1 /* mpi-gcd.c - MPI functions
2 * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
4 * This file is part of GnuPG.
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.
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.
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
21 #include "mpi-internal.h"
24 * Find the greatest common divisor G of A and B.
25 * Return: true if this 1, false in all other cases
27 int mpi_gcd(MPI g
, const MPI xa
, const MPI xb
)
29 MPI a
= NULL
, b
= NULL
;
31 if (mpi_copy(&a
, xa
) < 0)
34 if (mpi_copy(&b
, xb
) < 0)
37 /* TAOCP Vol II, 4.5.2, Algorithm A */
40 while (mpi_cmp_ui(b
, 0)) {
41 if (mpi_fdiv_r(g
, a
, b
) < 0) /* g used as temorary variable */
43 if (mpi_set(a
, b
) < 0)
45 if (mpi_set(b
, g
) < 0)
48 if (mpi_set(g
, a
) < 0)
53 return !mpi_cmp_ui(g
, 1);
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