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diff --git a/math/s_fdim.c b/math/s_fdim.c
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+/* Return positive difference between arguments.
+   Copyright (C) 1997, 2004 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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <math.h>
+
+double
+__fdim (double x, double y)
+{
+  int clsx = fpclassify (x);
+  int clsy = fpclassify (y);
+
+  if (clsx == FP_NAN || clsy == FP_NAN
+      || (y < 0 && clsx == FP_INFINITE && clsy == FP_INFINITE))
+    /* Raise invalid flag.  */
+    return x - y;
+
+  return x <= y ? 0 : x - y;
+}
+weak_alias (__fdim, fdim)
+#ifdef NO_LONG_DOUBLE
+strong_alias (__fdim, __fdiml)
+weak_alias (__fdim, fdiml)
+#endif