62 lines
2.2 KiB
C++
62 lines
2.2 KiB
C++
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/*=============================================================================
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Copyright (c) 2001-2014 Joel de Guzman
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Copyright (c) 2001-2011 Hartmut Kaiser
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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=============================================================================*/
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#if !defined(BOOST_SPIRIT_X3_CAST_CHAR_NOVEMBER_10_2006_0907AM)
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#define BOOST_SPIRIT_X3_CAST_CHAR_NOVEMBER_10_2006_0907AM
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#include <boost/type_traits/is_signed.hpp>
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#include <boost/type_traits/make_unsigned.hpp>
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#include <boost/type_traits/make_signed.hpp>
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namespace boost { namespace spirit { namespace x3 { namespace detail
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{
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// Here's the thing... typical encodings (except ASCII) deal with unsigned
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// integers > 127 (ASCII uses only 127). Yet, most char and wchar_t are signed.
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// Thus, a char with value > 127 is negative (e.g. char 233 is -23). When you
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// cast this to an unsigned int with 32 bits, you get 4294967273!
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//
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// The trick is to cast to an unsigned version of the source char first
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// before casting to the target. {P.S. Don't worry about the code, the
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// optimizer will optimize the if-else branches}
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template <typename TargetChar, typename SourceChar>
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TargetChar cast_char(SourceChar ch)
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{
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#if defined(_MSC_VER)
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# pragma warning(push)
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# pragma warning(disable: 4127) // conditional expression is constant
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#endif
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if (is_signed<TargetChar>::value != is_signed<SourceChar>::value)
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{
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if (is_signed<SourceChar>::value)
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{
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// source is signed, target is unsigned
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typedef typename make_unsigned<SourceChar>::type USourceChar;
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return TargetChar(USourceChar(ch));
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}
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else
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{
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// source is unsigned, target is signed
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typedef typename make_signed<SourceChar>::type SSourceChar;
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return TargetChar(SSourceChar(ch));
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}
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}
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else
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{
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// source and target has same signedness
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return TargetChar(ch); // just cast
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}
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#if defined(_MSC_VER)
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# pragma warning(pop)
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#endif
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}
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}}}}
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#endif
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