98 lines
1.7 KiB
C
98 lines
1.7 KiB
C
/*
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* Copyright (c) 1980 Regents of the University of California.
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* All rights reserved. The Berkeley software License Agreement
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* specifies the terms and conditions for redistribution.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)gcd.c 1.1 94/10/31 SMI"; /* from UCB 5.2 3/13/18 */
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#endif
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/* LINTLIBRARY */
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#include <mp.h>
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gcd(a,b,c)
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MINT *a,*b,*c;
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{
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MINT x,y,z,w;
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x.len = y.len = z.len = w.len = 0;
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_mp_move(a,&x);
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_mp_move(b,&y);
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while (y.len != 0) {
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mdiv(&x,&y,&w,&z);
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_mp_move(&y,&x);
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_mp_move(&z,&y);
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}
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_mp_move(&x,c);
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xfree(&x);
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xfree(&y);
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xfree(&z);
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xfree(&w);
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}
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invert(x1, x0, c)
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MINT *x1;
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MINT *x0;
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MINT *c;
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{
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MINT u2, u3;
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MINT v2, v3;
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MINT zero;
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MINT q, r;
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MINT t;
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MINT x0_prime;
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static MINT *one = (MINT *)0;
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/*
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* Minimize calls to allocators. Don't use pointers for local
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* variables, for the one "initialized" multiple precision
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* variable, do it just once.
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*/
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if (one == (MINT *)0)
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one = itom((short)1);
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zero.len = q.len = r.len = t.len = 0;
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x0_prime.len = u2.len = u3.len = 0;
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_mp_move(x0, &u3);
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_mp_move(x0, &x0_prime);
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v2.len = v3.len = 0;
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_mp_move(one, &v2);
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_mp_move(x1, &v3);
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while (mcmp(&v3,&zero) != 0) {
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/* invariant: x0*u1 + x1*u2 = u3 */
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/* invariant: x0*v1 + x2*v2 = v3 */
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/* invariant: x(n+1) = x(n-1) % x(n) */
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mdiv(&u3,&v3,&q,&r);
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_mp_move(&v3,&u3);
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_mp_move(&r,&v3);
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mult(&q,&v2,&t);
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msub(&u2,&t,&t);
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_mp_move(&v2,&u2);
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_mp_move(&t,&v2);
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}
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/* now x0*u1 + x1*u2 == 1, therefore, (u2*x1) % x0 == 1 */
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_mp_move(&u2,c);
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if (mcmp(c,&zero) < 0) {
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madd(&x0_prime, c, c);
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}
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xfree(&zero);
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xfree(&v2);
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xfree(&v3);
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xfree(&u2);
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xfree(&u3);
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xfree(&q);
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xfree(&r);
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xfree(&t);
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}
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