whose
//!has_pointer_plus_bits<>::value is non-zero can make use of these
//!operations to embed the bits in the pointer.
template<class Pointer, std::size_t NumBits>
struct pointer_plus_bits;

//!This is the specialization to embed extra bits of information
//!in a raw pointer. The extra bits are stored in the lower bit of the pointer.
template<class T, std::size_t NumBits>
struct pointer_plus_bits<T*, NumBits>
   static const std::size_t Mask = ((std::size_t(1u) << NumBits) - 1);
   typedef T*        pointer;

   static pointer get_pointer(pointer n)
   {  return pointer(std::size_t(n) & ~Mask);  }

   static void set_pointer(pointer &n, pointer p)
      BOOST_INTRUSIVE_INVARIANT_ASSERT(0 == (std::size_t(p) & Mask));
      n = pointer(std::size_t(p) | (std::size_t(n) & Mask)); 

   static std::size_t get_bits(pointer n)
   {  return (std::size_t(n) & Mask);  }

   static void set_bits(pointer &n, std::size_t c)
      n = pointer(std::size_t(get_pointer(n)) | c);

} //namespace intrusive 
} //namespace boost