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

/* high level subtraction (handles signs) */
int mp_sub(mp_int * a, mp_int * b, mp_int * c)
{
	int sa, sb, res;

	sa = a->sign;
	sb = b->sign;

	if (sa != sb) {
		/* subtract a negative from a positive, OR */
		/* subtract a positive from a negative. */
		/* In either case, ADD their magnitudes, */
		/* and use the sign of the first number. */
		c->sign = sa;
		res = s_mp_add(a, b, c);
	} else {
		/* subtract a positive from a positive, OR */
		/* subtract a negative from a negative. */
		/* First, take the difference between their */
		/* magnitudes, then... */
		if (mp_cmp_mag(a, b) != MP_LT) {
			/* Copy the sign from the first */
			c->sign = sa;
			/* The first has a larger or equal magnitude */
			res = s_mp_sub(a, b, c);
		} else {
			/* The result has the *opposite* sign from */
			/* the first number. */
			c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
			/* The second has a larger magnitude */
			res = s_mp_sub(b, a, c);
		}
	}
	return res;
}

#endif

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