boostorg/utility
1
0
Fork 1
mirror of https://github.com/boostorg/utility.git synced 2025-08-02 14:24:30 +02:00
Code Issues Packages Projects Releases Wiki Activity

added sample implementation using alignment_of

Browse Source 
[SVN r2021]
This commit is contained in:
Jonathan Turkanis
2004-03-04 02:29:06 +00:00
parent 9063a9706c
commit c0fad973aa
1 changed files with 41 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

56
include/boost/utility/select_by_size.hpp
View File

@@ -9,17 +9,20 @@
// Provides an arbitrary number of types (case_<0>, case_<1>, ...) for
// determining the results of overload resultion using 'sizeof', plus a uniform
// means of using the result. yes_type and no_type are typedefs for case_<1>
// and case_<0>.
// and case_<0>. A single case with negative argument, case_<-1>, is also
// provided, for convenience.
//
// This header may be included any number of times, with
// BOOST_SELECT_BY_SIZE_CASES defined to be the number of cases needed for a
// particular application. It defaults to 2.
// BOOST_SELECT_BY_SIZE_MAX_CASE defined to be the largest N such that case_<N>
// is needed for a particular application. It defaults to 2.
//
// This header depends only on Boost.Config and Boost.Preprocessor.
// This header depends only on Boost.Config and Boost.Preprocessor. Dependence
// on Type Traits or MPL was intentionally avoided, to leave open the
// possibility that select_by_size could be used by these libraries.
//
// Example usage:
//
// #define BOOST_SELECT_BY_SIZE_CASES 8 // Needed for > 2 cases.
// #define BOOST_SELECT_BY_SIZE_MAX_CASE 7 // Needed for > 2 cases.
// #include <boost/utility/select_by_size.hpp>
//
// using namespace boost::utility;
@@ -61,10 +64,31 @@
// specialized.
#define SELECT_BY_SIZE_MAX_SPECIALIZED 2
#include <boost/config.hpp> // BOOST_STATIC_CONSTANT, BOOST_NESTED_TEMPLATE
#include <boost/config.hpp> // BOOST_STATIC_CONSTANT.
#include <boost/preprocessor/arithmetic/inc.hpp>
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/repetition/repeat_from_to.hpp>
#include <boost/preprocessor/repetition/repeat_from_to.hpp>
/* Alternative implementation using max_align.
#include <boost/type_traits/alignment_of.hpp>
#include <boost/type_traits/type_with_alignment.hpp>
namespace boost { namespace utility {
template<int N>
struct case_ { char c[(N + 1) * alignment_of<detail::max_align>::value]; };
template<unsigned Size>
struct select_by_size {
BOOST_STATIC_CONSTANT(int, value =
(Size / alignment_of<detail::max_align>::value - 1));
};
} } // End namespaces utility, boost.
*/ // End alternate implementation.
namespace boost { namespace utility {
@@ -84,7 +108,7 @@ template<unsigned Size> struct select_by_size;
//--------------Definition of SELECT_BY_SIZE_SPEC-----------------------------//
// Sepecializes select_by_size for sizeof(case<n-1>). The decrement is used
// here because -1 cannot be passed
// here because the preprocessor library doesn't handle negative integers.
#define SELECT_BY_SIZE_SPEC(n) \
namespace boost { namespace utility { \
namespace detail { \
@@ -92,7 +116,8 @@ template<unsigned Size> struct select_by_size;
} \
template<> \
struct select_by_size< detail::BOOST_PP_CAT(sizeof_case_, n) > { \
BOOST_STATIC_CONSTANT(int, value = n - 1); \
struct type { BOOST_STATIC_CONSTANT(int, value = n - 1); }; \
BOOST_STATIC_CONSTANT(int, value = type::value); \
}; \
} } \
/**/
@@ -129,21 +154,22 @@ SELECT_BY_SIZE_SPEC(2) // select_by_size< sizeof(case<1>) >
#if !BOOST_PP_IS_ITERATING //-------------------------------------------------//
#include <boost/preprocessor/iteration/iterate.hpp>
#if !defined(BOOST_SELECT_BY_SIZE_CASES) || (BOOST_SELECT_BY_SIZE_CASES < 2)
#undef BOOST_SELECT_BY_SIZE_CASES
#define BOOST_SELECT_BY_SIZE_CASES 2
#if !defined(BOOST_SELECT_BY_SIZE_MAX_CASE) || \
(BOOST_SELECT_BY_SIZE_MAX_CASE < 2)
#undef BOOST_SELECT_BY_SIZE_MAX_CASE
#define BOOST_SELECT_BY_SIZE_MAX_CASE 2
#endif
#if (BOOST_SELECT_BY_SIZE_CASES > SELECT_BY_SIZE_MAX_SPECIALIZED)
#if (BOOST_SELECT_BY_SIZE_MAX_CASE > SELECT_BY_SIZE_MAX_SPECIALIZED)
#define BOOST_PP_FILENAME_1 <boost/utility/select_by_size.hpp>
#define BOOST_PP_ITERATION_LIMITS ( SELECT_BY_SIZE_MAX_SPECIALIZED, \
BOOST_SELECT_BY_SIZE_CASES )
BOOST_SELECT_BY_SIZE_MAX_CASE )
#include BOOST_PP_ITERATE()
#undef SELECT_BY_SIZE_MAX_SPECIALIZED
#define SELECT_BY_SIZE_MAX_SPECIALIZED BOOST_SELECT_BY_SIZE_CASES
#define SELECT_BY_SIZE_MAX_SPECIALIZED BOOST_SELECT_BY_SIZE_MAX_CASE
#endif // #if (BOOST_SELECT_BY_SIZE_CASES > SELECT_BY_SIZE_MAX_SPECIALIZED)
#undef BOOST_SELECT_BY_SIZE_CASES
#undef BOOST_SELECT_BY_SIZE_MAX_CASE
#else // #if !BOOST_PP_IS_ITERATING //----------------------------------------//
SELECT_BY_SIZE_SPEC(BOOST_PP_INC(BOOST_PP_ITERATION()))
#endif // #if !BOOST_PP_IS_ITERATING //---------------------------------------//