--- /dev/null
+/* 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 1996, 1997, 1998, 1999, 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 "gmp.h"
+#include "gmp-impl.h"
+
+int
+mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
+{
+ mpz_t gcd, tmp;
+ mp_size_t xsize, nsize, size;
+ TMP_DECL;
+
+ 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;
+
+ 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 (SIZ (gcd) != 1 || PTR(gcd)[0] != 1)
+ {
+ TMP_FREE;
+ 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;
+ return 1;
+}