63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
#include <tommath.h>
|
|
#ifdef BN_MP_PRIME_FERMAT_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis
|
|
*
|
|
* LibTomMath is a library that provides multiple-precision
|
|
* integer arithmetic as well as number theoretic functionality.
|
|
*
|
|
* The library was 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@gmail.com, http://libtom.org
|
|
*/
|
|
|
|
/* 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 composite */
|
|
*result = MP_NO;
|
|
|
|
/* ensure b > 1 */
|
|
if (mp_cmp_d(b, 1) != MP_GT) {
|
|
return MP_VAL;
|
|
}
|
|
|
|
/* 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 LBL_T;
|
|
}
|
|
|
|
/* is it equal to b? */
|
|
if (mp_cmp (&t, b) == MP_EQ) {
|
|
*result = MP_YES;
|
|
}
|
|
|
|
err = MP_OKAY;
|
|
LBL_T:mp_clear (&t);
|
|
return err;
|
|
}
|
|
#endif
|
|
|
|
/* $Source$ */
|
|
/* $Revision$ */
|
|
/* $Date$ */
|