Mercurial > dropbear
comparison libtommath/bn_mp_expt_u32.c @ 1739:13d834efc376 fuzz
merge from main
author | Matt Johnston <matt@ucc.asn.au> |
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date | Thu, 15 Oct 2020 19:55:15 +0800 |
parents | 1051e4eea25a |
children |
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1562:768ebf737aa0 | 1739:13d834efc376 |
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1 #include "tommath_private.h" | |
2 #ifdef BN_MP_EXPT_U32_C | |
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */ | |
4 /* SPDX-License-Identifier: Unlicense */ | |
5 | |
6 /* calculate c = a**b using a square-multiply algorithm */ | |
7 mp_err mp_expt_u32(const mp_int *a, uint32_t b, mp_int *c) | |
8 { | |
9 mp_err err; | |
10 | |
11 mp_int g; | |
12 | |
13 if ((err = mp_init_copy(&g, a)) != MP_OKAY) { | |
14 return err; | |
15 } | |
16 | |
17 /* set initial result */ | |
18 mp_set(c, 1uL); | |
19 | |
20 while (b > 0u) { | |
21 /* if the bit is set multiply */ | |
22 if ((b & 1u) != 0u) { | |
23 if ((err = mp_mul(c, &g, c)) != MP_OKAY) { | |
24 goto LBL_ERR; | |
25 } | |
26 } | |
27 | |
28 /* square */ | |
29 if (b > 1u) { | |
30 if ((err = mp_sqr(&g, &g)) != MP_OKAY) { | |
31 goto LBL_ERR; | |
32 } | |
33 } | |
34 | |
35 /* shift to next bit */ | |
36 b >>= 1; | |
37 } | |
38 | |
39 err = MP_OKAY; | |
40 | |
41 LBL_ERR: | |
42 mp_clear(&g); | |
43 return err; | |
44 } | |
45 | |
46 #endif |