[cfe-dev] Error when testing clang with VC++ RTL and Boost MPL

[Edward Diener]

On 11/13/2013 5:08 PM, David Blaikie wrote:
>
>
>
> On Wed, Nov 13, 2013 at 1:58 PM, Edward Diener
> <eldlistmailingz at tropicsoft.com
> <mailto:eldlistmailingz at tropicsoft.com>> wrote:
>
>     On 11/13/2013 2:59 PM, Jordan Rose wrote:
>
>
>         On Nov 13, 2013, at 11:47 , Edward Diener
>         <eldlistmailingz at tropicsoft.__com
>         <mailto:eldlistmailingz at tropicsoft.com>
>         <mailto:eldlistmailingz at __tropicsoft.com
>         <mailto:eldlistmailingz at tropicsoft.com>>>
>         wrote:
>
>             On 11/13/2013 9:46 AM, Edward Diener wrote:
>
>                 I am seeing this error when testing Boost MPL with clang
>                 using the VC++
>                 RTL:
>
>                 "bitwise.cpp(40,25) :  error: non-type template argument
>                 evaluates to
>                 4294967295, which cannot be narrowed to type 'long'
>                 [-Wc++11-narrowing]
>                 MPL_ASSERT_RELATION( (bitor_<_0,_ffffffff>::value), ==,
>                 0xffffffff );"
>
>                 The typedefs are:
>
>                 typedef integral_c<unsigned int, 0> _0;
>                 typedef integral_c<unsigned int, 0xffffffff> _ffffffff;
>
>                 The bitor_ in the Boost MPL is evaluating constants at
>                 compile time,
>                 doing a bitwise or ('|').
>
>                 Why does clang think that 0xffffffff is a 'long' when
>                 used in the
>                 comparison ? According to the C++ standard the type of
>                 0xffffffff is the
>                 first of int, unsigned int, long, unsigned long, long
>                 long, unsigned
>                 long long in which its value can fit ( section 2.14.2 ).
>                 Is this a clang
>                 bug ?
>
>
>             Sorry, the problem is not as I had assumed above. It is actually
>             because the MPL_ASSERT_RELATION macro devolves down to a
>             template
>             class where the values are of type 'long'. Is there
>             something in C++11
>             which says that implicit conversion of a value from an
>             'unsigned int'
>             to a 'long' is illegal ? That is what clang is telling me
>             but I can
>             find no such restriction in the C++11 standard regarding this.
>
>
>         I think it’s more likely that on Windows ‘long’ is the same size as
>         ‘int’, and so you have an overflow error. You need to fix the
>         template…which I guess means submitting a patch to Boost.
>
>
>     I tried a patch of the test code where I set:
>
>     typedef integral_c<int, 0xffffffff> _ffffffff;
>
>     but clang still complains that:
>
>     bitwise.cpp(23,24) :  error: non-type template argument evaluates to
>     4294967295, which cannot be narrowed to type 'int' [-Wc++11-narrowing]
>     typedef integral_c<int, 0xffffffff> _ffffffff;
>
>     This I do not understand. Why does 0xffffffff evaluate to 4294967295
>     rather than -1 ? Where in the C++ standard does it say that hex
>     literals are unsigned values by default ?
>
>
> Nothing to do with hex literals, just literals in general. If they don't
> fit in the range of an int, the literal is of unsigned int type so it
> can fit the value.

Is not -1 in the range of an 'int' ? Is not 0xffffffff equivalent to -1 
as a signed value ? What am I missing here ?