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diff --git a/rts/gmp/mpz/invert.c b/rts/gmp/mpz/invert.c
new file mode 100644
index 0000000..749a096
--- /dev/null
+++ b/rts/gmp/mpz/invert.c
@@ -0,0 +1,77 @@
+/* mpz_invert (inv, x, n).  Find multiplicative inverse of X in Z(N).
+   If X has an inverse, return non-zero and store inverse in INVERSE,
+   otherwise, return 0 and put garbage in INVERSE.
+
+Copyright (C) 1996, 1997, 1998, 1999, 2000 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 2.1 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; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+int
+#if __STDC__
+mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
+#else
+mpz_invert (inverse, x, n)
+     mpz_ptr inverse;
+     mpz_srcptr x, n;
+#endif
+{
+  mpz_t gcd, tmp;
+  mp_size_t xsize, nsize, size;
+  TMP_DECL (marker);
+
+  xsize = SIZ (x);
+  nsize = SIZ (n);
+  xsize = ABS (xsize);
+  nsize = ABS (nsize);
+  size = MAX (xsize, nsize) + 1;
+
+  /* No inverse exists if the leftside operand is 0.  Likewise, no
+     inverse exists if the mod operand is 1.  */
+  if (xsize == 0 || (nsize == 1 && (PTR (n))[0] == 1))
+    return 0;
+
+  TMP_MARK (marker);
+
+  MPZ_TMP_INIT (gcd, size);
+  MPZ_TMP_INIT (tmp, size);
+  mpz_gcdext (gcd, tmp, (mpz_ptr) 0, x, n);
+
+  /* If no inverse existed, return with an indication of that.  */
+  if (gcd->_mp_size != 1 || (gcd->_mp_d)[0] != 1)
+    {
+      TMP_FREE (marker);
+      return 0;
+    }
+
+  /* Make sure we return a positive inverse.  */
+  if (SIZ (tmp) < 0)
+    {
+      if (SIZ (n) < 0)
+	mpz_sub (inverse, tmp, n);
+      else
+	mpz_add (inverse, tmp, n);
+    }
+  else
+    mpz_set (inverse, tmp);
+
+  TMP_FREE (marker);
+  return 1;
+}