1 | #include <tommath.h> |
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2 | #ifdef BN_MP_DIV_2D_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 right by a certain bit count (store quotient in c, optional remainder in d) */ |
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19 | int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d) |
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20 | { |
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21 | mp_digit D, r, rr; |
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22 | int x, res; |
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23 | mp_int t; |
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24 | |
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25 | |
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26 | /* if the shift count is <= 0 then we do no work */ |
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27 | if (b <= 0) { |
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28 | res = mp_copy (a, c); |
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29 | if (d != NULL) { |
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30 | mp_zero (d); |
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31 | } |
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32 | return res; |
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33 | } |
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34 | |
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35 | if ((res = mp_init (&t)) != MP_OKAY) { |
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36 | return res; |
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37 | } |
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38 | |
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39 | /* get the remainder */ |
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40 | if (d != NULL) { |
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41 | if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) { |
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42 | mp_clear (&t); |
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43 | return res; |
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44 | } |
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45 | } |
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46 | |
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47 | /* copy */ |
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48 | if ((res = mp_copy (a, c)) != MP_OKAY) { |
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49 | mp_clear (&t); |
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50 | return res; |
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51 | } |
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52 | |
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53 | /* shift by as many digits in the bit count */ |
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54 | if (b >= (int)DIGIT_BIT) { |
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55 | mp_rshd (c, b / DIGIT_BIT); |
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56 | } |
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57 | |
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58 | /* shift any bit count < DIGIT_BIT */ |
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59 | D = (mp_digit) (b % DIGIT_BIT); |
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60 | if (D != 0) { |
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61 | register mp_digit *tmpc, mask, shift; |
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62 | |
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63 | /* mask */ |
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64 | mask = (((mp_digit)1) << D) - 1; |
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65 | |
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66 | /* shift for lsb */ |
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67 | shift = DIGIT_BIT - D; |
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68 | |
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69 | /* alias */ |
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70 | tmpc = c->dp + (c->used - 1); |
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71 | |
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72 | /* carry */ |
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73 | r = 0; |
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74 | for (x = c->used - 1; x >= 0; x--) { |
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75 | /* get the lower bits of this word in a temp */ |
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76 | rr = *tmpc & mask; |
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77 | |
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78 | /* shift the current word and mix in the carry bits from the previous word */ |
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79 | *tmpc = (*tmpc >> D) | (r << shift); |
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80 | --tmpc; |
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81 | |
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82 | /* set the carry to the carry bits of the current word found above */ |
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83 | r = rr; |
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84 | } |
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85 | } |
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86 | mp_clamp (c); |
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87 | if (d != NULL) { |
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88 | mp_exch (&t, d); |
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89 | } |
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90 | mp_clear (&t); |
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91 | return MP_OKAY; |
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92 | } |
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93 | #endif |
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94 | |
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95 | /* $Source: /cvsroot/tcl/libtommath/bn_mp_div_2d.c,v $ */ |
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96 | /* $Revision: 1.1.1.3 $ */ |
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97 | /* $Date: 2006/12/01 00:08:11 $ */ |
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