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1 #include <tommath.h> |
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2 #ifdef BN_MP_MUL_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, [email protected], http://math.libtomcrypt.org |
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16 */ |
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17 |
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18 /* shift left by a certain bit count */ |
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19 int mp_mul_2d (mp_int * a, int b, mp_int * c) |
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20 { |
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21 mp_digit d; |
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22 int res; |
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23 |
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24 /* copy */ |
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25 if (a != c) { |
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26 if ((res = mp_copy (a, c)) != MP_OKAY) { |
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27 return res; |
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28 } |
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29 } |
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30 |
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31 if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) { |
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32 if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) { |
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33 return res; |
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34 } |
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35 } |
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36 |
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37 /* shift by as many digits in the bit count */ |
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38 if (b >= (int)DIGIT_BIT) { |
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39 if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) { |
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40 return res; |
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41 } |
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42 } |
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43 |
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44 /* shift any bit count < DIGIT_BIT */ |
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45 d = (mp_digit) (b % DIGIT_BIT); |
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46 if (d != 0) { |
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47 register mp_digit *tmpc, shift, mask, r, rr; |
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48 register int x; |
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49 |
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50 /* bitmask for carries */ |
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51 mask = (((mp_digit)1) << d) - 1; |
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52 |
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53 /* shift for msbs */ |
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54 shift = DIGIT_BIT - d; |
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55 |
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56 /* alias */ |
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57 tmpc = c->dp; |
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58 |
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59 /* carry */ |
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60 r = 0; |
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61 for (x = 0; x < c->used; x++) { |
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62 /* get the higher bits of the current word */ |
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63 rr = (*tmpc >> shift) & mask; |
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64 |
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65 /* shift the current word and OR in the carry */ |
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66 *tmpc = ((*tmpc << d) | r) & MP_MASK; |
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67 ++tmpc; |
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68 |
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69 /* set the carry to the carry bits of the current word */ |
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70 r = rr; |
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71 } |
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72 |
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73 /* set final carry */ |
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74 if (r != 0) { |
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75 c->dp[(c->used)++] = r; |
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76 } |
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77 } |
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78 mp_clamp (c); |
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79 return MP_OKAY; |
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80 } |
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81 #endif |
