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include/boost/container_hash/detail/float_functions.hpp  view on Meta::CPAN

        template <> struct is<boost::hash_detail::not_found> { char x[40]; };
            
        // Used to convert the return type of a function to a type for sizeof.

        template <typename T> is<T> float_type(T);

        // call_ldexp
        //
        // This will get specialized for float and long double
        
        template <typename Float> struct call_ldexp
        {
            typedef double float_type;
            
            inline double operator()(double a, int b) const
            {
                using namespace std;
                return ldexp(a, b);
            }
        };

        // call_frexp
        //
        // This will get specialized for float and long double

        template <typename Float> struct call_frexp
        {
            typedef double float_type;
            
            inline double operator()(double a, int* b) const
            {
                using namespace std;
                return frexp(a, b);
            }
        };
    }
}
            
// A namespace for dummy functions to detect when the actual function we want
// isn't available. ldexpl, ldexpf etc. might be added tby the macros below.
//
// AFAICT these have to be outside of the boost namespace, as if they're in
// the boost namespace they'll always be preferable to any other function
// (since the arguments are built in types, ADL can't be used).

namespace boost_hash_detect_float_functions {
    template <class Float> boost::hash_detail::not_found ldexp(Float, int);
    template <class Float> boost::hash_detail::not_found frexp(Float, int*);    
}

// Macros for generating specializations of call_ldexp and call_frexp.
//
// check_cpp and check_c99 check if the C++ or C99 functions are available.
//
// Then the call_* functions select an appropriate implementation.
//
// I used c99_func in a few places just to get a unique name.
//
// Important: when using 'using namespace' at namespace level, include as
// little as possible in that namespace, as Visual C++ has an odd bug which
// can cause the namespace to be imported at the global level. This seems to
// happen mainly when there's a template in the same namesapce.

#define BOOST_HASH_CALL_FLOAT_FUNC(cpp_func, c99_func, type1, type2)    \
namespace boost_hash_detect_float_functions {                           \
    template <class Float>                                              \
    boost::hash_detail::not_found c99_func(Float, type2);               \
}                                                                       \
                                                                        \
namespace boost {                                                       \
    namespace hash_detail {                                             \
        namespace c99_func##_detect {                                   \
            using namespace std;                                        \
            using namespace boost_hash_detect_float_functions;          \
                                                                        \
            struct check {                                              \
                static type1 x;                                         \
                static type2 y;                                         \
                BOOST_STATIC_CONSTANT(bool, cpp =                       \
                    sizeof(float_type(cpp_func(x,y)))                   \
                        == sizeof(is<type1>));                          \
                BOOST_STATIC_CONSTANT(bool, c99 =                       \
                    sizeof(float_type(c99_func(x,y)))                   \
                        == sizeof(is<type1>));                          \
            };                                                          \
        }                                                               \
                                                                        \
        template <bool x>                                               \
        struct call_c99_##c99_func :                                    \
            boost::hash_detail::call_##cpp_func<double> {};             \
                                                                        \
        template <>                                                     \
        struct call_c99_##c99_func<true> {                              \
            typedef type1 float_type;                                   \
                                                                        \
            template <typename T>                                       \
            inline type1 operator()(type1 a, T b)  const                \
            {                                                           \
                using namespace std;                                    \
                return c99_func(a, b);                                  \
            }                                                           \
        };                                                              \
                                                                        \
        template <bool x>                                               \
        struct call_cpp_##c99_func :                                    \
            call_c99_##c99_func<                                        \
                ::boost::hash_detail::c99_func##_detect::check::c99     \
            > {};                                                       \
                                                                        \
        template <>                                                     \
        struct call_cpp_##c99_func<true> {                              \
            typedef type1 float_type;                                   \
                                                                        \
            template <typename T>                                       \
            inline type1 operator()(type1 a, T b)  const                \
            {                                                           \
                using namespace std;                                    \
                return cpp_func(a, b);                                  \
            }                                                           \
        };                                                              \
                                                                        \