Mercurial > dropbear

annotate libtommath/bn_mp_sqrt.c @ 510:b85507ade010

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- Update manuals, include section on authorized_keys - Change default PATH to /usr/bin:/bin - Mention DEBUG_TRACE in -v help text
author Matt Johnston <matt@ucc.asn.au>
date Wed, 05 Nov 2008 14:14:40 +0000
parents 5ff8218bcee9
children 60fc6476e044
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
284
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diff changeset
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 *
389
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
284
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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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Matt Johnston <matt@ucc.asn.au>
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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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diff changeset
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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parents:
diff changeset
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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parents:
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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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parents:
diff changeset
69
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parents:
diff changeset
70 mp_exch(&t1,ret);
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Matt Johnston <matt@ucc.asn.au>
parents:
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71
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
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diff changeset
72 E1: mp_clear(&t2);
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Matt Johnston <matt@ucc.asn.au>
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diff changeset
73 E2: mp_clear(&t1);
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Matt Johnston <matt@ucc.asn.au>
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74 return res;
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parents:
diff changeset
75 }
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parents:
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76
eed26cff980b propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
Matt Johnston <matt@ucc.asn.au>
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diff changeset
77 #endif
389
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parents: 284
diff changeset
78
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Matt Johnston <matt@ucc.asn.au>
parents: 284
diff changeset
79 /* $Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v $ */
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Matt Johnston <matt@ucc.asn.au>
parents: 284
diff changeset
80 /* $Revision: 1.3 $ */
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parents: 284
diff changeset
81 /* $Date: 2006/03/31 14:18:44 $ */