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1 #include <tommath_private.h> |
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2 #ifdef BN_MP_EXPT_D_EX_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://libtom.org |
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16 */ |
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17 |
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18 /* calculate c = a**b using a square-multiply algorithm */ |
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19 int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast) |
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20 { |
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21 int res; |
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22 unsigned int x; |
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23 |
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24 mp_int g; |
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25 |
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26 if ((res = mp_init_copy (&g, a)) != MP_OKAY) { |
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27 return res; |
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28 } |
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29 |
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30 /* set initial result */ |
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31 mp_set (c, 1); |
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32 |
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33 if (fast != 0) { |
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34 while (b > 0) { |
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35 /* if the bit is set multiply */ |
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36 if ((b & 1) != 0) { |
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37 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { |
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38 mp_clear (&g); |
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39 return res; |
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40 } |
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41 } |
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42 |
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43 /* square */ |
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44 if (b > 1) { |
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45 if ((res = mp_sqr (&g, &g)) != MP_OKAY) { |
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46 mp_clear (&g); |
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47 return res; |
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48 } |
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49 } |
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50 |
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51 /* shift to next bit */ |
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52 b >>= 1; |
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53 } |
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54 } |
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55 else { |
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56 for (x = 0; x < DIGIT_BIT; x++) { |
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57 /* square */ |
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58 if ((res = mp_sqr (c, c)) != MP_OKAY) { |
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59 mp_clear (&g); |
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60 return res; |
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61 } |
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62 |
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63 /* if the bit is set multiply */ |
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64 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) { |
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65 if ((res = mp_mul (c, &g, c)) != MP_OKAY) { |
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66 mp_clear (&g); |
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67 return res; |
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68 } |
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69 } |
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70 |
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71 /* shift to next bit */ |
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72 b <<= 1; |
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73 } |
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74 } /* if ... else */ |
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75 |
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76 mp_clear (&g); |
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77 return MP_OKAY; |
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78 } |
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79 #endif |
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80 |
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81 /* $Source$ */ |
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82 /* $Revision$ */ |
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83 /* $Date$ */ |
