[PATCH] libstdc++: Define __cpp_lib_stdbit_h and __cpp_lib_stdckdint_h feature test macros.

[Jonathan Wakely]

On Tue, 14 Apr 2026 at 15:39, Tomasz Kamiński <tkaminsk@redhat.com> wrote:
>
> This implements LWG4550: Need new feature test macros for <stdckdint.h>
> and <stdbit.h>.
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/version.def (stdbit_h, stdckdint_h): Define.
>         * include/bits/version.h: Regenerate.
>         * include/c_compatibility/stdbit.h (__cpp_lib_stdbit_h): Define
>         and use it in guards.
>         * include/c_compatibility/stdckdint.h (__cpp_lib_stdckdint_h):
>         Define and use it in guards.
> ---
> Testing on x86_64-linux. Dedicated tests 20_util/stdbit* and 26_numerics/stdckint*
> already passes, so valus seem correct.

OK. We should backport this to GCC 15 at some point too.


>
>  libstdc++-v3/include/bits/version.def         | 16 +++++++++++++++
>  libstdc++-v3/include/bits/version.h           | 20 +++++++++++++++++++
>  libstdc++-v3/include/c_compatibility/stdbit.h |  8 ++++++--
>  .../include/c_compatibility/stdckdint.h       |  8 ++++++--
>  4 files changed, 48 insertions(+), 4 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
> index 94fc1f85993..13dba4d6378 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -1871,6 +1871,22 @@ ftms = {
>    };
>  };
>
> +ftms = {
> +  name = stdbit_h;
> +  values = {
> +    v = 202603;
> +    cxxmin = 26;
> +  };
> +};
> +
> +ftms = {
> +  name = stdckdint_h;
> +  values = {
> +    v = 202603;
> +    cxxmin = 26;
> +  };
> +};
> +
>  ftms = {
>    name = adaptor_iterator_pair_constructor;
>    values = {
> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
> index 402e67580eb..743f7e29fe2 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -2076,6 +2076,26 @@
>  #endif /* !defined(__cpp_lib_stdatomic_h) */
>  #undef __glibcxx_want_stdatomic_h
>
> +#if !defined(__cpp_lib_stdbit_h)
> +# if (__cplusplus >  202302L)
> +#  define __glibcxx_stdbit_h 202603L
> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_stdbit_h)
> +#   define __cpp_lib_stdbit_h 202603L
> +#  endif
> +# endif
> +#endif /* !defined(__cpp_lib_stdbit_h) */
> +#undef __glibcxx_want_stdbit_h
> +
> +#if !defined(__cpp_lib_stdckdint_h)
> +# if (__cplusplus >  202302L)
> +#  define __glibcxx_stdckdint_h 202603L
> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_stdckdint_h)
> +#   define __cpp_lib_stdckdint_h 202603L
> +#  endif
> +# endif
> +#endif /* !defined(__cpp_lib_stdckdint_h) */
> +#undef __glibcxx_want_stdckdint_h
> +
>  #if !defined(__cpp_lib_adaptor_iterator_pair_constructor)
>  # if (__cplusplus >= 202100L) && _GLIBCXX_HOSTED
>  #  define __glibcxx_adaptor_iterator_pair_constructor 202106L
> diff --git a/libstdc++-v3/include/c_compatibility/stdbit.h b/libstdc++-v3/include/c_compatibility/stdbit.h
> index 1fb691e36c1..fa4ec0414c6 100644
> --- a/libstdc++-v3/include/c_compatibility/stdbit.h
> +++ b/libstdc++-v3/include/c_compatibility/stdbit.h
> @@ -29,7 +29,11 @@
>  #ifndef _GLIBCXX_STDBIT_H
>  #define _GLIBCXX_STDBIT_H
>
> -#if __cplusplus > 202302L
> +#define __glibcxx_want_stdbit_h
> +#include <bits/version.h>
> +
> +#ifdef __cpp_lib_stdbit_h // C++ >= 26
> +
>  #include <bit>
>
>  #define __STDC_VERSION_STDBIT_H__ 202311L
> @@ -577,6 +581,6 @@ _GLIBCXX_STDBIT_FUNC(stdc_bit_floor);
>  _GLIBCXX_STDBIT_FUNC(stdc_bit_ceil);
>  #undef _GLIBCXX_STDBIT_FUNC
>  #endif // !DOXYGEN
> -#endif // C++26
> +#endif // __cpp_lib_stdbit_h
>
>  #endif // _GLIBCXX_STDBIT_H
> diff --git a/libstdc++-v3/include/c_compatibility/stdckdint.h b/libstdc++-v3/include/c_compatibility/stdckdint.h
> index 5bdf4dc7b24..0f0b30cc899 100644
> --- a/libstdc++-v3/include/c_compatibility/stdckdint.h
> +++ b/libstdc++-v3/include/c_compatibility/stdckdint.h
> @@ -29,7 +29,11 @@
>  #ifndef _GLIBCXX_STDCKDINT_H
>  #define _GLIBCXX_STDCKDINT_H
>
> -#if __cplusplus > 202302L
> +#define __glibcxx_want_stdckdint_h
> +#include <bits/version.h>
> +
> +#ifdef __cpp_lib_stdckdint_h // C++ >= 26
> +
>  #include <type_traits>
>  #include <concepts>
>
> @@ -96,6 +100,6 @@ using __gnu_cxx::ckd_sub;
>  using __gnu_cxx::ckd_mul;
>  #endif
>
> -#endif // C++26
> +#endif // __cpp_lib_stdckdint_h
>
>  #endif // _GLIBCXX_STDCKDINT_H
> --
> 2.53.0
>