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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is library that provides for multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library is designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
*/
#include <tommath.h>

/* performs one Fermat test.
*
* If "a" were prime then b^a == b (mod a) since the order of
* the multiplicative sub-group would be phi(a) = a-1. That means
* it would be the same as b^(a mod (a-1)) == b^1 == b (mod a).
*
* Sets result to 1 if the congruence holds, or zero otherwise.
*/
int
mp_prime_fermat (mp_int * a, mp_int * b, int *result)
{
  mp_int t;
  int err;

  /* default to fail */
  *result = 0;

  /* init t */
  if ((err = mp_init (&t)) != MP_OKAY) {
    return err;
  }

  /* compute t = b^a mod a */
  if ((err = mp_exptmod (b, a, a, &t)) != MP_OKAY) {
    goto __T;
  }

  /* is it equal to b? */
  if (mp_cmp (&t, b) == MP_EQ) {
    *result = 1;
  }

  err = MP_OKAY;
__T:mp_clear (&t);
  return err;
}
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