Mercurial > dropbear

annotate libtommath/bn_mp_gcd.c @ 1717:295377ecbf49

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Add DEVELOPING.md
author Matt Johnston <matt@ucc.asn.au>
date Mon, 15 Jun 2020 22:30:28 +0800
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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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_GCD_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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4 /* SPDX-License-Identifier: Unlicense */
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5
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6 /* Greatest Common Divisor using the binary method */
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7 mp_err mp_gcd(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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9 mp_int u, v;
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10 int k, u_lsb, v_lsb;
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11 mp_err err;
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12
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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13 /* either zero than gcd is the largest */
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14 if (MP_IS_ZERO(a)) {
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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15 return mp_abs(b, c);
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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16 }
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17 if (MP_IS_ZERO(b)) {
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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18 return mp_abs(a, c);
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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19 }
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20
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21 /* get copies of a and b we can modify */
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22 if ((err = mp_init_copy(&u, a)) != MP_OKAY) {
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23 return err;
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24 }
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25
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26 if ((err = mp_init_copy(&v, b)) != MP_OKAY) {
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27 goto LBL_U;
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28 }
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29
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30 /* must be positive for the remainder of the algorithm */
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31 u.sign = v.sign = MP_ZPOS;
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32
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33 /* B1. Find the common power of two for u and v */
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34 u_lsb = mp_cnt_lsb(&u);
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35 v_lsb = mp_cnt_lsb(&v);
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36 k = MP_MIN(u_lsb, v_lsb);
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37
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38 if (k > 0) {
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39 /* divide the power of two out */
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40 if ((err = mp_div_2d(&u, k, &u, NULL)) != MP_OKAY) {
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41 goto LBL_V;
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42 }
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43
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44 if ((err = mp_div_2d(&v, k, &v, NULL)) != MP_OKAY) {
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45 goto LBL_V;
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46 }
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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47 }
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48
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49 /* divide any remaining factors of two out */
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50 if (u_lsb != k) {
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51 if ((err = mp_div_2d(&u, u_lsb - k, &u, NULL)) != MP_OKAY) {
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52 goto LBL_V;
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53 }
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54 }
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55
1655
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diff changeset
56 if (v_lsb != k) {
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57 if ((err = mp_div_2d(&v, v_lsb - k, &v, NULL)) != MP_OKAY) {
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58 goto LBL_V;
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59 }
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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60 }
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61
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62 while (!MP_IS_ZERO(&v)) {
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63 /* make sure v is the largest */
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64 if (mp_cmp_mag(&u, &v) == MP_GT) {
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65 /* swap u and v to make sure v is >= u */
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66 mp_exch(&u, &v);
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67 }
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68
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69 /* subtract smallest from largest */
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70 if ((err = s_mp_sub(&v, &u, &v)) != MP_OKAY) {
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71 goto LBL_V;
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72 }
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73
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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74 /* Divide out all factors of two */
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75 if ((err = mp_div_2d(&v, mp_cnt_lsb(&v), &v, NULL)) != MP_OKAY) {
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76 goto LBL_V;
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parents: 1470
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77 }
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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78 }
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79
1655
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diff changeset
80 /* multiply by 2**k which we divided out at the beginning */
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81 if ((err = mp_mul_2d(&u, k, c)) != MP_OKAY) {
1655
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82 goto LBL_V;
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parents: 1470
diff changeset
83 }
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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84 c->sign = MP_ZPOS;
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85 err = MP_OKAY;
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86 LBL_V:
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87 mp_clear(&u);
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88 LBL_U:
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Steffen Jaeckel <s_jaeckel@gmx.de>
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diff changeset
89 mp_clear(&v);
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diff changeset
90 return err;
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91 }
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diff changeset
92 #endif