#include <tommath.h>
#ifdef BN_MP_REDUCE_2K_L_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
 */

/* reduces a modulo n where n is of the form 2**p - d 
   This differs from reduce_2k since "d" can be larger
   than a single digit.
*/
int mp_reduce_2k_l(mp_int * a, mp_int * n, mp_int * d)
{
	mp_int q;
	int p, res;

	if ((res = mp_init(&q)) != MP_OKAY) {
		return res;
	}

	p = mp_count_bits(n);
top:
	/* q = a/2**p, a = a mod 2**p */
	if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
		goto ERR;
	}

	/* q = q * d */
	if ((res = mp_mul(&q, d, &q)) != MP_OKAY) {
		goto ERR;
	}

	/* a = a + q */
	if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
		goto ERR;
	}

	if (mp_cmp_mag(a, n) != MP_LT) {
		s_mp_sub(a, n, a);
		goto top;
	}

ERR:
	mp_clear(&q);
	return res;
}

#endif

/* $Source: /cvs/libtom/libtommath/bn_mp_reduce_2k_l.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2006/12/28 01:25:13 $ */