--- a/libquadmath/math/signbitq.c	Thu Oct 25 07:37:49 2018 +0900
+++ b/libquadmath/math/signbitq.c	Thu Feb 13 11:34:05 2020 +0900
@@ -1,10 +1,26 @@
+/* Return nonzero value if number is negative.
+   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.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   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, see
+   <http://www.gnu.org/licenses/>.  */
+
 #include "quadmath-imp.h"
 
-
 int
-signbitq (const __float128 x)
+signbitq (__float128 x)
 {
-  ieee854_float128 f;
-  f.value = x;
-  return f.ieee.negative;
+  return __builtin_signbit (x);
 }