|
2
|
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 |
