ceph/src/boost/libs/iostreams/include/boost/iostreams/detail/select_by_size.hpp

   1 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
   2 // (C) Copyright 2004-2007 Jonathan Turkanis
   3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
   5
   6 // See http://www.boost.org/libs/iostreams for documentation.
   7
   8 //
   9 // Intended as an alternative to type_traits::yes_type and type_traits::no_type.
  10 // Provides an arbitrary number of types (case_<0>, case_<1>, ...) for
  11 // determining the results of overload resultion using 'sizeof', plus a uniform
  12 // means of using the result. yes_type and no_type are typedefs for case_<1>
  13 // and case_<0>. A single case with negative argument, case_<-1>, is also
  14 // provided, for convenience.
  15 //
  16 // This header may be included any number of times, with
  17 // BOOST_SELECT_BY_SIZE_MAX_CASE defined to be the largest N such that case_<N>
  18 // is needed for a particular application. It defaults to 20.
  19 //
  20 // This header depends only on Boost.Config and Boost.Preprocessor. Dependence
  21 // on Type Traits or MPL was intentionally avoided, to leave open the
  22 // possibility that select_by_size could be used by these libraries.
  23 //
  24 // Example usage:
  25 //
  26 //    #define BOOST_SELECT_BY_SIZE_MAX_CASE 7   // (Needed when default was 2)
  27 //    #include <boost/utility/select_by_size.hpp>
  28 //
  29 //    using namespace boost::utility;
  30 //
  31 //    case_<0> helper(bool);
  32 //    case_<1> helper(int);
  33 //    case_<2> helper(unsigned);
  34 //    case_<3> helper(long);
  35 //    case_<4> helper(unsigned long);
  36 //    case_<5> helper(float);
  37 //    case_<6> helper(double);
  38 //    case_<7> helper(const char*);
  39 //
  40 //    struct test {
  41 //        static const int value =
  42 //            select_by_size< sizeof(helper(9876UL)) >::value;
  43 //        BOOST_STATIC_ASSERT(value == 4);
  44 //    };
  45 //
  46 // For compilers with integral constant expression problems, e.g. Borland 5.x,
  47 // one can also write
  48 //
  49 //    struct test {
  50 //        BOOST_SELECT_BY_SIZE(int, value, helper(9876UL));
  51 //    };
  52 //
  53 // to define a static integral constant 'value' equal to
  54 //
  55 //    select_by_size< sizeof(helper(9876UL)) >::value.
  56 //
  57
  58 // Include guards surround all contents of this header except for explicit
  59 // specializations of select_by_size for case_<N> with N > 2.
  60
  61 #ifndef BOOST_IOSTREAMS_DETAIL_SELECT_BY_SIZE_HPP_INCLUDED
  62 #define BOOST_IOSTREAMS_DETAIL_SELECT_BY_SIZE_HPP_INCLUDED
  63
  64 // The lowest N for which select_by_size< sizeof(case_<N>) > has not been
  65 // specialized.
  66 #define SELECT_BY_SIZE_MAX_SPECIALIZED 20
  67
  68 #include <boost/config.hpp>    // BOOST_STATIC_CONSTANT.
  69 #include <boost/preprocessor/cat.hpp>
  70 #include <boost/preprocessor/iteration/local.hpp>
  71
  72 /* Alternative implementation using max_align.
  73
  74 #include <boost/type_traits/alignment_of.hpp>
  75 #include <boost/type_traits/type_with_alignment.hpp>
  76
  77 namespace boost { namespace utility {
  78
  79 template<int N>
  80 struct case_ { char c[(N + 1) * alignment_of<detail::max_align>::value]; };
  81
  82 template<unsigned Size>
  83 struct select_by_size {
  84     BOOST_STATIC_CONSTANT(int, value =
  85         (Size / alignment_of<detail::max_align>::value - 1));
  86 };
  87
  88 } } // End namespaces utility, boost.
  89
  90 */              // End alternate implementation.
  91
  92 namespace boost { namespace iostreams { namespace detail {
  93
  94 //--------------Definition of case_-------------------------------------------//
  95
  96 template<int N> struct case_ { char c1; case_<N - 1> c2; };
  97 template<> struct case_<-1> { char c; };
  98 typedef case_<true> yes_type;
  99 typedef case_<false> no_type;
 100
 101 //--------------Declaration of select_by_size---------------------------------//
 102
 103 template<unsigned Size> struct select_by_size;
 104
 105 } } } // End namespaces detail, iostreams, boost.
 106
 107 //--------------Definition of SELECT_BY_SIZE_SPEC-----------------------------//
 108
 109 // Sepecializes select_by_size for sizeof(case<n-1>). The decrement is used
 110 // here because the preprocessor library doesn't handle negative integers.
 111 #define SELECT_BY_SIZE_SPEC(n) \
 112     namespace boost { namespace iostreams { namespace detail { \
 113       static const int BOOST_PP_CAT(sizeof_case_, n) = sizeof(case_<n - 1>); \
 114       template<> \
 115       struct select_by_size< BOOST_PP_CAT(sizeof_case_, n) > { \
 116           struct type { BOOST_STATIC_CONSTANT(int, value = n - 1); }; \
 117           BOOST_STATIC_CONSTANT(int, value = type::value); \
 118       }; \
 119     } } } \
 120     /**/
 121
 122 //--------------Default specializations of select_by_size---------------------//
 123
 124 #define BOOST_PP_LOCAL_MACRO(n) SELECT_BY_SIZE_SPEC(n)
 125 #define BOOST_PP_LOCAL_LIMITS (0, 20)
 126 #include BOOST_PP_LOCAL_ITERATE()
 127 #undef BOOST_PP_LOCAL_MACRO
 128
 129 //--------------Definition of SELECT_BY_SIZE----------------------------------//
 130
 131 #define BOOST_SELECT_BY_SIZE(type_, name, expr) \
 132     BOOST_STATIC_CONSTANT( \
 133         unsigned, \
 134         BOOST_PP_CAT(boost_select_by_size_temp_, name) = sizeof(expr) \
 135     ); \
 136     BOOST_STATIC_CONSTANT( \
 137         type_, \
 138         name = \
 139             ( ::boost::iostreams::detail::select_by_size< \
 140                 BOOST_PP_CAT(boost_select_by_size_temp_, name) \
 141               >::value ) \
 142     ) \
 143     /**/
 144
 145 #endif // #ifndef BOOST_IOSTREAMS_DETAIL_SELECT_BY_SIZE_HPP_INCLUDED
 146
 147 //----------Specializations of SELECT_BY_SIZE (outside main inclued guards)---//
 148
 149 #if defined(BOOST_SELECT_BY_SIZE_MAX_CASE) && \
 150     BOOST_SELECT_BY_SIZE_MAX_CASE > SELECT_BY_SIZE_MAX_SPECIALIZED
 151
 152 #define BOOST_PP_LOCAL_MACRO(n) SELECT_BY_SIZE_SPEC(n)
 153 #define BOOST_PP_LOCAL_LIMITS \
 154     (SELECT_BY_SIZE_MAX_SPECIALIZED, BOOST_SELECT_BY_SIZE_MAX_CASE) \
 155     /**/
 156 #include BOOST_PP_LOCAL_ITERATE()
 157 #undef BOOST_PP_LOCAL_MACRO
 158 #undef SELECT_BY_SIZE_MAX_SPECIALIZED
 159 #define SELECT_BY_SIZE_MAX_SPECIALIZED BOOST_SELECT_BY_SIZE_MAX_CASE
 160
 161 #endif