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/Src/Dependencies/Boost/boost/iostreams/detail/select_by_size.hpp

http://hadesmem.googlecode.com/
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  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
 77namespace boost { namespace utility {
 78
 79template<int N>
 80struct case_ { char c[(N + 1) * alignment_of<detail::max_align>::value]; };
 81
 82template<unsigned Size>
 83struct 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
 92namespace boost { namespace iostreams { namespace detail {
 93
 94//--------------Definition of case_-------------------------------------------//
 95
 96template<int N> struct case_ { char c1; case_<N - 1> c2; };
 97template<> struct case_<-1> { char c; };
 98typedef case_<true> yes_type;
 99typedef case_<false> no_type;
100
101//--------------Declaration of select_by_size---------------------------------//
102
103template<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 BOOST_SELECT_BY_SIZE_MAX_CASE > SELECT_BY_SIZE_MAX_SPECIALIZED
150
151#define BOOST_PP_LOCAL_MACRO(n) SELECT_BY_SIZE_SPEC(n)
152#define BOOST_PP_LOCAL_LIMITS \
153    (SELECT_BY_SIZE_MAX_SPECIALIZED, BOOST_SELECT_BY_SIZE_MAX_CASE) \
154    /**/
155#include BOOST_PP_LOCAL_ITERATE()
156#undef BOOST_PP_LOCAL_MACRO
157#undef SELECT_BY_SIZE_MAX_SPECIALIZED
158#define SELECT_BY_SIZE_MAX_SPECIALIZED BOOST_SELECT_BY_SIZE_MAX_CASE
159
160#endif