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comparison libtommath/bn_mp_add_d.c @ 399:a707e6148060

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merge of '5fdf69ca60d1683cdd9f4c2595134bed26394834' and '6b61c50f4cf888bea302ac8fcf5dbb573b443251'
author Matt Johnston <matt@ucc.asn.au>
date Sat, 03 Feb 2007 08:20:34 +0000
parents 5ff8218bcee9
children 60fc6476e044
comparison
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394:17d097fc111c 399:a707e6148060
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 $ */