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comparison bn_mp_expt_d.c @ 1:22d5cf7d4b1a libtommath

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Renaming branch
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:23:46 +0000
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-1:000000000000 1:22d5cf7d4b1a
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
2 *
3 * LibTomMath is a library that provides multiple-precision
4 * integer arithmetic as well as number theoretic functionality.
5 *
6 * The library was designed directly after the MPI library by
7 * Michael Fromberger but has been written from scratch with
8 * additional optimizations in place.
9 *
10 * The library is free for all purposes without any express
11 * guarantee it works.
12 *
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
14 */
15 #include <tommath.h>
16
17 /* calculate c = a**b using a square-multiply algorithm */
18 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
19 {
20 int res, x;
21 mp_int g;
22
23 if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
24 return res;
25 }
26
27 /* set initial result */
28 mp_set (c, 1);
29
30 for (x = 0; x < (int) DIGIT_BIT; x++) {
31 /* square */
32 if ((res = mp_sqr (c, c)) != MP_OKAY) {
33 mp_clear (&g);
34 return res;
35 }
36
37 /* if the bit is set multiply */
38 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
39 if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
40 mp_clear (&g);
41 return res;
42 }
43 }
44
45 /* shift to next bit */
46 b <<= 1;
47 }
48
49 mp_clear (&g);
50 return MP_OKAY;
51 }