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diff --git a/gmp/mpz/gcdext.c b/gmp/mpz/gcdext.c
new file mode 100644
index 00000000..b1001a1b
--- /dev/null
+++ b/gmp/mpz/gcdext.c
@@ -0,0 +1,126 @@
+/* mpz_gcdext(g, s, t, a, b) -- Set G to gcd(a, b), and S and T such that
+   g = as + bt.
+
+Copyright 1991, 1993, 1994, 1995, 1996, 1997, 2000, 2001, 2005 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 <stdio.h> /* for NULL */
+#include "gmp.h"
+#include "gmp-impl.h"
+
+void
+mpz_gcdext (mpz_ptr g, mpz_ptr s, mpz_ptr t, mpz_srcptr a, mpz_srcptr b)
+{
+  mp_size_t asize, bsize, usize, vsize;
+  mp_srcptr ap, bp;
+  mp_ptr up, vp;
+  mp_size_t gsize, ssize, tmp_ssize;
+  mp_ptr gp, sp, tmp_gp, tmp_sp;
+  mpz_srcptr u, v;
+  mpz_ptr ss, tt;
+  __mpz_struct stmp, gtmp;
+  TMP_DECL;
+
+  TMP_MARK;
+
+  /* mpn_gcdext requires that U >= V.  Therefore, we often have to swap U and
+     V.  This in turn leads to a lot of complications.  The computed cofactor
+     will be the wrong one, so we have to fix that up at the end.  */
+
+  asize = ABS (SIZ (a));
+  bsize = ABS (SIZ (b));
+  ap = PTR (a);
+  bp = PTR (b);
+  if (asize > bsize || (asize == bsize && mpn_cmp (ap, bp, asize) > 0))
+    {
+      usize = asize;
+      vsize = bsize;
+      up = (mp_ptr) TMP_ALLOC ((usize + 1) * BYTES_PER_MP_LIMB);
+      vp = (mp_ptr) TMP_ALLOC ((vsize + 1) * BYTES_PER_MP_LIMB);
+      MPN_COPY (up, ap, usize);
+      MPN_COPY (vp, bp, vsize);
+      u = a;
+      v = b;
+      ss = s;
+      tt = t;
+    }
+  else
+    {
+      usize = bsize;
+      vsize = asize;
+      up = (mp_ptr) TMP_ALLOC ((usize + 1) * BYTES_PER_MP_LIMB);
+      vp = (mp_ptr) TMP_ALLOC ((vsize + 1) * BYTES_PER_MP_LIMB);
+      MPN_COPY (up, bp, usize);
+      MPN_COPY (vp, ap, vsize);
+      u = b;
+      v = a;
+      ss = t;
+      tt = s;
+    }
+
+  tmp_gp = (mp_ptr) TMP_ALLOC ((usize + 1) * BYTES_PER_MP_LIMB);
+  tmp_sp = (mp_ptr) TMP_ALLOC ((usize + 1) * BYTES_PER_MP_LIMB);
+
+  if (vsize == 0)
+    {
+      tmp_sp[0] = 1;
+      tmp_ssize = 1;
+      MPN_COPY (tmp_gp, up, usize);
+      gsize = usize;
+    }
+  else
+    gsize = mpn_gcdext (tmp_gp, tmp_sp, &tmp_ssize, up, usize, vp, vsize);
+  ssize = ABS (tmp_ssize);
+
+  PTR (&gtmp) = tmp_gp;
+  SIZ (&gtmp) = gsize;
+
+  PTR (&stmp) = tmp_sp;
+  SIZ (&stmp) = (tmp_ssize ^ SIZ (u)) >= 0 ? ssize : -ssize;
+
+  if (tt != NULL)
+    {
+      if (SIZ (v) == 0)
+	SIZ (tt) = 0;
+      else
+	{
+	  mpz_t x;
+	  MPZ_TMP_INIT (x, ssize + usize + 1);
+	  mpz_mul (x, &stmp, u);
+	  mpz_sub (x, &gtmp, x);
+	  mpz_tdiv_q (tt, x, v);
+	}
+    }
+
+  if (ss != NULL)
+    {
+      if (ALLOC (ss) < ssize)
+	_mpz_realloc (ss, ssize);
+      sp = PTR (ss);
+      MPN_COPY (sp, tmp_sp, ssize);
+      SIZ (ss) = SIZ (&stmp);
+    }
+
+  if (ALLOC (g) < gsize)
+    _mpz_realloc (g, gsize);
+  gp = PTR (g);
+  MPN_COPY (gp, tmp_gp, gsize);
+  SIZ (g) = gsize;
+
+  TMP_FREE;
+}