Mercurial > dropbear

annotate libtommath/bn_mp_rshd.c @ 1687:f8d8af12ac14

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Make "dbclient -m help -c help" work
author Matt Johnston <matt@ucc.asn.au>
date Tue, 26 May 2020 20:15:39 +0800
parents f52919ffd3b1
children 1051e4eea25a
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_RSHD_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 /* shift right a certain amount of digits */
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16 void mp_rshd(mp_int *a, int b)
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17 {
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18 int x;
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19
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20 /* if b <= 0 then ignore it */
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21 if (b <= 0) {
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22 return;
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23 }
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25 /* if b > used then simply zero it and return */
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26 if (a->used <= b) {
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27 mp_zero(a);
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28 return;
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29 }
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31 {
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32 mp_digit *bottom, *top;
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33
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34 /* shift the digits down */
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36 /* bottom */
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37 bottom = a->dp;
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39 /* top [offset into digits] */
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40 top = a->dp + b;
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42 /* this is implemented as a sliding window where
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43 * the window is b-digits long and digits from
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44 * the top of the window are copied to the bottom
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45 *
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46 * e.g.
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48 b-2 | b-1 | b0 | b1 | b2 | ... | bb | ---->
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49 /\ | ---->
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50 \-------------------/ ---->
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51 */
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52 for (x = 0; x < (a->used - b); x++) {
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53 *bottom++ = *top++;
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54 }
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55
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56 /* zero the top digits */
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57 for (; x < a->used; x++) {
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58 *bottom++ = 0;
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59 }
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60 }
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61
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62 /* remove excess digits */
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63 a->used -= b;
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64 }
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65 #endif
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67 /* ref: HEAD -> master, tag: v1.1.0 */
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68 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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69 /* commit time: 2019-01-28 20:32:32 +0100 */