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comparison bn_mp_add.c @ 282:91fbc376f010 libtommath-orig libtommath-0.35

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Import of libtommath 0.35 From ltm-0.35.tar.bz2 SHA1 of 3f193dbae9351e92d02530994fa18236f7fde01c
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:16:18 +0000
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children 97db060d0ef5
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-1:000000000000 282:91fbc376f010
1 #include <tommath.h>
2 #ifdef BN_MP_ADD_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* high level addition (handles signs) */
19 int mp_add (mp_int * a, mp_int * b, mp_int * c)
20 {
21 int sa, sb, res;
22
23 /* get sign of both inputs */
24 sa = a->sign;
25 sb = b->sign;
26
27 /* handle two cases, not four */
28 if (sa == sb) {
29 /* both positive or both negative */
30 /* add their magnitudes, copy the sign */
31 c->sign = sa;
32 res = s_mp_add (a, b, c);
33 } else {
34 /* one positive, the other negative */
35 /* subtract the one with the greater magnitude from */
36 /* the one of the lesser magnitude. The result gets */
37 /* the sign of the one with the greater magnitude. */
38 if (mp_cmp_mag (a, b) == MP_LT) {
39 c->sign = sb;
40 res = s_mp_sub (b, a, c);
41 } else {
42 c->sign = sa;
43 res = s_mp_sub (a, b, c);
44 }
45 }
46 return res;
47 }
48
49 #endif