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// -*-c++-*-
/* $Id: modalg.h,v 1.4 1999/03/24 05:21:32 dm 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
*
*/
#ifndef _MODALG_H_
#define _MODALG_H_ 1
#include "bigint.h"
/* On the Pentium II, this sucks; it's slower than mpz_mod. */
class barrett {
const bigint *mp; // Modulus, M
mp_size_t k; // mpz_bitsperlimb * # of limbs in M
bigint bk1; // 2^((k+1) * mpz_bitsperlimb)
bigint u; // floor (2^mpz_bitsperlimb, M)
/* Workspace */
mutable bigint q, r1, r2;
static void sred (MP_INT *r, const barrett *t, const MP_INT *a)
{ t->mpz_reduce (r, a); }
public:
barrett () : mp (NULL) {}
explicit barrett (const bigint &m) { set (m); }
void set (const bigint &m);
/* Barrett reduction, returns a % M. */
void mpz_reduce (MP_INT *r, const MP_INT *a) const;
mpdelayed<const barrett *, const MP_INT *> reduce (const bigint &a) const
{ return mpdelayed<const barrett *, const MP_INT *> (sred, this, &a); }
};
class montgom {
static const bigint b; // 2^mpz_bitsperlimb
const bigint *mp; // Modulus, M
mp_limb_t mi; // -M^(-1) mod b
int n; // Number of limbs in M
bigint r; // 2^(n*mpz_bitsperlimb)
bigint rm; // r mod M
bigint ri; // r^(-1) mod M
bigint r2; // r^2 mod M
bigint mr; // m * r
/* Workspace */
mutable bigint mmr;
mutable bigint gm;
static void smred (MP_INT *r, const montgom *t, const MP_INT *a)
{ t->mpz_mreduce (r, a); }
static void smmul (MP_INT *r, const montgom *t,
const MP_INT *a, const MP_INT *b)
{ t->mpz_mmul (r, a, b); }
static void smexp (MP_INT *r, const montgom *t,
const MP_INT *a, const MP_INT *b)
{ t->mpz_powm (r, a, b); }
public:
montgom () : mp (NULL) {}
explicit montgom (const bigint &m) { set (m); }
void set (const bigint &m);
const bigint &getr () const { return r; }
const bigint &getri () const { return ri; }
const bigint &getr2 () const { return r2; }
/* Montgomery reduction, returns (t * ri) % M */
void mpz_mreduce (MP_INT *a, const MP_INT *t) const;
mpdelayed<const montgom *, const MP_INT *> mreduce (const bigint &a) const
{ return mpdelayed<const montgom *, const MP_INT *> (smred, this, &a); }
/* Montgomery multiplication, returns (x * y * ri) % M */
void mpz_mmul (MP_INT *a, const MP_INT *x, const MP_INT *y) const;
mpdelayed<const montgom *, const MP_INT *, const MP_INT *>
mreduce (const bigint &a, const bigint &b) const {
return mpdelayed<const montgom *, const MP_INT *,
const MP_INT *> (smmul, this, &a, &b);
}
/* Montgomery exponentiation, returs (g^e) % M */
void mpz_powm (MP_INT *r, const MP_INT *g, const MP_INT *e) const;
mpdelayed<const montgom *, const MP_INT *, const MP_INT *>
powm (const bigint &g, const bigint &e) const {
return mpdelayed<const montgom *, const MP_INT *,
const MP_INT *> (smexp, this, &g, &e);
}
};
#endif /* _MODALG_H_ */
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