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1 | /* -*-c-*- |
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2 | * |
3 | * Prime search stepper ensuring a low GCD for %$(p - 1)/2$% |
4 | * |
5 | * (c) 2000 Straylight/Edgeware |
6 | */ |
7 | |
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8 | /*----- Licensing notice --------------------------------------------------* |
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9 | * |
10 | * This file is part of Catacomb. |
11 | * |
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. |
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16 | * |
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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. |
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21 | * |
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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, |
25 | * MA 02111-1307, USA. |
26 | */ |
27 | |
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28 | /*----- Header files ------------------------------------------------------*/ |
29 | |
30 | #include "mp.h" |
31 | #include "pgen.h" |
32 | |
33 | /*----- Main code ---------------------------------------------------------*/ |
34 | |
35 | int pgen_gcdstep(int rq, pgen_event *ev, void *p) |
36 | { |
37 | pgen_gcdstepctx *g = p; |
38 | int rc = PGEN_ABORT; |
39 | |
40 | switch (rq) { |
41 | |
42 | /* --- Set everything up --- * |
43 | * |
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44 | * Call things off if @p@ and @jp@ have common factors, or if @q@, @r@ |
45 | * and @jq@ have common factors greater than @max@. |
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46 | */ |
47 | |
48 | case PGEN_BEGIN: { |
49 | mp *p = ev->m; |
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50 | mp_gcd(&g->g, 0, 0, p, g->jp.m); |
51 | if (MP_CMP(g->g, >, MP_ONE)) |
52 | return (PGEN_ABORT); |
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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); |
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56 | mp_gcd(&g->g, 0, 0, g->g, g->r); |
57 | if (MP_CMP(g->g, >, g->max)) { |
58 | mp_drop(g->q); |
59 | mp_drop(g->jq); |
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60 | return (PGEN_ABORT); |
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61 | } |
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62 | rc = pfilt_create(&g->p, p); |
63 | mp_drop(p); |
64 | } break; |
65 | |
66 | /* --- Grind through another iteration --- */ |
67 | |
68 | case PGEN_TRY: |
69 | mp_drop(ev->m); |
70 | rc = pfilt_jump(&g->p, &g->jp); |
71 | g->q = mp_add(g->q, g->q, g->jq); |
72 | break; |
73 | |
74 | /* --- Finished --- */ |
75 | |
76 | case PGEN_DONE: |
77 | pfilt_destroy(&g->p); |
78 | mp_drop(g->q); |
79 | mp_drop(g->jq); |
80 | return (PGEN_DONE); |
81 | } |
82 | |
83 | /* --- Step on until everything is OK --- */ |
84 | |
85 | for (;;) { |
86 | if (rc != PGEN_FAIL) { |
87 | mp_gcd(&g->g, 0, 0, g->r, g->q); |
88 | if (MP_CMP(g->g, >, g->max)) |
89 | rc = PGEN_FAIL; |
90 | } |
91 | if (rc != PGEN_FAIL) |
92 | break; |
93 | rc = pfilt_jump(&g->p, &g->jp); |
94 | g->q = mp_add(g->q, g->q, g->jq); |
95 | } |
96 | |
97 | ev->m = MP_COPY(g->p.m); |
98 | return (rc); |
99 | } |
100 | |
101 | /*----- That's all, folks -------------------------------------------------*/ |