Mercurial > dropbear

annotate libtommath/bn_mp_cnt_lsb.c @ 1656:a36e545fb43d

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Prime-related bugfixes (#81) * Merge pull request #180 from czurnieden/isprimeerror Fixed bug in mp_prime_isprime (cherry picked from commit f3ff7064f3301a2fc11b84d389fd67769862d437) * do 2 MR rounds for numbers >=2048bits * back-port modified mp_prime_next_prime()
author Steffen Jaeckel <s@jaeckel.eu>
date Tue, 17 Sep 2019 16:11:09 +0200
parents f52919ffd3b1
children 1051e4eea25a
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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 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * SPDX-License-Identifier: Unlicense
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13 */
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14
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15 static const int lnz[16] = {
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16 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
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17 };
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18
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19 /* Counts the number of lsbs which are zero before the first zero bit */
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20 int mp_cnt_lsb(const mp_int *a)
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21 {
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22 int x;
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23 mp_digit q, qq;
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25 /* easy out */
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26 if (mp_iszero(a) == MP_YES) {
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27 return 0;
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28 }
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30 /* scan lower digits until non-zero */
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31 for (x = 0; (x < a->used) && (a->dp[x] == 0u); x++) {}
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32 q = a->dp[x];
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33 x *= DIGIT_BIT;
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35 /* now scan this digit until a 1 is found */
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36 if ((q & 1u) == 0u) {
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37 do {
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38 qq = q & 15u;
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39 x += lnz[qq];
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40 q >>= 4;
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41 } while (qq == 0u);
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42 }
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43 return x;
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44 }
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46 #endif
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47
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48 /* ref: HEAD -> master, tag: v1.1.0 */
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49 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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50 /* commit time: 2019-01-28 20:32:32 +0100 */