mpi-mul.c

/* mpi-mul.c  -  MPI functions
 *	Copyright (C) 1994, 1996 Free Software Foundation, Inc.
 *	Copyright (C) 1998, 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
 *
 * Note: This code is heavily based on the GNU MP Library.
 *	 Actually it's the same code with only minor changes in the
 *	 way the data is stored; this is to support the abstraction
 *	 of an optional secure memory allocation which may be used
 *	 to avoid revealing of sensitive data due to paging etc.
 *	 The GNU MP Library itself is published under the LGPL;
 *	 however I decided to publish this code under the plain GPL.
 */

#include "mpi-internal.h"

int mpi_mul_ui(MPI prod, MPI mult, unsigned long small_mult)
{
	mpi_size_t size, prod_size;
	mpi_ptr_t prod_ptr;
	mpi_limb_t cy;
	int sign;

	size = mult->nlimbs;
	sign = mult->sign;

	if (!size || !small_mult) {
		prod->nlimbs = 0;
		prod->sign = 0;
		return 0;
	}

	prod_size = size + 1;
	if (prod->alloced < prod_size)
		if (mpi_resize(prod, prod_size) < 0)
			return -ENOMEM;
	prod_ptr = prod->d;

	cy = mpihelp_mul_1(prod_ptr, mult->d, size, (mpi_limb_t) small_mult);
	if (cy)
		prod_ptr[size++] = cy;
	prod->nlimbs = size;
	prod->sign = sign;
	return 0;
}

int mpi_mul_2exp(MPI w, MPI u, unsigned long cnt)
{
	mpi_size_t usize, wsize, limb_cnt;
	mpi_ptr_t wp;
	mpi_limb_t wlimb;
	int usign, wsign;

	usize = u->nlimbs;
	usign = u->sign;

	if (!usize) {
		w->nlimbs = 0;
		w->sign = 0;
		return 0;
	}

	limb_cnt = cnt / BITS_PER_MPI_LIMB;
	wsize = usize + limb_cnt + 1;
	if (w->alloced < wsize)
		if (mpi_resize(w, wsize) < 0)
			return -ENOMEM;
	wp = w->d;
	wsize = usize + limb_cnt;
	wsign = usign;

	cnt %= BITS_PER_MPI_LIMB;
	if (cnt) {
		wlimb = mpihelp_lshift(wp + limb_cnt, u->d, usize, cnt);
		if (wlimb) {
			wp[wsize] = wlimb;
			wsize++;
		}
	} else {
		MPN_COPY_DECR(wp + limb_cnt, u->d, usize);
	}

	/* Zero all whole limbs at low end.  Do it here and not before calling
	 * mpn_lshift, not to lose for U == W.  */
	MPN_ZERO(wp, limb_cnt);

	w->nlimbs = wsize;
	w->sign = wsign;
	return 0;
}

int mpi_mul(MPI w, MPI u, MPI v)
{
	int rc = -ENOMEM;
	mpi_size_t usize, vsize, wsize;
	mpi_ptr_t up, vp, wp;
	mpi_limb_t cy;
	int usign, vsign, sign_product;
	int assign_wp = 0;
	mpi_ptr_t tmp_limb = NULL;

	if (u->nlimbs < v->nlimbs) {	/* Swap U and V. */
		usize = v->nlimbs;
		usign = v->sign;
		up = v->d;
		vsize = u->nlimbs;
		vsign = u->sign;
		vp = u->d;
	} else {
		usize = u->nlimbs;
		usign = u->sign;
		up = u->d;
		vsize = v->nlimbs;
		vsign = v->sign;
		vp = v->d;
	}
	sign_product = usign ^ vsign;
	wp = w->d;

	/* Ensure W has space enough to store the result.  */
	wsize = usize + vsize;
	if (w->alloced < (size_t) wsize) {
		if (wp == up || wp == vp) {
			wp = mpi_alloc_limb_space(wsize);
			if (!wp)
				goto nomem;
			assign_wp = 1;
		} else {
			if (mpi_resize(w, wsize) < 0)
				goto nomem;
			wp = w->d;
		}
	} else {		/* Make U and V not overlap with W.      */
		if (wp == up) {
			/* W and U are identical.  Allocate temporary space for U.      */
			up = tmp_limb = mpi_alloc_limb_space(usize);
			if (!up)
				goto nomem;
			/* Is V identical too?  Keep it identical with U.  */
			if (wp == vp)
				vp = up;
			/* Copy to the temporary space.  */
			MPN_COPY(up, wp, usize);
		} else if (wp == vp) {
			/* W and V are identical.  Allocate temporary space for V.      */
			vp = tmp_limb = mpi_alloc_limb_space(vsize);
			if (!vp)
				goto nomem;
			/* Copy to the temporary space.  */
			MPN_COPY(vp, wp, vsize);
		}
	}

	if (!vsize)
		wsize = 0;
	else {
		if (mpihelp_mul(wp, up, usize, vp, vsize, &cy) < 0)
			goto nomem;
		wsize -= cy ? 0 : 1;
	}

	if (assign_wp)
		mpi_assign_limb_space(w, wp, wsize);

	w->nlimbs = wsize;
	w->sign = sign_product;
	rc = 0;
nomem:
	if (tmp_limb)
		mpi_free_limb_space(tmp_limb);
	return rc;
}

int mpi_mulm(MPI w, MPI u, MPI v, MPI m)
{
	if (mpi_mul(w, u, v) < 0)
		return -ENOMEM;
	return mpi_fdiv_r(w, w, m);
}