3 * Prime search stepper ensuring a low GCD for %$(p - 1)/2$%
5 * (c) 2000 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
12 * Catacomb is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as
14 * published by the Free Software Foundation; either version 2 of the
15 * License, or (at your option) any later version.
17 * Catacomb is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
22 * You should have received a copy of the GNU Library General Public
23 * License along with Catacomb; if not, write to the Free
24 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 /*----- Header files ------------------------------------------------------*/
33 /*----- Main code ---------------------------------------------------------*/
35 int pgen_gcdstep(int rq, pgen_event *ev, void *p)
37 pgen_gcdstepctx *g = p;
42 /* --- Set everything up --- *
44 * Call things off if @p@ and @jp@ have common factors, or if @q@, @r@
45 * and @jq@ have common factors greater than @max@.
50 mp_gcd(&g->g, 0, 0, p, g->jp.m);
51 if (MP_CMP(g->g, >, MP_ONE))
53 g->q = mp_lsr(MP_NEW, p, 1);
54 g->jq = mp_lsr(MP_NEW, g->jp.m, 1);
55 mp_gcd(&g->g, 0, 0, g->q, g->jq);
56 mp_gcd(&g->g, 0, 0, g->g, g->r);
57 if (MP_CMP(g->g, >, g->max)) {
62 rc = pfilt_create(&g->p, p);
66 /* --- Grind through another iteration --- */
70 rc = pfilt_jump(&g->p, &g->jp);
71 g->q = mp_add(g->q, g->q, g->jq);
74 /* --- Finished --- */
83 /* --- Step on until everything is OK --- */
86 if (rc != PGEN_FAIL) {
87 mp_gcd(&g->g, 0, 0, g->r, g->q);
88 if (MP_CMP(g->g, >, g->max))
93 rc = pfilt_jump(&g->p, &g->jp);
94 g->q = mp_add(g->q, g->q, g->jq);
97 ev->m = MP_COPY(g->p.m);
101 /*----- That's all, folks -------------------------------------------------*/