1 | #include <tommath.h> |
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2 | #ifdef BN_MP_MUL_D_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 | /* multiply by a digit */ |
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19 | int |
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20 | mp_mul_d (mp_int * a, mp_digit b, mp_int * c) |
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21 | { |
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22 | mp_digit u, *tmpa, *tmpc; |
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23 | mp_word r; |
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24 | int ix, res, olduse; |
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25 | |
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26 | /* make sure c is big enough to hold a*b */ |
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27 | if (c->alloc < a->used + 1) { |
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28 | if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) { |
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29 | return res; |
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30 | } |
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31 | } |
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32 | |
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33 | /* get the original destinations used count */ |
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34 | olduse = c->used; |
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35 | |
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36 | /* set the sign */ |
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37 | c->sign = a->sign; |
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38 | |
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39 | /* alias for a->dp [source] */ |
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40 | tmpa = a->dp; |
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41 | |
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42 | /* alias for c->dp [dest] */ |
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43 | tmpc = c->dp; |
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44 | |
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45 | /* zero carry */ |
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46 | u = 0; |
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47 | |
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48 | /* compute columns */ |
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49 | for (ix = 0; ix < a->used; ix++) { |
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50 | /* compute product and carry sum for this term */ |
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51 | r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b); |
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52 | |
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53 | /* mask off higher bits to get a single digit */ |
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54 | *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK)); |
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55 | |
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56 | /* send carry into next iteration */ |
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57 | u = (mp_digit) (r >> ((mp_word) DIGIT_BIT)); |
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58 | } |
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59 | |
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60 | /* store final carry [if any] and increment ix offset */ |
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61 | *tmpc++ = u; |
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62 | ++ix; |
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63 | |
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64 | /* now zero digits above the top */ |
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65 | while (ix++ < olduse) { |
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66 | *tmpc++ = 0; |
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67 | } |
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68 | |
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69 | /* set used count */ |
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70 | c->used = a->used + 1; |
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71 | mp_clamp(c); |
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72 | |
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73 | return MP_OKAY; |
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74 | } |
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75 | #endif |
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76 | |
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77 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_mul_d.c,v $ */ |
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78 | /* $Revision: 1.1.1.4 $ */ |
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79 | /* $Date: 2006/12/01 00:08:11 $ */ |
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