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comparison libtommath/bn_mp_reduce_2k_setup.c @ 285:1b9e69c058d2

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propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 20dccfc09627970a312d77fb41dc2970b62689c3) to branch 'au.asn.ucc.matt.dropbear' (head fdf4a7a3b97ae5046139915de7e40399cceb2c01)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:58 +0000
parents eed26cff980b
children 5ff8218bcee9
comparison
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281:997e6f7dc01e 285:1b9e69c058d2
1 #include <tommath.h>
2 #ifdef BN_MP_REDUCE_2K_SETUP_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 /* determines the setup value */
19 int mp_reduce_2k_setup(mp_int *a, mp_digit *d)
20 {
21 int res, p;
22 mp_int tmp;
23
24 if ((res = mp_init(&tmp)) != MP_OKAY) {
25 return res;
26 }
27
28 p = mp_count_bits(a);
29 if ((res = mp_2expt(&tmp, p)) != MP_OKAY) {
30 mp_clear(&tmp);
31 return res;
32 }
33
34 if ((res = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) {
35 mp_clear(&tmp);
36 return res;
37 }
38
39 *d = tmp.dp[0];
40 mp_clear(&tmp);
41 return MP_OKAY;
42 }
43 #endif