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mpi-bit.c
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/* mpi-bit.c - MPI bit level functions
* Copyright (C) 1998, 1999, 2001, 2002, 2006 Free Software Foundation, Inc.
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser 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 <config.h>
#include <stdio.h>
#include <stdlib.h>
#include "mpi-internal.h"
#include "longlong.h"
#ifdef MPI_INTERNAL_NEED_CLZ_TAB
#ifdef __STDC__
const
#endif
unsigned char
_gcry_clz_tab[] =
{
0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
};
#endif
#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
_gcry_mpi_normalize( gcry_mpi_t a )
{
if( mpi_is_opaque(a) )
return;
for( ; a->nlimbs && !a->d[a->nlimbs-1]; a->nlimbs-- )
;
}
/****************
* Return the number of bits in A.
*/
unsigned int
gcry_mpi_get_nbits( gcry_mpi_t a )
{
unsigned n;
if( mpi_is_opaque(a) ) {
return a->sign; /* which holds the number of bits */
}
_gcry_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;
}
/****************
* Test whether bit N is set.
*/
int
gcry_mpi_test_bit( gcry_mpi_t 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;
}
/****************
* Set bit N of A.
*/
void
gcry_mpi_set_bit( gcry_mpi_t a, unsigned int n )
{
unsigned int limbno, bitno;
limbno = n / BITS_PER_MPI_LIMB;
bitno = n % BITS_PER_MPI_LIMB;
if ( limbno >= a->nlimbs )
{
mpi_resize (a, limbno+1 );
a->nlimbs = limbno+1;
}
a->d[limbno] |= (A_LIMB_1<<bitno);
}
/****************
* Set bit N of A. and clear all bits above
*/
void
gcry_mpi_set_highbit( gcry_mpi_t a, unsigned int n )
{
unsigned int limbno, bitno;
limbno = n / BITS_PER_MPI_LIMB;
bitno = n % BITS_PER_MPI_LIMB;
if ( limbno >= a->nlimbs )
{
mpi_resize (a, limbno+1 );
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;
}
/****************
* clear bit N of A and all bits above
*/
void
gcry_mpi_clear_highbit( gcry_mpi_t a, unsigned int n )
{
unsigned int limbno, bitno;
limbno = n / BITS_PER_MPI_LIMB;
bitno = n % BITS_PER_MPI_LIMB;
if( limbno >= a->nlimbs )
return; /* not allocated, therefore no 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
gcry_mpi_clear_bit( gcry_mpi_t a, unsigned int n )
{
unsigned int 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 COUNT limbs to the right
* This is used only within the MPI library
*/
void
_gcry_mpi_rshift_limbs( gcry_mpi_t 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;
}
/*
* Shift A by N bits to the right.
*/
void
gcry_mpi_rshift ( gcry_mpi_t x, gcry_mpi_t 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);
if ( x == a )
{
/* In-place operation. */
if ( nlimbs >= x->nlimbs )
{
x->nlimbs = 0;
return;
}
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 )
_gcry_mpih_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;
RESIZE_IF_NEEDED (x, xsize);
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;
}
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 )
_gcry_mpih_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;
RESIZE_IF_NEEDED (x, xsize);
x->nlimbs = xsize;
if ( xsize )
{
if (nbits )
_gcry_mpih_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);
}
/****************
* Shift A by COUNT limbs to the left
* This is used only within the MPI library
*/
void
_gcry_mpi_lshift_limbs (gcry_mpi_t a, unsigned int count)
{
mpi_ptr_t ap;
int n = a->nlimbs;
int i;
if (!count || !n)
return;
RESIZE_IF_NEEDED (a, n+count);
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;
}
/*
* Shift A by N bits to the left.
*/
void
gcry_mpi_lshift ( gcry_mpi_t x, gcry_mpi_t a, unsigned int n )
{
unsigned int nlimbs = (n/BITS_PER_MPI_LIMB);
unsigned int nbits = (n%BITS_PER_MPI_LIMB);
if (x == a && !n)
return; /* In-place shift with an amount of zero. */
if ( x != a )
{
/* Copy A to X. */
unsigned int alimbs = a->nlimbs;
int asign = a->sign;
mpi_ptr_t xp, ap;
RESIZE_IF_NEEDED (x, alimbs+nlimbs+1);
xp = x->d;
ap = a->d;
MPN_COPY (xp, ap, alimbs);
x->nlimbs = alimbs;
x->flags = a->flags;
x->sign = asign;
}
if (nlimbs && !nbits)
{
/* Shift a full number of limbs. */
_gcry_mpi_lshift_limbs (x, nlimbs);
}
else if (n)
{
/* We use a very dump approach: Shift left by the number of
limbs plus one and than fix it up by an rshift. */
_gcry_mpi_lshift_limbs (x, nlimbs+1);
gcry_mpi_rshift (x, x, BITS_PER_MPI_LIMB - nbits);
}
MPN_NORMALIZE (x->d, x->nlimbs);
}

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