libgcrypt-1.4.6/mpi/mpi-bit.c

/* mpi-bit.c  -  MPI bit level fucntions
 * 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);
}