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/* mpi-bit.c - MPI bit level functions
* 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)
n = count_leading_zeros(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 int n)
{
unsigned int 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;
}
EXPORT_SYMBOL_GPL(mpi_test_bit);
/****************
* Set bit N of A.
*/
int mpi_set_bit(MPI a, unsigned int n)
{
unsigned int i, limbno, bitno;
int err;
limbno = n / BITS_PER_MPI_LIMB;
bitno = n % BITS_PER_MPI_LIMB;
if (limbno >= a->nlimbs) {
for (i = a->nlimbs; i < a->alloced; i++)
a->d[i] = 0;
err = mpi_resize(a, limbno+1);
if (err)
return err;
a->nlimbs = limbno+1;
}
a->d[limbno] |= (A_LIMB_1<<bitno);
return 0;
}
/*
* Shift A by N bits to the right.
*/
int mpi_rshift(MPI x, MPI a, unsigned int n)
{
mpi_size_t xsize;
unsigned int i;
unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
unsigned int nbits = (n%BITS_PER_MPI_LIMB);
int err;
if (x == a) {
/* In-place operation. */
if (nlimbs >= x->nlimbs) {
x->nlimbs = 0;
return 0;
}
if (nlimbs) {
for (i = 0; i < x->nlimbs - nlimbs; i++)
x->d[i] = x->d[i+nlimbs];
x->d[i] = 0;
x->nlimbs -= nlimbs;
}
if (x->nlimbs && nbits)
mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
} else if (nlimbs) {
/* Copy and shift by more or equal bits than in a limb. */
xsize = a->nlimbs;
x->sign = a->sign;
err = RESIZE_IF_NEEDED(x, xsize);
if (err)
return err;
x->nlimbs = xsize;
for (i = 0; i < a->nlimbs; i++)
x->d[i] = a->d[i];
x->nlimbs = i;
if (nlimbs >= x->nlimbs) {
x->nlimbs = 0;
return 0;
}
for (i = 0; i < x->nlimbs - nlimbs; i++)
x->d[i] = x->d[i+nlimbs];
x->d[i] = 0;
x->nlimbs -= nlimbs;
if (x->nlimbs && nbits)
mpihelp_rshift(x->d, x->d, x->nlimbs, nbits);
} else {
/* Copy and shift by less than bits in a limb. */
xsize = a->nlimbs;
x->sign = a->sign;
err = RESIZE_IF_NEEDED(x, xsize);
if (err)
return err;
x->nlimbs = xsize;
if (xsize) {
if (nbits)
mpihelp_rshift(x->d, a->d, x->nlimbs, nbits);
else {
/* The rshift helper function is not specified for
* NBITS==0, thus we do a plain copy here.
*/
for (i = 0; i < x->nlimbs; i++)
x->d[i] = a->d[i];
}
}
}
MPN_NORMALIZE(x->d, x->nlimbs);
return 0;
}
EXPORT_SYMBOL_GPL(mpi_rshift);
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