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annotate libtommath/bn_mp_div_2.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_DIV_2_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 /* b = a/2 */
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16 int mp_div_2(const mp_int *a, mp_int *b)
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17 {
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18 int x, res, oldused;
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20 /* copy */
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21 if (b->alloc < a->used) {
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22 if ((res = mp_grow(b, a->used)) != MP_OKAY) {
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23 return res;
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24 }
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25 }
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27 oldused = b->used;
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28 b->used = a->used;
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29 {
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30 mp_digit r, rr, *tmpa, *tmpb;
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32 /* source alias */
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33 tmpa = a->dp + b->used - 1;
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35 /* dest alias */
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36 tmpb = b->dp + b->used - 1;
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38 /* carry */
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39 r = 0;
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40 for (x = b->used - 1; x >= 0; x--) {
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41 /* get the carry for the next iteration */
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42 rr = *tmpa & 1u;
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44 /* shift the current digit, add in carry and store */
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45 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
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47 /* forward carry to next iteration */
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48 r = rr;
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49 }
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51 /* zero excess digits */
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52 tmpb = b->dp + b->used;
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53 for (x = b->used; x < oldused; x++) {
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54 *tmpb++ = 0;
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55 }
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56 }
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57 b->sign = a->sign;
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58 mp_clamp(b);
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59 return MP_OKAY;
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60 }
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61 #endif
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63 /* ref: HEAD -> master, tag: v1.1.0 */
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64 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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65 /* commit time: 2019-01-28 20:32:32 +0100 */