3 * $Id: mpbarrett.h,v 1.1 1999/12/10 23:22:00 mdw Exp $
5 * Barrett modular reduction
7 * (c) 1999 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: mpbarrett.h,v $
33 * Revision 1.1 1999/12/10 23:22:00 mdw
34 * Barrett reduction support: works with even moduli.
38 /*----- Notes on Barrett reduction ----------------------------------------*
40 * Barrett reduction is a technique for computing modular residues. Unlike
41 * Montgomery reduction, it doesn't have restrictions on the modulus (except
42 * that it be positive) and doesn't confuse matters by putting an extra
43 * factor all the way through your computation.
45 * It's useful for slightly less heavy-duty work than Montgomery reduction
46 * because the precomputation phase is rather simpler, involving a single
49 * Sometimes it's useful to exponentiate modulo an even number, so there's a
50 * modexp routine provided which uses Barrett reduction rather than
51 * Montgomery reduction. This is handy when you're working on indices in an
52 * even-order cyclic group or something.
55 #ifndef CATACOMB_MPBARRETT_H
56 #define CATACOMB_MPBARRETT_H
62 /*----- Header files ------------------------------------------------------*/
68 /*----- Data structures ---------------------------------------------------*/
70 typedef struct mpbarrett
{
76 /*----- Functions provided ------------------------------------------------*/
78 /* --- @mpbarrett_create@ --- *
80 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
81 * @mp *m@ = modulus to work to
86 * Use: Initializes a Barrett reduction context ready for use.
89 extern void mpbarrett_create(mpbarrett */
*mb*/
, mp */
*m*/
);
91 /* --- @mpbarrett_destroy@ --- *
93 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
97 * Use: Destroys a Barrett reduction context releasing any resources
101 extern void mpbarrett_destroy(mpbarrett */
*mb*/
);
103 /* --- @mpbarrett_reduce@ --- *
105 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
106 * @mp *d@ = destination for result
107 * @mp *m@ = number to reduce
109 * Returns: The residue of @m@ modulo the number in the reduction
112 * Use: Performs an efficient modular reduction. The argument is
113 * assumed to be positive.
116 extern mp
*mpbarrett_reduce(mpbarrett */
*mb*/
, mp */
*d*/
, mp */
*m*/
);
118 /* --- @mpbarrett_exp@ --- *
120 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
121 * @mp *d@ = fake destination
125 * Returns: Result, %$a^e \bmod m$%.
128 extern mp
*mpbarrett_exp(mpbarrett */
*mb*/
, mp */
*d*/
, mp */
*a*/
, mp */
*e*/
);
130 /*----- That's all, folks -------------------------------------------------*/