annotate bn_mp_count_bits.c @ 283:bd240aa12ba7 libtommath-dropbear

* Changes imported from Dropbear 0.47. * bn_mp_clear.c is changed so that some vars are volatile, so that the compiler won't optimise away
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:22:52 +0000
parents 91fbc376f010
children 97db060d0ef5
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
282
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
1 #include <tommath.h>
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
2 #ifdef BN_MP_COUNT_BITS_C
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
4 *
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
5 * LibTomMath is a library that provides multiple-precision
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
6 * integer arithmetic as well as number theoretic functionality.
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
7 *
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
8 * The library was designed directly after the MPI library by
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
9 * Michael Fromberger but has been written from scratch with
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
10 * additional optimizations in place.
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
11 *
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
12 * The library is free for all purposes without any express
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
13 * guarantee it works.
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
14 *
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
16 */
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
17
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
18 /* returns the number of bits in an int */
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
19 int
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
20 mp_count_bits (mp_int * a)
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
21 {
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
22 int r;
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
23 mp_digit q;
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
24
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
25 /* shortcut */
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
26 if (a->used == 0) {
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
27 return 0;
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
28 }
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
29
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
30 /* get number of digits and add that */
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
31 r = (a->used - 1) * DIGIT_BIT;
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
32
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
33 /* take the last digit and count the bits in it */
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
34 q = a->dp[a->used - 1];
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
35 while (q > ((mp_digit) 0)) {
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
36 ++r;
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
37 q >>= ((mp_digit) 1);
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
38 }
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
39 return r;
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
40 }
91fbc376f010 Import of libtommath 0.35
Matt Johnston <matt@ucc.asn.au>
parents:
diff changeset
41 #endif