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diff --git a/gmp/mpn/generic/gcd_subdiv_step.c b/gmp/mpn/generic/gcd_subdiv_step.c
new file mode 100644
index 00000000..47c0c26c
--- /dev/null
+++ b/gmp/mpn/generic/gcd_subdiv_step.c
@@ -0,0 +1,104 @@
+/* gcd_subdiv_step.c.
+
+   THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES.  IT IS ONLY
+   SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
+   GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
+
+Copyright 2003, 2004, 2005, 2008 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP 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 3 of the License, or (at your
+option) any later version.
+
+The GNU MP 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 MP Library.  If not, see http://www.gnu.org/licenses/.  */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+/* Used when mpn_hgcd or mpn_hgcd2 has failed. Then either one of a or
+   b is small, or the difference is small. Perform one subtraction
+   followed by one division. If the gcd is found, stores it in gp and
+   *gn, and returns zero. Otherwise, compute the reduced a and b, and
+   return the new size. */
+
+/* FIXME: Check when the smaller number is a single limb, and invoke
+ * mpn_gcd_1. */
+mp_size_t
+mpn_gcd_subdiv_step (mp_ptr gp, mp_size_t *gn,
+		     mp_ptr ap, mp_ptr bp, mp_size_t n, mp_ptr tp)
+{
+  mp_size_t an, bn;
+
+  ASSERT (n > 0);
+  ASSERT (ap[n-1] > 0 || bp[n-1] > 0);
+
+  an = bn = n;
+  MPN_NORMALIZE (ap, an);
+  MPN_NORMALIZE (bp, bn);
+
+  if (UNLIKELY (an == 0))
+    {
+    return_b:
+      MPN_COPY (gp, bp, bn);
+      *gn = bn;
+      return 0;
+    }
+  else if (UNLIKELY (bn == 0))
+    {
+    return_a:
+      MPN_COPY (gp, ap, an);
+      *gn = an;
+      return 0;
+    }
+
+  /* Arrange so that a > b, subtract an -= bn, and maintain
+     normalization. */
+  if (an < bn)
+    MPN_PTR_SWAP (ap, an, bp, bn);
+  else if (an == bn)
+    {
+      int c;
+      MPN_CMP (c, ap, bp, an);
+      if (UNLIKELY (c == 0))
+	goto return_a;
+      else if (c < 0)
+	MP_PTR_SWAP (ap, bp);
+    }
+
+  ASSERT_NOCARRY (mpn_sub (ap, ap, an, bp, bn));
+  MPN_NORMALIZE (ap, an);
+  ASSERT (an > 0);
+
+  /* Arrange so that a > b, and divide a = q b + r */
+  /* FIXME: an < bn happens when we have cancellation. If that is the
+     common case, then we could reverse the roles of a and b to avoid
+     the swap. */
+  if (an < bn)
+    MPN_PTR_SWAP (ap, an, bp, bn);
+  else if (an == bn)
+    {
+      int c;
+      MPN_CMP (c, ap, bp, an);
+      if (UNLIKELY (c == 0))
+	goto return_a;
+      else if (c < 0)
+	MP_PTR_SWAP (ap, bp);
+    }
+
+  mpn_tdiv_qr (tp, ap, 0, ap, an, bp, bn);
+
+  if (mpn_zero_p (ap, bn))
+    goto return_b;
+
+  return bn;
+}