Line | Count | Source |
1 | #include "tommath_private.h" | |
2 | #ifdef BN_MP_CNT_LSB_C | |
3 | /* LibTomMath, multiple-precision integer library -- Tom St Denis */ | |
4 | /* SPDX-License-Identifier: Unlicense */ | |
5 | ||
6 | static const int lnz[16] = { | |
7 | 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0 | |
8 | }; | |
9 | ||
10 | /* Counts the number of lsbs which are zero before the first zero bit */ | |
11 | int mp_cnt_lsb(const mp_int *a) | |
12 | 1.96k | { |
13 | 1.96k | int x; |
14 | 1.96k | mp_digit q, qq; |
15 | ||
16 | /* easy out */ | |
17 | 1.96k | if (MP_IS_ZERO(a)) { |
18 | 0 | return 0; |
19 | 0 | } |
20 | ||
21 | /* scan lower digits until non-zero */ | |
22 | 2.99k | for (x = 0; (x < a->used) && (a->dp[x] == 0u); x++) {} |
23 | 1.96k | q = a->dp[x]; |
24 | 1.96k | x *= MP_DIGIT_BIT; |
25 | ||
26 | /* now scan this digit until a 1 is found */ | |
27 | 1.96k | if ((q & 1u) == 0u) { |
28 | 6.96k | do { |
29 | 6.96k | qq = q & 15u; |
30 | 6.96k | x += lnz[qq]; |
31 | 6.96k | q >>= 4; |
32 | 6.96k | } while (qq == 0u); |
33 | 1.76k | } |
34 | 1.96k | return x; |
35 | 1.96k | } |
36 | ||
37 | #endif |