annotate bn_mp_count_bits.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 /* returns the number of bits in an int */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
18 int
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
19 mp_count_bits (mp_int * a)
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
20 {
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
21 int r;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
22 mp_digit q;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
23
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
24 /* shortcut */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
25 if (a->used == 0) {
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
26 return 0;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
27 }
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
28
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
29 /* get number of digits and add that */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
30 r = (a->used - 1) * DIGIT_BIT;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
31
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
32 /* take the last digit and count the bits in it */
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
33 q = a->dp[a->used - 1];
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
34 while (q > ((mp_digit) 0)) {
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
35 ++r;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
36 q >>= ((mp_digit) 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 return r;
22d5cf7d4b1a Renaming branch
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
39 }