#include <tommath.h>
#ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_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
 */

/*
 * shifts with subtractions when the result is greater than b.
 *
 * The method is slightly modified to shift B unconditionally upto just under
 * the leading bit of b.  This saves alot of multiple precision shifting.
 */
int mp_montgomery_calc_normalization(mp_int * a, mp_int * b)
{
	int x, bits, res;

	/* how many bits of last digit does b use */
	bits = mp_count_bits(b) % DIGIT_BIT;

	if (b->used > 1) {
		if ((res =
		     mp_2expt(a,
			      (b->used - 1) * DIGIT_BIT + bits - 1)) !=
		    MP_OKAY) {
			return res;
		}
	} else {
		mp_set(a, 1);
		bits = 1;
	}

	/* now compute C = A * B mod b */
	for (x = bits - 1; x < (int)DIGIT_BIT; x++) {
		if ((res = mp_mul_2(a, a)) != MP_OKAY) {
			return res;
		}
		if (mp_cmp_mag(a, b) != MP_LT) {
			if ((res = s_mp_sub(a, b, a)) != MP_OKAY) {
				return res;
			}
		}
	}

	return MP_OKAY;
}
#endif

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