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235 lines
7.5 KiB
C++
235 lines
7.5 KiB
C++
// (c) Copyright Fernando Luis Cacciola Carballal 2000-2004
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// Use, modification, and distribution is subject to the Boost Software
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// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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// See library home page at http://www.boost.org/libs/numeric/conversion
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//
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// Contact the author at: fernando_cacciola@hotmail.com
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//
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#ifndef BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
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#define BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
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#include "boost/config.hpp"
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#include "boost/limits.hpp"
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#include "boost/mpl/int.hpp"
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#include "boost/mpl/multiplies.hpp"
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#include "boost/mpl/less.hpp"
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#include "boost/mpl/equal_to.hpp"
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#include "boost/type_traits/is_same.hpp"
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#include "boost/numeric/conversion/detail/meta.hpp"
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#include "boost/numeric/conversion/detail/int_float_mixture.hpp"
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#include "boost/numeric/conversion/detail/sign_mixture.hpp"
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#include "boost/numeric/conversion/detail/udt_builtin_mixture.hpp"
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namespace boost { namespace numeric { namespace convdetail
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{
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//---------------------------------------------------------------
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// Implementations of the compile time predicate "T is subranged"
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//---------------------------------------------------------------
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// for integral to integral conversions
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template<class T,class S>
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struct subranged_Sig2Unsig
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{
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// Signed to unsigned conversions are 'subranged' because of possible loose
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// of negative values.
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typedef mpl::true_ type ;
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} ;
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// for unsigned integral to signed integral conversions
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template<class T,class S>
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struct subranged_Unsig2Sig
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{
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// IMPORTANT NOTE:
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//
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// This code assumes that signed/unsigned integral values are represented
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// such that:
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//
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// numeric_limits<signed T>::digits + 1 == numeric_limits<unsigned T>::digits
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//
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// The '+1' is required since numeric_limits<>::digits gives 1 bit less for signed integral types.
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//
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// This fact is used by the following logic:
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//
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// if ( (numeric_limits<T>::digits+1) < (2*numeric_limits<S>::digits) )
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// then the conversion is subranged.
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//
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typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
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typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
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// T is signed, so take digits+1
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typedef typename T_digits::next u_T_digits ;
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typedef mpl::int_<2> Two ;
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typedef typename mpl::multiplies<S_digits,Two>::type S_digits_times_2 ;
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typedef typename mpl::less<u_T_digits,S_digits_times_2>::type type ;
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} ;
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// for integral to integral conversions of the same sign.
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template<class T,class S>
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struct subranged_SameSign
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{
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// An integral conversion of the same sign is subranged if digits(T) < digits(S).
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typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
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typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
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typedef typename mpl::less<T_digits,S_digits>::type type ;
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} ;
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// for integral to float conversions
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template<class T,class S>
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struct subranged_Int2Float
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{
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typedef mpl::false_ type ;
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} ;
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// for float to integral conversions
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template<class T,class S>
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struct subranged_Float2Int
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{
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typedef mpl::true_ type ;
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} ;
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// for float to float conversions
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template<class T,class S>
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struct subranged_Float2Float
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{
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// If both T and S are floats,
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// compare exponent bits and if they match, mantisa bits.
