boost/functional/hash/detail/float_functions.hpp
// Copyright 2005-2009 Daniel James. // Distributed under the Boost Software License, Version 1.0. (See accompanying // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) #if !defined(BOOST_FUNCTIONAL_HASH_DETAIL_FLOAT_FUNCTIONS_HPP) #define BOOST_FUNCTIONAL_HASH_DETAIL_FLOAT_FUNCTIONS_HPP #include <boost/config.hpp> #include <boost/config/no_tr1/cmath.hpp> #if defined(_MSC_VER) && (_MSC_VER >= 1020) # pragma once #endif // The C++ standard requires that the C float functions are overloarded // for float, double and long double in the std namespace, but some of the older // library implementations don't support this. On some that don't, the C99 // float functions (frexpf, frexpl, etc.) are available. // // The following tries to automatically detect which are available. namespace boost { namespace hash_detail { // Returned by dummy versions of the float functions. struct not_found { // Implicitly convertible to float and long double in order to avoid // a compile error when the dummy float functions are used. inline operator float() const { return 0; } inline operator long double() const { return 0; } }; // A type for detecting the return type of functions. template <typename T> struct is; template <> struct is<float> { char x[10]; }; template <> struct is<double> { char x[20]; }; template <> struct is<long double> { char x[30]; }; 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); \ } \ }; \ \ template <> \ struct call_##cpp_func<type1> : \ call_cpp_##c99_func< \ ::boost::hash_detail::c99_func##_detect::check::cpp \ > {}; \ } \ } #define BOOST_HASH_CALL_FLOAT_MACRO(cpp_func, c99_func, type1, type2) \ namespace boost { \ namespace hash_detail { \ \ template <> \ struct call_##cpp_func<type1> { \ typedef type1 float_type; \ inline type1 operator()(type1 x, type2 y) const { \ return c99_func(x, y); \ } \ }; \ } \ } #if defined(ldexpf) BOOST_HASH_CALL_FLOAT_MACRO(ldexp, ldexpf, float, int) #else BOOST_HASH_CALL_FLOAT_FUNC(ldexp, ldexpf, float, int) #endif #if defined(ldexpl) BOOST_HASH_CALL_FLOAT_MACRO(ldexp, ldexpl, long double, int) #else BOOST_HASH_CALL_FLOAT_FUNC(ldexp, ldexpl, long double, int) #endif #if defined(frexpf) BOOST_HASH_CALL_FLOAT_MACRO(frexp, frexpf, float, int*) #else BOOST_HASH_CALL_FLOAT_FUNC(frexp, frexpf, float, int*) #endif #if defined(frexpl) BOOST_HASH_CALL_FLOAT_MACRO(frexp, frexpl, long double, int*) #else BOOST_HASH_CALL_FLOAT_FUNC(frexp, frexpl, long double, int*) #endif #undef BOOST_HASH_CALL_FLOAT_MACRO #undef BOOST_HASH_CALL_FLOAT_FUNC namespace boost { namespace hash_detail { template <typename Float1, typename Float2> struct select_hash_type_impl { typedef double type; }; template <> struct select_hash_type_impl<float, float> { typedef float type; }; template <> struct select_hash_type_impl<long double, long double> { typedef long double type; }; // select_hash_type // // If there is support for a particular floating point type, use that // otherwise use double (there's always support for double). template <typename Float> struct select_hash_type : select_hash_type_impl< BOOST_DEDUCED_TYPENAME call_ldexp<Float>::float_type, BOOST_DEDUCED_TYPENAME call_frexp<Float>::float_type > {}; } } #endif