LXR linux/lib/mpi/mpi-bit.c

   1/* mpi-bit.c  -  MPI bit level fucntions
   2 * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
   3 *
   4 * This file is part of GnuPG.
   5 *
   6 * GnuPG is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License as published by
   8 * the Free Software Foundation; either version 2 of the License, or
   9 * (at your option) any later version.
  10 *
  11 * GnuPG is distributed in the hope that it will be useful,
  12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 * GNU General Public License for more details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with this program; if not, write to the Free Software
  18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19 */
  20
  21#include "mpi-internal.h"
  22#include "longlong.h"
  23
  24#define A_LIMB_1 ((mpi_limb_t) 1)
  25
  26/****************
  27 * Sometimes we have MSL (most significant limbs) which are 0;
  28 * this is for some reasons not good, so this function removes them.
  29 */
  30void mpi_normalize(MPI a)
  31{
  32        for (; a->nlimbs && !a->d[a->nlimbs - 1]; a->nlimbs--)
  33                ;
  34}
  35
  36/****************
  37 * Return the number of bits in A.
  38 */
  39unsigned mpi_get_nbits(MPI a)
  40{
  41        unsigned n;
  42
  43        mpi_normalize(a);
  44
  45        if (a->nlimbs) {
  46                mpi_limb_t alimb = a->d[a->nlimbs - 1];
  47                if (alimb)
  48                        n = count_leading_zeros(alimb);
  49                else
  50                        n = BITS_PER_MPI_LIMB;
  51                n = BITS_PER_MPI_LIMB - n + (a->nlimbs - 1) * BITS_PER_MPI_LIMB;
  52        } else
  53                n = 0;
  54        return n;
  55}
  56EXPORT_SYMBOL_GPL(mpi_get_nbits);
  57