[PATCH] libstdc++: Use explicit cast to unsigned in std::rotr and std::rotl

[Jonathan Wakely]

On Tue, 3 Jun 2025 at 09:23, Tomasz Kaminski <tkaminsk@redhat.com> wrote:
>
>
>
>
> On Mon, Jun 2, 2025 at 7:28 PM Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>> This suppresses some -Wsign-conversion warnings from Clang when
>> compiling with -Wsystem-headers.
>>
>> libstdc++-v3/ChangeLog:
>>
>>         * include/std/bit (__rotl, __rotr): Use static_cast for
>>         conversion from int to unsigned.
>> ---
>>
>> Tested x86_64-linux.
>
> LGTM.
>>
>>
>>  libstdc++-v3/include/std/bit | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit
>> index 5187c96182f5..02d7189f1a3d 100644
>> --- a/libstdc++-v3/include/std/bit
>> +++ b/libstdc++-v3/include/std/bit
>> @@ -166,7 +166,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>           // Variant for power of two _Nd which the compiler can
>>           // easily pattern match.
>>           constexpr unsigned __uNd = _Nd;
>> -         const unsigned __r = __s;
>> +         const unsigned __r = static_cast<unsigned>(__s);
>
> I would define the variable as const auto, given the cast.

Done (in both places) and pushed now, thanks.


>>
>>           return (__x << (__r % __uNd)) | (__x >> ((-__r) % __uNd));
>>         }
>>        const int __r = __s % _Nd;
>> @@ -188,7 +188,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>           // Variant for power of two _Nd which the compiler can
>>           // easily pattern match.
>>           constexpr unsigned __uNd = _Nd;
>> -         const unsigned __r = __s;
>> +         const unsigned __r = static_cast<unsigned>(__s);
>>           return (__x >> (__r % __uNd)) | (__x << ((-__r) % __uNd));
>>         }
>>        const int __r = __s % _Nd;
>> --
>> 2.49.0
>>