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annotate libtommath/bn_mp_mod_2d.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_MOD_2D_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 /* calc a value mod 2**b */
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16 int mp_mod_2d(const mp_int *a, int b, mp_int *c)
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17 {
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18 int x, res;
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20 /* if b is <= 0 then zero the int */
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21 if (b <= 0) {
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22 mp_zero(c);
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23 return MP_OKAY;
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24 }
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26 /* if the modulus is larger than the value than return */
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27 if (b >= (a->used * DIGIT_BIT)) {
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28 res = mp_copy(a, c);
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29 return res;
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30 }
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32 /* copy */
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33 if ((res = mp_copy(a, c)) != MP_OKAY) {
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34 return res;
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35 }
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37 /* zero digits above the last digit of the modulus */
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38 for (x = (b / DIGIT_BIT) + (((b % DIGIT_BIT) == 0) ? 0 : 1); x < c->used; x++) {
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39 c->dp[x] = 0;
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40 }
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41 /* clear the digit that is not completely outside/inside the modulus */
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42 c->dp[b / DIGIT_BIT] &=
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43 ((mp_digit)1 << (mp_digit)(b % DIGIT_BIT)) - (mp_digit)1;
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44 mp_clamp(c);
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45 return MP_OKAY;
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46 }
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47 #endif
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48
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49 /* ref: HEAD -> master, tag: v1.1.0 */
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50 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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51 /* commit time: 2019-01-28 20:32:32 +0100 */