On Thu, 1 Jun 2023 at 10:30, Christophe Lyon via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> Hi,
>
>
> On Wed, 31 May 2023 at 14:25, Jonathan Wakely via Gcc-patches <
> gcc-patches@gcc.gnu.org> wrote:
>
> > Tested powerpc64le-linux. Pushed to trunk.
> >
> > -- >8 --
> >
> > We use the from_chars_strtod function with __strtof128 to read a
> > _Float128 value, but from_chars_strtod is not defined unless uselocale
> > is available. This can lead to compilation failures for some targets,
> > because we try to define the _Flaot128 overload in terms of a
> > non-existing from_chars_strtod function.
> >
> > Only try to use __strtof128 if uselocale is available, otherwise
> > fallback to the long double overload of std::from_chars (which might
> > fallback to the double overload, which should use fast_float).
> >
> > This ensures we always define the full set of overloads, even if they
> > are not always accurate for all values of the wider types.
> >
> > libstdc++-v3/ChangeLog:
> >
> > PR libstdc++/109921
> > * src/c++17/floating_from_chars.cc (USE_STRTOF128_FOR_FROM_CHARS):
> > Only define when USE_STRTOD_FOR_FROM_CHARS is also defined.
> > (USE_STRTOD_FOR_FROM_CHARS): Do not undefine when long double is
> > binary64.
> > (from_chars(const char*, const char*, double&, chars_format)):
> > Check __LDBL_MANT_DIG__ == __DBL_MANT_DIG__ here.
> > (from_chars(const char*, const char*, _Float128&, chars_format))
> > Only use from_chars_strtod when USE_STRTOD_FOR_FROM_CHARS is
> > defined, otherwise parse a long double and convert to _Float128.
> >
>
>
> This is causing a regression on aarch64:
> FAIL: libstdc++-abi/abi_check
This is now PR 110077.
>
> The log says:
>
> 3 added symbols
> 0
> _ZNSt7__cxx1112basic_stringIwSt11char_traitsIwESaIwEE11_S_allocateERS3_m
> std::__cxx11::basic_string<wchar_t, std::char_traits<wchar_t>,
> std::allocator<wchar_t> >::_S_allocate(std::allocator<wchar_t>&, unsigned
> long)
> version status: compatible
> GLIBCXX_3.4.32
> type: function
> status: added
>
> 1
> _ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE11_S_allocateERS3_m
> std::__cxx11::basic_string<char, std::char_traits<char>,
> std::allocator<char> >::_S_allocate(std::allocator<char>&, unsigned long)
> version status: compatible
> GLIBCXX_3.4.32
> type: function
> status: added
>
> 2
> _ZSt10from_charsPKcS0_RDF128_St12chars_format
> std::from_chars(char const*, char const*, _Float128&, std::chars_format)
> version status: incompatible
> GLIBCXX_3.4.31
> type: function
> status: added
>
>
> 2 undesignated symbols
> 0
> _ZSt11__once_call
> std::__once_call
> version status: compatible
> GLIBCXX_3.4.11
> type: tls
> type size: 8
> status: undesignated
>
> 1
> _ZSt15__once_callable
> std::__once_callable
> version status: compatible
> GLIBCXX_3.4.11
> type: tls
> type size: 8
> status: undesignated
>
>
> 1 incompatible symbols
> 0
> _ZSt10from_charsPKcS0_RDF128_St12chars_format
> std::from_chars(char const*, char const*, _Float128&, std::chars_format)
> version status: incompatible
> GLIBCXX_3.4.31
> type: function
> status: added
>
>
>
> ==== libstdc++-v3 check-abi Summary ====
>
> # of added symbols: 3
> # of missing symbols: 0
> # of undesignated symbols: 2
> # of incompatible symbols: 1
>
>
> Can you have a look?
>
> Thanks,
> Christophe
>
> ---
> > libstdc++-v3/src/c++17/floating_from_chars.cc | 20 ++++++++++++-------
> > 1 file changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/libstdc++-v3/src/c++17/floating_from_chars.cc
> > b/libstdc++-v3/src/c++17/floating_from_chars.cc
> > index ebd428d5be3..eea878072b0 100644
> > --- a/libstdc++-v3/src/c++17/floating_from_chars.cc
> > +++ b/libstdc++-v3/src/c++17/floating_from_chars.cc
> > @@ -64,7 +64,7 @@
> > // strtold for __ieee128
> > extern "C" __ieee128 __strtoieee128(const char*, char**);
> > #elif __FLT128_MANT_DIG__ == 113 && __LDBL_MANT_DIG__ != 113 \
> > - && defined(__GLIBC_PREREQ)
> > + && defined(__GLIBC_PREREQ) && defined(USE_STRTOD_FOR_FROM_CHARS)
> > #define USE_STRTOF128_FOR_FROM_CHARS 1
> > extern "C" _Float128 __strtof128(const char*, char**)
> > __asm ("strtof128")
> > @@ -77,10 +77,6 @@ extern "C" _Float128 __strtof128(const char*, char**)
> > #if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64 \
> > && __SIZE_WIDTH__ >= 32
> > # define USE_LIB_FAST_FLOAT 1
> > -# if __LDBL_MANT_DIG__ == __DBL_MANT_DIG__
> > -// No need to use strtold.
> > -# undef USE_STRTOD_FOR_FROM_CHARS
> > -# endif
> > #endif
> >
> > #if USE_LIB_FAST_FLOAT
> > @@ -1261,7 +1257,7 @@ from_chars_result
> > from_chars(const char* first, const char* last, long double& value,
> > chars_format fmt) noexcept
> > {
> > -#if ! USE_STRTOD_FOR_FROM_CHARS
> > +#if __LDBL_MANT_DIG__ == __DBL_MANT_DIG__ || !defined
> > USE_STRTOD_FOR_FROM_CHARS
> > // Either long double is the same as double, or we can't use strtold.
> > // In the latter case, this might give an incorrect result (e.g. values
> > // out of range of double give an error, even if they fit in long
> > double).
> > @@ -1329,13 +1325,23 @@
> > _ZSt10from_charsPKcS0_RDF128_St12chars_format(const char* first,
> > __ieee128& value,
> > chars_format fmt) noexcept
> > __attribute__((alias
> > ("_ZSt10from_charsPKcS0_Ru9__ieee128St12chars_format")));
> > -#elif defined(USE_STRTOF128_FOR_FROM_CHARS)
> > +#else
> > from_chars_result
> > from_chars(const char* first, const char* last, _Float128& value,
> > chars_format fmt) noexcept
> > {
> > +#ifdef USE_STRTOF128_FOR_FROM_CHARS
> > // fast_float doesn't support IEEE binary128 format, but we can use
> > strtold.
> > return from_chars_strtod(first, last, value, fmt);
> > +#else
> > + // Read a long double. This might give an incorrect result (e.g. values
> > + // out of range of long double give an error, even if they fit in
> > _Float128).
> > + long double ldbl_val;
> > + auto res = std::from_chars(first, last, ldbl_val, fmt);
> > + if (res.ec == errc{})
> > + value = ldbl_val;
> > + return res;
> > +#endif
> > }
> > #endif
> >
> > --
> > 2.40.1
> >
> >
