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invmod.c
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00001 /*
00002  *  invmod.c
00003  *
00004  *  Compute modular inverses
00005  *
00006  * ***** BEGIN LICENSE BLOCK *****
00007  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00008  *
00009  * The contents of this file are subject to the Mozilla Public License Version
00010  * 1.1 (the "License"); you may not use this file except in compliance with
00011  * the License. You may obtain a copy of the License at
00012  * http://www.mozilla.org/MPL/
00013  *
00014  * Software distributed under the License is distributed on an "AS IS" basis,
00015  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00016  * for the specific language governing rights and limitations under the
00017  * License.
00018  *
00019  * The Original Code is the MPI Arbitrary Precision Integer Arithmetic library.
00020  *
00021  * The Initial Developer of the Original Code is
00022  * Michael J. Fromberger.
00023  * Portions created by the Initial Developer are Copyright (C) 1997
00024  * the Initial Developer. All Rights Reserved.
00025  *
00026  * Contributor(s):
00027  *
00028  * Alternatively, the contents of this file may be used under the terms of
00029  * either the GNU General Public License Version 2 or later (the "GPL"), or
00030  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00031  * in which case the provisions of the GPL or the LGPL are applicable instead
00032  * of those above. If you wish to allow use of your version of this file only
00033  * under the terms of either the GPL or the LGPL, and not to allow others to
00034  * use your version of this file under the terms of the MPL, indicate your
00035  * decision by deleting the provisions above and replace them with the notice
00036  * and other provisions required by the GPL or the LGPL. If you do not delete
00037  * the provisions above, a recipient may use your version of this file under
00038  * the terms of any one of the MPL, the GPL or the LGPL.
00039  *
00040  * ***** END LICENSE BLOCK ***** */
00041 /* $Id: invmod.c,v 1.3 2004/04/27 23:04:37 gerv%gerv.net Exp $ */
00042 
00043 #include <stdio.h>
00044 #include <stdlib.h>
00045 
00046 #include "mpi.h"
00047 
00048 int main(int argc, char *argv[])
00049 {
00050   mp_int    a, m;
00051   mp_err    res;
00052   char     *buf;
00053   int       len, out = 0;
00054 
00055   if(argc < 3) {
00056     fprintf(stderr, "Usage: %s <a> <m>\n", argv[0]);
00057     return 1;
00058   }
00059 
00060   mp_init(&a); mp_init(&m);
00061   mp_read_radix(&a, argv[1], 10);
00062   mp_read_radix(&m, argv[2], 10);
00063 
00064   if(mp_cmp(&a, &m) > 0)
00065     mp_mod(&a, &m, &a);
00066 
00067   switch((res = mp_invmod(&a, &m, &a))) {
00068   case MP_OKAY:
00069     len = mp_radix_size(&a, 10);
00070     buf = malloc(len);
00071 
00072     mp_toradix(&a, buf, 10);
00073     printf("%s\n", buf);
00074     free(buf);
00075     break;
00076 
00077   case MP_UNDEF:
00078     printf("No inverse\n");
00079     out = 1;
00080     break;
00081 
00082   default:
00083     printf("error: %s (%d)\n", mp_strerror(res), res);
00084     out = 2;
00085     break;
00086   }
00087 
00088   mp_clear(&a);
00089   mp_clear(&m);
00090 
00091   return out;
00092 }