1/* mpi-gcd.c  -  MPI functions
2 *	Copyright (C) 1998, 2001, 2002, 2003 Free Software Foundation, Inc.
3 *
4 * This file is part of Libgcrypt.
5 *
6 * Libgcrypt is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU Lesser General Public License as
8 * published by the Free Software Foundation; either version 2.1 of
9 * the License, or (at your option) any later version.
10 *
11 * Libgcrypt 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 Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License 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 <config.h>
22#include <stdio.h>
23#include <stdlib.h>
24#include "mpi-internal.h"
25
26/****************
27 * Find the greatest common divisor G of A and B.
28 * Return: true if this 1, false in all other cases
29 */
30int
31gcry_mpi_gcd( gcry_mpi_t g, gcry_mpi_t xa, gcry_mpi_t xb )
32{
33    gcry_mpi_t a, b;
34
35    a = mpi_copy(xa);
36    b = mpi_copy(xb);
37
38    /* TAOCP Vol II, 4.5.2, Algorithm A */
39    a->sign = 0;
40    b->sign = 0;
41    while( gcry_mpi_cmp_ui( b, 0 ) ) {
42	_gcry_mpi_fdiv_r( g, a, b ); /* g used as temorary variable */
43	mpi_set(a,b);
44	mpi_set(b,g);
45    }
46    mpi_set(g, a);
47
48    mpi_free(a);
49    mpi_free(b);
50    return !gcry_mpi_cmp_ui( g, 1);
51}
52