Mercurial > dropbear
comparison libtommath/bn_mp_expt_d.c @ 389:5ff8218bcee9
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> |
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date | Thu, 11 Jan 2007 03:14:55 +0000 |
parents | eed26cff980b |
children | 60fc6476e044 |
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388:fb54020f78e1 | 389:5ff8218bcee9 |
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1 #include <tommath.h> | |
2 #ifdef BN_MP_EXPT_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 /* calculate c = a**b using a square-multiply algorithm */ | |
19 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c) | |
20 { | |
21 int res, x; | |
22 mp_int g; | |
23 | |
24 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { | |
25 return res; | |
26 } | |
27 | |
28 /* set initial result */ | |
29 mp_set (c, 1); | |
30 | |
31 for (x = 0; x < (int) DIGIT_BIT; x++) { | |
32 /* square */ | |
33 if ((res = mp_sqr (c, c)) != MP_OKAY) { | |
34 mp_clear (&g); | |
35 return res; | |
36 } | |
37 | |
38 /* if the bit is set multiply */ | |
39 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { | |
40 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { | |
41 mp_clear (&g); | |
42 return res; | |
43 } | |
44 } | |
45 | |
46 /* shift to next bit */ | |
47 b <<= 1; | |
48 } | |
49 | |
50 mp_clear (&g); | |
51 return MP_OKAY; | |
52 } | |
53 #endif | |
54 | |
55 /* $Source: /cvs/libtom/libtommath/bn_mp_expt_d.c,v $ */ | |
56 /* $Revision: 1.3 $ */ | |
57 /* $Date: 2006/03/31 14:18:44 $ */ |