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1 | /* -*-c-*- |
2 | * | |
05dfc037 | 3 | * $Id$ |
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4 | * |
5 | * Simple linear congruential generator | |
6 | * | |
7 | * (c) 1999 Straylight/Edgeware | |
8 | * (c) 2000 Mark Wooding | |
9 | */ | |
10 | ||
11 | /*----- Licensing notice --------------------------------------------------* | |
12 | * | |
13 | * Copyright (c) 2000 Mark Wooding | |
14 | * All rights reserved. | |
15 | * | |
16 | * Redistribution and use in source and binary forms, with or without | |
17 | * modification, are permitted provided that the following conditions are | |
18 | * met: | |
19 | * | |
20 | * 1. Redistributions of source code must retain the above copyright | |
21 | * notice, this list of conditions and the following disclaimer. | |
22 | * | |
23 | * 2, Redistributions in binary form must reproduce the above copyright | |
24 | * notice, this list of conditions and the following disclaimer in the | |
25 | * documentation and/or other materials provided with the distribution. | |
26 | * | |
27 | * 3. The name of the authors may not be used to endorse or promote | |
28 | * products derived from this software without specific prior written | |
29 | * permission. | |
30 | * | |
31 | * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED | |
32 | * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF | |
33 | * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN | |
6b2d9d76 | 34 | * NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, |
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35 | * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES |
36 | * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR | |
37 | * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
38 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, | |
39 | * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN | |
40 | * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE | |
41 | * POSSIBILITY OF SUCH DAMAGE. | |
42 | * | |
43 | * Instead of accepting the above terms, you may redistribute and/or modify | |
44 | * this software under the terms of either the GNU General Public License, | |
45 | * or the GNU Library General Public License, published by the Free | |
46 | * Software Foundation; either version 2 of the License, or (at your | |
47 | * option) any later version. | |
48 | */ | |
49 | ||
50 | /*----- Revision history --------------------------------------------------* | |
51 | * | |
52 | * $Log: lcrand.c,v $ | |
6b2d9d76 MW |
53 | * Revision 1.2 2000/07/02 15:21:20 mdw |
54 | * Fix licence text. | |
55 | * | |
e6e0e332 MW |
56 | * Revision 1.1 2000/05/21 11:28:30 mdw |
57 | * Initial check-in. | |
58 | * | |
59 | * --- Past lives (Catacomb) --- * | |
60 | * | |
61 | * Revision 1.2 1999/12/13 15:34:01 mdw | |
62 | * Add support for seeding from a generic pseudorandom source. | |
63 | * | |
64 | * Revision 1.1 1999/12/10 23:15:27 mdw | |
65 | * Noncryptographic random number generator. | |
66 | * | |
67 | */ | |
68 | ||
69 | /*----- Header files ------------------------------------------------------*/ | |
70 | ||
71 | #include <stdio.h> | |
72 | #include <stdlib.h> | |
73 | #include <string.h> | |
74 | ||
75 | #include "bits.h" | |
76 | #include "lcrand.h" | |
77 | ||
78 | /*----- Magic numbers -----------------------------------------------------*/ | |
79 | ||
80 | /* --- The generator parameters --- */ | |
