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comparison libtommath/bn_mp_expt_d_ex.c @ 1436:60fc6476e044

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Update to libtommath v1.0
author Matt Johnston <matt@ucc.asn.au>
date Sat, 24 Jun 2017 22:37:14 +0800
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children 8bba51a55704
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1435:f849a5ca2efc 1436:60fc6476e044
1 #include <tommath_private.h>
2 #ifdef BN_MP_EXPT_D_EX_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://libtom.org
16 */
17
18 /* calculate c = a**b using a square-multiply algorithm */
19 int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast)
20 {
21 int res;
22 unsigned int x;
23
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 if (fast != 0) {
34 while (b > 0) {
35 /* if the bit is set multiply */
36 if ((b & 1) != 0) {
37 if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
38 mp_clear (&g);
39 return res;
40 }
41 }
42
43 /* square */
44 if (b > 1) {
45 if ((res = mp_sqr (&g, &g)) != MP_OKAY) {
46 mp_clear (&g);
47 return res;
48 }
49 }
50
51 /* shift to next bit */
52 b >>= 1;
53 }
54 }
55 else {
56 for (x = 0; x < DIGIT_BIT; x++) {
57 /* square */
58 if ((res = mp_sqr (c, c)) != MP_OKAY) {
59 mp_clear (&g);
60 return res;
61 }
62
63 /* if the bit is set multiply */
64 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
65 if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
66 mp_clear (&g);
67 return res;
68 }
69 }
70
71 /* shift to next bit */
72 b <<= 1;
73 }
74 } /* if ... else */
75
76 mp_clear (&g);
77 return MP_OKAY;
78 }
79 #endif
80
81 /* $Source$ */
82 /* $Revision$ */
83 /* $Date$ */