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comparison bn_mp_add.c @ 1:22d5cf7d4b1a libtommath

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Renaming branch
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:23:46 +0000
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-1:000000000000 1:22d5cf7d4b1a
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
2 *
3 * LibTomMath is a library that provides multiple-precision
4 * integer arithmetic as well as number theoretic functionality.
5 *
6 * The library was designed directly after the MPI library by
7 * Michael Fromberger but has been written from scratch with
8 * additional optimizations in place.
9 *
10 * The library is free for all purposes without any express
11 * guarantee it works.
12 *
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
14 */
15 #include <tommath.h>
16
17 /* high level addition (handles signs) */
18 int mp_add (mp_int * a, mp_int * b, mp_int * c)
19 {
20 int sa, sb, res;
21
22 /* get sign of both inputs */
23 sa = a->sign;
24 sb = b->sign;
25
26 /* handle two cases, not four */
27 if (sa == sb) {
28 /* both positive or both negative */
29 /* add their magnitudes, copy the sign */
30 c->sign = sa;
31 res = s_mp_add (a, b, c);
32 } else {
33 /* one positive, the other negative */
34 /* subtract the one with the greater magnitude from */
35 /* the one of the lesser magnitude. The result gets */
36 /* the sign of the one with the greater magnitude. */
37 if (mp_cmp_mag (a, b) == MP_LT) {
38 c->sign = sb;
39 res = s_mp_sub (b, a, c);
40 } else {
41 c->sign = sa;
42 res = s_mp_sub (a, b, c);
43 }
44 }
45 return res;
46 }
47