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annotate libtommath/bn_mp_lshd.c @ 1731:cddc90de1b6f

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update CHANGES for 2020.80
author Matt Johnston <matt@ucc.asn.au>
date Fri, 26 Jun 2020 20:55:56 +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_LSHD_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 /* shift left a certain amount of digits */
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7 mp_err mp_lshd(mp_int *a, int b)
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8 {
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9 int x;
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10 mp_err err;
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11 mp_digit *top, *bottom;
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12
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13 /* if its less than zero return */
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14 if (b <= 0) {
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15 return MP_OKAY;
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16 }
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17 /* no need to shift 0 around */
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18 if (MP_IS_ZERO(a)) {
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19 return MP_OKAY;
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20 }
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21
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22 /* grow to fit the new digits */
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23 if (a->alloc < (a->used + b)) {
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24 if ((err = mp_grow(a, a->used + b)) != MP_OKAY) {
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25 return err;
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26 }
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27 }
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29 /* increment the used by the shift amount then copy upwards */
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30 a->used += b;
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31
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32 /* top */
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33 top = a->dp + a->used - 1;
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34
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35 /* base */
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36 bottom = (a->dp + a->used - 1) - b;
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37
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38 /* much like mp_rshd this is implemented using a sliding window
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39 * except the window goes the otherway around. Copying from
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40 * the bottom to the top. see bn_mp_rshd.c for more info.
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41 */
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42 for (x = a->used - 1; x >= b; x--) {
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43 *top-- = *bottom--;
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44 }
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45
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46 /* zero the lower digits */
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47 MP_ZERO_DIGITS(a->dp, b);
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48
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49 return MP_OKAY;
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50 }
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51 #endif