Gate std::float128_t support

It seems the type can exist without any library support, which is no good.

* ra/ra.hh (RA_FLOAT128): New #define.
* test/types.cc: Reuse RA_FLOAT128.

Author: lloda

ra/ra.hh

@@ -32,7 +32,8 @@ template <class T> constexpr void cast(ra::noarg);
 // Scalar overloads.
 // ---------------------------
 
-#if defined(__STDCPP_FLOAT128_T__)
+#define RA_FLOAT128 (1==__STDCPP_FLOAT128_T__ && defined(_GLIBCXX_HAVE_FLOAT128_MATH))
+#if RA_FLOAT128
     #include <stdfloat>
 #define RA_FLOATS float, double, std::float128_t
 #define RA_OP_QUAD_DOUBLE(OP, R, C)                                     \
@@ -46,7 +47,7 @@ RA_FE(RA_QUAD_DOUBLE, +, -, /, *)
 #undef RA_OP_QUAD_DOUBLE_OP
 #else
     #define RA_FLOATS float, double
-#endif
+#endif // RA_FLOAT128
 
 // abs() works for ra:: types through ADL, should work on pods. std::max/min are special, see RA_NAME. FIXME let user decide?
 using std::max, std::min, std::abs, std::fma, std::sqrt, std::pow, std::exp, std::swap,

test/cellrank.cc

@@ -8,9 +8,6 @@
 // later version.
 
 #include "ra/test.hh"
-#ifdef __STDCPP_FLOAT128_T__
-#include <stdfloat>
-#endif
 
 using std::cout, std::endl, std::flush, ra::TestRecorder;
 

test/types.cc

@@ -87,12 +87,12 @@ int main()
                  false, false, false, true, false);
         TESTPRED(std::complex<double>,
                  false, false, false, true, false);
-#ifdef __STDCPP_FLOAT128_T__
+#if RA_FLOAT128
         TESTPRED(std::float128_t,
                  false, false, false, true, false);
         TESTPRED(std::complex<std::float128_t>,
                  false, false, false, true, false);
-#endif // __STDCPP_FLOAT128_T__
+#endif // RA_FLOAT128
         TESTPRED(decltype(std::declval<ra::Unique<int, 2>>()),
                  true, true, false, false, false);
         TESTPRED(decltype(std::declval<ra::Unique<int, 2>>()) const,
@@ -242,8 +242,12 @@ int main()
     }
     tr.section("mixed float128/double ops");
     {
+#if RA_FLOAT128
         tr.test_eq(9., real(std::complex<std::float128_t>(3.) * 3.));
         tr.test_eq(9., real(std::complex<double>(3.) * std::float128_t(3.)));
+#else
+        std::println(std::cout, "no float128_t support!");
+#endif // RA_FLOAT128
     }
     return tr.summary();
 }