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#include "tommath_private.h"
#ifdef BN_MP_PRIME_FERMAT_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* 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
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