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Austin Schuhdace2a62020-08-18 10:56:48 -07001/* mpz_invert (inv, x, n). Find multiplicative inverse of X in Z(N).
2 If X has an inverse, return non-zero and store inverse in INVERSE,
3 otherwise, return 0 and put garbage in INVERSE.
4
5Copyright 1996-2001, 2005, 2012, 2014 Free Software Foundation, Inc.
6
7This file is part of the GNU MP Library.
8
9The GNU MP Library is free software; you can redistribute it and/or modify
10it under the terms of either:
11
12 * the GNU Lesser General Public License as published by the Free
13 Software Foundation; either version 3 of the License, or (at your
14 option) any later version.
15
16or
17
18 * the GNU General Public License as published by the Free Software
19 Foundation; either version 2 of the License, or (at your option) any
20 later version.
21
22or both in parallel, as here.
23
24The GNU MP Library is distributed in the hope that it will be useful, but
25WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
26or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
27for more details.
28
29You should have received copies of the GNU General Public License and the
30GNU Lesser General Public License along with the GNU MP Library. If not,
31see https://www.gnu.org/licenses/. */
32
33#include "gmp-impl.h"
34
35int
36mpz_invert (mpz_ptr inverse, mpz_srcptr x, mpz_srcptr n)
37{
38 mpz_t gcd, tmp;
39 mp_size_t xsize, nsize, size;
40 TMP_DECL;
41
42 xsize = ABSIZ (x);
43 nsize = ABSIZ (n);
44
45 size = MAX (xsize, nsize) + 1;
46 TMP_MARK;
47
48 MPZ_TMP_INIT (gcd, size);
49 MPZ_TMP_INIT (tmp, size);
50 mpz_gcdext (gcd, tmp, (mpz_ptr) 0, x, n);
51
52 /* If no inverse existed, return with an indication of that. */
53 if (!MPZ_EQUAL_1_P (gcd))
54 {
55 TMP_FREE;
56 return 0;
57 }
58
59 /* Make sure we return a positive inverse. */
60 if (SIZ (tmp) < 0)
61 {
62 if (SIZ (n) < 0)
63 mpz_sub (inverse, tmp, n);
64 else
65 mpz_add (inverse, tmp, n);
66 }
67 else
68 mpz_set (inverse, tmp);
69
70 TMP_FREE;
71 return 1;
72}