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annotate libtommath/bn_mp_mul_2.c @ 1934:83b6a47759a8

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Add m_snprintf() that won't return negative
author Matt Johnston <matt@ucc.asn.au>
date Fri, 01 Apr 2022 12:10:48 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_MUL_2_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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6 /* b = a*2 */
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7 mp_err mp_mul_2(const mp_int *a, mp_int *b)
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8 {
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9 int x, oldused;
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10 mp_err err;
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11
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12 /* grow to accomodate result */
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13 if (b->alloc < (a->used + 1)) {
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14 if ((err = mp_grow(b, a->used + 1)) != MP_OKAY) {
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15 return err;
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16 }
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17 }
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19 oldused = b->used;
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20 b->used = a->used;
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21
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22 {
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23 mp_digit r, rr, *tmpa, *tmpb;
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24
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25 /* alias for source */
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26 tmpa = a->dp;
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27
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28 /* alias for dest */
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29 tmpb = b->dp;
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31 /* carry */
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32 r = 0;
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33 for (x = 0; x < a->used; x++) {
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34
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35 /* get what will be the *next* carry bit from the
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36 * MSB of the current digit
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37 */
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38 rr = *tmpa >> (mp_digit)(MP_DIGIT_BIT - 1);
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39
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40 /* now shift up this digit, add in the carry [from the previous] */
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41 *tmpb++ = ((*tmpa++ << 1uL) | r) & MP_MASK;
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42
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43 /* copy the carry that would be from the source
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44 * digit into the next iteration
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45 */
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46 r = rr;
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47 }
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49 /* new leading digit? */
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50 if (r != 0u) {
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51 /* add a MSB which is always 1 at this point */
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52 *tmpb = 1;
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53 ++(b->used);
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54 }
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55
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56 /* now zero any excess digits on the destination
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57 * that we didn't write to
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58 */
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59 MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);
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60 }
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61 b->sign = a->sign;
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62 return MP_OKAY;
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63 }
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64 #endif