kc3-lang/libtommath/mp_prime_miller_rabin.c

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• Hash : 7a68f128
  Author :
  Date : 2019-10-19T16:24:39
  

  Execute move.sh - Rename files from bn_* to match the function names. * git blame <renamed-file> is not affected * git log --follow <renamed-file> can be used to show log across renames

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• mp_prime_miller_rabin.c

• #include "tommath_private.h"
  #ifdef MP_PRIME_MILLER_RABIN_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* Miller-Rabin test of "a" to the base of "b" as described in
   * HAC pp. 139 Algorithm 4.24
   *
   * Sets result to 0 if definitely composite or 1 if probably prime.
   * Randomly the chance of error is no more than 1/4 and often
   * very much lower.
   */
  mp_err mp_prime_miller_rabin(const mp_int *a, const mp_int *b, mp_bool *result)
  {
     mp_int  n1, y, r;
     mp_err  err;
     int     s, j;
  
     /* default */
     *result = MP_NO;
  
     /* ensure b > 1 */
     if (mp_cmp_d(b, 1uL) != MP_GT) {
        return MP_VAL;
     }
  
     /* get n1 = a - 1 */
     if ((err = mp_init_copy(&n1, a)) != MP_OKAY) {
        return err;
     }
     if ((err = mp_sub_d(&n1, 1uL, &n1)) != MP_OKAY) {
        goto LBL_N1;
     }
  
     /* set 2**s * r = n1 */
     if ((err = mp_init_copy(&r, &n1)) != MP_OKAY) {
        goto LBL_N1;
     }
  
     /* count the number of least significant bits
      * which are zero
      */
     s = mp_cnt_lsb(&r);
  
     /* now divide n - 1 by 2**s */
     if ((err = mp_div_2d(&r, s, &r, NULL)) != MP_OKAY) {
        goto LBL_R;
     }
  
     /* compute y = b**r mod a */
     if ((err = mp_init(&y)) != MP_OKAY) {
        goto LBL_R;
     }
     if ((err = mp_exptmod(b, &r, a, &y)) != MP_OKAY) {
        goto LBL_Y;
     }
  
     /* if y != 1 and y != n1 do */
     if ((mp_cmp_d(&y, 1uL) != MP_EQ) && (mp_cmp(&y, &n1) != MP_EQ)) {
        j = 1;
        /* while j <= s-1 and y != n1 */
        while ((j <= (s - 1)) && (mp_cmp(&y, &n1) != MP_EQ)) {
           if ((err = mp_sqrmod(&y, a, &y)) != MP_OKAY) {
              goto LBL_Y;
           }
  
           /* if y == 1 then composite */
           if (mp_cmp_d(&y, 1uL) == MP_EQ) {
              goto LBL_Y;
           }
  
           ++j;
        }
  
        /* if y != n1 then composite */
        if (mp_cmp(&y, &n1) != MP_EQ) {
           goto LBL_Y;
        }
     }
  
     /* probably prime now */
     *result = MP_YES;
  LBL_Y:
     mp_clear(&y);
  LBL_R:
     mp_clear(&r);
  LBL_N1:
     mp_clear(&n1);
     return err;
  }
  #endif
  

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