lib/mpi/mpi-gcd.c

   1 /* mpi-gcd.c  -  MPI functions
   2  * Copyright (C) 1998, 1999, 2000, 2001 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
  23 /****************
  24  * Find the greatest common divisor G of A and B.
  25  * Return: true if this 1, false in all other cases
  26  */
  27 int mpi_gcd(MPI g, const MPI xa, const MPI xb)
  28 {
  29         MPI a = NULL, b = NULL;
  30
  31         if (mpi_copy(&a, xa) < 0)
  32                 goto nomem;
  33
  34         if (mpi_copy(&b, xb) < 0)
  35                 goto nomem;
  36
  37         /* TAOCP Vol II, 4.5.2, Algorithm A */
  38         a->sign = 0;
  39         b->sign = 0;
  40         while (mpi_cmp_ui(b, 0)) {
  41                 if (mpi_fdiv_r(g, a, b) < 0)    /* g used as temorary variable */
  42                         goto nomem;
  43                 if (mpi_set(a, b) < 0)
  44                         goto nomem;
  45                 if (mpi_set(b, g) < 0)
  46                         goto nomem;
  47         }
  48         if (mpi_set(g, a) < 0)
  49                 goto nomem;
  50
  51         mpi_free(a);
  52         mpi_free(b);
  53         return !mpi_cmp_ui(g, 1);
  54
  55 nomem:
  56         mpi_free(a);
  57         mpi_free(b);
  58         return -ENOMEM;
  59 }