ceph/src/boost/boost/numeric/conversion/detail/is_subranged.hpp

   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
  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