Mercurial > dropbear

annotate libtommath/bn_mp_sqrt.c @ 1734:73646de50f13 DROPBEAR_2020.80

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version 2020.80
author Matt Johnston <matt@ucc.asn.au>
date Fri, 26 Jun 2020 21:45:59 +0800
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1655
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
diff changeset
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 /* SPDX-License-Identifier: Unlicense */
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6 /* this function is less generic than mp_n_root, simpler and faster */
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7 mp_err mp_sqrt(const mp_int *arg, mp_int *ret)
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8 {
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9 mp_err err;
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10 mp_int t1, t2;
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11
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12 /* must be positive */
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13 if (arg->sign == MP_NEG) {
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14 return MP_VAL;
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15 }
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16
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17 /* easy out */
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18 if (MP_IS_ZERO(arg)) {
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19 mp_zero(ret);
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20 return MP_OKAY;
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21 }
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22
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23 if ((err = mp_init_copy(&t1, arg)) != MP_OKAY) {
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24 return err;
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25 }
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26
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27 if ((err = mp_init(&t2)) != MP_OKAY) {
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28 goto E2;
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29 }
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30
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31 /* First approx. (not very bad for large arg) */
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32 mp_rshd(&t1, t1.used/2);
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33
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34 /* t1 > 0 */
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35 if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
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36 goto E1;
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37 }
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38 if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
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39 goto E1;
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40 }
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41 if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
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42 goto E1;
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43 }
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44 /* And now t1 > sqrt(arg) */
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45 do {
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46 if ((err = 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 ((err = 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 ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
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53 goto E1;
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54 }
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55 /* t1 >= sqrt(arg) >= t2 at this point */
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56 } while (mp_cmp_mag(&t1, &t2) == MP_GT);
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57
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58 mp_exch(&t1, ret);
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59
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60 E1:
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61 mp_clear(&t2);
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62 E2:
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63 mp_clear(&t1);
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64 return err;
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65 }
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66
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67 #endif