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: fernando_cacciola@hotmail.com
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
28namespace 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