On Wed, 14 May 2025 at 20:50, Iain Sandoe <idsan...@googlemail.com> wrote:
>
>
>
> > On 14 May 2025, at 18:42, Rainer Orth <r...@cebitec.uni-bielefeld.de> wrote:
> >
> > Hi Jonathan,
> >
> >> On 14/05/25 10:01 +0200, Tomasz Kamiński wrote:
> >>> This commits adjust the way how the arguments are stored in the _Arg_value
> >>> (and thus basic_format_args), by preserving the types of fixed width
> >>> floating-point types, that were previously converted to float, double,
> >>> long double.
> >>>
> >>> The _Arg_value union now contains alternatives with std::bfloat16_t,
> >>> std::float16_t, std::float32_t, std::float64_t that use pre-existing
> >>> _Arg_bf16, _Arg_f16, _Arg_f32, _Arg_f32 argument types.
> >>>
> >>> This does not affect formatting, as specialization of formatters for fixed
> >>> width floating-point types formats them by casting to the corresponding
> >>> standard floating point type.
> >>>
> >>> For the 128bit floating we need to handle the ppc64 architecture,
> >>> (_GLIBCXX_LONG_DOUBLE_ALT128_COMPAT) for which the long double may (per TU
> >>> basis) designate either __ibm128 and __ieee128 type, we need to store both
> >>> types in the _Arg_value and have two _Arg_types (_Arg_ibm128,
> >>> _Arg_ieee128).
> >>> On other architectures we use extra enumerator value to store __float128,
> >>> that is different from long double and _Float128. This is consistent with
> >>> ppc64,
> >>> for which __float128, if present, is same type as __ieee128. We use
> >> _Arg_float128
> >>> _M_float128 names that deviate from _Arg_fN naming scheme, to emphasize
> >>> that
> >>> this flag is not used for std::float128_t (_Float128) type, that is
> >>> consistenly
> >>> formatted via handle.
> >>>
> >>> The __format::__float128_t type is renamed to __format::__flt128_t, to
> >>> mitigate
> >>> visual confusion between this type and __float128. We also introduce
> >>> __bflt16_t
> >>> typedef instead of using of decltype.
> >>>
> >>> We add new alternative for the _Arg_value and allow them to be accessed
> >> via _S_get,
> >>> when the types are available. However, we produce and handle corresponding
> >> _Arg_type,
> >>> only when we can format them. See also r14-3329-g27d0cfcb2b33de.
> >>>
> >>> The formatter<_Float128, _CharT> that formats via __format::__flt128_t is
> >>> always
> >>> provided, when type is available. It is still correct when
> >>> __format::__flt128_t
> >>> is _Float128.
> >>>
> >>> We also provide formatter<__float128, _CharT> that formats via __flt128_t.
> >>> As this type may be disabled (-mno-float128), extra care needs to be
> >>> taken,
> >>> for situation when __float128 is same as long double. If the formatter
> >>> would be
> >>> defined in such case, the formatter<long double, _CharT> would be
> >>> generated
> >>> from different specializations, and have different mangling:
> >>> * formatter<__float128, _CharT> if __float128 is present,
> >>> * formatter<__format::__formattable_float, _CharT> otherwise.
> >>> To best of my knowledge this happens only on ppc64 for __ieee128 and
> >>> __float128,
> >>> so the formatter is not defined in this case. static_assert is added to
> >>> detect
> >>> other configurations like that. In such case we should replace it with
> >> constraint.
> >>>
> >>> PR libstdc++/119246
> >>>
> >>> libstdc++-v3/ChangeLog:
> >>>
> >>> * include/std/format (__format::__bflt16_t): Define.
> >>> (_GLIBCXX_FORMAT_F128): Separate value for cases where _Float128
> >>> is used.
> >>> (__format::__float128_t): Renamed to __format::__flt128_t.
> >>> (std::formatter<_Float128, _CharT>): Define always if there is
> >>> formattable 128bit float.
> >>> (std::formatter<__float128, _CharT>): Define.
> >>> (_Arg_type::_Arg_f128): Rename to _Arg_float128 and adjust value.
> >>> (_Arg_type::_Arg_ibm128): Change value to _Arg_ldbl.
> >>> (_Arg_type::_Arg_ieee128): Define as alias to _Arg_float128.
> >>> (_Arg_value::_M_f128): Replaced with _M_ieee128 and _M_float128.
> >>> (_Arg_value::_M_ieee128, _Arg_value::_M_float128)
> >>> (_Arg_value::_M_bf16, _Arg_value::_M_f16, _Arg_value::_M_f32)
> >>> _Arg_value::_M_f64): Define.
> >>> (_Arg_value::_S_get, basic_format_arg::_S_to_enum): Handle __bflt16,
> >>> _Float16, _Float32, _Float64, and __float128 types.
> >>> (basic_format_arg::_S_to_arg_type): Preserve _bflt16, _Float16,
> >>> _Float32, _Float64 and __float128 types.
> >>> (basic_format_arg::_M_visit): Handle _Arg_float128, _Arg_ieee128,
> >>> _Arg_b16, _Arg_f16, _Arg_f32, _Arg_f64.
> >>> * testsuite/std/format/arguments/args.cc: Updated to illustrate
> >>> that extended floating point types use handles now. Added test
> >>> for __float128.
> >>> * testsuite/std/format/parse_ctx.cc: Extended test to cover class
> >>> to check_dynamic_spec with floating point types and handles.
> >>> ---
> >>> I believe I have fixed all the typos. OK for trunk?
> >>
> >>
> >> OK, thanks
> >
> > this patch broke Solaris bootstrap, both i386-pc-solaris2.11 and
> > sparc-sun-solaris2.11:
> >
> > In file included from
> > /vol/gcc/src/hg/master/local/libstdc++-v3/src/c++20/format.cc:29:
> > /var/gcc/regression/master/11.4-gcc/build/i386-pc-solaris2.11/libstdc++-v3/include/format:
> > In member function ‘typename std::basic_format_context<_Out,
> > _CharT>::iterator std::formatter<__float128, _CharT>::format(__float128,
> > std::basic_format_context<_Out, _CharT>&) const’:
> > /var/gcc/regression/master/11.4-gcc/build/i386-pc-solaris2.11/libstdc++-v3/include/format:2994:41:
> > error: ‘__flt128_t’ is not a member of ‘std::__format’; did you mean
> > ‘__bflt16_t’? [-Wtemplate-body]
> > 2994 | { return _M_f.format((__format::__flt128_t)__u, __fc); }
> > | ^~~~~~~~~~
> > | __bflt16_t
> >
> > and one more instance.
>
> And on x86_64-darwin too.
Tomasz, should this be:
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -2973,7 +2973,7 @@ namespace __format
};
#endif
-#if defined(__SIZEOF_FLOAT128__) && _GLIBCXX_FORMAT_F128 != 1
+#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
>
> Iain
>
> >
> > Rainer
> >
> > --
> > -----------------------------------------------------------------------------
> > Rainer Orth, Center for Biotechnology, Bielefeld University
>
