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lib/mpi/mpi-gcd.c
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/* mpi-gcd.c - MPI functions
* Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GnuPG 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include "mpi-internal.h"
/****************
* Find the greatest common divisor G of A and B.
* Return: true if this 1, false in all other cases
*/
int mpi_gcd(MPI g, const MPI xa, const MPI xb)
{
MPI a = NULL, b = NULL;
if (mpi_copy(&a, xa) < 0)
goto nomem;
if (mpi_copy(&b, xb) < 0)
goto nomem;
/* TAOCP Vol II, 4.5.2, Algorithm A */
a->sign = 0;
b->sign = 0;
while (mpi_cmp_ui(b, 0)) {
if (mpi_fdiv_r(g, a, b) < 0) /* g used as temorary variable */
goto nomem;
if (mpi_set(a, b) < 0)
goto nomem;
if (mpi_set(b, g) < 0)
goto nomem;
}
if (mpi_set(g, a) < 0)
goto nomem;
mpi_free(a);
mpi_free(b);
return !mpi_cmp_ui(g, 1);
nomem:
mpi_free(a);
mpi_free(b);
return -ENOMEM;
}
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