lib/mpi/mpi-bit.c

/* mpi-bit.c  -  MPI bit level fucntions
 * Copyright (C) 1998, 1999 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
 */

#include "mpi-internal.h"
#include "longlong.h"

#define A_LIMB_1 ((mpi_limb_t) 1)

/****************
 * Sometimes we have MSL (most significant limbs) which are 0;
 * this is for some reasons not good, so this function removes them.
 */
void mpi_normalize(MPI a)
{
	for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
		;
}

/****************
 * Return the number of bits in A.
 */
unsigned mpi_get_nbits(MPI a)
{
	unsigned n;

	mpi_normalize(a);

	if (a->nlimbs) {
		mpi_limb_t alimb = a->d[a->nlimbs - 1];
		if (alimb)
			count_leading_zeros(n, alimb);
		else
			n = BITS_PER_MPI_LIMB;
		n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
	} else
		n = 0;
	return n;
}
EXPORT_SYMBOL_GPL(mpi_get_nbits);

/****************
 * Test whether bit N is set.
 */
int mpi_test_bit(MPI a, unsigned n)
{
	unsigned limbno, bitno;
	mpi_limb_t limb;

	limbno = n / BITS_PER_MPI_LIMB;
	bitno = n % BITS_PER_MPI_LIMB;

	if (limbno >= a->nlimbs)
		return 0;	/* too far left: this is a 0 */
	limb = a->d[limbno];
	return (limb & (A_LIMB_1 << bitno)) ? 1 : 0;
}

/****************
 * Set bit N of A.
 */
int mpi_set_bit(MPI a, unsigned n)
{
	unsigned limbno, bitno;

	limbno = n / BITS_PER_MPI_LIMB;
	bitno = n % BITS_PER_MPI_LIMB;

	if (limbno >= a->nlimbs) {	/* resize */
		if (a->alloced >= limbno)
			if (mpi_resize(a, limbno + 1) < 0)
				return -ENOMEM;
		a->nlimbs = limbno + 1;
	}
	a->d[limbno] |= (A_LIMB_1 << bitno);
	return 0;
}

/****************
 * Set bit N of A. and clear all bits above
 */
int mpi_set_highbit(MPI a, unsigned n)
{
	unsigned limbno, bitno;

	limbno = n / BITS_PER_MPI_LIMB;
	bitno = n % BITS_PER_MPI_LIMB;

	if (limbno >= a->nlimbs) {	/* resize */
		if (a->alloced >= limbno)
			if (mpi_resize(a, limbno + 1) < 0)
				return -ENOMEM;
		a->nlimbs = limbno + 1;
	}
	a->d[limbno] |= (A_LIMB_1 << bitno);
	for (bitno++; bitno < BITS_PER_MPI_LIMB; bitno++)
		a->d[limbno] &= ~(A_LIMB_1 << bitno);
	a->nlimbs = limbno + 1;
	return 0;
}

/****************
 * clear bit N of A and all bits above
 */
void mpi_clear_highbit(MPI a, unsigned n)
{
	unsigned limbno, bitno;

	limbno = n / BITS_PER_MPI_LIMB;
	bitno = n % BITS_PER_MPI_LIMB;

	if (limbno >= a->nlimbs)
		return;		/* not allocated, so need to clear bits :-) */

	for (; bitno < BITS_PER_MPI_LIMB; bitno++)
		a->d[limbno] &= ~(A_LIMB_1 << bitno);
	a->nlimbs = limbno + 1;
}

/****************
 * Clear bit N of A.
 */
void mpi_clear_bit(MPI a, unsigned n)
{
	unsigned limbno, bitno;

	limbno = n / BITS_PER_MPI_LIMB;
	bitno = n % BITS_PER_MPI_LIMB;

	if (limbno >= a->nlimbs)
		return;		/* don't need to clear this bit, it's to far to left */
	a->d[limbno] &= ~(A_LIMB_1 << bitno);
}

/****************
 * Shift A by N bits to the right
 * FIXME: should use alloc_limb if X and A are same.
 */
int mpi_rshift(MPI x, MPI a, unsigned n)
{
	mpi_ptr_t xp;
	mpi_size_t xsize;

	xsize = a->nlimbs;
	x->sign = a->sign;
	if (RESIZE_IF_NEEDED(x, (size_t) xsize) < 0)
		return -ENOMEM;
	xp = x->d;

	if (xsize) {
		mpihelp_rshift(xp, a->d, xsize, n);
		MPN_NORMALIZE(xp, xsize);
	}
	x->nlimbs = xsize;
	return 0;
}

/****************
 * Shift A by COUNT limbs to the left
 * This is used only within the MPI library
 */
int mpi_lshift_limbs(MPI a, unsigned int count)
{
	const int n = a->nlimbs;
	mpi_ptr_t ap;
	int i;

	if (!count || !n)
		return 0;

	if (RESIZE_IF_NEEDED(a, n + count) < 0)
		return -ENOMEM;

	ap = a->d;
	for (i = n - 1; i >= 0; i--)
		ap[i + count] = ap[i];
	for (i = 0; i < count; i++)
		ap[i] = 0;
	a->nlimbs += count;
	return 0;
}

/****************
 * Shift A by COUNT limbs to the right
 * This is used only within the MPI library
 */
void mpi_rshift_limbs(MPI a, unsigned int count)
{
	mpi_ptr_t ap = a->d;
	mpi_size_t n = a->nlimbs;
	unsigned int i;

	if (count >= n) {
		a->nlimbs = 0;
		return;
	}

	for (i = 0; i < n - count; i++)
		ap[i] = ap[i + count];
	ap[i] = 0;
	a->nlimbs -= count;
}