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comparison bn_mp_2expt.c @ 2:86e0b50a9b58 libtommath-orig ltm-0.30-orig

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ltm 0.30 orig import
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:22 +0000
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-1:000000000000 2:86e0b50a9b58
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 /* computes a = 2**b
18 *
19 * Simple algorithm which zeroes the int, grows it then just sets one bit
20 * as required.
21 */
22 int
23 mp_2expt (mp_int * a, int b)
24 {
25 int res;
26
27 /* zero a as per default */
28 mp_zero (a);
29
30 /* grow a to accomodate the single bit */
31 if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
32 return res;
33 }
34
35 /* set the used count of where the bit will go */
36 a->used = b / DIGIT_BIT + 1;
37
38 /* put the single bit in its place */
39 a->dp[b / DIGIT_BIT] = 1 << (b % DIGIT_BIT);
40
41 return MP_OKAY;
42 }