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3rdparty/boost_1_81_0/libs/mpl/example/integer.cpp 1.81 KB
73ef4ff3   Hu Chunming   提交三方库
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  // Copyright Aleksey Gurtovoy 2001-2004
  //
  // Distributed under the Boost Software License, Version 1.0. 
  // (See accompanying file LICENSE_1_0.txt or copy at 
  // http://www.boost.org/LICENSE_1_0.txt)
  //
  // See http://www.boost.org/libs/mpl for documentation.
  
  // $Id$
  // $Date$
  // $Revision$
  
  #include <boost/mpl/multiplies.hpp>
  #include <boost/mpl/list.hpp>
  #include <boost/mpl/lower_bound.hpp>
  #include <boost/mpl/transform_view.hpp>
  #include <boost/mpl/sizeof.hpp>
  #include <boost/mpl/int.hpp>
  #include <boost/mpl/identity.hpp>
  #include <boost/mpl/base.hpp>
  #include <boost/mpl/eval_if.hpp>
  #include <boost/mpl/deref.hpp>
  #include <boost/mpl/begin_end.hpp>
  #include <boost/mpl/assert.hpp>
  
  #include <boost/type_traits/is_same.hpp>
  
  namespace mpl = boost::mpl;
  using namespace mpl::placeholders;
  
  template< int bit_size >
  class big_int
  {
      // ...
  };
  
  template< int bit_size >
  struct integer
  {
      typedef mpl::list<char,short,int,long> builtins_;
      typedef typename mpl::base< typename mpl::lower_bound<
            mpl::transform_view< builtins_
              , mpl::multiplies< mpl::sizeof_<_1>, mpl::int_<8> >
              >
          , mpl::int_<bit_size>
          >::type >::type iter_;
  
      typedef typename mpl::end<builtins_>::type last_;
      typedef typename mpl::eval_if<
            boost::is_same<iter_,last_>
          , mpl::identity< big_int<bit_size> >
          , mpl::deref<iter_>
          >::type type;
  };
  
  typedef integer<1>::type int1;
  typedef integer<5>::type int5;
  typedef integer<15>::type int15;
  typedef integer<32>::type int32;
  typedef integer<100>::type int100;
  
  BOOST_MPL_ASSERT(( boost::is_same< int1, char > ));
  BOOST_MPL_ASSERT(( boost::is_same< int5, char > ));
  BOOST_MPL_ASSERT(( boost::is_same< int15, short > ));
  BOOST_MPL_ASSERT(( boost::is_same< int32, int > ));
  BOOST_MPL_ASSERT(( boost::is_same< int100, big_int<100> > ));