3 * $Id: mpbarrett.h,v 1.2 2000/10/08 12:03:44 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 1.2 2000/10/08 12:03:44 mdw
34 * (mpbarrett_reduce): Cope with negative numbers.
36 * Revision 1.1 1999/12/10 23:22:00 mdw
37 * Barrett reduction support: works with even moduli.
41 /*----- Notes on Barrett reduction ----------------------------------------*
43 * Barrett reduction is a technique for computing modular residues. Unlike
44 * Montgomery reduction, it doesn't have restrictions on the modulus (except
45 * that it be positive) and doesn't confuse matters by putting an extra
46 * factor all the way through your computation.
48 * It's useful for slightly less heavy-duty work than Montgomery reduction
49 * because the precomputation phase is rather simpler, involving a single
52 * Sometimes it's useful to exponentiate modulo an even number, so there's a
53 * modexp routine provided which uses Barrett reduction rather than
54 * Montgomery reduction. This is handy when you're working on indices in an
55 * even-order cyclic group or something.
58 #ifndef CATACOMB_MPBARRETT_H
59 #define CATACOMB_MPBARRETT_H
65 /*----- Header files ------------------------------------------------------*/
71 /*----- Data structures ---------------------------------------------------*/
73 typedef struct mpbarrett
{
79 /*----- Functions provided ------------------------------------------------*/
81 /* --- @mpbarrett_create@ --- *
83 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
84 * @mp *m@ = modulus to work to
89 * Use: Initializes a Barrett reduction context ready for use.
92 extern void mpbarrett_create(mpbarrett */
*mb*/
, mp */
*m*/
);
94 /* --- @mpbarrett_destroy@ --- *
96 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
100 * Use: Destroys a Barrett reduction context releasing any resources
104 extern void mpbarrett_destroy(mpbarrett */
*mb*/
);
106 /* --- @mpbarrett_reduce@ --- *
108 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
109 * @mp *d@ = destination for result
110 * @mp *m@ = number to reduce
112 * Returns: The residue of @m@ modulo the number in the reduction
115 * Use: Performs an efficient modular reduction.
118 extern mp
*mpbarrett_reduce(mpbarrett */
*mb*/
, mp */
*d*/
, mp */
*m*/
);
120 /* --- @mpbarrett_exp@ --- *
122 * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context
123 * @mp *d@ = fake destination
127 * Returns: Result, %$a^e \bmod m$%.
130 extern mp
*mpbarrett_exp(mpbarrett */
*mb*/
, mp */
*d*/
, mp */
*a*/
, mp */
*e*/
);
132 /*----- That's all, folks -------------------------------------------------*/