https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104772
Bug ID: 104772
Summary: std::numeric_limits<__float128> should be specialized
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Depends on: 99708, 98202
Target Milestone: ---
We should provide a specialization of numeric_limits<__float128> when that type
is valid (even if is_floating_point_v<__float128> is false due to
__STRICT_ANSI__ being defined).
It might also be useful to do the same for __float80 on x86, although that's
less widely used. That could be done fairly easily:
#ifdef __SIZEOF_FLOAT80__
template<>
numeric_limits<__float80> : numeric_limits<long double> { };
#endif
For __float128 we need to define it fully. The compiler gives us the info we
need:
#define __FLT128_DECIMAL_DIG__ 36
#define __FLT128_DENORM_MIN__ 6.47517511943802511092443895822764655e-4966F128
#define __FLT128_DIG__ 33
#define __FLT128_EPSILON__ 1.92592994438723585305597794258492732e-34F128
#define __FLT128_HAS_DENORM__ 1
#define __FLT128_HAS_INFINITY__ 1
#define __FLT128_HAS_QUIET_NAN__ 1
#define __FLT128_IS_IEC_60559__ 2
#define __FLT128_MANT_DIG__ 113
#define __FLT128_MAX_10_EXP__ 4932
#define __FLT128_MAX_EXP__ 16384
#define __FLT128_MAX__ 1.18973149535723176508575932662800702e+4932F128
#define __FLT128_MIN_10_EXP__ (-4931)
#define __FLT128_MIN_EXP__ (-16381)
#define __FLT128_MIN__ 3.36210314311209350626267781732175260e-4932F128
#define __FLT128_NORM_MAX__ 1.18973149535723176508575932662800702e+4932F128
The F128 suffixes are a problem though, see PR 98202 comment 7.
Detecting __float128 reliably is blocked by PR 99708 comment 8.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98202
[Bug 98202] C++ cannot parse F128 suffix for float128 literals
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99708
[Bug 99708] __SIZEOF_FLOAT128__ not defined on powerpc64le-linux
