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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: grand.c,v 1.2 2000/12/06 20:31:06 mdw Exp $ |
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4 | * |
5 | * Generic interface to random number generators |
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: grand.c,v $ |
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33 | * Revision 1.2 2000/12/06 20:31:06 mdw |
34 | * Simplify uniform range transformation. |
35 | * |
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36 | * Revision 1.1 1999/12/10 23:16:01 mdw |
37 | * Generic interface. |
38 | * |
39 | */ |
40 | |
41 | /*----- Header files ------------------------------------------------------*/ |
42 | |
43 | #include <stddef.h> |
44 | |
45 | #include <mLib/bits.h> |
46 | |
47 | #include "grand.h" |
48 | |
49 | /*----- Main code ---------------------------------------------------------*/ |
50 | |
51 | /* --- @grand_byte@ --- * |
52 | * |
53 | * Arguments: @grand *r@ = pointet to generic generator |
54 | * |
55 | * Returns: A uniformly-distributed pseudorandom integer in the interval |
56 | * %$[0, 256)$%. |
57 | */ |
58 | |
59 | octet grand_byte(grand *r) |
60 | { |
61 | if (r->ops->byte != grand_byte) |
62 | return (r->ops->byte(r)); |
63 | else if (r->ops->word != grand_word) |
64 | return (r->ops->word(r) & 0xff); |
65 | else if (r->ops->fill != grand_fill) { |
66 | octet o; |
67 | r->ops->fill(r, &o, 1); |
68 | return (o); |
69 | } else |
70 | return (grand_range(r, 256)); |
71 | } |
72 | |
73 | /* --- @grand_word@ --- * |
74 | * |
75 | * Arguments: @grand *r@ = pointet to generic generator |
76 | * |
77 | * Returns: A uniformly-distributed pseudorandom integer in the interval |
78 | * %$[0, 2^{32})$%. |
79 | */ |
80 | |
81 | uint32 grand_word(grand *r) |
82 | { |
83 | if (r->ops->word != grand_word) |
84 | return (r->ops->word(r)); |
85 | else { |
86 | octet b[4]; |
87 | grand_fill(r, b, sizeof(b)); |
88 | return (LOAD32(b)); |
89 | } |
90 | } |
91 | |
92 | /* --- @grand_range@ --- * |
93 | * |
94 | * Arguments: @grand *r@ = pointet to generic generator |
95 | * @uint32 l@ = limit for acceptable results |
96 | * |
97 | * Returns: A uniformly-distributed pseudorandom integer in the interval |
98 | * %$[0, l)$%. |
99 | */ |
100 | |
101 | uint32 grand_range(grand *r, uint32 l) |
102 | { |
103 | if (r->ops->range != grand_range) |
104 | return (r->ops->range(r, l)); |
105 | else { |
106 | uint32 m, z; |
107 | uint32 (*w)(grand */*r*/); |
108 | uint32 x; |
109 | |
110 | /* --- Decide where to get data from --- * |
111 | * |
112 | * The choice of %$2^{32} - 1$% as a limit when using @grand_word@ isn't |
113 | * wonderful, but working with %$2^{32}$% is awkward and the loss of a |
114 | * few return values isn't significant. The algorithm below still |
115 | * successfully returns uniformly distributed results. |
116 | */ |
117 | |
118 | if (r->ops->max) { |
119 | w = r->ops->raw; |
120 | m = r->ops->max; |
121 | } else { |
122 | w = grand_word; |
123 | m = 0xffffffff; |
124 | } |
125 | |
126 | /* --- Work out maximum acceptable return value --- * |
127 | * |
128 | * This will be the highest multiple of @l@ less than @m@. |
129 | */ |
130 | |
131 | z = m - (m % l); |
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132 | |
133 | /* --- Generate numbers until something acceptable is found --- * |
134 | * |
135 | * This will require an expected number of attempts less than 2. |
136 | */ |
137 | |
138 | do x = w(r); while (x >= z); |
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139 | return (x % l); |
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140 | } |
141 | } |
142 | |
143 | /* --- @grand_fill@ --- * |
144 | * |
145 | * Arguments: @grand *r@ = pointet to generic generator |
146 | * @void *p@ = pointer to a buffer |
147 | * @size_t sz@ = size of the buffer |
148 | * |
149 | * Returns: --- |
150 | * |
151 | * Use: Fills a buffer with uniformly distributed pseudorandom bytes |
152 | * (see @grand_byte@). |
153 | */ |
154 | |
155 | void grand_fill(grand *r, void *p, size_t sz) |
156 | { |
157 | if (r->ops->fill != grand_fill) |
158 | r->ops->fill(r, p, sz); |
159 | else { |
160 | octet *q = p; |
161 | while (sz) { |
162 | *q++ = r->ops->byte(r); |
163 | sz--; |
164 | } |
165 | } |
166 | } |
167 | |
168 | /*----- That's all, folks -------------------------------------------------*/ |