Mercurial > dropbear

comparison tomsfastmath/src/bit/fp_cnt_lsb.c @ 643:a362b62d38b2 dropbear-tfm

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a with Makefile.in renamed
author Matt Johnston <matt@ucc.asn.au>
date Wed, 23 Nov 2011 18:10:20 +0700
parents
children
comparison
equal deleted inserted replaced
642:33fd2f3499d2 643:a362b62d38b2
1 /* TomsFastMath, a fast ISO C bignum library.
2 *
3 * This project is meant to fill in where LibTomMath
4 * falls short. That is speed ;-)
5 *
6 * This project is public domain and free for all purposes.
7 *
8 * Tom St Denis, [email protected]
9 */
10 #include <tfm.h>
11
12 static const int lnz[16] = {
13 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
14 };
15
16 /* Counts the number of lsbs which are zero before the first zero bit */
17 int fp_cnt_lsb(fp_int *a)
18 {
19 int x;
20 fp_digit q, qq;
21
22 /* easy out */
23 if (fp_iszero(a) == 1) {
24 return 0;
25 }
26
27 /* scan lower digits until non-zero */
28 for (x = 0; x < a->used && a->dp[x] == 0; x++);
29 q = a->dp[x];
30 x *= DIGIT_BIT;
31
32 /* now scan this digit until a 1 is found */
33 if ((q & 1) == 0) {
34 do {
35 qq = q & 15;
36 x += lnz[qq];
37 q >>= 4;
38 } while (qq == 0);
39 }
40 return x;
41 }
42
43
44 /* $Source$ */
45 /* $Revision$ */
46 /* $Date$ */