1/*	$NetBSD: bn_mp_sub.c,v 1.2 2017/01/28 21:31:47 christos Exp $	*/
2
3#include <tommath.h>
4#ifdef BN_MP_SUB_C
5/* LibTomMath, multiple-precision integer library -- Tom St Denis
6 *
7 * LibTomMath is a library that provides multiple-precision
8 * integer arithmetic as well as number theoretic functionality.
9 *
10 * The library was designed directly after the MPI library by
11 * Michael Fromberger but has been written from scratch with
12 * additional optimizations in place.
13 *
14 * The library is free for all purposes without any express
15 * guarantee it works.
16 *
17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
18 */
19
20/* high level subtraction (handles signs) */
21int
22mp_sub (mp_int * a, mp_int * b, mp_int * c)
23{
24  int     sa, sb, res;
25
26  sa = a->sign;
27  sb = b->sign;
28
29  if (sa != sb) {
30    /* subtract a negative from a positive, OR */
31    /* subtract a positive from a negative. */
32    /* In either case, ADD their magnitudes, */
33    /* and use the sign of the first number. */
34    c->sign = sa;
35    res = s_mp_add (a, b, c);
36  } else {
37    /* subtract a positive from a positive, OR */
38    /* subtract a negative from a negative. */
39    /* First, take the difference between their */
40    /* magnitudes, then... */
41    if (mp_cmp_mag (a, b) != MP_LT) {
42      /* Copy the sign from the first */
43      c->sign = sa;
44      /* The first has a larger or equal magnitude */
45      res = s_mp_sub (a, b, c);
46    } else {
47      /* The result has the *opposite* sign from */
48      /* the first number. */
49      c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
50      /* The second has a larger magnitude */
51      res = s_mp_sub (b, a, c);
52    }
53  }
54  return res;
55}
56
57#endif
58
59/* Source: /cvs/libtom/libtommath/bn_mp_sub.c,v  */
60/* Revision: 1.4  */
61/* Date: 2006/12/28 01:25:13  */
62