#include <tommath.h>
#ifdef BN_MP_PRIME_MILLER_RABIN_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, tomstdenis@gmail.com, http://libtom.org
 */

/* 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.
 */
int mp_prime_miller_rabin(mp_int * a, mp_int * b, int *result)
{
	mp_int n1, y, r;
	int s, j, err;

	/* default */
	*result = MP_NO;

	/* ensure b > 1 */
	if (mp_cmp_d(b, 1) != 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, 1, &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, 1) != 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, 1) == 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

/* $Source: /cvs/libtom/libtommath/bn_mp_prime_miller_rabin.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2006/12/28 01:25:13 $ */