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comparison libtommath/bn_mp_expt_d.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
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children 5ff8218bcee9
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283:bd240aa12ba7 284:eed26cff980b
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.org
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