pollard.cal

Calc Software Package for Number Calc

/*
 * pollard - factor using Pollard's p-1 method
 *
 * Copyright (C) 1999  David I. Bell
 *
 * Calc is open software; you can redistribute it and/or modify it under
 * the terms of the version 2.1 of the GNU Lesser General Public License
 * as published by the Free Software Foundation.
 *
 * Calc 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 Lesser General
 * Public License for more details.
 *
 * A copy of version 2.1 of the GNU Lesser General Public License is
 * distributed with calc under the filename COPYING-LGPL.  You should have
 * received a copy with calc; if not, write to Free Software Foundation, Inc.
 * 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
 *
 * @(#) $Revision: 29.2 $
 * @(#) $Id: pollard.cal,v 29.2 2000/06/07 14:02:25 chongo Exp $
 * @(#) $Source: /usr/local/src/cmd/calc/cal/RCS/pollard.cal,v $
 *
 * Under source code control:	1991/05/22 21:56:37
 * File existed as early as:	1991
 *
 * Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
 */


define pfactor(N, B, ai, af)
{
	local	a, k, i, d;

	if (isnull(B))
		B = 1000;
	if (isnull(ai))
		ai = 2;
	if (isnull(af))
		af = ai + 20;
	k = lcmfact(B);
	d = lfactor(N, B);
	if (d > 1)
		return d;
	for (a = ai; a <= af; a++) {
		i = pmod(a, k, N);
		d = gcd(i - 1, N);
		if ((d > 1) && (d != N))
			return d;
	}
	return 1;
}