void
mp_invert(MINT *x1, MINT *x0, MINT *c)
{
MINT u2, u3;
MINT v2, v3;
MINT zero;
MINT q, r;
MINT t;
MINT x0_prime;
static MINT *one = NULL;
/*
* Minimize calls to allocators. Don't use pointers for local
* variables, for the one "initialized" multiple precision
* variable, do it just once.
*/
if (one == NULL)
one = mp_itom(1);
zero.len = q.len = r.len = t.len = 0;
x0_prime.len = u2.len = u3.len = 0;
_mp_move(x0, &u3);
_mp_move(x0, &x0_prime);
v2.len = v3.len = 0;
_mp_move(one, &v2);
_mp_move(x1, &v3);
while (mp_mcmp(&v3, &zero) != 0) {
/* invariant: x0*u1 + x1*u2 = u3 */
/* invariant: x0*v1 + x2*v2 = v3 */
/* invariant: x(n+1) = x(n-1) % x(n) */
mp_mdiv(&u3, &v3, &q, &r);
_mp_move(&v3, &u3);
_mp_move(&r, &v3);
mp_mult(&q, &v2, &t);
mp_msub(&u2, &t, &t);
_mp_move(&v2, &u2);
_mp_move(&t, &v2);
}
/* now x0*u1 + x1*u2 == 1, therefore, (u2*x1) % x0 == 1 */
_mp_move(&u2, c);
if (mp_mcmp(c, &zero) < 0) {
mp_madd(&x0_prime, c, c);
}
_mp_xfree(&zero);
_mp_xfree(&v2);
_mp_xfree(&v3);
_mp_xfree(&u2);
_mp_xfree(&u3);
_mp_xfree(&q);
_mp_xfree(&r);
_mp_xfree(&t);
}
static void
testmcmp(const MINT *mp1, const MINT *mp2, const char *tname)
{
if (mp_mcmp(mp1, mp2) == 0)
printf("ok %d - %s\n", ++tnr, tname);
else
printf("not ok - %d %s\n", ++tnr, tname);
}
int mcmp(MINT *a, MINT *b) { return (mp_mcmp(a, b)); }
