|
282
|
1 #include <tommath.h> |
|
|
2 #ifdef BN_S_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 /* low level addition, based on HAC pp.594, Algorithm 14.7 */ |
|
|
19 int |
|
|
20 s_mp_add (mp_int * a, mp_int * b, mp_int * c) |
|
|
21 { |
|
|
22 mp_int *x; |
|
|
23 int olduse, res, min, max; |
|
|
24 |
|
|
25 /* find sizes, we let |a| <= |b| which means we have to sort |
|
|
26 * them. "x" will point to the input with the most digits |
|
|
27 */ |
|
|
28 if (a->used > b->used) { |
|
|
29 min = b->used; |
|
|
30 max = a->used; |
|
|
31 x = a; |
|
|
32 } else { |
|
|
33 min = a->used; |
|
|
34 max = b->used; |
|
|
35 x = b; |
|
|
36 } |
|
|
37 |
|
|
38 /* init result */ |
|
|
39 if (c->alloc < max + 1) { |
|
|
40 if ((res = mp_grow (c, max + 1)) != MP_OKAY) { |
|
|
41 return res; |
|
|
42 } |
|
|
43 } |
|
|
44 |
|
|
45 /* get old used digit count and set new one */ |
|
|
46 olduse = c->used; |
|
|
47 c->used = max + 1; |
|
|
48 |
|
|
49 { |
|
|
50 register mp_digit u, *tmpa, *tmpb, *tmpc; |
|
|
51 register int i; |
|
|
52 |
|
|
53 /* alias for digit pointers */ |
|
|
54 |
|
|
55 /* first input */ |
|
|
56 tmpa = a->dp; |
|
|
57 |
|
|
58 /* second input */ |
|
|
59 tmpb = b->dp; |
|
|
60 |
|
|
61 /* destination */ |
|
|
62 tmpc = c->dp; |
|
|
63 |
|
|
64 /* zero the carry */ |
|
|
65 u = 0; |
|
|
66 for (i = 0; i < min; i++) { |
|
|
67 /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */ |
|
|
68 *tmpc = *tmpa++ + *tmpb++ + u; |
|
|
69 |
|
|
70 /* U = carry bit of T[i] */ |
|
|
71 u = *tmpc >> ((mp_digit)DIGIT_BIT); |
|
|
72 |
|
|
73 /* take away carry bit from T[i] */ |
|
|
74 *tmpc++ &= MP_MASK; |
|
|
75 } |
|
|
76 |
|
|
77 /* now copy higher words if any, that is in A+B |
|
|
78 * if A or B has more digits add those in |
|
|
79 */ |
|
|
80 if (min != max) { |
|
|
81 for (; i < max; i++) { |
|
|
82 /* T[i] = X[i] + U */ |
|
|
83 *tmpc = x->dp[i] + u; |
|
|
84 |
|
|
85 /* U = carry bit of T[i] */ |
|
|
86 u = *tmpc >> ((mp_digit)DIGIT_BIT); |
|
|
87 |
|
|
88 /* take away carry bit from T[i] */ |
|
|
89 *tmpc++ &= MP_MASK; |
|
|
90 } |
|
|
91 } |
|
|
92 |
|
|
93 /* add carry */ |
|
|
94 *tmpc++ = u; |
|
|
95 |
|
|
96 /* clear digits above oldused */ |
|
|
97 for (i = c->used; i < olduse; i++) { |
|
|
98 *tmpc++ = 0; |
|
|
99 } |
|
|
100 } |
|
|
101 |
|
|
102 mp_clamp (c); |
|
|
103 return MP_OKAY; |
|
|
104 } |
|
|
105 #endif |
