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diff --git a/sysdeps/ieee754/flt-32/reduce_aux.h b/sysdeps/ieee754/flt-32/reduce_aux.h
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+++ b/sysdeps/ieee754/flt-32/reduce_aux.h
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+/* Auxiliary routine for the Bessel functions (j0f, y0f, j1f, y1f).
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_REDUCE_AUX_H
+#define _MATH_REDUCE_AUX_H
+
+#include <math.h>
+#include <math_private.h>
+#include <s_sincosf.h>
+
+/* Return h and update n such that:
+   Now x - pi/4 - alpha = h + n*pi/2 mod (2*pi).  */
+static inline double
+reduce_aux (float x, int *n, double alpha)
+{
+  double h;
+  h = reduce_large (asuint (x), n);
+  /* Now |x| = h+n*pi/2 mod 2*pi.  */
+  /* Recover sign.  */
+  if (x < 0)
+    {
+      h = -h;
+      *n = -*n;
+    }
+  /* Subtract pi/4.  */
+  double piover2 = 0xc.90fdaa22168cp-3;
+  if (h >= 0)
+    h -= piover2 / 2;
+  else
+    {
+      h += piover2 / 2;
+      (*n) --;
+    }
+  /* Subtract alpha and reduce if needed mod pi/2.  */
+  h -= alpha;
+  if (h > piover2)
+    {
+      h -= piover2;
+      (*n) ++;
+    }
+  else if (h < -piover2)
+    {
+      h += piover2;
+      (*n) --;
+    }
+  return h;
+}
+
+#endif