1/* mpi-gcd.c  -  MPI functions
 2 * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
 3 *
 4 * This file is part of GnuPG.
 5 *
 6 * GnuPG is free software; you can redistribute it and/or modify
 7 * it under the terms of the GNU General Public License as published by
 8 * the Free Software Foundation; either version 2 of the License, or
 9 * (at your option) any later version.
10 *
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 */
20
21#include "mpi-internal.h"
22
23/****************
24 * Find the greatest common divisor G of A and B.
25 * Return: true if this 1, false in all other cases
26 */
27int mpi_gcd(MPI g, const MPI xa, const MPI xb)
28{
29	MPI a = NULL, b = NULL;
30
31	if (mpi_copy(&a, xa) < 0)
32		goto nomem;
33
34	if (mpi_copy(&b, xb) < 0)
35		goto nomem;
36
37	/* TAOCP Vol II, 4.5.2, Algorithm A */
38	a->sign = 0;
39	b->sign = 0;
40	while (mpi_cmp_ui(b, 0)) {
41		if (mpi_fdiv_r(g, a, b) < 0)	/* g used as temorary variable */
42			goto nomem;
43		if (mpi_set(a, b) < 0)
44			goto nomem;
45		if (mpi_set(b, g) < 0)
46			goto nomem;
47	}
48	if (mpi_set(g, a) < 0)
49		goto nomem;
50
51	mpi_free(a);
52	mpi_free(b);
53	return !mpi_cmp_ui(g, 1);
54
55nomem:
56	mpi_free(a);
57	mpi_free(b);
58	return -ENOMEM;
59}