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annotate libtommath/bn_mp_sqrt.c @ 1663:c795520269f9

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Fallback for key gen without hard link support (#89) Add a non-atomic fallback for key generation on platforms where link() is not permitted (such as most stock Android installs) or on filesystems without hard link support (such as FAT).
author Matt Robinson <git@nerdoftheherd.com>
date Sat, 14 Mar 2020 14:37:35 +0000
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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76 #endif
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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 */