--- a/libquadmath/math/fdimq.c	Thu Oct 25 07:37:49 2018 +0900
+++ b/libquadmath/math/fdimq.c	Thu Feb 13 11:34:05 2020 +0900
@@ -1,5 +1,5 @@
 /* Return positive difference between arguments.
-   Copyright (C) 1997, 2004, 2009 Free Software Foundation, Inc.
+   Copyright (C) 1997-2018 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
 
@@ -14,29 +14,19 @@
    Lesser General Public License for more details.
 
    You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, write to the Free
-   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
-   02111-1307 USA.  */
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
 #include "quadmath-imp.h"
 
 __float128
 fdimq (__float128 x, __float128 y)
 {
-  int clsx = fpclassifyq (x);
-  int clsy = fpclassifyq (y);
+  if (__builtin_islessequal (x, y))
+    return 0;
 
-  if (clsx == QUADFP_NAN || clsy == QUADFP_NAN
-      || (y < 0 && clsx == QUADFP_INFINITE && clsy == QUADFP_INFINITE))
-    /* Raise invalid flag.  */
-    return x - y;
-
-  if (x <= y)
-    return 0.0Q;
-
-  __float128 r = x - y;
-  if (isinfq (r))
+  __float128 r = math_narrow_eval (x - y);
+  if (isinfq (r) && !isinfq (x) && !isinfq (y))
     errno = ERANGE;
 
   return r;