1 | #include <tommath.h> |
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2 | #ifdef BN_MP_DIV_2_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 | /* b = a/2 */ |
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19 | int mp_div_2(mp_int * a, mp_int * b) |
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20 | { |
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21 | int x, res, oldused; |
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22 | |
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23 | /* copy */ |
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24 | if (b->alloc < a->used) { |
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25 | if ((res = mp_grow (b, a->used)) != MP_OKAY) { |
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26 | return res; |
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27 | } |
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28 | } |
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29 | |
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30 | oldused = b->used; |
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31 | b->used = a->used; |
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32 | { |
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33 | register mp_digit r, rr, *tmpa, *tmpb; |
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34 | |
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35 | /* source alias */ |
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36 | tmpa = a->dp + b->used - 1; |
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37 | |
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38 | /* dest alias */ |
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39 | tmpb = b->dp + b->used - 1; |
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40 | |
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41 | /* carry */ |
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42 | r = 0; |
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43 | for (x = b->used - 1; x >= 0; x--) { |
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44 | /* get the carry for the next iteration */ |
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45 | rr = *tmpa & 1; |
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46 | |
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47 | /* shift the current digit, add in carry and store */ |
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48 | *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1)); |
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49 | |
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50 | /* forward carry to next iteration */ |
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51 | r = rr; |
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52 | } |
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53 | |
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54 | /* zero excess digits */ |
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55 | tmpb = b->dp + b->used; |
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56 | for (x = b->used; x < oldused; x++) { |
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57 | *tmpb++ = 0; |
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58 | } |
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59 | } |
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60 | b->sign = a->sign; |
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61 | mp_clamp (b); |
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62 | return MP_OKAY; |
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63 | } |
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64 | #endif |
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65 | |
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66 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_div_2.c,v $ */ |
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67 | /* $Revision: 1.1.1.3 $ */ |
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68 | /* $Date: 2006/12/01 00:08:11 $ */ |
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