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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 by a certain bit count */ |
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18 int mp_mul_2d (mp_int * a, int b, mp_int * c) |
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19 { |
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20 mp_digit d; |
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21 int res; |
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22 |
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23 /* copy */ |
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24 if (a != c) { |
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25 if ((res = mp_copy (a, c)) != 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 if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) { |
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31 if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) { |
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32 return res; |
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33 } |
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34 } |
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35 |
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36 /* shift by as many digits in the bit count */ |
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37 if (b >= (int)DIGIT_BIT) { |
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38 if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) { |
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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 /* shift any bit count < DIGIT_BIT */ |
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44 d = (mp_digit) (b % DIGIT_BIT); |
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45 if (d != 0) { |
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46 register mp_digit *tmpc, shift, mask, r, rr; |
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47 register int x; |
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48 |
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49 /* bitmask for carries */ |
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50 mask = (((mp_digit)1) << d) - 1; |
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51 |
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52 /* shift for msbs */ |
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53 shift = DIGIT_BIT - d; |
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54 |
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55 /* alias */ |
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56 tmpc = c->dp; |
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57 |
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58 /* carry */ |
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59 r = 0; |
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60 for (x = 0; x < c->used; x++) { |
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61 /* get the higher bits of the current word */ |
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62 rr = (*tmpc >> shift) & mask; |
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63 |
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64 /* shift the current word and OR in the carry */ |
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65 *tmpc = ((*tmpc << d) | r) & MP_MASK; |
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66 ++tmpc; |
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67 |
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68 /* set the carry to the carry bits of the current word */ |
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69 r = rr; |
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70 } |
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71 |
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72 /* set final carry */ |
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73 if (r != 0) { |
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74 c->dp[(c->used)++] = r; |
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75 } |
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76 } |
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77 mp_clamp (c); |
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78 return MP_OKAY; |
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79 } |
