From d21776ef90361e66401cd99c8ff0d98b46d3b0d6 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 12 Nov 2020 13:31:02 +0000
Subject: [PATCH] libstdc++: Simplify __numeric_traits definition

This changes the __numeric_traits primary template to assume its
argument is an integer type. For the three floating point types that are
supported by __numeric_traits_floating an explicit specialization of
__numeric_traits chooses the right base class.

This improves the failure mode for using __numeric_traits with an
unsupported type. Previously it would use __numeric_traits_floating as
the base class, and give somewhat obscure errors for trying to access
the static data members. Now it will use __numeric_traits_integer which
has a static_assert to check for supported types.

As a side effect of this change there is no need to instantiate
__conditional_type to decide which base class to use.

libstdc++-v3/ChangeLog:

	* include/ext/numeric_traits.h (__numeric_traits): Change
	primary template to always derive from __numeric_traits_integer.
	(__numeric_traits<float>, __numeric_traits<double>)
	(__numeric_traits<long double>): Add explicit specializations.
---
 libstdc++-v3/include/ext/numeric_traits.h | 29 ++++++++++++++++-------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/libstdc++-v3/include/ext/numeric_traits.h b/libstdc++-v3/include/ext/numeric_traits.h
index c29f9f21d1a..2cac7f1d1ed 100644
--- a/libstdc++-v3/include/ext/numeric_traits.h
+++ b/libstdc++-v3/include/ext/numeric_traits.h
@@ -176,19 +176,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Value>
     const int __numeric_traits_floating<_Value>::__max_exponent10;
 
+#undef __glibcxx_floating
+#undef __glibcxx_max_digits10
+#undef __glibcxx_digits10
+#undef __glibcxx_max_exponent10
+
   template<typename _Value>
     struct __numeric_traits
-    : public __conditional_type<__is_integer_nonstrict<_Value>::__value,
-				__numeric_traits_integer<_Value>,
-				__numeric_traits_floating<_Value> >::__type
+    : public __numeric_traits_integer<_Value>
+    { };
+
+  template<>
+    struct __numeric_traits<float>
+    : public __numeric_traits_floating<float>
+    { };
+
+  template<>
+    struct __numeric_traits<double>
+    : public __numeric_traits_floating<double>
+    { };
+
+  template<>
+    struct __numeric_traits<long double>
+    : public __numeric_traits_floating<long double>
     { };
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#undef __glibcxx_floating
-#undef __glibcxx_max_digits10
-#undef __glibcxx_digits10
-#undef __glibcxx_max_exponent10
-
 #endif
-- 
2.30.2