3 * $Id: group-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
5 * Exponentiation for abstract groups
7 * (c) 2004 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
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.)
42 /*----- Header files ------------------------------------------------------*/
45 #include "group-exp.h"
47 /*----- Main code ---------------------------------------------------------*/
49 /* --- @group_stdexp@ --- *
51 * Arguments: @group *g@ = abstract group
52 * @ge *d@ = destination pointer
53 * @ge *x@ = base element
58 * Use: Computes %$d = x^n$% efficiently.
61 void group_stdexp(group
*gg
, ge
*d
, ge
*x
, mp
*n
)
75 if (MP_LEN(n
) < EXP_THRESH
)
83 /* --- @group_stdmexp@ --- *
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
92 * Use: Computes %$d = g_0^{x_0} g_1^{x_1} \ldots$% efficiently.
98 void group_stdmexp(group
*gg
, ge
*d
, const group_expfactor
*f
, size_t n
)
100 group_expfactor
*ff
= xmalloc(n
* sizeof(group_expfactor
));
103 for (i
= 0; i
< n
; i
++) {
104 ff
[i
].base
= G_CREATE(gg
);
106 if (f
[i
].exp
->f
& MP_NEG
)
107 G_INV(gg
, ff
[i
].base
, f
[i
].base
);
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
;
114 G_COPY(gg
, d
, gg
->i
);
116 for (i
= 0; i
< n
; i
++)
117 G_DESTROY(gg
, ff
[i
].base
);
121 /*----- That's all, folks -------------------------------------------------*/