| ///////////////////////////////////////////////////////////////////////////// |
| // |
| // (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 |