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1 | ///////////////////////////////////////////////////////////////////////////// |
2 | // | |
3 | // (C) Copyright Ion Gaztanaga 2007-2013 | |
4 | // | |
5 | // Distributed under the Boost Software License, Version 1.0. | |
6 | // (See accompanying file LICENSE_1_0.txt or copy at | |
7 | // http://www.boost.org/LICENSE_1_0.txt) | |
8 | // | |
9 | // See http://www.boost.org/libs/intrusive for documentation. | |
10 | // | |
11 | ///////////////////////////////////////////////////////////////////////////// | |
12 | ||
13 | #ifndef BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP | |
14 | #define BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP | |
15 | ||
16 | #include <boost/intrusive/detail/config_begin.hpp> | |
17 | #include <boost/intrusive/intrusive_fwd.hpp> | |
18 | #include <boost/intrusive/detail/mpl.hpp> //ls_zeros | |
19 | #include <boost/intrusive/detail/assert.hpp> //BOOST_INTRUSIVE_INVARIANT_ASSERT | |
20 | ||
21 | #if defined(BOOST_HAS_PRAGMA_ONCE) | |
22 | # pragma once | |
23 | #endif | |
24 | ||
25 | namespace boost { | |
26 | namespace intrusive { | |
27 | ||
28 | //!This trait class is used to know if a pointer | |
29 | //!can embed extra bits of information if | |
30 | //!it's going to be used to point to objects | |
31 | //!with an alignment of "Alignment" bytes. | |
32 | template<class VoidPointer, std::size_t Alignment> | |
33 | struct max_pointer_plus_bits | |
34 | { | |
35 | static const std::size_t value = 0; | |
36 | }; | |
37 | ||
38 | //!This is a specialization for raw pointers. | |
39 | //!Raw pointers can embed extra bits in the lower bits | |
40 | //!if the alignment is multiple of 2pow(NumBits). | |
41 | template<std::size_t Alignment> | |
42 | struct max_pointer_plus_bits<void*, Alignment> | |
43 | { | |
44 | static const std::size_t value = detail::ls_zeros<Alignment>::value; | |
45 | }; | |
46 | ||
47 | //!This is class that is supposed to have static methods | |
48 | //!to embed extra bits of information in a pointer. | |
49 | //!This is a declaration and there is no default implementation, | |
50 | //!because operations to embed the bits change with every pointer type. | |
51 | //! | |
52 | //!An implementation that detects that a pointer type whose | |
53 | //!has_pointer_plus_bits<>::value is non-zero can make use of these | |
54 | //!operations to embed the bits in the pointer. | |
55 | template<class Pointer, std::size_t NumBits> | |
56 | struct pointer_plus_bits | |
57 | #ifdef BOOST_INTRUSIVE_DOXYGEN_INVOKED | |
58 | {} | |
59 | #endif | |
60 | ; | |
61 | ||
62 | //!This is the specialization to embed extra bits of information | |
63 | //!in a raw pointer. The extra bits are stored in the lower bits of the pointer. | |
64 | template<class T, std::size_t NumBits> | |
65 | struct pointer_plus_bits<T*, NumBits> | |
66 | { | |
67 | static const uintptr_t Mask = uintptr_t((uintptr_t(1u) << NumBits) - 1); | |
68 | typedef T* pointer; | |
69 | ||
70 | BOOST_INTRUSIVE_FORCEINLINE static pointer get_pointer(pointer n) | |
71 | { return pointer(uintptr_t(n) & uintptr_t(~Mask)); } | |
72 | ||
73 | BOOST_INTRUSIVE_FORCEINLINE static void set_pointer(pointer &n, pointer p) | |
74 | { | |
75 | BOOST_INTRUSIVE_INVARIANT_ASSERT(0 == (uintptr_t(p) & Mask)); | |
76 | n = pointer(uintptr_t(p) | (uintptr_t(n) & Mask)); | |
77 | } | |
78 | ||
79 | BOOST_INTRUSIVE_FORCEINLINE static std::size_t get_bits(pointer n) | |
80 | { return std::size_t(uintptr_t(n) & Mask); } | |
81 | ||
82 | BOOST_INTRUSIVE_FORCEINLINE static void set_bits(pointer &n, std::size_t c) | |
83 | { | |
84 | BOOST_INTRUSIVE_INVARIANT_ASSERT(uintptr_t(c) <= Mask); | |
85 | n = pointer(uintptr_t((get_pointer)(n)) | uintptr_t(c)); | |
86 | } | |
87 | }; | |
88 | ||
89 | } //namespace intrusive | |
90 | } //namespace boost | |
91 | ||
92 | #include <boost/intrusive/detail/config_end.hpp> | |
93 | ||
94 | #endif //BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP |