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1 #include <tommath.h> |
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2 #ifdef BN_MP_SQRT_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.com |
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16 */ |
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17 |
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18 /* this function is less generic than mp_n_root, simpler and faster */ |
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19 int mp_sqrt(mp_int *arg, mp_int *ret) |
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20 { |
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21 int res; |
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22 mp_int t1,t2; |
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23 |
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24 /* must be positive */ |
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25 if (arg->sign == MP_NEG) { |
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26 return MP_VAL; |
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27 } |
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28 |
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29 /* easy out */ |
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30 if (mp_iszero(arg) == MP_YES) { |
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31 mp_zero(ret); |
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32 return MP_OKAY; |
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33 } |
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34 |
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35 if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) { |
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36 return res; |
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37 } |
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38 |
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39 if ((res = mp_init(&t2)) != MP_OKAY) { |
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40 goto E2; |
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41 } |
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42 |
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43 /* First approx. (not very bad for large arg) */ |
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44 mp_rshd (&t1,t1.used/2); |
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45 |
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46 /* t1 > 0 */ |
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47 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { |
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48 goto E1; |
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49 } |
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50 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) { |
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51 goto E1; |
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52 } |
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53 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) { |
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54 goto E1; |
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55 } |
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56 /* And now t1 > sqrt(arg) */ |
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57 do { |
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58 if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { |
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59 goto E1; |
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60 } |
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61 if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) { |
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62 goto E1; |
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63 } |
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64 if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) { |
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65 goto E1; |
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66 } |
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67 /* t1 >= sqrt(arg) >= t2 at this point */ |
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68 } while (mp_cmp_mag(&t1,&t2) == MP_GT); |
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69 |
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70 mp_exch(&t1,ret); |
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71 |
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72 E1: mp_clear(&t2); |
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73 E2: mp_clear(&t1); |
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74 return res; |
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75 } |
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76 |
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77 #endif |
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78 |
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79 /* $Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v $ */ |
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80 /* $Revision: 1.3 $ */ |
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81 /* $Date: 2006/03/31 14:18:44 $ */ |
