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

[Richard Smith]

On Wed, Nov 13, 2013 at 1:58 PM, Edward Diener <
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>> 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 ?


2.14.2/2
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