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 /*

  *  exptmod.c

  *

  * Command line tool to perform modular exponentiation on arbitrary

  * precision integers.

  *

  * This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 #include <stdio.h>

 #include <stdlib.h>

 #include <string.h>

 #include "mpi.h"

 int main(int argc, char *argv[])

 {

   mp_int  a, b, m;

   mp_err  res;

   char   *str;

   int     len, rval = 0;

   if(argc < 3) {

     fprintf(stderr, "Usage: %s <a> <b> <m>\n", argv[0]);

     return 1;

   }

   mp_init(&a); mp_init(&b); mp_init(&m);

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

   mp_read_radix(&b, argv[2], 10);

   mp_read_radix(&m, argv[3], 10);

   if((res = mp_exptmod(&a, &b, &m, &a)) != MP_OKAY) {

     fprintf(stderr, "%s: error: %s\n", argv[0], mp_strerror(res));

     rval = 1;

   } else {

     len = mp_radix_size(&a, 10);

     str = calloc(len, sizeof(char));

     mp_toradix(&a, str, 10);

     printf("%s\n", str);

     free(str);

   }

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

   return rval;

 }