/*
 *  invmod.c
 *
 *  Compute modular inverses
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is the MPI Arbitrary Precision Integer Arithmetic library.
 *
 * The Initial Developer of the Original Code is
 * Michael J. Fromberger.
 * Portions created by the Initial Developer are Copyright (C) 1997
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */
/* $Id: invmod.c,v 1.3 2004/04/27 23:04:37 gerv%gerv.net Exp $ */

#include <stdio.h>
#include <stdlib.h>

#include "mpi.h"

int main(int argc, char *argv[])
{
  mp_int    a, m;
  mp_err    res;
  char     *buf;
  int       len, out = 0;

  if(argc < 3) {
    fprintf(stderr, "Usage: %s <a> <m>\n", argv[0]);
    return 1;
  }

  mp_init(&a); mp_init(&m);
  mp_read_radix(&a, argv[1], 10);
  mp_read_radix(&m, argv[2], 10);

  if(mp_cmp(&a, &m) > 0)
    mp_mod(&a, &m, &a);

  switch((res = mp_invmod(&a, &m, &a))) {
  case MP_OKAY:
    len = mp_radix_size(&a, 10);
    buf = malloc(len);

    mp_toradix(&a, buf, 10);
    printf("%s\n", buf);
    free(buf);
    break;

  case MP_UNDEF:
    printf("No inverse\n");
    out = 1;
    break;

  default:
    printf("error: %s (%d)\n", mp_strerror(res), res);
    out = 2;
    break;
  }

  mp_clear(&a);
  mp_clear(&m);

  return out;
}
