On Mon, 8 Dec 2025 at 15:23, Patrick Palka <[email protected]> wrote:
>
>
>
> On Mon, 8 Dec 2025, Jonathan Wakely wrote:
>
> > We have __is_signed_integer and __is_unsigned_integer traits which
> > should have been updated by r16-2190-g4faa42ac0dee2c when making
> > __int128 an extended integer type (for PR libstdc++/96710). Currently
> > they check whether the type is a signed integer type or an unsigned
> > integer type, or a cv-qualified version of one of those. This doesn't
> > match the standard's definition, which does not include cv-qualified
> > types. This change ensures that signed __int128 and unsigned __int128
> > are included in those traits in strict -std modes, and it removes the
> > use of remove_cv_t so that they are not true for cv-qualified types.
> > This makes the traits match the meaning of "signed integer type" and
> > "unsigned integer type" in the standard ([basic.fundamental]).
> >
> > We also have an __is_standard_integer trait, which is true if either
> > __is_signed_integer or __is_unsigned_integer is true, but that's also
> > not a match for the definition in the standard. The definitions of
> > "signed integer type" and "unsigned integer type" include both standard
> > and extended integer types, so only saying "standard" in the trait name
> > is misleading (even before this change, because in non-strict -std modes
> > the __GLIBCXX_TYPE_INT_N_0 .. __GLIBCXX_TYPE_INT_N_3 types were always
> > included in the trait, and they aren't standard integer types).
> >
> > This change renames __is_standard_integer to the more accurate
> > __is_signed_or_unsigned_integer_type. Because the set of signed and
>
> In the code __is_signed_or_unsigned_integer is the new name, no
> _type suffix? Besides that LGTM, this is a nice improvement.
Oops, yes, and then I used vim's autocomplete for the rest of the
commit message and so it says _type everywhere below.
I'll fix that, thanks.
> Btw we probably should define __is_signed/unsigned_integer via explicit
> specializations instead of the __is_one_of helper, so that it's O(1)
> instead of O(n) to check.
Yes, it's tedious, but probably worth it.
I think the reason I didn't do that originally is because we already
have explicit specializations of __is_integral_helper for every
integral type, and it seemed like error-prone duplication to have two
more sets of explicit specializations that would need updating for new
integer types. But apart from char8_t, there haven't been any new
integral types added since the INT_N ones.
Another option would be to add a boolean to __is_integral_helper that
says whether it's a signed integer type, an unsigned integer type, or
a character type. __is_integral_helper already only handles
cv-unqualified types (because is_integral uses remove_cv_t) and every
cv-unqualified integral type is either a signed integer type, and
unsigned integer type, a character type, or bool.
So something like:
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -348,78 +348,81 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: public true_type { };
/// @cond undocumented
+
+ enum class _Integer_kind { _Character, _Signed, _Unsigned, _Other };
+
template<typename>
struct __is_integral_helper
- : public false_type { };
+ : false_type { static constexpr _S_kind = _Integer_kind::_Other; };
template<>
struct __is_integral_helper<bool>
- : public true_type { };
+ : true_type { static constexpr _S_kind = _Integer_kind::_Other; };
template<>
struct __is_integral_helper<char>
etc.
and then:
@@ -824,50 +827,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using __is_one_of = __or_<is_same<_Tp, _Types>...>;
// Check if a type is one of the signed integer types.
- __extension__
template<typename _Tp>
- using __is_signed_integer = __is_one_of<_Tp,
- signed char, signed short, signed int, signed long,
- signed long long
-#if defined(__GLIBCXX_TYPE_INT_N_0)
- , signed __GLIBCXX_TYPE_INT_N_0
-#endif
-#if defined(__GLIBCXX_TYPE_INT_N_1)
- , signed __GLIBCXX_TYPE_INT_N_1
-#endif
-#if defined(__GLIBCXX_TYPE_INT_N_2)
- , signed __GLIBCXX_TYPE_INT_N_2
-#endif
-#if defined(__GLIBCXX_TYPE_INT_N_3)
- , signed __GLIBCXX_TYPE_INT_N_3
-#endif
-#if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
- , signed __int128
-#endif
- >;
+ using __is_signed_integer
+ = __bool_constant<__is_integral_helper<_Tp>::_S_kind
+ == _Integer_kind::_Signed>
// Check if a type is one of the unsigned integer types.
__extension__
template<typename _Tp>
- using __is_unsigned_integer = __is_one_of<_Tp,
- unsigned char, unsigned short, unsigned int, unsigned long,
- unsigned long long
-#if defined(__GLIBCXX_TYPE_INT_N_0)
- , unsigned __GLIBCXX_TYPE_INT_N_0
-#endif
-#if defined(__GLIBCXX_TYPE_INT_N_1)
- , unsigned __GLIBCXX_TYPE_INT_N_1
-#endif
-#if defined(__GLIBCXX_TYPE_INT_N_2)
- , unsigned __GLIBCXX_TYPE_INT_N_2
-#endif
-#if defined(__GLIBCXX_TYPE_INT_N_3)
- , unsigned __GLIBCXX_TYPE_INT_N_3
-#endif
-#if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
- , unsigned __int128
-#endif
- >;
+ using __is_unsigned_integer
+ = __bool_constant<__is_integral_helper<_Tp>::_S_kind
+ == _Integer_kind::_Unsigned>
// Check if a type is one of the signed or unsigned integer types.
// i.e. an integral type except bool, char, wchar_t, and charN_t.
