1 // © Copyright Fernando Luis Cacciola Carballal 2000-2004
2 // Use, modification, and distribution is subject to the Boost Software
3 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
4 // http://www.boost.org/LICENSE_1_0.txt)
6 // See library home page at http://www.boost.org/libs/numeric/conversion
8 // Contact the author at: fernando_cacciola@hotmail.com
10 #ifndef BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
11 #define BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
13 #include "boost/config.hpp"
14 #include "boost/limits.hpp"
16 #include "boost/mpl/int.hpp"
17 #include "boost/mpl/multiplies.hpp"
18 #include "boost/mpl/less.hpp"
19 #include "boost/mpl/equal_to.hpp"
21 #include "boost/type_traits/is_same.hpp"
23 #include "boost/numeric/conversion/detail/meta.hpp"
24 #include "boost/numeric/conversion/detail/int_float_mixture.hpp"
25 #include "boost/numeric/conversion/detail/sign_mixture.hpp"
26 #include "boost/numeric/conversion/detail/udt_builtin_mixture.hpp"
28 namespace boost { namespace numeric { namespace convdetail
30 //---------------------------------------------------------------
31 // Implementations of the compile time predicate "T is subranged"
32 //---------------------------------------------------------------
34 // for integral to integral conversions
35 template<class T,class S>
36 struct subranged_Sig2Unsig
38 // Signed to unsigned conversions are 'subranged' because of possible loose
39 // of negative values.
40 typedef mpl::true_ type ;
43 // for unsigned integral to signed integral conversions
44 template<class T,class S>
45 struct subranged_Unsig2Sig
49 // This code assumes that signed/unsigned integral values are represented
52 // numeric_limits<signed T>::digits + 1 == numeric_limits<unsigned T>::digits
54 // The '+1' is required since numeric_limits<>::digits gives 1 bit less for signed integral types.
56 // This fact is used by the following logic:
58 // if ( (numeric_limits<T>::digits+1) < (2*numeric_limits<S>::digits) )
59 // then the conversion is subranged.
62 typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
63 typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
65 // T is signed, so take digits+1
66 typedef typename T_digits::next u_T_digits ;
68 typedef mpl::int_<2> Two ;
70 typedef typename mpl::multiplies<S_digits,Two>::type S_digits_times_2 ;
72 typedef typename mpl::less<u_T_digits,S_digits_times_2>::type type ;
75 // for integral to integral conversions of the same sign.
76 template<class T,class S>
77 struct subranged_SameSign
79 // An integral conversion of the same sign is subranged if digits(T) < digits(S).
81 typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
82 typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
84 typedef typename mpl::less<T_digits,S_digits>::type type ;
87 // for integral to float conversions
88 template<class T,class S>
89 struct subranged_Int2Float
91 typedef mpl::false_ type ;
94 // for float to integral conversions
95 template<class T,class S>
96 struct subranged_Float2Int
98 typedef mpl::true_ type ;
101 // for float to float conversions
102 template<class T,class S>
103 struct subranged_Float2Float
105 // If both T and S are floats,
106 // compare exponent bits and if they match, mantisa bits.
108 typedef mpl::int_< ::std::numeric_limits<S>::digits > S_mantisa ;
109 typedef mpl::int_< ::std::numeric_limits<T>::digits > T_mantisa ;
111 typedef mpl::int_< ::std::numeric_limits<S>::max_exponent > S_exponent ;
112 typedef mpl::int_< ::std::numeric_limits<T>::max_exponent > T_exponent ;
114 typedef typename mpl::less<T_exponent,S_exponent>::type T_smaller_exponent ;
116 typedef typename mpl::equal_to<T_exponent,S_exponent>::type equal_exponents ;
118 typedef mpl::less<T_mantisa,S_mantisa> T_smaller_mantisa ;
120 typedef mpl::eval_if<equal_exponents,T_smaller_mantisa,mpl::false_> not_bigger_exponent_case ;
123 mpl::eval_if<T_smaller_exponent,mpl::true_,not_bigger_exponent_case>::type
127 // for Udt to built-in conversions
128 template<class T,class S>
129 struct subranged_Udt2BuiltIn
131 typedef mpl::true_ type ;
134 // for built-in to Udt conversions
135 template<class T,class S>
136 struct subranged_BuiltIn2Udt
138 typedef mpl::false_ type ;
141 // for Udt to Udt conversions
142 template<class T,class S>
143 struct subranged_Udt2Udt
145 typedef mpl::false_ type ;
148 //-------------------------------------------------------------------
149 // Selectors for the implementations of the subranged predicate
150 //-------------------------------------------------------------------
152 template<class T,class S>
153 struct get_subranged_Int2Int
155 typedef subranged_SameSign<T,S> Sig2Sig ;
156 typedef subranged_Sig2Unsig<T,S> Sig2Unsig ;
157 typedef subranged_Unsig2Sig<T,S> Unsig2Sig ;
158 typedef Sig2Sig Unsig2Unsig ;
160 typedef typename get_sign_mixture<T,S>::type sign_mixture ;
163 for_sign_mixture<sign_mixture, Sig2Sig, Sig2Unsig, Unsig2Sig, Unsig2Unsig>::type
167 template<class T,class S>
168 struct get_subranged_BuiltIn2BuiltIn
170 typedef get_subranged_Int2Int<T,S> Int2IntQ ;
172 typedef subranged_Int2Float <T,S> Int2Float ;
173 typedef subranged_Float2Int <T,S> Float2Int ;
174 typedef subranged_Float2Float<T,S> Float2Float ;
176 typedef mpl::identity<Int2Float > Int2FloatQ ;
177 typedef mpl::identity<Float2Int > Float2IntQ ;
178 typedef mpl::identity<Float2Float> Float2FloatQ ;
180 typedef typename get_int_float_mixture<T,S>::type int_float_mixture ;
182 typedef for_int_float_mixture<int_float_mixture, Int2IntQ, Int2FloatQ, Float2IntQ, Float2FloatQ> for_ ;
184 typedef typename for_::type selected ;
186 typedef typename selected::type type ;
189 template<class T,class S>
192 typedef get_subranged_BuiltIn2BuiltIn<T,S> BuiltIn2BuiltInQ ;
194 typedef subranged_BuiltIn2Udt<T,S> BuiltIn2Udt ;
195 typedef subranged_Udt2BuiltIn<T,S> Udt2BuiltIn ;
196 typedef subranged_Udt2Udt<T,S> Udt2Udt ;
198 typedef mpl::identity<BuiltIn2Udt> BuiltIn2UdtQ ;
199 typedef mpl::identity<Udt2BuiltIn> Udt2BuiltInQ ;
200 typedef mpl::identity<Udt2Udt > Udt2UdtQ ;
202 typedef typename get_udt_builtin_mixture<T,S>::type udt_builtin_mixture ;
205 for_udt_builtin_mixture<udt_builtin_mixture, BuiltIn2BuiltInQ, BuiltIn2UdtQ, Udt2BuiltInQ, Udt2UdtQ>::type
208 typedef typename selected::type selected2 ;
210 typedef typename selected2::type type ;
214 //-------------------------------------------------------------------
215 // Top level implementation selector.
216 //-------------------------------------------------------------------
217 template<class T, class S>
218 struct get_is_subranged
220 typedef get_subranged<T,S> non_trivial_case ;
221 typedef mpl::identity<mpl::false_> trivial_case ;
223 typedef is_same<T,S> is_trivial ;
225 typedef typename mpl::if_<is_trivial,trivial_case,non_trivial_case>::type selected ;
227 typedef typename selected::type type ;
230 } } } // namespace boost::numeric::convdetail