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comparison libtommath/bn_mp_add_d.c @ 330:5488db2e9e4e

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merge of 332f709a4cb39cde4cedab7c3be89e05f3023067 and ca4ca78b82c5d430c69ce01bf794e8886ce81431
author Matt Johnston <matt@ucc.asn.au>
date Sat, 10 Jun 2006 16:39:40 +0000
parents eed26cff980b
children 5ff8218bcee9
comparison
equal deleted inserted replaced
329:8ed0dce45126 330:5488db2e9e4e
1 #include <tommath.h>
2 #ifdef BN_MP_ADD_D_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 /* single digit addition */
19 int
20 mp_add_d (mp_int * a, mp_digit b, mp_int * c)
21 {
22 int res, ix, oldused;
23 mp_digit *tmpa, *tmpc, mu;
24
25 /* grow c as required */
26 if (c->alloc < a->used + 1) {
27 if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) {
28 return res;
29 }
30 }
31
32 /* if a is negative and |a| >= b, call c = |a| - b */
33 if (a->sign == MP_NEG && (a->used > 1 || a->dp[0] >= b)) {
34 /* temporarily fix sign of a */
35 a->sign = MP_ZPOS;
36
37 /* c = |a| - b */
38 res = mp_sub_d(a, b, c);
39
40 /* fix sign */
41 a->sign = c->sign = MP_NEG;
42
43 return res;
44 }
45
46 /* old number of used digits in c */
47 oldused = c->used;
48
49 /* sign always positive */
50 c->sign = MP_ZPOS;
51
52 /* source alias */
53 tmpa = a->dp;
54
55 /* destination alias */
56 tmpc = c->dp;
57
58 /* if a is positive */
59 if (a->sign == MP_ZPOS) {
60 /* add digit, after this we're propagating
61 * the carry.
62 */
63 *tmpc = *tmpa++ + b;
64 mu = *tmpc >> DIGIT_BIT;
65 *tmpc++ &= MP_MASK;
66
67 /* now handle rest of the digits */
68 for (ix = 1; ix < a->used; ix++) {
69 *tmpc = *tmpa++ + mu;
70 mu = *tmpc >> DIGIT_BIT;
71 *tmpc++ &= MP_MASK;
72 }
73 /* set final carry */
74 ix++;
75 *tmpc++ = mu;
76
77 /* setup size */
78 c->used = a->used + 1;
79 } else {
80 /* a was negative and |a| < b */
81 c->used = 1;
82
83 /* the result is a single digit */
84 if (a->used == 1) {
85 *tmpc++ = b - a->dp[0];
86 } else {
87 *tmpc++ = b;
88 }
89
90 /* setup count so the clearing of oldused
91 * can fall through correctly
92 */
93 ix = 1;
94 }
95
96 /* now zero to oldused */
97 while (ix++ < oldused) {
98 *tmpc++ = 0;
99 }
100 mp_clamp(c);
101
102 return MP_OKAY;
103 }
104
105 #endif