libstdc++: Fix chrono::__detail::ceil to work with C++11

In C++11 constexpr functions can only have a return statement, so we
need to fix __detail::ceil to make it valid in C++11. This can be done
by moving the comparison and increment into a new function, __ceil_impl,
and calling that with the result of the duration_cast.

This would mean the standard C++17 std::chrono::ceil function would make
two further calls, which would add too much overhead when not inlined.
For C++17 and later use a using-declaration to add chrono::ceil to
namespace __detail. For C++11 and C++14 define chrono::__detail::__ceil
as a C++11-compatible constexpr function template.

libstdc++-v3/ChangeLog:

	* include/std/chrono [C++17] (chrono::__detail::ceil): Add
	using declaration to make chrono::ceil available for internal
	use with a consistent name.
	(chrono::__detail::__ceil_impl): New function template.
	(chrono::__detail::ceil): Use __ceil_impl to compare and
	increment the value. Remove SFINAE constraint.

diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index 893d1f6b2c91b9f7756c46c15b3484533134f5c1..7539d7184ea4a507b10c3004e7c28ab9d5c2849f 100644 (file)
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -329,20 +329,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 #endif // C++20
 
-    // We want to use ceil even when compiling for earlier standards versions
-    namespace __detail
-    {
-      template<typename _ToDur, typename _Rep, typename _Period>
-       constexpr __enable_if_is_duration<_ToDur>
-       ceil(const duration<_Rep, _Period>& __d)
-       {
-         auto __to = chrono::duration_cast<_ToDur>(__d);
-         if (__to < __d)
-           return __to + _ToDur{1};
-         return __to;
-       }
-    }
-
 #if __cplusplus >= 201703L
 # define __cpp_lib_chrono 201611
 
@@ -360,7 +346,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       constexpr __enable_if_is_duration<_ToDur>
       ceil(const duration<_Rep, _Period>& __d)
       {
-       return __detail::ceil<_ToDur>(__d);
+       auto __to = chrono::duration_cast<_ToDur>(__d);
+       if (__to < __d)
+         return __to + _ToDur{1};
+       return __to;
       }
 
     template <typename _ToDur, typename _Rep, typename _Period>
@@ -394,6 +383,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          return __d;
        return -__d;
       }
+
+    // Make chrono::ceil<D> also usable as chrono::__detail::ceil<D>.
+    namespace __detail { using chrono::ceil; }
+
+#else // ! C++17
+
+    // We want to use ceil even when compiling for earlier standards versions.
+    // C++11 only allows a single statement in a constexpr function, so we
+    // need to move the comparison into a separate function, __ceil_impl.
+    namespace __detail
+    {
+      template<typename _Tp, typename _Up>
+       constexpr _Tp
+       __ceil_impl(const _Tp& __t, const _Up& __u)
+       {
+         return (__t < __u) ? (__t + _Tp{1}) : __t;
+       }
+
+      // C++11-friendly version of std::chrono::ceil<D> for internal use.
+      template<typename _ToDur, typename _Rep, typename _Period>
+       constexpr _ToDur
+       ceil(const duration<_Rep, _Period>& __d)
+       {
+         return __detail::__ceil_impl(chrono::duration_cast<_ToDur>(__d), __d);
+       }
+    }
 #endif // C++17
 
     /// duration_values