Mercurial > dropbear

comparison libtommath/bn_mp_add_d.c @ 389:5ff8218bcee9

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 2af95f00ebd5bb7a28b3817db1218442c935388e) to branch 'au.asn.ucc.matt.dropbear' (head ecd779509ef23a8cdf64888904fc9b31d78aa933)
author Matt Johnston <matt@ucc.asn.au>
date Thu, 11 Jan 2007 03:14:55 +0000
parents eed26cff980b
children 60fc6476e044
comparison
equal deleted inserted replaced
388:fb54020f78e1 389:5ff8218bcee9
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.com
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 /* clamp */
44 mp_clamp(c);
45
46 return res;
47 }
48
49 /* old number of used digits in c */
50 oldused = c->used;
51
52 /* sign always positive */
53 c->sign = MP_ZPOS;
54
55 /* source alias */
56 tmpa = a->dp;
57
58 /* destination alias */
59 tmpc = c->dp;
60
61 /* if a is positive */
62 if (a->sign == MP_ZPOS) {
63 /* add digit, after this we're propagating
64 * the carry.
65 */
66 *tmpc = *tmpa++ + b;
67 mu = *tmpc >> DIGIT_BIT;
68 *tmpc++ &= MP_MASK;
69
70 /* now handle rest of the digits */
71 for (ix = 1; ix < a->used; ix++) {
72 *tmpc = *tmpa++ + mu;
73 mu = *tmpc >> DIGIT_BIT;
74 *tmpc++ &= MP_MASK;
75 }
76 /* set final carry */
77 ix++;
78 *tmpc++ = mu;
79
80 /* setup size */
81 c->used = a->used + 1;
82 } else {
83 /* a was negative and |a| < b */
84 c->used = 1;
85
86 /* the result is a single digit */
87 if (a->used == 1) {
88 *tmpc++ = b - a->dp[0];
89 } else {
90 *tmpc++ = b;
91 }
92
93 /* setup count so the clearing of oldused
94 * can fall through correctly
95 */
96 ix = 1;
97 }
98
99 /* now zero to oldused */
100 while (ix++ < oldused) {
101 *tmpc++ = 0;
102 }
103 mp_clamp(c);
104
105 return MP_OKAY;
106 }
107
108 #endif
109
110 /* $Source: /cvs/libtom/libtommath/bn_mp_add_d.c,v $ */
111 /* $Revision: 1.4 $ */
112 /* $Date: 2006/03/31 14:18:44 $ */