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  */
  30 void 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  */
  39 unsigned 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                         count_leading_zeros(n, 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 }
  56 EXPORT_SYMBOL_GPL(mpi_get_nbits);