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Release calc version 2.11.1t1
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cal/mersenne.cal
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61
cal/mersenne.cal
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/*
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* mersenne - perform a primality test of 2^p-1, for prime p>1
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*
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* Copyright (C) 1999 David I. Bell and Landon Curt Noll
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*
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* Primary author: David I. Bell
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*
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* Calc is open software; you can redistribute it and/or modify it under
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* the terms of the version 2.1 of the GNU Lesser General Public License
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* as published by the Free Software Foundation.
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*
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* Calc is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
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* Public License for more details.
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*
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* A copy of version 2.1 of the GNU Lesser General Public License is
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* distributed with calc under the filename COPYING-LGPL. You should have
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* received a copy with calc; if not, write to Free Software Foundation, Inc.
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
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*
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* @(#) $Revision: 29.1 $
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* @(#) $Id: mersenne.cal,v 29.1 1999/12/14 09:15:31 chongo Exp $
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* @(#) $Source: /usr/local/src/cmd/calc/cal/RCS/mersenne.cal,v $
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*
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* Under source code control: 1991/05/22 21:56:36
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* File existed as early as: 1991
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*
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* Share and enjoy! :-) http://reality.sgi.com/chongo/tech/comp/calc/
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*/
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/*
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* NOTE: See lucas.cal for a more general routine.
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*/
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define mersenne(p)
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{
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local u, i, p_mask;
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/* firewall */
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if (! isint(p))
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quit "p is not an integer";
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/* two is a special case */
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if (p == 2)
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return 1;
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/* if p is not prime, then 2^p-1 is not prime */
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if (! ptest(p,1))
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return 0;
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/* lltest: u(i+1) = u(i)^2 - 2 mod 2^p-1 */
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u = 4;
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for (i = 2; i < p; ++i) {
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u = hnrmod(u^2 - 2, 1, p, -1);
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}
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/* 2^p-1 is prime iff u(p) = 0 mod 2^p-1 */
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return (u == 0);
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}
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