[u/mdw/catacomb] / pgen-gcd.c

/* -*-c-*-
 *
 * $Id: pgen-gcd.c,v 1.3 2004/04/08 01:36:15 mdw Exp $
 *
 * Prime search stepper ensuring a low GCD for %$(p - 1)/2$%
 *
 * (c) 2000 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include "mp.h"
#include "pgen.h"

/*----- Main code ---------------------------------------------------------*/

int pgen_gcdstep(int rq, pgen_event *ev, void *p)
{
  pgen_gcdstepctx *g = p;
  int rc = PGEN_ABORT;

  switch (rq) {

    /* --- Set everything up --- *
     *
     * Call things off if @p@ and @jp@ have common factors, or if @q@, @r@
     * and @jq@ have common factors greater than @max@.
     */

    case PGEN_BEGIN: {
      mp *p = ev->m;
      mp_gcd(&g->g, 0, 0, p, g->jp.m);
      if (MP_CMP(g->g, >, MP_ONE))
	return (PGEN_ABORT);
      g->q = mp_lsr(MP_NEW, p, 1);
      g->jq = mp_lsr(MP_NEW, g->jp.m, 1);
      mp_gcd(&g->g, 0, 0, g->q, g->jq);
      mp_gcd(&g->g, 0, 0, g->g, g->r);
      if (MP_CMP(g->g, >, g->max)) {
	mp_drop(g->q);
	mp_drop(g->jq);
	return (PGEN_ABORT);
      }
      rc = pfilt_create(&g->p, p);
      mp_drop(p);
    } break;

    /* --- Grind through another iteration --- */

    case PGEN_TRY:
      mp_drop(ev->m);
      rc = pfilt_jump(&g->p, &g->jp);
      g->q = mp_add(g->q, g->q, g->jq);
      break;

    /* --- Finished --- */

    case PGEN_DONE:
      pfilt_destroy(&g->p);
      mp_drop(g->q);
      mp_drop(g->jq);
      return (PGEN_DONE);
  }

  /* --- Step on until everything is OK --- */

  for (;;) {
    if (rc != PGEN_FAIL) {
      mp_gcd(&g->g, 0, 0, g->r, g->q);
      if (MP_CMP(g->g, >, g->max))
	rc = PGEN_FAIL;
    }
    if (rc != PGEN_FAIL)
      break;
    rc = pfilt_jump(&g->p, &g->jp);
    g->q = mp_add(g->q, g->q, g->jq);
  }

  ev->m = MP_COPY(g->p.m);
  return (rc);
}

/*----- That's all, folks -------------------------------------------------*/
Commit	Line	Data
423c89a3	1	/* --c--
423c89a3	2	*
b817bfc6	3	* $Id: pgen-gcd.c,v 1.3 2004/04/08 01:36:15 mdw Exp $
423c89a3	4	*
	5	* Prime search stepper ensuring a low GCD for %$(p - 1)/2$%
	6	*
	7	* (c) 2000 Straylight/Edgeware
	8	*/
	9
45c0fd36	10	/----- Licensing notice --------------------------------------------------
423c89a3	11	*
	12	* This file is part of Catacomb.
	13	*
	14	* Catacomb is free software; you can redistribute it and/or modify
	15	* it under the terms of the GNU Library General Public License as
	16	* published by the Free Software Foundation; either version 2 of the
	17	* License, or (at your option) any later version.
45c0fd36	18	*
423c89a3	19	* Catacomb is distributed in the hope that it will be useful,
	20	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	21	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	22	* GNU Library General Public License for more details.
45c0fd36	23	*
423c89a3	24	* You should have received a copy of the GNU Library General Public
	25	* License along with Catacomb; if not, write to the Free
	26	* Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
	27	* MA 02111-1307, USA.
	28	*/
	29
423c89a3	30	/----- Header files ------------------------------------------------------/
	31
	32	#include "mp.h"
	33	#include "pgen.h"
	34
	35	/----- Main code ---------------------------------------------------------/
	36
	37	int pgen_gcdstep(int rq, pgen_event ev, void p)
	38	{
	39	pgen_gcdstepctx *g = p;
	40	int rc = PGEN_ABORT;
	41
	42	switch (rq) {
	43
	44	/* --- Set everything up --- *
	45	*
8615bf7e	46	* Call things off if @p@ and @jp@ have common factors, or if @q@, @r@
8615bf7e	47	* and @jq@ have common factors greater than @max@.
423c89a3	48	*/
	49
	50	case PGEN_BEGIN: {
	51	mp *p = ev->m;
8615bf7e	52	mp_gcd(&g->g, 0, 0, p, g->jp.m);
	53	if (MP_CMP(g->g, >, MP_ONE))
	54	return (PGEN_ABORT);
423c89a3	55	g->q = mp_lsr(MP_NEW, p, 1);
	56	g->jq = mp_lsr(MP_NEW, g->jp.m, 1);
	57	mp_gcd(&g->g, 0, 0, g->q, g->jq);
8615bf7e	58	mp_gcd(&g->g, 0, 0, g->g, g->r);
	59	if (MP_CMP(g->g, >, g->max)) {
	60	mp_drop(g->q);
	61	mp_drop(g->jq);
423c89a3	62	return (PGEN_ABORT);
8615bf7e	63	}
423c89a3	64	rc = pfilt_create(&g->p, p);
	65	mp_drop(p);
	66	} break;
	67
	68	/* --- Grind through another iteration --- */
	69
	70	case PGEN_TRY:
	71	mp_drop(ev->m);
	72	rc = pfilt_jump(&g->p, &g->jp);
	73	g->q = mp_add(g->q, g->q, g->jq);
	74	break;
	75
	76	/* --- Finished --- */
	77
	78	case PGEN_DONE:
	79	pfilt_destroy(&g->p);
	80	mp_drop(g->q);
	81	mp_drop(g->jq);
	82	return (PGEN_DONE);
	83	}
	84
	85	/* --- Step on until everything is OK --- */
	86
	87	for (;;) {
	88	if (rc != PGEN_FAIL) {
	89	mp_gcd(&g->g, 0, 0, g->r, g->q);
	90	if (MP_CMP(g->g, >, g->max))
	91	rc = PGEN_FAIL;
	92	}
	93	if (rc != PGEN_FAIL)
	94	break;
	95	rc = pfilt_jump(&g->p, &g->jp);
	96	g->q = mp_add(g->q, g->q, g->jq);
	97	}
	98
	99	ev->m = MP_COPY(g->p.m);
	100	return (rc);
	101	}
	102
	103	/----- That's all, folks -------------------------------------------------/