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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: pgen-gcd.c,v 1.2 2000/07/01 11:09:20 mdw Exp $ |
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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 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: pgen-gcd.c,v $ |
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33 | * Revision 1.2 2000/07/01 11:09:20 mdw |
34 | * (pgen_gcd): Bug fix -- check the GCDs of the right things when deciding |
35 | * whether to abort. |
36 | * |
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37 | * Revision 1.1 2000/06/17 11:51:53 mdw |
38 | * Filter which imposes additional restrictions on GCD of %$(p - 1)/2$% |
39 | * with a given integer. |
40 | * |
41 | */ |
42 | |
43 | /*----- Header files ------------------------------------------------------*/ |
44 | |
45 | #include "mp.h" |
46 | #include "pgen.h" |
47 | |
48 | /*----- Main code ---------------------------------------------------------*/ |
49 | |
50 | int pgen_gcdstep(int rq, pgen_event *ev, void *p) |
51 | { |
52 | pgen_gcdstepctx *g = p; |
53 | int rc = PGEN_ABORT; |
54 | |
55 | switch (rq) { |
56 | |
57 | /* --- Set everything up --- * |
58 | * |
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59 | * Call things off if @p@ and @jp@ have common factors, or if @q@, @r@ |
60 | * and @jq@ have common factors greater than @max@. |
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61 | */ |
62 | |
63 | case PGEN_BEGIN: { |
64 | mp *p = ev->m; |
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65 | mp_gcd(&g->g, 0, 0, p, g->jp.m); |
66 | if (MP_CMP(g->g, >, MP_ONE)) |
67 | return (PGEN_ABORT); |
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68 | g->q = mp_lsr(MP_NEW, p, 1); |
69 | g->jq = mp_lsr(MP_NEW, g->jp.m, 1); |
70 | mp_gcd(&g->g, 0, 0, g->q, g->jq); |
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71 | mp_gcd(&g->g, 0, 0, g->g, g->r); |
72 | if (MP_CMP(g->g, >, g->max)) { |
73 | mp_drop(g->q); |
74 | mp_drop(g->jq); |
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75 | return (PGEN_ABORT); |
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76 | } |
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77 | rc = pfilt_create(&g->p, p); |
78 | mp_drop(p); |
79 | } break; |
80 | |
81 | /* --- Grind through another iteration --- */ |
82 | |
83 | case PGEN_TRY: |
84 | mp_drop(ev->m); |
85 | rc = pfilt_jump(&g->p, &g->jp); |
86 | g->q = mp_add(g->q, g->q, g->jq); |
87 | break; |
88 | |
89 | /* --- Finished --- */ |
90 | |
91 | case PGEN_DONE: |
92 | pfilt_destroy(&g->p); |
93 | mp_drop(g->q); |
94 | mp_drop(g->jq); |
95 | return (PGEN_DONE); |
96 | } |
97 | |
98 | /* --- Step on until everything is OK --- */ |
99 | |
100 | for (;;) { |
101 | if (rc != PGEN_FAIL) { |
102 | mp_gcd(&g->g, 0, 0, g->r, g->q); |
103 | if (MP_CMP(g->g, >, g->max)) |
104 | rc = PGEN_FAIL; |
105 | } |
106 | if (rc != PGEN_FAIL) |
107 | break; |
108 | rc = pfilt_jump(&g->p, &g->jp); |
109 | g->q = mp_add(g->q, g->q, g->jq); |
110 | } |
111 | |
112 | ev->m = MP_COPY(g->p.m); |
113 | return (rc); |
114 | } |
115 | |
116 | /*----- That's all, folks -------------------------------------------------*/ |