kc3-lang/libtommath/bn_mp_prime_fermat.c

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• Hash : 4e3f1344
  Author :
  Date : 2015-11-12T01:49:07
  

  provide tommath_private.h tommath.h contains declarations for the public part of the library. tommath_private.h contains the functions which are private to ltm and should not be exposed to the public.

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• bn_mp_prime_fermat.c

• #include <tommath_private.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, tstdenis82@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
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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