boost/intrusive/pointer_plus_bit.hpp
/////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2007
//
// 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_POINTER_PLUS_BIT_HPP
#define BOOST_INTRUSIVE_POINTER_PLUS_BIT_HPP
namespace boost {
namespace intrusive {
//!This trait class is used to know if a pointer
//!can embed an extra bit 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 has_pointer_plus_bit
{
static const bool value = false;
};
//!This is an specialization for raw pointers.
//!Raw pointers can embed an extra bit in the lower bit
//!if the alignment is multiple of 2.
template<std::size_t N>
struct has_pointer_plus_bit<void*, N>
{
static const bool value = (N % 2u == 0);
};
//!This is class that is supposed to have static methods
//!to embed an extra bit of information in a pointer.
//!This is a declaration and there is no default implementation,
//!because operations to embed the bit change with every pointer type.
//!
//!An implementation that detects that a pointer type whose
//!has_pointer_plus_bit<>::value is non-zero can make use of these
//!operations to embed the bit in the pointer.
template<class Pointer>
struct pointer_plus_bit
{
static const bool value = false;
};
//!This is the specialization to embed an extra bit of information
//!in a raw pointer. The extra bit is stored in the lower bit of the pointer.
template<class T>
struct pointer_plus_bit<T*>
{
typedef T* pointer;
static pointer get_pointer(pointer n)
{ return pointer(std::size_t(n) & ~std::size_t(1u)); }
static void set_pointer(pointer &n, pointer p)
{
assert(0 == (std::size_t(p) & std::size_t(1u)));
n = pointer(std::size_t(p) | (std::size_t(n) & std::size_t(1u)));
}
static bool get_bit(pointer n)
{ return (std::size_t(n) & std::size_t(1u)) != 0; }
static void set_bit(pointer &n, bool c)
{ n = pointer(std::size_t(get_pointer(n)) | std::size_t(c)); }
};
} //namespace intrusive
} //namespace boost
#endif //BOOST_INTRUSIVE_POINTER_PLUS_BIT_HPP