annotate bn_mp_2expt.c @ 1:22d5cf7d4b1a libtommath

Renaming branch
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:23:46 +0000
parents
children d29b64170cf0
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
2 *
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
3 * LibTomMath is a library that provides multiple-precision
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
4 * integer arithmetic as well as number theoretic functionality.
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
5 *
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
6 * The library was designed directly after the MPI library by
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
7 * Michael Fromberger but has been written from scratch with
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
8 * additional optimizations in place.
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
9 *
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
10 * The library is free for all purposes without any express
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
11 * guarantee it works.
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
12 *
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
14 */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
15 #include <tommath.h>
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
16
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
17 /* computes a = 2**b
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
18 *
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
19 * Simple algorithm which zeroes the int, grows it then just sets one bit
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
20 * as required.
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
21 */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
22 int
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
23 mp_2expt (mp_int * a, int b)
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
24 {
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
25 int res;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
26
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
27 /* zero a as per default */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
28 mp_zero (a);
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
29
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
30 /* grow a to accomodate the single bit */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
31 if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
32 return res;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
33 }
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
34
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
35 /* set the used count of where the bit will go */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
36 a->used = b / DIGIT_BIT + 1;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
37
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
38 /* put the single bit in its place */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
39 a->dp[b / DIGIT_BIT] = 1 << (b % DIGIT_BIT);
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
40
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
41 return MP_OKAY;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
42 }