libtommath/bn_mp_prime_is_divisible.c

#include <tommath_private.h>
#ifdef BN_MP_PRIME_IS_DIVISIBLE_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.
 */

/* determines if an integers is divisible by one
 * of the first PRIME_SIZE primes or not
 *
 * sets result to 0 if not, 1 if yes
 */
int mp_prime_is_divisible(const mp_int *a, int *result)
{
   int     err, ix;
   mp_digit res;

   /* default to not */
   *result = MP_NO;

   for (ix = 0; ix < PRIME_SIZE; ix++) {
      /* what is a mod LBL_prime_tab[ix] */
      if ((err = mp_mod_d(a, ltm_prime_tab[ix], &res)) != MP_OKAY) {
         return err;
      }

      /* is the residue zero? */
      if (res == 0u) {
         *result = MP_YES;
         return MP_OKAY;
      }
   }

   return MP_OKAY;
}
#endif

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