ceph/src/boost/libs/intrusive/include/boost/intrusive/pointer_plus_bits.hpp

   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