Mercurial > dropbear

annotate libtommath/bn_mp_cnt_lsb.c @ 1659:d32bcb5c557d

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Add Ed25519 support (#91) * Add support for Ed25519 as a public key type Ed25519 is a elliptic curve signature scheme that offers better security than ECDSA and DSA and good performance. It may be used for both user and host keys. OpenSSH key import and fuzzer are not supported yet. Initially inspired by Peter Szabo. * Add curve25519 and ed25519 fuzzers * Add import and export of Ed25519 keys
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Wed, 11 Mar 2020 21:09:45 +0500
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 */