ceph/src/boost/libs/intrusive/include/boost/intrusive/detail/parent_from_member.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 #ifndef BOOST_INTRUSIVE_DETAIL_PARENT_FROM_MEMBER_HPP
  13 #define BOOST_INTRUSIVE_DETAIL_PARENT_FROM_MEMBER_HPP
  14
  15 #ifndef BOOST_CONFIG_HPP
  16 #  include <boost/config.hpp>
  17 #endif
  18
  19 #if defined(BOOST_HAS_PRAGMA_ONCE)
  20 #  pragma once
  21 #endif
  22
  23 #include <boost/intrusive/detail/config_begin.hpp>
  24 #include <boost/intrusive/detail/workaround.hpp>
  25 #include <cstddef>
  26
  27 #if defined(_MSC_VER)
  28    #define BOOST_INTRUSIVE_MSVC_ABI_PTR_TO_MEMBER
  29    #include <boost/static_assert.hpp>
  30 #endif
  31
  32 namespace boost {
  33 namespace intrusive {
  34 namespace detail {
  35
  36 template<class Parent, class Member>
  37 BOOST_INTRUSIVE_FORCEINLINE std::ptrdiff_t offset_from_pointer_to_member(const Member Parent::* ptr_to_member)
  38 {
  39    //The implementation of a pointer to member is compiler dependent.
  40    #if defined(BOOST_INTRUSIVE_MSVC_ABI_PTR_TO_MEMBER)
  41
  42    //MSVC compliant compilers use their the first 32 bits as offset (even in 64 bit mode)
  43    union caster_union
  44    {
  45       const Member Parent::* ptr_to_member;
  46       int offset;
  47    } caster;
  48
  49    //MSVC ABI can use up to 3 int32 to represent pointer to member data
  50    //with virtual base classes, in those cases there is no simple to
  51    //obtain the address of the parent. So static assert to avoid runtime errors
  52    BOOST_STATIC_ASSERT( sizeof(caster) == sizeof(int) );
  53
  54    caster.ptr_to_member = ptr_to_member;
  55    return std::ptrdiff_t(caster.offset);
  56    //Additional info on MSVC behaviour for the future. For 2/3 int ptr-to-member
  57    //types dereference seems to be:
  58    //
  59    // vboffset = [compile_time_offset if 2-int ptr2memb] /
  60    //            [ptr2memb.i32[2] if 3-int ptr2memb].
  61    // vbtable = *(this + vboffset);
  62    // adj = vbtable[ptr2memb.i32[1]];
  63    // var = adj + (this + vboffset) + ptr2memb.i32[0];
  64    //
  65    //To reverse the operation we need to
  66    // - obtain vboffset (in 2-int ptr2memb implementation only)
  67    // - Go to Parent's vbtable and obtain adjustment at index ptr2memb.i32[1]
  68    // - parent = member - adj - vboffset - ptr2memb.i32[0]
  69    //
  70    //Even accessing to RTTI we might not be able to obtain this information
  71    //so anyone who thinks it's possible, please send a patch.
  72
  73    //This works with gcc, msvc, ac++, ibmcpp
  74    #elif defined(__GNUC__)   || defined(__HP_aCC) || defined(BOOST_INTEL) || \
  75          defined(__IBMCPP__) || defined(__DECCXX)
  76    const Parent * const parent = 0;
  77    const char *const member = static_cast<const char*>(static_cast<const void*>(&(parent->*ptr_to_member)));
  78    return std::ptrdiff_t(member - static_cast<const char*>(static_cast<const void*>(parent)));
  79    #else
  80    //This is the traditional C-front approach: __MWERKS__, __DMC__, __SUNPRO_CC
  81    union caster_union
  82    {
  83       const Member Parent::* ptr_to_member;
  84       std::ptrdiff_t offset;
  85    } caster;
  86    caster.ptr_to_member = ptr_to_member;
  87    return caster.offset - 1;
  88    #endif
  89 }
  90
  91 template<class Parent, class Member>
  92 BOOST_INTRUSIVE_FORCEINLINE Parent *parent_from_member(Member *member, const Member Parent::* ptr_to_member)
  93 {
  94    return static_cast<Parent*>
  95       (
  96          static_cast<void*>
  97          (
  98             static_cast<char*>(static_cast<void*>(member)) - offset_from_pointer_to_member(ptr_to_member)
  99          )
 100       );
 101 }
 102
 103 template<class Parent, class Member>
 104 BOOST_INTRUSIVE_FORCEINLINE const Parent *parent_from_member(const Member *member, const Member Parent::* ptr_to_member)
 105 {
 106    return static_cast<const Parent*>
 107       (
 108          static_cast<const void*>
 109          (
 110             static_cast<const char*>(static_cast<const void*>(member)) - offset_from_pointer_to_member(ptr_to_member)
 111          )
 112       );
 113 }
 114
 115 }  //namespace detail {
 116 }  //namespace intrusive {
 117 }  //namespace boost {
 118
 119 #include <boost/intrusive/detail/config_end.hpp>
 120
 121 #endif   //#ifndef BOOST_INTRUSIVE_DETAIL_PARENT_FROM_MEMBER_HPP