Implement P0092R1 for C++1z

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@252195 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/time/time.duration/time.duration.alg/abs.pass.cpp

@@ -0,0 +1,50 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14
+
+// <chrono>
+
+// abs
+
+// template <class Rep, class Period>
+//   constexpr duration<Rep, Period> abs(duration<Rep, Period> d)
+
+#include <chrono>
+#include <type_traits>
+#include <cassert>
+
+template <class Duration>
+void
+test(const Duration& f, const Duration& d)
+{
+    {
+    typedef decltype(std::chrono::abs(f)) R;
+    static_assert((std::is_same<R, Duration>::value), "");
+    assert(std::chrono::abs(f) == d);
+    }
+}
+
+int main()
+{
+//  7290000ms is 2 hours, 1 minute, and 30 seconds
+    test(std::chrono::milliseconds( 7290000), std::chrono::milliseconds( 7290000));
+    test(std::chrono::milliseconds(-7290000), std::chrono::milliseconds( 7290000));
+    test(std::chrono::minutes( 122), std::chrono::minutes( 122));
+    test(std::chrono::minutes(-122), std::chrono::minutes( 122));
+    test(std::chrono::hours(0), std::chrono::hours(0));
+
+    {
+//  9000000ms is 2 hours and 30 minutes
+    constexpr std::chrono::hours h1 = std::chrono::abs(std::chrono::hours(-3));
+    static_assert(h1.count() == 3, "");
+    constexpr std::chrono::hours h2 = std::chrono::abs(std::chrono::hours(3));
+    static_assert(h2.count() == 3, "");
+    }
+}