///////////////////////////////////////////////////////////////////////////// | |
// | |
// (C) Copyright Ion Gaztanaga 2007-2009 | |
// | |
// 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_BITS_HPP | |
#define BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP | |
#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 bits 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) | |
{ | |
BOOST_INTRUSIVE_INVARIANT_ASSERT(c <= Mask); | |
n = pointer(std::size_t(get_pointer(n)) | c); | |
} | |
}; | |
} //namespace intrusive | |
} //namespace boost | |
#endif //BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP |