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 
26 //GCC reports uninitialized values when an uninitialized pointer plus bits type
27 //is asigned some bits or some pointer value, but that's ok, because we don't want
28 //to default initialize parts that are not being updated.
29 #if defined(BOOST_GCC)
30 #  if (BOOST_GCC >= 40600)
31 #     pragma GCC diagnostic push
32 #     pragma GCC diagnostic ignored "-Wuninitialized"
33 #     if (BOOST_GCC >= 40700)
34 #        pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
35 #     endif
36 #  endif
37 #endif
38 
39 namespace boost {
40 namespace intrusive {
41 
42 //!This trait class is used to know if a pointer
43 //!can embed extra bits of information if
44 //!it's going to be used to point to objects
45 //!with an alignment of "Alignment" bytes.
46 template<class VoidPointer, std::size_t Alignment>
47 struct max_pointer_plus_bits
48 {
49    static const std::size_t value = 0;
50 };
51 
52 //!This is a specialization for raw pointers.
53 //!Raw pointers can embed extra bits in the lower bits
54 //!if the alignment is multiple of 2pow(NumBits).
55 template<std::size_t Alignment>
56 struct max_pointer_plus_bits<void*, Alignment>
57 {
58    static const std::size_t value = detail::ls_zeros<Alignment>::value;
59 };
60 
61 //!This is class that is supposed to have static methods
62 //!to embed extra bits of information in a pointer.
63 //!This is a declaration and there is no default implementation,
64 //!because operations to embed the bits change with every pointer type.
65 //!
66 //!An implementation that detects that a pointer type whose
67 //!has_pointer_plus_bits<>::value is non-zero can make use of these
68 //!operations to embed the bits in the pointer.
69 template<class Pointer, std::size_t NumBits>
70 struct pointer_plus_bits
71    #ifdef BOOST_INTRUSIVE_DOXYGEN_INVOKED
72    {}
73    #endif
74 ;
75 
76 //!This is the specialization to embed extra bits of information
77 //!in a raw pointer. The extra bits are stored in the lower bits of the pointer.
78 template<class T, std::size_t NumBits>
79 struct pointer_plus_bits<T*, NumBits>
80 {
81    static const uintptr_t Mask = uintptr_t((uintptr_t(1u) << NumBits) - 1);
82    typedef T*        pointer;
83 
get_pointerboost::intrusive::pointer_plus_bits84    BOOST_INTRUSIVE_FORCEINLINE static pointer get_pointer(pointer n)
85    {  return pointer(uintptr_t(n) & uintptr_t(~Mask));  }
86 
set_pointerboost::intrusive::pointer_plus_bits87    BOOST_INTRUSIVE_FORCEINLINE static void set_pointer(pointer &n, pointer p)
88    {
89       BOOST_INTRUSIVE_INVARIANT_ASSERT(0 == (uintptr_t(p) & Mask));
90       n = pointer(uintptr_t(p) | (uintptr_t(n) & Mask));
91    }
92 
get_bitsboost::intrusive::pointer_plus_bits93    BOOST_INTRUSIVE_FORCEINLINE static std::size_t get_bits(pointer n)
94    {  return std::size_t(uintptr_t(n) & Mask);  }
95 
set_bitsboost::intrusive::pointer_plus_bits96    BOOST_INTRUSIVE_FORCEINLINE static void set_bits(pointer &n, std::size_t c)
97    {
98       BOOST_INTRUSIVE_INVARIANT_ASSERT(uintptr_t(c) <= Mask);
99       n = pointer(uintptr_t((get_pointer)(n)) | uintptr_t(c));
100    }
101 };
102 
103 } //namespace intrusive
104 } //namespace boost
105 
106 #if defined(BOOST_GCC) && (BOOST_GCC >= 40600)
107 #  pragma GCC diagnostic pop
108 #endif
109 
110 #include <boost/intrusive/detail/config_end.hpp>
111 
112 #endif //BOOST_INTRUSIVE_POINTER_PLUS_BITS_HPP
113