boost/boost/type_traits/type_with_alignment.hpp

   1
   2 // (C) Copyright John Maddock 2000.
   3 // Permission to copy, use, modify, sell and distribute this software is
   4 // granted provided this copyright notice appears in all copies. This
   5 // software is provided "as is" without express or implied warranty,
   6 // and with no claim as to its suitability for any purpose.
   7
   8 #ifndef BOOST_TT_TYPE_WITH_ALIGNMENT_INCLUDED
   9 #define BOOST_TT_TYPE_WITH_ALIGNMENT_INCLUDED
  10
  11 #include "boost/mpl/if.hpp"
  12 #include "boost/preprocessor/list/for_each_i.hpp"
  13 #include "boost/preprocessor/tuple/to_list.hpp"
  14 #include "boost/preprocessor/cat.hpp"
  15 #include "boost/type_traits/alignment_of.hpp"
  16 #include "boost/type_traits/is_pod.hpp"
  17 #include "boost/static_assert.hpp"
  18 #include "boost/config.hpp"
  19
  20 // should be the last #include
  21 #include "boost/type_traits/detail/bool_trait_def.hpp"
  22
  23 #include <cstddef>
  24
  25 #ifdef BOOST_MSVC
  26 #   pragma warning(push)
  27 #   pragma warning(disable: 4121) // alignment is sensitive to packing
  28 #endif
  29
  30 namespace boost {
  31
  32 #ifndef __BORLANDC__
  33
  34 namespace detail {
  35
  36 class alignment_dummy;
  37 typedef void (*function_ptr)();
  38 typedef int (alignment_dummy::*member_ptr);
  39 typedef int (alignment_dummy::*member_function_ptr)();
  40
  41 #define BOOST_TT_ALIGNMENT_TYPES BOOST_PP_TUPLE_TO_LIST( \
  42         11, ( \
  43         char, short, int, long, float, double, long double \
  44         , void*, function_ptr, member_ptr, member_function_ptr))
  45
  46 #define BOOST_TT_CHOOSE_MIN_ALIGNMENT(R,P,I,T) \
  47         typename mpl::if_c< \
  48            alignment_of<T>::value <= target, T, char>::type BOOST_PP_CAT(t,I);
  49
  50 #define BOOST_TT_CHOOSE_T(R,P,I,T) T BOOST_PP_CAT(t,I);
  51
  52 template <std::size_t target>
  53 union lower_alignment
  54 {
  55     BOOST_PP_LIST_FOR_EACH_I(
  56           BOOST_TT_CHOOSE_MIN_ALIGNMENT
  57         , ignored
  58         , BOOST_TT_ALIGNMENT_TYPES
  59         )
  60 };
  61
  62 union max_align
  63 {
  64     BOOST_PP_LIST_FOR_EACH_I(
  65           BOOST_TT_CHOOSE_T
  66         , ignored
  67         , BOOST_TT_ALIGNMENT_TYPES
  68         )
  69 };
  70
  71 #undef BOOST_TT_ALIGNMENT_TYPES
  72 #undef BOOST_TT_CHOOSE_MIN_ALIGNMENT
  73 #undef BOOST_TT_CHOOSE_T
  74
  75 template<int TAlign, int Align>
  76 struct is_aligned
  77 {
  78     BOOST_STATIC_CONSTANT(bool,
  79         value = (TAlign >= Align) & (TAlign % Align == 0)
  80         );
  81 };
  82
  83 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::max_align,true)
  84 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<1> ,true)
  85 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<2> ,true)
  86 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<4> ,true)
  87 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<8> ,true)
  88 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<10> ,true)
  89 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<16> ,true)
  90 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::detail::lower_alignment<32> ,true)
  91
  92 } // namespace detail
  93
  94 // This alignment method originally due to Brian Parker, implemented by David
  95 // Abrahams, and then ported here by Doug Gregor.
  96 template <int Align>
  97 class type_with_alignment
  98 {
  99     typedef detail::lower_alignment<Align> t1;
 100     typedef typename mpl::if_c<
 101           ::boost::detail::is_aligned< ::boost::alignment_of<t1>::value,Align >::value
 102         , t1
 103         , detail::max_align
 104         >::type align_t;
 105
 106     BOOST_STATIC_CONSTANT(std::size_t, found = alignment_of<align_t>::value);
 107
 108 #ifndef __BORLANDC__
 109     BOOST_STATIC_ASSERT(found >= Align);
 110     BOOST_STATIC_ASSERT(found % Align == 0);
 111 #else
 112     BOOST_STATIC_ASSERT(::boost::type_with_alignment<Align>::found >= Align);
 113     BOOST_STATIC_ASSERT(::boost::type_with_alignment<Align>::found % Align == 0);
 114 #endif
 115
 116  public:
 117     typedef align_t type;
 118 };
 119
 120 #else
 121
 122 //
 123 // Borland specific version, we have this for two reasons:
 124 // 1) The version above doesn't always compile (with the new test cases for example)
 125 // 2) Because of Borlands #pragma option we can create types with alignments that are
 126 //    greater that the largest aligned builtin type.
 127
 128 namespace align{
 129 #pragma option push -a16
 130 struct a2{ short s; };
 131 struct a4{ int s; };
 132 struct a8{ double s; };
 133 struct a16{ long double s; };
 134 #pragma option pop
 135 }
 136
 137 namespace detail {
 138 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::align::a2,true)
 139 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::align::a4,true)
 140 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::align::a8,true)
 141 BOOST_TT_AUX_BOOL_TRAIT_IMPL_SPEC1(is_pod,::boost::align::a16,true)
 142 }
 143
 144 template <std::size_t N> struct type_with_alignment
 145 {
 146    // We should never get to here, but if we do use the maximally
 147    // aligned type:
 148    // BOOST_STATIC_ASSERT(0);
 149    typedef align::a16 type;
 150 };
 151 template <> struct type_with_alignment<1>{ typedef char type; };
 152 template <> struct type_with_alignment<2>{ typedef align::a2 type; };
 153 template <> struct type_with_alignment<4>{ typedef align::a4 type; };
 154 template <> struct type_with_alignment<8>{ typedef align::a8 type; };
 155 template <> struct type_with_alignment<16>{ typedef align::a16 type; };
 156
 157 #endif
 158
 159 } // namespace boost
 160
 161 #ifdef BOOST_MSVC
 162 #   pragma warning(pop)
 163 #endif
 164
 165 #include "boost/type_traits/detail/bool_trait_undef.hpp"
 166
 167 #endif // BOOST_TT_TYPE_WITH_ALIGNMENT_INCLUDED
 168
 169