21a7c4b1 |
1 | /* -*-c-*- |
2 | * |
3 | * $Id: mpbarrett.h,v 1.1 1999/12/10 23:22:00 mdw Exp $ |
4 | * |
5 | * Barrett modular reduction |
6 | * |
7 | * (c) 1999 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: mpbarrett.h,v $ |
33 | * Revision 1.1 1999/12/10 23:22:00 mdw |
34 | * Barrett reduction support: works with even moduli. |
35 | * |
36 | */ |
37 | |
38 | /*----- Notes on Barrett reduction ----------------------------------------* |
39 | * |
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. |
44 | * |
45 | * It's useful for slightly less heavy-duty work than Montgomery reduction |
46 | * because the precomputation phase is rather simpler, involving a single |
47 | * division operation. |
48 | * |
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. |
53 | */ |
54 | |
55 | #ifndef CATACOMB_MPBARRETT_H |
56 | #define CATACOMB_MPBARRETT_H |
57 | |
58 | #ifdef __cplusplus |
59 | extern "C" { |
60 | #endif |
61 | |
62 | /*----- Header files ------------------------------------------------------*/ |
63 | |
64 | #ifndef CATACOMB_MP_H |
65 | # include "mp.h" |
66 | #endif |
67 | |
68 | /*----- Data structures ---------------------------------------------------*/ |
69 | |
70 | typedef struct mpbarrett { |
71 | mp *m; |
72 | mp *mu; |
73 | size_t k; |
74 | } mpbarrett; |
75 | |
76 | /*----- Functions provided ------------------------------------------------*/ |
77 | |
78 | /* --- @mpbarrett_create@ --- * |
79 | * |
80 | * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context |
81 | * @mp *m@ = modulus to work to |
82 | * |
83 | * |
84 | * Returns: --- |
85 | * |
86 | * Use: Initializes a Barrett reduction context ready for use. |
87 | */ |
88 | |
89 | extern void mpbarrett_create(mpbarrett */*mb*/, mp */*m*/); |
90 | |
91 | /* --- @mpbarrett_destroy@ --- * |
92 | * |
93 | * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context |
94 | * |
95 | * Returns: --- |
96 | * |
97 | * Use: Destroys a Barrett reduction context releasing any resources |
98 | * claimed. |
99 | */ |
100 | |
101 | extern void mpbarrett_destroy(mpbarrett */*mb*/); |
102 | |
103 | /* --- @mpbarrett_reduce@ --- * |
104 | * |
105 | * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context |
106 | * @mp *d@ = destination for result |
107 | * @mp *m@ = number to reduce |
108 | * |
109 | * Returns: The residue of @m@ modulo the number in the reduction |
110 | * context. |
111 | * |
112 | * Use: Performs an efficient modular reduction. The argument is |
113 | * assumed to be positive. |
114 | */ |
115 | |
116 | extern mp *mpbarrett_reduce(mpbarrett */*mb*/, mp */*d*/, mp */*m*/); |
117 | |
118 | /* --- @mpbarrett_exp@ --- * |
119 | * |
120 | * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context |
121 | * @mp *d@ = fake destination |
122 | * @mp *a@ = base |
123 | * @mp *e@ = exponent |
124 | * |
125 | * Returns: Result, %$a^e \bmod m$%. |
126 | */ |
127 | |
128 | extern mp *mpbarrett_exp(mpbarrett */*mb*/, mp */*d*/, mp */*a*/, mp */*e*/); |
129 | |
130 | /*----- That's all, folks -------------------------------------------------*/ |
131 | |
132 | #ifdef __cplusplus |
133 | } |
134 | #endif |
135 | |
136 | #endif |