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// -*-c++-*-
/* $Id: modalg.C,v 1.5 2005/10/12 00:04:15 fubob Exp $ */
/*
*
* Copyright (C) 1998 David Mazieres (dm@uun.org)
*
* This program 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, or (at
* your option) any later version.
*
* This program 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 "modalg.h"
#include "amisc.h"
#undef setbit
void
barrett::set (const bigint &m)
{
assert (sgn (m) > 0);
assert (m.getbit (0));
mp = &m;
k = ((*mp).nbits () + mpz_bitsperlimb - 1) / mpz_bitsperlimb;
bk1 = 0;
bk1.setbit ((k + 1) * mpz_bitsperlimb, 1);
u = 0;
u.setbit (2 * mpz_bitsperlimb * k, 1);
u = u / *mp;
}
void
barrett::mpz_reduce (MP_INT *r, const MP_INT *a) const
{
assert (a->_mp_size >= 0 && a->_mp_size <= 2 * k);
mpz_tdiv_q_2exp (&q, a, (k-1) * mpz_bitsperlimb);
q *= u;
q >>= (k+1) * mpz_bitsperlimb;
mpz_tdiv_r_2exp (&r1, a, (k+1) * mpz_bitsperlimb);
r2 = q * *mp;
r2.trunc ((k+1) * mpz_bitsperlimb);
mpz_sub (r, &r1, &r2);
if (mpz_sgn (r) < 0)
mpz_add (r, r, &bk1);
while (mpz_cmp (r, mp) > 0)
mpz_sub (r, r, mp);
}
const bigint montgom::b (bigint (1) << ((int)(mpz_bitsperlimb)));
void
montgom::set (const bigint &m)
{
mp = &m;
assert (sgn (*mp) > 0 && mp->getbit (0));
/* Yuck, but this isn't on the ciritcal path */
bigint mitmp;
mpz_invert (&mitmp, mp, &b);
mitmp = b - mitmp;
mi = mitmp.getui ();
n = mp->_mp_size;
r = 0;
r.setbit (n * mpz_bitsperlimb, 1);
rm = mod (r, *mp);
ri = invert (rm, *mp);
r2 = 0;
r2.setbit (n * 2 * mpz_bitsperlimb, 1);
r2 = mod (r2, *mp);
mr = *mp * r;
}
void
montgom::mpz_mreduce (MP_INT *a, const MP_INT *t) const
{
assert (t->_mp_size >= 0 && t->_mp_size <= 2 * n);
assert (mpz_cmp (t, &mr) < 0);
int sa = 2 * n + 1;
if (a->_mp_alloc < sa)
_mpz_realloc (a, sa);
mpz_set (a, t);
mp_limb_t *ap = a->_mp_d;
bzero (ap + a->_mp_size, (sa - a->_mp_size) * sizeof (mp_limb_t));
const mp_limb_t *mpp = mp->_mp_d;
for (int i = 0; i < n; i++) {
mp_limb_t u = ap[i] * mi;
u = mpn_addmul_1 (ap + i, mpp, n, u);
mpn_add_1 (ap + n + i, ap + n + i, n - i + 1, u);
}
while (sa && !ap[sa - 1])
sa--;
a->_mp_size = sa;
mpz_tdiv_q_2exp (a, a, n * mpz_bitsperlimb);
if (mpz_cmp (a, mp) >= 0)
mpz_sub (a, a, mp);
}
void
montgom::mpz_mmul (MP_INT *a, const MP_INT *x, const MP_INT *y) const
{
assert (x->_mp_size >= 0 && x->_mp_size <= n);
assert (y->_mp_size >= 0 && y->_mp_size <= n);
if (!x->_mp_size || !y->_mp_size) {
a->_mp_size = 0;
return;
}
MP_INT *rp = a;
if (rp == x || rp == y)
rp = &mmr;
int sa = 2 * n + 1;
if (rp->_mp_alloc < sa)
_mpz_realloc (rp, sa);
mp_limb_t *ap = rp->_mp_d;
bzero (ap, sa * sizeof (mp_limb_t));
const mp_limb_t *mpp = mp->_mp_d;
const mp_limb_t *xp = x->_mp_d;
const mp_limb_t *yp = y->_mp_d;
int sx = x->_mp_size, sy = y->_mp_size;
for (int i = 0; i < n; i++) {
mp_limb_t xi = i < sx ? xp[i] : 0;
mp_limb_t u = (ap[i] + xi * yp[0]) * mi;
u = mpn_addmul_1 (ap + i, mpp, n, u);
mpn_add_1 (ap + n + i, ap + n + i, n - i + 1, u);
u = mpn_addmul_1 (ap + i, yp, sy, xi);
mpn_add_1 (ap + sy + i, ap + sy + i, sa - sy - i, u);
}
while (sa && !ap[sa - 1])
sa--;
rp->_mp_size = sa;
mpz_tdiv_q_2exp (rp, rp, n * mpz_bitsperlimb);
if (mpz_cmp (rp, mp) >= 0)
mpz_sub (rp, rp, mp);
if (a == x || a == y)
mmr.swap (a);
}
void
montgom::mpz_powm (MP_INT *a, const MP_INT *g, const MP_INT *e) const
{
mpz_mmul (&gm, g, &r2);
mpz_set (a, &rm);
for (int i = mpz_sizeinbase2 (e); i-- > 0;) {
mpz_mmul (a, a, a);
if (mpz_getbit (e, i))
mpz_mmul (a, a, &gm);
}
mpz_mreduce (a, a);
}
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