### view libtommath/bn_mp_prime_fermat.c @ 1692:1051e4eea25a

Update LibTomMath to 1.2.0 (#84) * update C files * update other files * update headers * update makefiles * remove mp_set/get_double() * use ltm 1.2.0 API * update ltm_desc * use bundled tommath if system-tommath is too old * XMALLOC etc. were changed to MP_MALLOC etc.
author Steffen Jaeckel Tue, 26 May 2020 17:36:47 +0200 f52919ffd3b1
line wrap: on
line source
```#include "tommath_private.h"
#ifdef BN_MP_PRIME_FERMAT_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */

/* 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.
*/
mp_err mp_prime_fermat(const mp_int *a, const mp_int *b, mp_bool *result)
{
mp_int  t;
mp_err  err;

/* default to composite  */
*result = MP_NO;

/* ensure b > 1 */
if (mp_cmp_d(b, 1uL) != 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
```