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, tomstdenis@gmail.com, http://math.libtomcrypt.com |
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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 |
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64 | |
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65 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_lshd.c,v $ */ |
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66 | /* $Revision: 1.1.1.3 $ */ |
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67 | /* $Date: 2006/12/01 00:08:11 $ */ |
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