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1 | /* -*-c-*- |
2 | * |
3 | * $Id: group-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $ |
4 | * |
5 | * Exponentiation for abstract groups |
6 | * |
7 | * (c) 2004 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: group-exp.c,v $ |
33 | * Revision 1.1 2004/04/01 12:50:09 mdw |
34 | * Add cyclic group abstraction, with test code. Separate off exponentation |
35 | * functions for better static linking. Fix a buttload of bugs on the way. |
36 | * Generally ensure that negative exponents do inversion correctly. Add |
37 | * table of standard prime-field subgroups. (Binary field subgroups are |
38 | * currently unimplemented but easy to add if anyone ever finds a good one.) |
39 | * |
40 | */ |
41 | |
42 | /*----- Header files ------------------------------------------------------*/ |
43 | |
44 | #include "group.h" |
45 | #include "group-exp.h" |
46 | |
47 | /*----- Main code ---------------------------------------------------------*/ |
48 | |
49 | /* --- @group_stdexp@ --- * |
50 | * |
51 | * Arguments: @group *g@ = abstract group |
52 | * @ge *d@ = destination pointer |
53 | * @ge *x@ = base element |
54 | * @mp *n@ = exponent |
55 | * |
56 | * Returns: --- |
57 | * |
58 | * Use: Computes %$d = x^n$% efficiently. |
59 | */ |
60 | |
61 | void group_stdexp(group *gg, ge *d, ge *x, mp *n) |
62 | { |
63 | ge *t = G_CREATE(gg); |
64 | |
65 | G_COPY(gg, t, x); |
66 | MP_SHRINK(n); |
67 | G_COPY(gg, d, gg->i); |
68 | if (n->f & MP_BURN) |
69 | G_BURN(gg, t); |
70 | if (MP_LEN(n) == 0) |
71 | ; |
72 | else { |
73 | if (n->f & MP_NEG) |
74 | G_INV(gg, t, t); |
75 | if (MP_LEN(n) < EXP_THRESH) |
76 | EXP_SIMPLE(d, t, n); |
77 | else |
78 | EXP_WINDOW(d, t, n); |
79 | } |
80 | G_DESTROY(gg, t); |
81 | } |
82 | |
83 | /* --- @group_stdmexp@ --- * |
84 | * |
85 | * Arguments: @group *g@ = abstract group |
86 | * @ge *d@ = destination pointer |
87 | * @const group_expfactor *f@ = vector of factors |
88 | * @size_t n@ = number of factors |
89 | * |
90 | * Returns: --- |
91 | * |
92 | * Use: Computes %$d = g_0^{x_0} g_1^{x_1} \ldots$% efficiently. |
93 | */ |
94 | |
95 | #undef EXP_WINSZ |
96 | #define EXP_WINSZ 3 |
97 | |
98 | void group_stdmexp(group *gg, ge *d, const group_expfactor *f, size_t n) |
99 | { |
100 | group_expfactor *ff = xmalloc(n * sizeof(group_expfactor)); |
101 | size_t i; |
102 | |
103 | for (i = 0; i < n; i++) { |
104 | ff[i].base = G_CREATE(gg); |
105 | MP_SHRINK(f[i].exp); |
106 | if (f[i].exp->f & MP_NEG) |
107 | G_INV(gg, ff[i].base, f[i].base); |
108 | else |
109 | G_COPY(gg, ff[i].base, f[i].base); |
110 | if (f[i].exp->f & MP_BURN) |
111 | G_BURN(gg, ff[i].base); |
112 | ff[i].exp = f[i].exp; |
113 | } |
114 | G_COPY(gg, d, gg->i); |
115 | EXP_SIMUL(d, ff, n); |
116 | for (i = 0; i < n; i++) |
117 | G_DESTROY(gg, ff[i].base); |
118 | xfree(ff); |
119 | } |
120 | |
121 | /*----- That's all, folks -------------------------------------------------*/ |