Specialize std::numbers constants for __float128

* include/std/numbers [!__STRICT_ANSI__ && _GLIBCXX_USE_FLOAT128]
	(e_v, log2e_v, log10e_v, pi_v, inv_pi_v, inv_sqrtpi_v, ln2_v, ln10_v)
	(sqrt2_v, sqrt3_v, inv_sqrt3, egamma_v, phi_v): Add explicit
	specializations for __float128.
	* testsuite/26_numerics/numbers/float128.cc: New test.

From-SVN: r274145

libstdc++-v3/ChangeLog

@@ -1,3 +1,11 @@
+2019-08-06  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/numbers [!__STRICT_ANSI__ && _GLIBCXX_USE_FLOAT128]
+	(e_v, log2e_v, log10e_v, pi_v, inv_pi_v, inv_sqrtpi_v, ln2_v, ln10_v)
+	(sqrt2_v, sqrt3_v, inv_sqrt3, egamma_v, phi_v): Add explicit
+	specializations for __float128.
+	* testsuite/26_numerics/numbers/float128.cc: New test.
+
 2019-08-04  Gerald Pfeifer  <gerald@pfeifer.com>
 
 	* doc/xml/manual/documentation_hacking.xml: doxygen.org is now

libstdc++-v3/include/std/numbers

@@ -133,6 +133,72 @@ namespace numbers
   inline constexpr double egamma = egamma_v<double>;
   inline constexpr double phi = phi_v<double>;
 
+#if !defined(__STRICT_ANSI__) && defined(_GLIBCXX_USE_FLOAT128)
+  template<>
+    inline constexpr __float128 e_v<__float128>
+      = 2.718281828459045235360287471352662498Q;
+
+  /// log_2 e
+  template<>
+    inline constexpr __float128 log2e_v<__float128>
+      = 1.442695040888963407359924681001892137Q;
+
+  /// log_10 e
+  template<>
+    inline constexpr __float128 log10e_v<__float128>
+      = 0.434294481903251827651128918916605082Q;
+
+  /// pi
+  template<>
+    inline constexpr __float128 pi_v<__float128>
+      = 3.141592653589793238462643383279502884Q;
+
+  /// 1/pi
+  template<>
+    inline constexpr __float128 inv_pi_v<__float128>
+      = 0.318309886183790671537767526745028724Q;
+
+  /// 1/sqrt(pi)
+  template<>
+    inline constexpr __float128 inv_sqrtpi_v<__float128>
+      = 0.564189583547756286948079451560772586Q;
+
+  /// log_e 2
+  template<>
+    inline constexpr __float128 ln2_v<__float128>
+      = 0.693147180559945309417232121458176568Q;
+
+  /// log_e 10
+  template<>
+    inline constexpr __float128 ln10_v<__float128>
+      = 2.302585092994045684017991454684364208Q;
+
+  /// sqrt(2)
+  template<>
+    inline constexpr __float128 sqrt2_v<__float128>
+      = 1.414213562373095048801688724209698079Q;
+
+  /// sqrt(3)
+  template<>
+    inline constexpr __float128 sqrt3_v<__float128>
+      = 1.732050807568877293527446341505872367Q;
+
+  /// 1/sqrt(3)
+  template<>
+    inline constexpr __float128 inv_sqrt3_v<__float128>
+      = 0.577350269189625764509148780501957456Q;
+
+  /// The Euler-Mascheroni constant
+  template<>
+    inline constexpr __float128 egamma_v<__float128>
+      = 0.577215664901532860606512090082402431Q;
+
+  /// The golden ratio, (1+sqrt(5))/2
+  template<>
+    inline constexpr __float128 phi_v<__float128>
+      = 1.618033988749894848204586834365638118Q;
+#endif // USE_FLOAT128
+
 } // namespace numbers
 /// @}
 _GLIBCXX_END_NAMESPACE_VERSION

libstdc++-v3/testsuite/26_numerics/numbers/float128.cc

@@ -0,0 +1,41 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <numbers>
+
+#if defined(_GLIBCXX_USE_FLOAT128)
+void
+test01()
+{
+  const __float128* d1  = &std::numbers::e_v<__float128>;
+  const __float128* d2  = &std::numbers::log2e_v<__float128>;
+  const __float128* d3  = &std::numbers::log10e_v<__float128>;
+  const __float128* d4  = &std::numbers::pi_v<__float128>;
+  const __float128* d5  = &std::numbers::inv_pi_v<__float128>;
+  const __float128* d6  = &std::numbers::inv_sqrtpi_v<__float128>;
+  const __float128* d7  = &std::numbers::ln2_v<__float128>;
+  const __float128* d8  = &std::numbers::ln10_v<__float128>;
+  const __float128* d9  = &std::numbers::sqrt2_v<__float128>;
+  const __float128* d10 = &std::numbers::sqrt3_v<__float128>;
+  const __float128* d11 = &std::numbers::inv_sqrt3_v<__float128>;
+  const __float128* d12 = &std::numbers::egamma_v<__float128>;
+  const __float128* d13 = &std::numbers::phi_v<__float128>;
+}
+#endif