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1 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
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2 * |
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3 * LibTomMath is a library that provides multiple-precision |
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4 * integer arithmetic as well as number theoretic functionality. |
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5 * |
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6 * The library was designed directly after the MPI library by |
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7 * Michael Fromberger but has been written from scratch with |
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8 * additional optimizations in place. |
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9 * |
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10 * The library is free for all purposes without any express |
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11 * guarantee it works. |
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12 * |
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13 * Tom St Denis, [email protected], http://math.libtomcrypt.org |
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14 */ |
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15 #include <tommath.h> |
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16 |
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17 /* shift left a certain amount of digits */ |
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18 int mp_lshd (mp_int * a, int b) |
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19 { |
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20 int x, res; |
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21 |
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22 /* if its less than zero return */ |
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23 if (b <= 0) { |
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24 return MP_OKAY; |
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25 } |
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26 |
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27 /* grow to fit the new digits */ |
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28 if (a->alloc < a->used + b) { |
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29 if ((res = mp_grow (a, a->used + b)) != MP_OKAY) { |
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30 return res; |
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31 } |
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32 } |
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33 |
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34 { |
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35 register mp_digit *top, *bottom; |
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36 |
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37 /* increment the used by the shift amount then copy upwards */ |
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38 a->used += b; |
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39 |
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40 /* top */ |
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41 top = a->dp + a->used - 1; |
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42 |
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43 /* base */ |
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44 bottom = a->dp + a->used - 1 - b; |
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45 |
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46 /* much like mp_rshd this is implemented using a sliding window |
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47 * except the window goes the otherway around. Copying from |
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48 * the bottom to the top. see bn_mp_rshd.c for more info. |
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49 */ |
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50 for (x = a->used - 1; x >= b; x--) { |
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51 *top-- = *bottom--; |
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52 } |
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53 |
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54 /* zero the lower digits */ |
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55 top = a->dp; |
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56 for (x = 0; x < b; x++) { |
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57 *top++ = 0; |
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58 } |
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59 } |
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60 return MP_OKAY; |
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61 } |
