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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 /* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */ |
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18 int |
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19 s_mp_sqr (mp_int * a, mp_int * b) |
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20 { |
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21 mp_int t; |
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22 int res, ix, iy, pa; |
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23 mp_word r; |
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24 mp_digit u, tmpx, *tmpt; |
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25 |
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26 pa = a->used; |
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27 if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) { |
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28 return res; |
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29 } |
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30 |
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31 /* default used is maximum possible size */ |
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32 t.used = 2*pa + 1; |
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33 |
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34 for (ix = 0; ix < pa; ix++) { |
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35 /* first calculate the digit at 2*ix */ |
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36 /* calculate double precision result */ |
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37 r = ((mp_word) t.dp[2*ix]) + |
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38 ((mp_word)a->dp[ix])*((mp_word)a->dp[ix]); |
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39 |
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40 /* store lower part in result */ |
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41 t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK)); |
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42 |
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43 /* get the carry */ |
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44 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); |
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45 |
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46 /* left hand side of A[ix] * A[iy] */ |
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47 tmpx = a->dp[ix]; |
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48 |
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49 /* alias for where to store the results */ |
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50 tmpt = t.dp + (2*ix + 1); |
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51 |
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52 for (iy = ix + 1; iy < pa; iy++) { |
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53 /* first calculate the product */ |
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54 r = ((mp_word)tmpx) * ((mp_word)a->dp[iy]); |
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55 |
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56 /* now calculate the double precision result, note we use |
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57 * addition instead of *2 since it's easier to optimize |
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58 */ |
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59 r = ((mp_word) *tmpt) + r + r + ((mp_word) u); |
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60 |
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61 /* store lower part */ |
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62 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); |
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63 |
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64 /* get carry */ |
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65 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); |
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66 } |
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67 /* propagate upwards */ |
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68 while (u != ((mp_digit) 0)) { |
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69 r = ((mp_word) *tmpt) + ((mp_word) u); |
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70 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); |
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71 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); |
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72 } |
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73 } |
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74 |
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75 mp_clamp (&t); |
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76 mp_exch (&t, b); |
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77 mp_clear (&t); |
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78 return MP_OKAY; |
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79 } |
