1 //  (c) 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)
5 
6 //  See library home page at http://www.boost.org/libs/numeric/conversion
7 //
8 // Contact the author at: [email protected]
9 //
10 #ifndef BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
11 #define BOOST_NUMERIC_CONVERSION_DETAIL_IS_SUBRANGED_FLC_12NOV2002_HPP
12 
13 #include "boost/config.hpp"
14 #include "boost/limits.hpp"
15 
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"
20 
21 #include "boost/type_traits/is_same.hpp"
22 
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"
27 
28 namespace boost { namespace numeric { namespace convdetail
29 {
30   //---------------------------------------------------------------
31   // Implementations of the compile time predicate "T is subranged"
32   //---------------------------------------------------------------
33 
34     // for integral to integral conversions
35     template<class T,class S>
36     struct subranged_Sig2Unsig
37     {
38       // Signed to unsigned conversions are 'subranged' because of possible loose
39       // of negative values.
40       typedef mpl::true_ type ;
41     } ;
42 
43     // for unsigned integral to signed integral conversions
44     template<class T,class S>
45     struct subranged_Unsig2Sig
46     {
47        // IMPORTANT NOTE:
48        //
49        // This code assumes that signed/unsigned integral values are represented
50        // such that:
51        //
52        //  numeric_limits<signed T>::digits + 1 == numeric_limits<unsigned T>::digits
53        //
54        // The '+1' is required since numeric_limits<>::digits gives 1 bit less for signed integral types.
55        //
56        // This fact is used by the following logic:
57        //
58        //  if ( (numeric_limits<T>::digits+1) < (2*numeric_limits<S>::digits) )
59        //    then the conversion is subranged.
60        //
61 
62        typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
63        typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
64 
65        // T is signed, so take digits+1
66        typedef typename T_digits::next u_T_digits ;
67 
68        typedef mpl::int_<2> Two ;
69 
70        typedef typename mpl::multiplies<S_digits,Two>::type S_digits_times_2 ;
71 
72        typedef typename mpl::less<u_T_digits,S_digits_times_2>::type type ;
73     } ;
74 
75     // for integral to integral conversions of the same sign.
76     template<class T,class S>
77     struct subranged_SameSign
78     {
79        // An integral conversion of the same sign is subranged if digits(T) < digits(S).
80 
81        typedef mpl::int_< ::std::numeric_limits<S>::digits > S_digits ;
82        typedef mpl::int_< ::std::numeric_limits<T>::digits > T_digits ;
83 
84        typedef typename mpl::less<T_digits,S_digits>::type type ;
85     } ;
86 
87     // for integral to float conversions
88     template<class T,class S>
89     struct subranged_Int2Float
90     {
91       typedef mpl::false_ type ;
92     } ;
93 
94     // for float to integral conversions
95     template<class T,class S>
96     struct subranged_Float2Int
97     {
98       typedef mpl::true_ type ;
99     } ;
100 
101     // for float to float conversions
102     template<class T,class S>
103     struct subranged_Float2Float
104     {
105       // If both T and S are floats,
106       // compare exponent bits and if they match, mantisa bits.
