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, tomstdenis (at) gmail.com, http://math.libtomcrypt.com 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 79 80 /* $Source: /cvs/libtom/libtommath/bn_mp_exteuclid.c,v $ */ 81 /* $Revision: 1.3 $ */ 82 /* $Date: 2006/03/31 14:18:44 $ */ 83
