Replace non-constexpr decrement in std::chrono::floor

	* include/std/chrono (floor): Replace non-constexpr operation.
	* testsuite/20_util/duration_cast/rounding.cc: Test conversion to
	durations with floating pointer representations.

From-SVN: r241122

libstdc++-v3/ChangeLog

 2016-10-13  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/chrono (floor): Replace non-constexpr operation.
+	* testsuite/20_util/duration_cast/rounding.cc: Test conversion to
+	durations with floating pointer representations.
+
 	* src/c++11/compatibility-thread-c++0x.cc (_Bind_simple)
 	(_Bind_simple_helper, __bind_simple): Restore for ABI compat symbols.
 

libstdc++-v3/include/std/chrono

@@ -224,7 +224,7 @@ _GLIBCXX_END_NAMESPACE_VERSION
       {
 	auto __to = chrono::duration_cast<_ToDur>(__d);
 	if (__to > __d)
-	  --__to;
+	  return __to - _ToDur{1};
 	return __to;
       }
 

libstdc++-v3/testsuite/20_util/duration_cast/rounding.cc

@@ -27,6 +27,8 @@
 using namespace std::chrono_literals;
 using std::chrono::seconds;
 
+using fp_seconds = std::chrono::duration<float>;
+
 static_assert( std::chrono::floor<seconds>(1000ms) == 1s );
 static_assert( std::chrono::floor<seconds>(1001ms) == 1s );
 static_assert( std::chrono::floor<seconds>(1500ms) == 1s );
@@ -34,6 +36,7 @@ static_assert( std::chrono::floor<seconds>(1999ms) == 1s );
 static_assert( std::chrono::floor<seconds>(2000ms) == 2s );
 static_assert( std::chrono::floor<seconds>(2001ms) == 2s );
 static_assert( std::chrono::floor<seconds>(2500ms) == 2s );
+static_assert( std::chrono::floor<fp_seconds>(500ms) == fp_seconds{0.5f} );
 
 static_assert( std::chrono::ceil<seconds>(1000ms) == 1s );
 static_assert( std::chrono::ceil<seconds>(1001ms) == 2s );
@@ -42,6 +45,7 @@ static_assert( std::chrono::ceil<seconds>(1999ms) == 2s );
 static_assert( std::chrono::ceil<seconds>(2000ms) == 2s );
 static_assert( std::chrono::ceil<seconds>(2001ms) == 3s );
 static_assert( std::chrono::ceil<seconds>(2500ms) == 3s );
+static_assert( std::chrono::ceil<fp_seconds>(500ms) == fp_seconds{0.5f} );
 
 static_assert( std::chrono::round<seconds>(1000ms) == 1s );
 static_assert( std::chrono::round<seconds>(1001ms) == 1s );