1 /* $NetBSD: bn_mp_exteuclid.c,v 1.2 2017/01/28 21:31:47 christos Exp $ */
2
3 #include <tommath.h>
4 #ifdef BN_MP_EXTEUCLID_C
5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
6 *
7 * LibTomMath is a library that provides multiple-precision
8 * integer arithmetic as well as number theoretic functionality.
9 *
10 * The library was designed directly after the MPI library by
11 * Michael Fromberger but has been written from scratch with
12 * additional optimizations in place.
13 *
14 * The library is free for all purposes without any express
15 * guarantee it works.
16 *
17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
18 */
19
20 /* Extended euclidean algorithm of (a, b) produces
21 a*u1 + b*u2 = u3
22 */
mp_exteuclid(mp_int * a,mp_int * b,mp_int * U1,mp_int * U2,mp_int * U3)23 int mp_exteuclid(mp_int *a, mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3)
24 {
25 mp_int u1,u2,u3,v1,v2,v3,t1,t2,t3,q,tmp;
26 int err;
27
28 if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) {
29 return err;
30 }
31
32 /* initialize, (u1,u2,u3) = (1,0,a) */
33 mp_set(&u1, 1);
34 if ((err = mp_copy(a, &u3)) != MP_OKAY) { goto _ERR; }
35
36 /* initialize, (v1,v2,v3) = (0,1,b) */
37 mp_set(&v2, 1);
38 if ((err = mp_copy(b, &v3)) != MP_OKAY) { goto _ERR; }
39
40 /* loop while v3 != 0 */
41 while (mp_iszero(&v3) == MP_NO) {
42 /* q = u3/v3 */
43 if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY) { goto _ERR; }
44
45 /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */
46 if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY) { goto _ERR; }
47 if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY) { goto _ERR; }
48 if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY) { goto _ERR; }
49 if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY) { goto _ERR; }
50 if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY) { goto _ERR; }
51 if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY) { goto _ERR; }
52
53 /* (u1,u2,u3) = (v1,v2,v3) */
54 if ((err = mp_copy(&v1, &u1)) != MP_OKAY) { goto _ERR; }
55 if ((err = mp_copy(&v2, &u2)) != MP_OKAY) { goto _ERR; }
56 if ((err = mp_copy(&v3, &u3)) != MP_OKAY) { goto _ERR; }
57
58 /* (v1,v2,v3) = (t1,t2,t3) */
59 if ((err = mp_copy(&t1, &v1)) != MP_OKAY) { goto _ERR; }
60 if ((err = mp_copy(&t2, &v2)) != MP_OKAY) { goto _ERR; }
61 if ((err = mp_copy(&t3, &v3)) != MP_OKAY) { goto _ERR; }
62 }
63
64 /* make sure U3 >= 0 */
65 if (u3.sign == MP_NEG) {
66 mp_neg(&u1, &u1);
67 mp_neg(&u2, &u2);
68 mp_neg(&u3, &u3);
69 }
70
71 /* copy result out */
72 if (U1 != NULL) { mp_exch(U1, &u1); }
73 if (U2 != NULL) { mp_exch(U2, &u2); }
74 if (U3 != NULL) { mp_exch(U3, &u3); }
75
76 err = MP_OKAY;
77 _ERR: mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL);
78 return err;
79 }
80 #endif
81
82 /* Source: /cvs/libtom/libtommath/bn_mp_exteuclid.c,v */
83 /* Revision: 1.4 */
84 /* Date: 2006/12/28 01:25:13 */
85