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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: grand.c,v 1.3 2004/04/08 01:36:15 mdw Exp $ |
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4 | * |
5 | * Generic interface to random number generators |
6 | * |
7 | * (c) 1999 Straylight/Edgeware |
8 | */ |
9 | |
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10 | /*----- Licensing notice --------------------------------------------------* |
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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. |
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18 | * |
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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. |
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23 | * |
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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 | |
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30 | /*----- Header files ------------------------------------------------------*/ |
31 | |
32 | #include <stddef.h> |
33 | |
34 | #include <mLib/bits.h> |
35 | |
36 | #include "grand.h" |
37 | |
38 | /*----- Main code ---------------------------------------------------------*/ |
39 | |
40 | /* --- @grand_byte@ --- * |
41 | * |
42 | * Arguments: @grand *r@ = pointet to generic generator |
43 | * |
44 | * Returns: A uniformly-distributed pseudorandom integer in the interval |
45 | * %$[0, 256)$%. |
46 | */ |
47 | |
48 | octet grand_byte(grand *r) |
49 | { |
50 | if (r->ops->byte != grand_byte) |
51 | return (r->ops->byte(r)); |
52 | else if (r->ops->word != grand_word) |
53 | return (r->ops->word(r) & 0xff); |
54 | else if (r->ops->fill != grand_fill) { |
55 | octet o; |
56 | r->ops->fill(r, &o, 1); |
57 | return (o); |
58 | } else |
59 | return (grand_range(r, 256)); |
60 | } |
61 | |
62 | /* --- @grand_word@ --- * |
63 | * |
64 | * Arguments: @grand *r@ = pointet to generic generator |
65 | * |
66 | * Returns: A uniformly-distributed pseudorandom integer in the interval |
67 | * %$[0, 2^{32})$%. |
68 | */ |
69 | |
70 | uint32 grand_word(grand *r) |
71 | { |
72 | if (r->ops->word != grand_word) |
73 | return (r->ops->word(r)); |
74 | else { |
75 | octet b[4]; |
76 | grand_fill(r, b, sizeof(b)); |
77 | return (LOAD32(b)); |
78 | } |
79 | } |
80 | |
81 | /* --- @grand_range@ --- * |
82 | * |
83 | * Arguments: @grand *r@ = pointet to generic generator |
84 | * @uint32 l@ = limit for acceptable results |
85 | * |
86 | * Returns: A uniformly-distributed pseudorandom integer in the interval |
87 | * %$[0, l)$%. |
88 | */ |
89 | |
90 | uint32 grand_range(grand *r, uint32 l) |
91 | { |
92 | if (r->ops->range != grand_range) |
93 | return (r->ops->range(r, l)); |
94 | else { |
95 | uint32 m, z; |
96 | uint32 (*w)(grand */*r*/); |
97 | uint32 x; |
98 | |
99 | /* --- Decide where to get data from --- * |
100 | * |
101 | * The choice of %$2^{32} - 1$% as a limit when using @grand_word@ isn't |
102 | * wonderful, but working with %$2^{32}$% is awkward and the loss of a |
103 | * few return values isn't significant. The algorithm below still |
104 | * successfully returns uniformly distributed results. |
105 | */ |
106 | |
107 | if (r->ops->max) { |
108 | w = r->ops->raw; |
109 | m = r->ops->max; |
110 | } else { |
111 | w = grand_word; |
112 | m = 0xffffffff; |
113 | } |
114 | |
115 | /* --- Work out maximum acceptable return value --- * |
116 | * |
117 | * This will be the highest multiple of @l@ less than @m@. |
118 | */ |
119 | |
120 | z = m - (m % l); |
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121 | |
122 | /* --- Generate numbers until something acceptable is found --- * |
123 | * |
124 | * This will require an expected number of attempts less than 2. |
125 | */ |
126 | |
127 | do x = w(r); while (x >= z); |
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128 | return (x % l); |
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129 | } |
130 | } |
131 | |
132 | /* --- @grand_fill@ --- * |
133 | * |
134 | * Arguments: @grand *r@ = pointet to generic generator |
135 | * @void *p@ = pointer to a buffer |
136 | * @size_t sz@ = size of the buffer |
137 | * |
138 | * Returns: --- |
139 | * |
140 | * Use: Fills a buffer with uniformly distributed pseudorandom bytes |
141 | * (see @grand_byte@). |
142 | */ |
143 | |
144 | void grand_fill(grand *r, void *p, size_t sz) |
145 | { |
146 | if (r->ops->fill != grand_fill) |
147 | r->ops->fill(r, p, sz); |
148 | else { |
149 | octet *q = p; |
150 | while (sz) { |
151 | *q++ = r->ops->byte(r); |
152 | sz--; |
153 | } |
154 | } |
155 | } |
156 | |
157 | /*----- That's all, folks -------------------------------------------------*/ |