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annotate libtommath/bn_mp_2expt.c @ 1663:c795520269f9

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Fallback for key gen without hard link support (#89) Add a non-atomic fallback for key generation on platforms where link() is not permitted (such as most stock Android installs) or on filesystems without hard link support (such as FAT).
author Matt Robinson <git@nerdoftheherd.com>
date Sat, 14 Mar 2020 14:37:35 +0000
parents f52919ffd3b1
children 1051e4eea25a
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_2EXPT_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 /* computes a = 2**b
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16 *
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17 * Simple algorithm which zeroes the int, grows it then just sets one bit
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18 * as required.
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19 */
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20 int mp_2expt(mp_int *a, int b)
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21 {
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22 int res;
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24 /* zero a as per default */
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25 mp_zero(a);
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27 /* grow a to accomodate the single bit */
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28 if ((res = mp_grow(a, (b / DIGIT_BIT) + 1)) != MP_OKAY) {
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29 return res;
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30 }
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32 /* set the used count of where the bit will go */
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33 a->used = (b / DIGIT_BIT) + 1;
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35 /* put the single bit in its place */
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36 a->dp[b / DIGIT_BIT] = (mp_digit)1 << (mp_digit)(b % DIGIT_BIT);
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38 return MP_OKAY;
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39 }
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40 #endif
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42 /* ref: HEAD -> master, tag: v1.1.0 */
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43 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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44 /* commit time: 2019-01-28 20:32:32 +0100 */