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comparison bn_mp_reduce_2k_setup.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 /* determines the setup value */
18 int
19 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 }