On Fri, 16 May 2025 at 12:04, Tomasz Kamiński wrote:
>
> For powerpc64 and sparc architectures that both have __float128 and 128bit
> long double,
> the __float128 is same type as long double/__iee128 and already formattable.
__ieee128
>
> Remaining specializaiton make __float128 formattable on x86_64 via _Float128,
"The remaining specialization makes ..."
> however __float128 is now not formattable on x86_32 (-m32) with
> -mlong-double-128,
I don't think we need to care about that.
> where __float128 is distinct type from long double that is 128bit IEEE.
>
> PR libstdc++/119246
>
> libstdc++-v3/ChangeLog:
>
> * include/std/format (formatter<__float128, _Char_T): Define if
> _GLIBCXX_FORMAT_F128 == 2.
> ---
> This patch avoids dealing with cases when long double is 128bit and thus
> __float128 may be same as long double (it is same for powerpc and will be for
> sparc),
> but distinct for x86_32/-mlong-double-128.
>
> This preserve support formatting __float128 on x84_64, where it is formatted
> using _Float128.
>
> Tested on x86_64, powerpc64. For format test checked both
> -mabi=ibmlongdouble,-mabi=ieeelongdouble.
> Rainer Orth confirmed that this also work with his patch adding __float128
> for sparc.
>
> OK for trunk?
OK with the typos above fixed, and "IEE" in the first line of the
commit fixed to "IEEE".
>
> libstdc++-v3/include/std/format | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
> index b1823db83bc..d1ca05105f9 100644
> --- a/libstdc++-v3/include/std/format
> +++ b/libstdc++-v3/include/std/format
> @@ -2973,11 +2973,9 @@ namespace __format
> };
> #endif
>
> -#if defined(__SIZEOF_FLOAT128__) && _GLIBCXX_FORMAT_F128 > 1
> - // Reuse __formatter_fp<C>::format<__format::__flt128_t, Out> for
> __float128.
> - // This formatter is not declared if _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT is
> true,
> - // as __float128 when present is same type as __ieee128, which may be same
> as
> - // long double.
> +#if defined(__SIZEOF_FLOAT128__) && _GLIBCXX_FORMAT_F128 == 2
> + // Use __formatter_fp<C>::format<__format::__flt128_t, Out> for __float128,
> + // when long double is not 128bit IEEE type.
> template<__format::__char _CharT>
> struct formatter<__float128, _CharT>
> {
> @@ -2995,9 +2993,6 @@ namespace __format
>
> private:
> __format::__formatter_fp<_CharT> _M_f;
> -
> - static_assert( !is_same_v<__float128, long double>,
> - "This specialization should not be used for long double"
> );
> };
> #endif
>
> --
> 2.49.0
>
