Mercurial > dropbear

annotate libtommath/bn_mp_exteuclid.c @ 1493:72fd994fe7bd

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Update build instructions for localoptions, and tidy
author Matt Johnston <matt@ucc.asn.au>
date Wed, 14 Feb 2018 00:24:32 +0800
parents 8bba51a55704
children f52919ffd3b1
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_EXTEUCLID_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 *
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15 * Tom St Denis, [email protected], http://libtom.org
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16 */
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17
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18 /* Extended euclidean algorithm of (a, b) produces
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19 a*u1 + b*u2 = u3
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20 */
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21 int mp_exteuclid(mp_int *a, mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
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22 {
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23 mp_int u1,u2,u3,v1,v2,v3,t1,t2,t3,q,tmp;
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24 int err;
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25
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26 if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
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27 return err;
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28 }
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29
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30 /* initialize, (u1,u2,u3) = (1,0,a) */
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31 mp_set(&u1, 1);
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32 if ((err = mp_copy(a, &u3)) != MP_OKAY) { goto LBL_ERR; }
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33
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34 /* initialize, (v1,v2,v3) = (0,1,b) */
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35 mp_set(&v2, 1);
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36 if ((err = mp_copy(b, &v3)) != MP_OKAY) { goto LBL_ERR; }
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37
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38 /* loop while v3 != 0 */
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39 while (mp_iszero(&v3) == MP_NO) {
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40 /* q = u3/v3 */
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41 if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY) { goto LBL_ERR; }
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42
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43 /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
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44 if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY) { goto LBL_ERR; }
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45 if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY) { goto LBL_ERR; }
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46 if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY) { goto LBL_ERR; }
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47 if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY) { goto LBL_ERR; }
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48 if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY) { goto LBL_ERR; }
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49 if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY) { goto LBL_ERR; }
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50
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51 /* (u1,u2,u3) = (v1,v2,v3) */
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52 if ((err = mp_copy(&v1, &u1)) != MP_OKAY) { goto LBL_ERR; }
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53 if ((err = mp_copy(&v2, &u2)) != MP_OKAY) { goto LBL_ERR; }
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54 if ((err = mp_copy(&v3, &u3)) != MP_OKAY) { goto LBL_ERR; }
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55
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56 /* (v1,v2,v3) = (t1,t2,t3) */
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57 if ((err = mp_copy(&t1, &v1)) != MP_OKAY) { goto LBL_ERR; }
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58 if ((err = mp_copy(&t2, &v2)) != MP_OKAY) { goto LBL_ERR; }
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59 if ((err = mp_copy(&t3, &v3)) != MP_OKAY) { goto LBL_ERR; }
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60 }
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61
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62 /* make sure U3 >= 0 */
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63 if (u3.sign == MP_NEG) {
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64 if ((err = mp_neg(&u1, &u1)) != MP_OKAY) { goto LBL_ERR; }
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65 if ((err = mp_neg(&u2, &u2)) != MP_OKAY) { goto LBL_ERR; }
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66 if ((err = mp_neg(&u3, &u3)) != MP_OKAY) { goto LBL_ERR; }
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67 }
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68
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69 /* copy result out */
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70 if (U1 != NULL) { mp_exch(U1, &u1); }
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71 if (U2 != NULL) { mp_exch(U2, &u2); }
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72 if (U3 != NULL) { mp_exch(U3, &u3); }
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73
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74 err = MP_OKAY;
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75 LBL_ERR:
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76 mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
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77 return err;
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78 }
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79 #endif
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80
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81 /* ref: $Format:%D$ */
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82 /* git commit: $Format:%H$ */
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83 /* commit time: $Format:%ai$ */