Mercurial > dropbear

annotate libtommath/bn_mp_lshd.c @ 374:87ae4565679d channel-fix

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merge of 'a94c5265558121fe936519b5d9a5eb27f95e9d9d' and 'd348546b80847bc0d42a7b5208bb31a54f1fdfaf'
author Matt Johnston <matt@ucc.asn.au>
date Tue, 05 Dec 2006 13:28:44 +0000
parents eed26cff980b
children 5ff8218bcee9
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284
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1 #include <tommath.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 *
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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 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
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16 */
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17
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18 /* shift left a certain amount of digits */
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19 int mp_lshd (mp_int * a, int b)
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20 {
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21 int x, res;
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22
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23 /* if its less than zero return */
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24 if (b <= 0) {
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25 return MP_OKAY;
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26 }
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27
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28 /* grow to fit the new digits */
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29 if (a->alloc < a->used + b) {
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30 if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
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31 return res;
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32 }
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33 }
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34
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35 {
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36 register mp_digit *top, *bottom;
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37
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38 /* increment the used by the shift amount then copy upwards */
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39 a->used += b;
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40
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41 /* top */
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42 top = a->dp + a->used - 1;
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43
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44 /* base */
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45 bottom = a->dp + a->used - 1 - b;
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46
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47 /* much like mp_rshd this is implemented using a sliding window
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48 * except the window goes the otherway around. Copying from
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49 * the bottom to the top. see bn_mp_rshd.c for more info.
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50 */
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51 for (x = a->used - 1; x >= b; x--) {
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52 *top-- = *bottom--;
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53 }
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54
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55 /* zero the lower digits */
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56 top = a->dp;
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57 for (x = 0; x < b; x++) {
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58 *top++ = 0;
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59 }
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60 }
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61 return MP_OKAY;
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62 }
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63 #endif