tommath/bn_mp_prime_is_prime.c

#include "tommath_private.h"
#ifdef BN_MP_PRIME_IS_PRIME_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.
 */

/* performs a variable number of rounds of Miller-Rabin
 *
 * Probability of error after t rounds is no more than

 *
 * Sets result to 1 if probably prime, 0 otherwise
 */
int mp_prime_is_prime(const mp_int *a, int t, int *result)
{
   mp_int  b;
   int     ix, err, res;

   /* default to no */
   *result = MP_NO;

   /* valid value of t? */
   if ((t <= 0) || (t > PRIME_SIZE)) {
      return MP_VAL;
   }

   /* is the input equal to one of the primes in the table? */
   for (ix = 0; ix < PRIME_SIZE; ix++) {
      if (mp_cmp_d(a, ltm_prime_tab[ix]) == MP_EQ) {
         *result = 1;
         return MP_OKAY;
      }
   }

   /* first perform trial division */
   if ((err = mp_prime_is_divisible(a, &res)) != MP_OKAY) {
      return err;
   }

   /* return if it was trivially divisible */
   if (res == MP_YES) {
      return MP_OKAY;
   }

   /* now perform the miller-rabin rounds */
   if ((err = mp_init(&b)) != MP_OKAY) {
      return err;
   }

   for (ix = 0; ix < t; ix++) {
      /* set the prime */
      mp_set(&b, ltm_prime_tab[ix]);

      if ((err = mp_prime_miller_rabin(a, &b, &res)) != MP_OKAY) {
         goto LBL_B;
      }

      if (res == MP_NO) {
         goto LBL_B;
      }
   }

   /* passed the test */
   *result = MP_YES;
LBL_B:
   mp_clear(&b);
   return err;
}
#endif

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