107 
108       typedef mpl::int_< ::std::numeric_limits<S>::digits > S_mantisa ;
109       typedef mpl::int_< ::std::numeric_limits<T>::digits > T_mantisa ;
110 
111       typedef mpl::int_< ::std::numeric_limits<S>::max_exponent > S_exponent ;
112       typedef mpl::int_< ::std::numeric_limits<T>::max_exponent > T_exponent ;
113 
114       typedef typename mpl::less<T_exponent,S_exponent>::type T_smaller_exponent ;
115 
116       typedef typename mpl::equal_to<T_exponent,S_exponent>::type equal_exponents ;
117 
118       typedef mpl::less<T_mantisa,S_mantisa> T_smaller_mantisa ;
119 
120       typedef mpl::eval_if<equal_exponents,T_smaller_mantisa,mpl::false_> not_bigger_exponent_case ;
121 
122       typedef typename
123         mpl::eval_if<T_smaller_exponent,mpl::true_,not_bigger_exponent_case>::type
124           type ;
125     } ;
126 
127     // for Udt to built-in conversions
128     template<class T,class S>
129     struct subranged_Udt2BuiltIn
130     {
131       typedef mpl::true_ type ;
132     } ;
133 
134     // for built-in to Udt conversions
135     template<class T,class S>
136     struct subranged_BuiltIn2Udt
137     {
138       typedef mpl::false_ type ;
139     } ;
140 
141     // for Udt to Udt conversions
142     template<class T,class S>
143     struct subranged_Udt2Udt
144     {
145       typedef mpl::false_ type ;
146     } ;
147 
148   //-------------------------------------------------------------------
149   // Selectors for the implementations of the subranged predicate
150   //-------------------------------------------------------------------
151 
152     template<class T,class S>
153     struct get_subranged_Int2Int
154     {
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 ;
159 
160       typedef typename get_sign_mixture<T,S>::type sign_mixture ;
161 
162       typedef typename
163         for_sign_mixture<sign_mixture, Sig2Sig, Sig2Unsig, Unsig2Sig, Unsig2Unsig>::type
164            type ;
165     } ;
166 
167     template<class T,class S>
168     struct get_subranged_BuiltIn2BuiltIn
169     {
170       typedef get_subranged_Int2Int<T,S> Int2IntQ ;
171 
172       typedef subranged_Int2Float  <T,S> Int2Float   ;
173       typedef subranged_Float2Int  <T,S> Float2Int   ;
174       typedef subranged_Float2Float<T,S> Float2Float ;
175 
176       typedef mpl::identity<Int2Float  > Int2FloatQ   ;
177       typedef mpl::identity<Float2Int  > Float2IntQ   ;
178       typedef mpl::identity<Float2Float> Float2FloatQ ;
179 
180       typedef typename get_int_float_mixture<T,S>::type int_float_mixture ;
181 
182       typedef for_int_float_mixture<int_float_mixture, Int2IntQ, Int2FloatQ, Float2IntQ, Float2FloatQ> for_ ;
183 
184       typedef typename for_::type selected ;
185 
186       typedef typename selected::type type ;
187     } ;
188 
189     template<class T,class S>
190     struct get_subranged
191     {
192       typedef get_subranged_BuiltIn2BuiltIn<T,S> BuiltIn2BuiltInQ ;
193 
194       typedef subranged_BuiltIn2Udt<T,S> BuiltIn2Udt ;
195       typedef subranged_Udt2BuiltIn<T,S> Udt2BuiltIn ;
196       typedef subranged_Udt2Udt<T,S>     Udt2Udt ;
197 
198       typedef mpl::identity<BuiltIn2Udt> BuiltIn2UdtQ ;
199       typedef mpl::identity<Udt2BuiltIn> Udt2BuiltInQ ;
200       typedef mpl::identity<Udt2Udt    > Udt2UdtQ     ;
201 
202       typedef typename get_udt_builtin_mixture<T,S>::type udt_builtin_mixture ;
203 
204       typedef typename
205         for_udt_builtin_mixture<udt_builtin_mixture, BuiltIn2BuiltInQ, BuiltIn2UdtQ, Udt2BuiltInQ, Udt2UdtQ>::type
206           selected ;
207 
208       typedef typename selected::type selected2 ;
209 
210       typedef typename selected2::type type ;
211     } ;
212 
213 
214   //-------------------------------------------------------------------
215   // Top level implementation selector.
216   //-------------------------------------------------------------------
217   template<class T, class S>
218   struct get_is_subranged
219   {
220     typedef get_subranged<T,S>         non_trivial_case ;
221     typedef mpl::identity<mpl::false_> trivial_case ;
222 
223     typedef is_same<T,S> is_trivial ;
224 
225     typedef typename mpl::if_<is_trivial,trivial_case,non_trivial_case>::type selected ;
226 
227     typedef typename selected::type type ;
228   } ;
229 
230 } } } // namespace boost::numeric::convdetail
231 
232 #endif
233 
234 
235