Mercurial > dropbear

annotate libtommath/bn_mp_sqrt.c @ 1667:986126448688

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Update remaining advise to edit options.h You should edit localoptions.h instead.
author Alexander Dahl <ada@thorsis.com>
date Tue, 10 Mar 2020 15:38:38 +0100
parents f52919ffd3b1
children 1051e4eea25a
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 #include "tommath_private.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 * SPDX-License-Identifier: Unlicense
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13 */
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14
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15 /* this function is less generic than mp_n_root, simpler and faster */
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16 int mp_sqrt(const mp_int *arg, mp_int *ret)
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17 {
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18 int res;
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19 mp_int t1, t2;
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20
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21 /* must be positive */
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22 if (arg->sign == MP_NEG) {
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23 return MP_VAL;
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24 }
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25
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26 /* easy out */
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27 if (mp_iszero(arg) == MP_YES) {
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28 mp_zero(ret);
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29 return MP_OKAY;
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30 }
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31
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32 if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
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33 return res;
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34 }
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35
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36 if ((res = mp_init(&t2)) != MP_OKAY) {
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37 goto E2;
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38 }
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39
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40 /* First approx. (not very bad for large arg) */
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41 mp_rshd(&t1, t1.used/2);
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42
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43 /* t1 > 0 */
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44 if ((res = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
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45 goto E1;
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46 }
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47 if ((res = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
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48 goto E1;
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49 }
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50 if ((res = mp_div_2(&t1, &t1)) != MP_OKAY) {
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51 goto E1;
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52 }
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53 /* And now t1 > sqrt(arg) */
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54 do {
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55 if ((res = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
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56 goto E1;
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57 }
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58 if ((res = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
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59 goto E1;
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60 }
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61 if ((res = mp_div_2(&t1, &t1)) != MP_OKAY) {
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62 goto E1;
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63 }
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64 /* t1 >= sqrt(arg) >= t2 at this point */
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65 } while (mp_cmp_mag(&t1, &t2) == MP_GT);
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66
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67 mp_exch(&t1, ret);
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68
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69 E1:
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70 mp_clear(&t2);
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71 E2:
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72 mp_clear(&t1);
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73 return res;
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74 }
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75
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76 #endif
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77
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78 /* ref: HEAD -> master, tag: v1.1.0 */
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79 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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80 /* commit time: 2019-01-28 20:32:32 +0100 */