| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: pgen-gcd.c,v 1.3 2004/04/08 01:36:15 mdw Exp $ |
| 4 | * |
| 5 | * Prime search stepper ensuring a low GCD for %$(p - 1)/2$% |
| 6 | * |
| 7 | * (c) 2000 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 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. |
| 18 | * |
| 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. |
| 23 | * |
| 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 | |
| 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 | * |
| 46 | * Call things off if @p@ and @jp@ have common factors, or if @q@, @r@ |
| 47 | * and @jq@ have common factors greater than @max@. |
| 48 | */ |
| 49 | |
| 50 | case PGEN_BEGIN: { |
| 51 | mp *p = ev->m; |
| 52 | mp_gcd(&g->g, 0, 0, p, g->jp.m); |
| 53 | if (MP_CMP(g->g, >, MP_ONE)) |
| 54 | return (PGEN_ABORT); |
| 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); |
| 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); |
| 62 | return (PGEN_ABORT); |
| 63 | } |
| 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 -------------------------------------------------*/ |