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