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, tomstdenis@gmail.com, http://math.libtomcrypt.com |
---|
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 |
---|
106 | |
---|
107 | /* $Source: /cvsroot/tcl/libtommath/bn_s_mp_add.c,v $ */ |
---|
108 | /* $Revision: 1.1.1.3 $ */ |
---|
109 | /* $Date: 2006/12/01 00:08:11 $ */ |
---|