/*
 * Copyright (c) 1980 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 */

#ifndef lint
static	char sccsid[] = "@(#)gcd.c 1.1 94/10/31 SMI"; /* from UCB 5.2 3/13/18 */
#endif

/* LINTLIBRARY */

#include <mp.h>

gcd(a,b,c) 
	MINT *a,*b,*c;
{	
	MINT x,y,z,w;

	x.len = y.len = z.len = w.len = 0;
	_mp_move(a,&x);
	_mp_move(b,&y);
	while (y.len != 0) {	
		mdiv(&x,&y,&w,&z);
		_mp_move(&y,&x);
		_mp_move(&z,&y);
	}
	_mp_move(&x,c);
	xfree(&x);
	xfree(&y);
	xfree(&z);
	xfree(&w);
}




invert(x1, x0, c)
	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 = (MINT *)0;

	/* 
	 * Minimize calls to allocators.  Don't use pointers for local
	 * variables, for the one "initialized" multiple precision 
	 * variable, do it just once.
	 */
	if (one == (MINT *)0)
		one = itom((short)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 (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) */
		mdiv(&u3,&v3,&q,&r);
		_mp_move(&v3,&u3);
		_mp_move(&r,&v3);

		mult(&q,&v2,&t);
		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 (mcmp(c,&zero) < 0) {
		madd(&x0_prime, c, c);
	}
	xfree(&zero);
	xfree(&v2);
	xfree(&v3);
	xfree(&u2);
	xfree(&u3);
	xfree(&q);
	xfree(&r);
	xfree(&t);
}


