1 /*=============================================================================
2 Copyright (c) 2001-2014 Joel de Guzman
3 Copyright (c) 2001-2011 Hartmut Kaiser
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
11 #include <boost/type_traits/is_signed.hpp>
12 #include <boost/type_traits/make_unsigned.hpp>
13 #include <boost/type_traits/make_signed.hpp>
15 namespace boost { namespace spirit { namespace x3 { namespace detail
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!
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}
26 template <typename TargetChar, typename SourceChar>
27 TargetChar cast_char(SourceChar ch)
29 if (is_signed<TargetChar>::value != is_signed<SourceChar>::value)
31 if (is_signed<SourceChar>::value)
33 // source is signed, target is unsigned
34 typedef typename make_unsigned<SourceChar>::type USourceChar;
35 return TargetChar(USourceChar(ch));
39 // source is unsigned, target is signed
40 typedef typename make_signed<SourceChar>::type SSourceChar;
41 return TargetChar(SSourceChar(ch));
46 // source and target has same signedness
47 return TargetChar(ch); // just cast