diff options
Diffstat (limited to 'libtommath/bn_mp_exteuclid.c')
| -rw-r--r-- | libtommath/bn_mp_exteuclid.c | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/libtommath/bn_mp_exteuclid.c b/libtommath/bn_mp_exteuclid.c new file mode 100644 index 0000000..9730fa0 --- /dev/null +++ b/libtommath/bn_mp_exteuclid.c @@ -0,0 +1,82 @@ +#include <tommath.h> +#ifdef BN_MP_EXTEUCLID_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis + * + * LibTomMath is a library that provides multiple-precision + * integer arithmetic as well as number theoretic functionality. + * + * The library was designed directly after the MPI library by + * Michael Fromberger but has been written from scratch with + * additional optimizations in place. + * + * The library is free for all purposes without any express + * guarantee it works. + * + * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com + */ + +/* Extended euclidean algorithm of (a, b) produces + a*u1 + b*u2 = u3 + */ +int mp_exteuclid(mp_int *a, mp_int *b, mp_int *U1, mp_int *U2, mp_int *U3) +{ + mp_int u1,u2,u3,v1,v2,v3,t1,t2,t3,q,tmp; + int err; + + if ((err = mp_init_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL)) != MP_OKAY) { + return err; + } + + /* initialize, (u1,u2,u3) = (1,0,a) */ + mp_set(&u1, 1); + if ((err = mp_copy(a, &u3)) != MP_OKAY) { goto _ERR; } + + /* initialize, (v1,v2,v3) = (0,1,b) */ + mp_set(&v2, 1); + if ((err = mp_copy(b, &v3)) != MP_OKAY) { goto _ERR; } + + /* loop while v3 != 0 */ + while (mp_iszero(&v3) == MP_NO) { + /* q = u3/v3 */ + if ((err = mp_div(&u3, &v3, &q, NULL)) != MP_OKAY) { goto _ERR; } + + /* (t1,t2,t3) = (u1,u2,u3) - (v1,v2,v3)q */ + if ((err = mp_mul(&v1, &q, &tmp)) != MP_OKAY) { goto _ERR; } + if ((err = mp_sub(&u1, &tmp, &t1)) != MP_OKAY) { goto _ERR; } + if ((err = mp_mul(&v2, &q, &tmp)) != MP_OKAY) { goto _ERR; } + if ((err = mp_sub(&u2, &tmp, &t2)) != MP_OKAY) { goto _ERR; } + if ((err = mp_mul(&v3, &q, &tmp)) != MP_OKAY) { goto _ERR; } + if ((err = mp_sub(&u3, &tmp, &t3)) != MP_OKAY) { goto _ERR; } + + /* (u1,u2,u3) = (v1,v2,v3) */ + if ((err = mp_copy(&v1, &u1)) != MP_OKAY) { goto _ERR; } + if ((err = mp_copy(&v2, &u2)) != MP_OKAY) { goto _ERR; } + if ((err = mp_copy(&v3, &u3)) != MP_OKAY) { goto _ERR; } + + /* (v1,v2,v3) = (t1,t2,t3) */ + if ((err = mp_copy(&t1, &v1)) != MP_OKAY) { goto _ERR; } + if ((err = mp_copy(&t2, &v2)) != MP_OKAY) { goto _ERR; } + if ((err = mp_copy(&t3, &v3)) != MP_OKAY) { goto _ERR; } + } + + /* make sure U3 >= 0 */ + if (u3.sign == MP_NEG) { + mp_neg(&u1, &u1); + mp_neg(&u2, &u2); + mp_neg(&u3, &u3); + } + + /* copy result out */ + if (U1 != NULL) { mp_exch(U1, &u1); } + if (U2 != NULL) { mp_exch(U2, &u2); } + if (U3 != NULL) { mp_exch(U3, &u3); } + + err = MP_OKAY; +_ERR: mp_clear_multi(&u1, &u2, &u3, &v1, &v2, &v3, &t1, &t2, &t3, &q, &tmp, NULL); + return err; +} +#endif + +/* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_exteuclid.c,v $ */ +/* $Revision: 1.1.1.4 $ */ +/* $Date: 2006/12/01 00:08:11 $ */ |