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annotate libtommath/bn_mp_sub.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_SUB_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 /* high level subtraction (handles signs) */
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16 int mp_sub(const mp_int *a, const mp_int *b, mp_int *c)
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17 {
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18 int sa, sb, res;
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19
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20 sa = a->sign;
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21 sb = b->sign;
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22
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23 if (sa != sb) {
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24 /* subtract a negative from a positive, OR */
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25 /* subtract a positive from a negative. */
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26 /* In either case, ADD their magnitudes, */
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27 /* and use the sign of the first number. */
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28 c->sign = sa;
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29 res = s_mp_add(a, b, c);
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30 } else {
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31 /* subtract a positive from a positive, OR */
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32 /* subtract a negative from a negative. */
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33 /* First, take the difference between their */
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34 /* magnitudes, then... */
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35 if (mp_cmp_mag(a, b) != MP_LT) {
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36 /* Copy the sign from the first */
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37 c->sign = sa;
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38 /* The first has a larger or equal magnitude */
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39 res = s_mp_sub(a, b, c);
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40 } else {
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41 /* The result has the *opposite* sign from */
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42 /* the first number. */
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43 c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
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44 /* The second has a larger magnitude */
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45 res = s_mp_sub(b, a, c);
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46 }
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47 }
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48 return res;
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49 }
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50
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51 #endif
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52
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53 /* ref: HEAD -> master, tag: v1.1.0 */
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54 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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55 /* commit time: 2019-01-28 20:32:32 +0100 */