ceph/src/boost/boost/spirit/home/x3/char/detail/cast_char.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2014 Joel de Guzman
   3     Copyright (c) 2001-2011 Hartmut Kaiser
   4
   5     Distributed under the Boost Software License, Version 1.0. (See accompanying
   6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 =============================================================================*/
   8 #if !defined(BOOST_SPIRIT_X3_CAST_CHAR_NOVEMBER_10_2006_0907AM)
   9 #define BOOST_SPIRIT_X3_CAST_CHAR_NOVEMBER_10_2006_0907AM
  10
  11 #include <boost/type_traits/is_signed.hpp>
  12 #include <boost/type_traits/make_unsigned.hpp>
  13 #include <boost/type_traits/make_signed.hpp>
  14
  15 namespace boost { namespace spirit { namespace x3 { namespace detail
  16 {
  17     // Here's the thing... typical encodings (except ASCII) deal with unsigned
  18     // integers > 127 (ASCII uses only 127). Yet, most char and wchar_t are signed.
  19     // Thus, a char with value > 127 is negative (e.g. char 233 is -23). When you
  20     // cast this to an unsigned int with 32 bits, you get 4294967273!
  21     //
  22     // The trick is to cast to an unsigned version of the source char first
  23     // before casting to the target. {P.S. Don't worry about the code, the
  24     // optimizer will optimize the if-else branches}
  25
  26     template <typename TargetChar, typename SourceChar>
  27     TargetChar cast_char(SourceChar ch)
  28     {
  29         if (is_signed<TargetChar>::value != is_signed<SourceChar>::value)
  30         {
  31             if (is_signed<SourceChar>::value)
  32             {
  33                  // source is signed, target is unsigned
  34                 typedef typename make_unsigned<SourceChar>::type USourceChar;
  35                 return TargetChar(USourceChar(ch));
  36             }
  37             else
  38             {
  39                  // source is unsigned, target is signed
  40                 typedef typename make_signed<SourceChar>::type SSourceChar;
  41                 return TargetChar(SSourceChar(ch));
  42             }
  43         }
  44         else
  45         {
  46             // source and target has same signedness
  47             return TargetChar(ch); // just cast
  48         }
  49     }
  50 }}}}
  51
  52 #endif
  53
  54