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comparison libtommath/bn_mp_exteuclid.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
parents
children 5ff8218bcee9
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283:bd240aa12ba7 284:eed26cff980b
1 #include <tommath.h>
2 #ifdef BN_MP_EXTEUCLID_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* Extended euclidean algorithm of (a, b) produces
19 a*u1 + b*u2 = u3
20 */
21 int mp_exteuclid(mp_int *a, mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
22 {
23 mp_int u1,u2,u3,v1,v2,v3,t1,t2,t3,q,tmp;
24 int err;
25
26 if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
27 return err;
28 }
29
30 /* initialize, (u1,u2,u3) = (1,0,a) */
31 mp_set(&u1, 1);
32 if ((err = mp_copy(a, &u3)) != MP_OKAY) { goto _ERR; }
33
34 /* initialize, (v1,v2,v3) = (0,1,b) */
35 mp_set(&v2, 1);
36 if ((err = mp_copy(b, &v3)) != MP_OKAY) { goto _ERR; }
37
38 /* loop while v3 != 0 */
39 while (mp_iszero(&v3) == MP_NO) {
40 /* q = u3/v3 */
41 if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY) { goto _ERR; }
42
43 /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
44 if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY) { goto _ERR; }
45 if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY) { goto _ERR; }
46 if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY) { goto _ERR; }
47 if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY) { goto _ERR; }
48 if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY) { goto _ERR; }
49 if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY) { goto _ERR; }
50
51 /* (u1,u2,u3) = (v1,v2,v3) */
52 if ((err = mp_copy(&v1, &u1)) != MP_OKAY) { goto _ERR; }
53 if ((err = mp_copy(&v2, &u2)) != MP_OKAY) { goto _ERR; }
54 if ((err = mp_copy(&v3, &u3)) != MP_OKAY) { goto _ERR; }
55
56 /* (v1,v2,v3) = (t1,t2,t3) */
57 if ((err = mp_copy(&t1, &v1)) != MP_OKAY) { goto _ERR; }
58 if ((err = mp_copy(&t2, &v2)) != MP_OKAY) { goto _ERR; }
59 if ((err = mp_copy(&t3, &v3)) != MP_OKAY) { goto _ERR; }
60 }
61
62 /* make sure U3 >= 0 */
63 if (u3.sign == MP_NEG) {
64 mp_neg(&u1, &u1);
65 mp_neg(&u2, &u2);
66 mp_neg(&u3, &u3);
67 }
68
69 /* copy result out */
70 if (U1 != NULL) { mp_exch(U1, &u1); }
71 if (U2 != NULL) { mp_exch(U2, &u2); }
72 if (U3 != NULL) { mp_exch(U3, &u3); }
73
74 err = MP_OKAY;
75 _ERR: mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
76 return err;
77 }
78 #endif