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typedef mpl::int_< ::std::numeric_limits<S>::digits > S_mantisa ;
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typedef mpl::int_< ::std::numeric_limits<T>::digits > T_mantisa ;
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typedef mpl::int_< ::std::numeric_limits<S>::max_exponent > S_exponent ;
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typedef mpl::int_< ::std::numeric_limits<T>::max_exponent > T_exponent ;
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typedef typename mpl::less<T_exponent,S_exponent>::type T_smaller_exponent ;
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typedef typename mpl::equal_to<T_exponent,S_exponent>::type equal_exponents ;
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typedef mpl::less<T_mantisa,S_mantisa> T_smaller_mantisa ;
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typedef mpl::eval_if<equal_exponents,T_smaller_mantisa,mpl::false_> not_bigger_exponent_case ;
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typedef typename
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mpl::eval_if<T_smaller_exponent,mpl::true_,not_bigger_exponent_case>::type
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type ;
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} ;
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// for Udt to built-in conversions
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template<class T,class S>
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struct subranged_Udt2BuiltIn
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{
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typedef mpl::true_ type ;
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} ;
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// for built-in to Udt conversions
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template<class T,class S>
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struct subranged_BuiltIn2Udt
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{
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typedef mpl::false_ type ;
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} ;
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// for Udt to Udt conversions
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template<class T,class S>
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struct subranged_Udt2Udt
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{
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typedef mpl::false_ type ;
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} ;
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//-------------------------------------------------------------------
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// Selectors for the implementations of the subranged predicate
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//-------------------------------------------------------------------
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template<class T,class S>
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struct get_subranged_Int2Int
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{
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typedef subranged_SameSign<T,S> Sig2Sig ;
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typedef subranged_Sig2Unsig<T,S> Sig2Unsig ;
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typedef subranged_Unsig2Sig<T,S> Unsig2Sig ;
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typedef Sig2Sig Unsig2Unsig ;
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typedef typename get_sign_mixture<T,S>::type sign_mixture ;
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typedef typename
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for_sign_mixture<sign_mixture, Sig2Sig, Sig2Unsig, Unsig2Sig, Unsig2Unsig>::type
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type ;
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} ;
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template<class T,class S>
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struct get_subranged_BuiltIn2BuiltIn
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{
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typedef get_subranged_Int2Int<T,S> Int2IntQ ;
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typedef subranged_Int2Float <T,S> Int2Float ;
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typedef subranged_Float2Int <T,S> Float2Int ;
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typedef subranged_Float2Float<T,S> Float2Float ;
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typedef mpl::identity<Int2Float > Int2FloatQ ;
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typedef mpl::identity<Float2Int > Float2IntQ ;
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typedef mpl::identity<Float2Float> Float2FloatQ ;
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typedef typename get_int_float_mixture<T,S>::type int_float_mixture ;
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typedef for_int_float_mixture<int_float_mixture, Int2IntQ, Int2FloatQ, Float2IntQ, Float2FloatQ> for_ ;
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typedef typename for_::type selected ;
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typedef typename selected::type type ;
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} ;
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template<class T,class S>
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struct get_subranged
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{
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typedef get_subranged_BuiltIn2BuiltIn<T,S> BuiltIn2BuiltInQ ;
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typedef subranged_BuiltIn2Udt<T,S> BuiltIn2Udt ;
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typedef subranged_Udt2BuiltIn<T,S> Udt2BuiltIn ;
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typedef subranged_Udt2Udt<T,S> Udt2Udt ;
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typedef mpl::identity<BuiltIn2Udt> BuiltIn2UdtQ ;
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typedef mpl::identity<Udt2BuiltIn> Udt2BuiltInQ ;
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typedef mpl::identity<Udt2Udt > Udt2UdtQ ;
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typedef typename get_udt_builtin_mixture<T,S>::type udt_builtin_mixture ;
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typedef typename
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for_udt_builtin_mixture<udt_builtin_mixture, BuiltIn2BuiltInQ, BuiltIn2UdtQ, Udt2BuiltInQ, Udt2UdtQ>::type
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selected ;
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typedef typename selected::type selected2 ;
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typedef typename selected2::type type ;
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} ;
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//-------------------------------------------------------------------
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// Top level implementation selector.
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//-------------------------------------------------------------------
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template<class T, class S>
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struct get_is_subranged
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{
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typedef get_subranged<T,S> non_trivial_case ;
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typedef mpl::identity<mpl::false_> trivial_case ;
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typedef is_same<T,S> is_trivial ;
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typedef typename mpl::if_<is_trivial,trivial_case,non_trivial_case>::type selected ;
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typedef typename selected::type type ;
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} ;
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} } } // namespace boost::numeric::convdetail
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#endif
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