Mercurial > dropbear

annotate libtommath/bn_mp_cnt_lsb.c @ 1838:60cd5cdb165c

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Update .hgignore and .gitignore with tests
author Matt Johnston <matt@codeconstruct.com.au>
date Mon, 18 Oct 2021 14:26:59 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
Steffen Jaeckel <s_jaeckel@gmx.de>
parents: 1470
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_CNT_LSB_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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5
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6 static const int lnz[16] = {
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7 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
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8 };
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9
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10 /* Counts the number of lsbs which are zero before the first zero bit */
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parents: 1470
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11 int mp_cnt_lsb(const mp_int *a)
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12 {
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13 int x;
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14 mp_digit q, qq;
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16 /* easy out */
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17 if (MP_IS_ZERO(a)) {
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18 return 0;
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19 }
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21 /* scan lower digits until non-zero */
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parents: 1470
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22 for (x = 0; (x < a->used) && (a->dp[x] == 0u); x++) {}
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23 q = a->dp[x];
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24 x *= MP_DIGIT_BIT;
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26 /* now scan this digit until a 1 is found */
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27 if ((q & 1u) == 0u) {
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28 do {
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29 qq = q & 15u;
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30 x += lnz[qq];
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31 q >>= 4;
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parents: 1470
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32 } while (qq == 0u);
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33 }
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34 return x;
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35 }
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37 #endif