util: fix clang 3.4 time::abs compilation error

This commit also adds a test case for time::abs function template.

refs #3698

Change-Id: I32c3d15362d5515841a95ce6d9804be11df632b5

src/util/time.hpp

@@ -48,7 +48,7 @@ using boost::chrono::duration_cast;
  *        unless std::numeric_limits<Rep>::is_signed is true.
  */
 template<typename Rep, typename Period,
-         typename = typename std::enable_if<duration<Rep, Period>::min() < duration<Rep, Period>::zero()>::type>
+         typename = typename std::enable_if<std::numeric_limits<Rep>::is_signed>::type>
 constexpr duration<Rep, Period>
 abs(duration<Rep, Period> d)
 {

tests/unit-tests/util/time.t.cpp

@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2015 Regents of the University of California.
+ * Copyright (c) 2013-2016 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -26,7 +26,8 @@
 namespace ndn {
 namespace tests {
 
-BOOST_AUTO_TEST_SUITE(UtilTime)
+BOOST_AUTO_TEST_SUITE(Util)
+BOOST_AUTO_TEST_SUITE(TestTime)
 
 BOOST_AUTO_TEST_CASE(SystemClock)
 {
@@ -73,7 +74,15 @@ BOOST_AUTO_TEST_CASE(SteadyClock)
   BOOST_CHECK_GT(newValue, oldValue);
 }
 
-BOOST_AUTO_TEST_SUITE_END()
+BOOST_AUTO_TEST_CASE(Abs)
+{
+  BOOST_CHECK_EQUAL(time::abs(time::nanoseconds(24422)), time::nanoseconds(24422));
+  BOOST_CHECK_EQUAL(time::abs(time::microseconds(0)), time::microseconds(0));
+  BOOST_CHECK_EQUAL(time::abs(time::milliseconds(-15583)), time::milliseconds(15583));
+}
+
+BOOST_AUTO_TEST_SUITE_END() // TestTime
+BOOST_AUTO_TEST_SUITE_END() // Util
 
 } // namespace tests
 } // namespace ndn