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e655314f73
The only template mechanism now used is full specialization, so this should hopefully be more portable to compilers we don't test. [SVN r53247]
237 lines
10 KiB
C++
237 lines
10 KiB
C++
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// Copyright 2005-2009 Daniel James.
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#if !defined(BOOST_FUNCTIONAL_HASH_DETAIL_FLOAT_FUNCTIONS_HPP)
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#define BOOST_FUNCTIONAL_HASH_DETAIL_FLOAT_FUNCTIONS_HPP
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#include <boost/config.hpp>
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#include <boost/config/no_tr1/cmath.hpp>
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#if defined(_MSC_VER) && (_MSC_VER >= 1020)
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# pragma once
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#endif
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// The C++ standard requires that the C float functions are overloarded
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// for float, double and long double in the std namespace, but some of the older
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// library implementations don't support this. On some that don't, the C99
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// float functions (frexpf, frexpl, etc.) are available.
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//
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// The following tries to automatically detect which are available.
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namespace boost {
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namespace hash_detail {
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// Returned by dummy versions of the float functions.
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struct not_found {
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// Implicitly convertible to float and long double in order to avoid
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// a compile error when the dummy float functions are used.
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inline operator float() const { return 0; }
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inline operator long double() const { return 0; }
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};
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// A type for detecting the return type of functions.
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template <typename T> struct is;
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template <> struct is<float> { char x[10]; };
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template <> struct is<double> { char x[20]; };
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template <> struct is<long double> { char x[30]; };
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template <> struct is<boost::hash_detail::not_found> { char x[40]; };
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// Used to convert the return type of a function to a type for sizeof.
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template <typename T> is<T> float_type(T);
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// call_ldexp
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//
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// This will get specialized for float and long double
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template <typename Float> struct call_ldexp
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{
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typedef double float_type;
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inline double operator()(double a, int b) const
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{
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using namespace std;
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return ldexp(a, b);
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}
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};
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// call_frexp
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//
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// This will get specialized for float and long double
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template <typename Float> struct call_frexp
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{
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typedef double float_type;
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inline double operator()(double a, int* b) const
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{
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using namespace std;
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return frexp(a, b);
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}
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};
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}
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}
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// A namespace for dummy functions to detect when the actual function we want
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// isn't available. ldexpl, ldexpf etc. might be added tby the macros below.
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//
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// AFAICT these have to be outside of the boost namespace, as if they're in
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// the boost namespace they'll always be preferable to any other function
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// (since the arguments are built in types, ADL can't be used).
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namespace BOOST_HASH_DETECT_FLOAT_FUNCTIONS {
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template <class Float> boost::hash_detail::not_found ldexp(Float, int);
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template <class Float> boost::hash_detail::not_found frexp(Float, int*);
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}
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// Macros for generating specializations of call_ldexp and call_frexp.
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//
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// check_cpp and check_c99 check if the C++ or C99 functions are available.
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//
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// Then the call_* functions select an appropriate implementation.
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//
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// I used c99_func in a few places just to get a unique name.
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#define BOOST_HASH_CALL_FLOAT_FUNC(cpp_func, c99_func, type1, type2) \
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namespace BOOST_HASH_DETECT_FLOAT_FUNCTIONS { \
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boost::hash_detail::not_found c99_func(int, type2); \
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} \
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\
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namespace boost { \
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namespace hash_detail { \
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namespace c99_func##_detect { \
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using namespace std; \
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using namespace BOOST_HASH_DETECT_FLOAT_FUNCTIONS; \
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\
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struct check { \
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static type1 x; \
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static type2 y; \
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BOOST_STATIC_CONSTANT(bool, cpp = \
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sizeof(float_type(cpp_func(x,y))) \
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== sizeof(is<type1>)); \
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BOOST_STATIC_CONSTANT(bool, c99 = \
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sizeof(float_type(c99_func(x,y))) \
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== sizeof(is<type1>)); \
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}; \
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} \
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\
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template <bool x> \
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struct call_##c99_func##_c99 : \
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call_##cpp_func<double> {}; \
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\
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template <> \
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struct call_##c99_func##_c99<true> { \
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typedef type1 float_type; \
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\
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inline type1 operator()(type1 a, type2 b) const \
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{ \
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return c99_func(a, b); \
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} \
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}; \
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\
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template <bool x> \
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struct call_##c99_func##_cpp : \
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call_##c99_func##_c99< \
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::boost::hash_detail::c99_func##_detect::check::c99 \
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> {}; \
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\
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template <> \
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struct call_##c99_func##_cpp<true> { \
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typedef type1 float_type; \
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\
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inline type1 operator()(type1 a, type2 b) const \
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{ \
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return cpp_func(a, b); \
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} \
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}; \
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\
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template <> \
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struct call_##cpp_func<type1> : \
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call_##c99_func##_cpp< \
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::boost::hash_detail::c99_func##_detect::check::cpp \
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> {}; \
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} \
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}
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#define BOOST_HASH_CALL_FLOAT_MACRO(cpp_func, c99_func, type1, type2) \
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namespace boost { \
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namespace hash_detail { \
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\
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template <> \
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struct call_##cpp_func<type1> { \
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typedef type1 float_type; \
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inline type1 operator()(type1 x, type2 y) const { \
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return c99_func(x, y); \
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} \
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}; \
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} \
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}
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#if defined(ldexpf)
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BOOST_HASH_CALL_FLOAT_MACRO(ldexp, ldexpf, float, int)
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#else
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BOOST_HASH_CALL_FLOAT_FUNC(ldexp, ldexpf, float, int)
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#endif
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#if defined(ldexpl)
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BOOST_HASH_CALL_FLOAT_MACRO(ldexp, ldexpl, long double, int)
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#else
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BOOST_HASH_CALL_FLOAT_FUNC(ldexp, ldexpl, long double, int)
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#endif
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#if defined(frexpf)
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BOOST_HASH_CALL_FLOAT_MACRO(frexp, frexpf, float, int*)
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#else
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BOOST_HASH_CALL_FLOAT_FUNC(frexp, frexpf, float, int*)
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#endif
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#if defined(frexpl)
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BOOST_HASH_CALL_FLOAT_MACRO(frexp, frexpl, long double, int*)
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#else
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BOOST_HASH_CALL_FLOAT_FUNC(frexp, frexpl, long double, int*)
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#endif
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#undef BOOST_HASH_CALL_FLOAT_MACRO
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#undef BOOST_HASH_CALL_FLOAT_FUNC
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namespace boost
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{
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namespace hash_detail
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{
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template <typename Float1, typename Float2>
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struct select_hash_type_impl {
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typedef double type;
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};
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template <>
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struct select_hash_type_impl<float, float> {
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typedef float type;
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};
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template <>
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struct select_hash_type_impl<long double, long double> {
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typedef long double type;
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};
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// select_hash_type
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//
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// If there is support for a particular floating point type, use that
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// otherwise use double (there's always support for double).
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template <typename Float>
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struct select_hash_type : select_hash_type_impl<
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BOOST_DEDUCED_TYPENAME call_ldexp<Float>::float_type,
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BOOST_DEDUCED_TYPENAME call_frexp<Float>::float_type
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> {};
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}
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}
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#endif
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