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comparison libtommath/bn_mp_2expt.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
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children 5ff8218bcee9
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283:bd240aa12ba7 284:eed26cff980b
1 #include <tommath.h>
2 #ifdef BN_MP_2EXPT_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 /* computes a = 2**b
19 *
20 * Simple algorithm which zeroes the int, grows it then just sets one bit
21 * as required.
22 */
23 int
24 mp_2expt (mp_int * a, int b)
25 {
26 int res;
27
28 /* zero a as per default */
29 mp_zero (a);
30
31 /* grow a to accomodate the single bit */
32 if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
33 return res;
34 }
35
36 /* set the used count of where the bit will go */
37 a->used = b / DIGIT_BIT + 1;
38
39 /* put the single bit in its place */
40 a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT);
41
42 return MP_OKAY;
43 }
44 #endif