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 */ 23int 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