https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109921
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The proposed change would result in ABI changes for some targets.
I think the correct fix is something more like this:
--- 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 (rec.ec == errc{})
+ value = ldbl_val;
+ return res;
+#endif
}
#endif
We should not use strtof128 unless we can use strtod.
We should not #undef USE_STRTOD_FOR_FROM_CHARS on line 82 just because we don't
need it for long double, as we might still need it for _Float128.
