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libstdc++: Correct preprocessing checks for floatX_t and bfloat_16 formatting

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Floating points types _Float16, _Float32, _Float64, and bfloat16,
can be formatted only if std::to_chars overloads for such types
were provided. Currently this is only the case for architectures
where float and double are 32-bits and 64-bits IEEE floating points types.

This patch updates the preprocessing checks for formatters
for above types to check _GLIBCXX_FLOAT_IS_IEEE_BINARY32
and _GLIBCXX_DOUBLE_IS_IEEE_BINARY64. Making them non-formattable
on non-IEEE architectures.

Remove a potential UB, where we could produce basic_format_arg
with _M_type set to _Arg_fp32 or _Arg_fp64, that was later not
handled by `_M_visit`.

libstdc++-v3/ChangeLog:

	* include/std/format (formatter<_Float16, _CharT>): Define only if
	_GLIBCXX_FLOAT_IS_IEEE_BINARY32 macro is defined.
	(formatter<_Float16, _CharT>): As above.
	(formatter<__gnu_cxx::__bfloat16_t, _CharT>): As above.
	(formatter<_Float64, _CharT>): Define only if
	_GLIBCXX_DOUBLE_IS_IEEE_BINARY64 is defined.
	(basic_format_arg::_S_to_arg_type): Normalize _Float32 and _Float64
	only to float and double respectivelly.
	(basic_format_arg::_S_to_enum): Remove handling of _Float32 and _Float64.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
This commit is contained in:
Tomasz Kamiński 2025-03-11 11:59:36 +01:00
parent 2ac842a1e8
commit 445128c12c
1 changed files with 8 additions and 24 deletions
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32
libstdc++-v3/include/std/format
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@ -2276,7 +2276,7 @@ namespace __format
};
#endif
#ifdef __STDCPP_FLOAT16_T__
#if defined(__STDCPP_FLOAT16_T__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
// Reuse __formatter_fp<C>::format<float, Out> for _Float16.
template<__format::__char _CharT>
struct formatter<_Float16, _CharT>
@ -2298,7 +2298,7 @@ namespace __format
};
#endif
#if defined(__FLT32_DIG__)
#if defined(__FLT32_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
// Reuse __formatter_fp<C>::format<float, Out> for _Float32.
template<__format::__char _CharT>
struct formatter<_Float32, _CharT>
@ -2320,7 +2320,7 @@ namespace __format
};
#endif
#if defined(__FLT64_DIG__)
#if defined(__FLT64_DIG__) && defined(_GLIBCXX_DOUBLE_IS_IEEE_BINARY64)
// Reuse __formatter_fp<C>::format<double, Out> for _Float64.
template<__format::__char _CharT>
struct formatter<_Float64, _CharT>
@ -2364,7 +2364,7 @@ namespace __format
};
#endif
#ifdef __STDCPP_BFLOAT16_T__
#if defined(__STDCPP_BFLOAT16_T__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
// Reuse __formatter_fp<C>::format<float, Out> for bfloat16_t.
template<__format::__char _CharT>
struct formatter<__gnu_cxx::__bfloat16_t, _CharT>
@ -3443,22 +3443,16 @@ namespace __format
return type_identity<float>();
#endif
#ifdef __FLT32_DIG__
#if defined(__FLT32_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
else if constexpr (is_same_v<_Td, _Float32>)
# ifdef _GLIBCXX_FLOAT_IS_IEEE_BINARY32
return type_identity<float>();
# else
return type_identity<_Float32>();
# endif
#endif
#ifdef __FLT64_DIG__
#if defined(__FLT64_DIG__) && defined(_GLIBCXX_DOUBLE_IS_IEEE_BINARY64)
else if constexpr (is_same_v<_Td, _Float64>)
# ifdef _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
return type_identity<double>();
# else
return type_identity<_Float64>();
# endif
#endif
#if _GLIBCXX_FORMAT_F128
# if __FLT128_DIG__
else if constexpr (is_same_v<_Td, _Float128>)
@ -3538,16 +3532,6 @@ namespace __format
return _Arg_u128;
#endif
// N.B. some of these types will never actually be used here,
// because they get normalized to a standard floating-point type.
#if defined __FLT32_DIG__ && ! _GLIBCXX_FLOAT_IS_IEEE_BINARY32
else if constexpr (is_same_v<_Tp, _Float32>)
return _Arg_f32;
#endif
#if defined __FLT64_DIG__ && ! _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
else if constexpr (is_same_v<_Tp, _Float64>)
return _Arg_f64;
#endif
#if _GLIBCXX_FORMAT_F128 == 2
else if constexpr (is_same_v<_Tp, __format::__float128_t>)
return _Arg_f128;