1 /* $NetBSD: bn_mp_expt_d.c,v 1.2 2017/01/28 21:31:47 christos Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_EXPT_D_C
5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
6 *
7 * LibTomMath is a library that provides multiple-precision
8 * integer arithmetic as well as number theoretic functionality.
9 *
10 * The library was designed directly after the MPI library by
11 * Michael Fromberger but has been written from scratch with
12 * additional optimizations in place.
13 *
14 * The library is free for all purposes without any express
15 * guarantee it works.
16 *
17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
18 */
19
20 /* calculate c = a**b using a square-multiply algorithm */
mp_expt_d(mp_int * a,mp_digit b,mp_int * c)21 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
22 {
23 int res, x;
24 mp_int g;
25
26 if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
27 return res;
28 }
29
30 /* set initial result */
31 mp_set (c, 1);
32
33 for (x = 0; x < (int) DIGIT_BIT; x++) {
34 /* square */
35 if ((res = mp_sqr (c, c)) != MP_OKAY) {
36 mp_clear (&g);
37 return res;
38 }
39
40 /* if the bit is set multiply */
41 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
42 if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
43 mp_clear (&g);
44 return res;
45 }
46 }
47
48 /* shift to next bit */
49 b <<= 1;
50 }
51
52 mp_clear (&g);
53 return MP_OKAY;
54 }
55 #endif
56
57 /* Source: /cvs/libtom/libtommath/bn_mp_expt_d.c,v */
58 /* Revision: 1.4 */
59 /* Date: 2006/12/28 01:25:13 */
60