81 | ||
82 | #define P LCRAND_P /* Modulus */ | |
83 | #define A LCRAND_A /* Multiplier (primitive mod @p@) */ | |
84 | #define C LCRAND_C /* Additive constant */ | |
85 | ||
86 | /* --- Precomputed values for modular reduction --- */ | |
87 | ||
88 | #define D 5 /* %$p = 2^{32} - d$% */ | |
89 | ||
90 | /* --- Other useful bits --- */ | |
91 | ||
92 | #define P256 4294967040u /* Highest multiple of 256 < %$p$% */ | |
93 | ||
94 | /*----- Main code ---------------------------------------------------------*/ | |
95 | ||
96 | /* --- @lcrand@ --- * | |
97 | * | |
98 | * Arguments: @uint32 x@ = seed value | |
99 | * | |
100 | * Returns: New state of the generator. | |
101 | * | |
102 | * Use: Steps the generator. Returns %$ax + c \bmod p$%. | |
103 | */ | |
104 | ||
105 | uint32 lcrand(uint32 x) | |
106 | { | |
107 | uint32 a[2], xx[2]; | |
108 | uint32 yy[2]; | |
109 | ||
110 | /* --- Unpack things into the arrays --- */ | |
111 | ||
112 | a[0] = U16(A); a[1] = U16(A >> 16); | |
113 | xx[0] = U16(x); xx[1] = U16(x >> 16); | |
114 | ||
115 | /* --- Multiply everything together --- * | |
116 | * | |
117 | * This is plain old long multiplication, although it looks a bit strange. | |
118 | * I set up the top and bottom partial products directly where they're | |
119 | * supposed to be. The cross terms I add together, with the low 16 bits in | |
120 | * @q@ and the high 32 bits in @p@. These I then add into the product. | |
121 | */ | |
122 | ||
123 | { | |
124 | uint32 p, q; | |
125 | ||
126 | yy[0] = a[0] * xx[0]; | |
127 | yy[1] = a[1] * xx[1]; | |
128 | ||
129 | p = a[0] * xx[1]; | |
130 | q = p + a[1] * xx[0]; | |
131 | p = ((q < p) << 16) + (q >> 16); | |
132 | q = U16(q) << 16; | |
133 | ||
134 | q += yy[0]; | |
135 | if (q < yy[0]) | |
136 | p++; | |
137 | else | |
138 | p += (q >> 16) >> 16; | |
139 | yy[0] = q; | |
140 | ||
141 | yy[1] += p; | |
142 | } | |
143 | ||
144 | /* --- Now reduce mod p --- * | |
145 | * | |
146 | * I'm using shifts and adds to do the multiply step here. This needs to | |
147 | * be changed if @D@ ever becomes something other than 5. | |
148 | */ | |
149 | ||
150 | #if D != 5 | |
151 | # error "Change shift sequence!" | |
152 | #endif | |
153 | ||
154 | { | |
155 | uint32 q; | |
156 | ||
157 | q = yy[1]; | |
158 | x = yy[0]; | |
159 | ||
160 | while (q) { | |
161 | uint32 y, z; | |
162 | y = q >> 30; | |
163 | z = q << 2; | |
164 | z += q; | |
165 | if (z < q) | |
166 | y++; | |
167 | else | |
168 | y += (q >> 16) >> 16; | |
169 | q = y; | |
170 | x += z; | |
171 | if (x < z || x > P) | |
172 | x -= P; | |
173 | } | |
174 | } | |
175 | ||
176 | /* --- Now add on the constant --- */ | |
177 | ||
178 | x += C; | |
179 | if (x < C || x >= P) | |
180 | x -= P; | |
181 | ||
182 | /* --- Done --- */ | |
183 | ||
184 | return (x); | |
185 | } | |
186 | ||
187 | /* --- @lcrand_range@ --- * | |
188 | * | |
189 | * Arguments: @uint32 *x@ = pointer to seed value (updated) | |
190 | * @uint32 m@ = limit allowable | |
191 | * | |
192 | * Returns: A uniformly distributed pseudorandom integer in the interval | |
193 | * %$[0, m)$%. | |
194 | */ | |
195 | ||
196 | uint32 lcrand_range(uint32 *x, uint32 m) | |
197 | { | |
198 | uint32 xx = *x; | |
199 | uint32 r = P - P % m; | |
200 | do xx = lcrand(xx); while (xx >= r); | |
201 | *x = xx; | |
202 | return (xx / (r / m)); | |
203 | } | |
204 | ||
205 | /*----- That's all, folks -------------------------------------------------*/ |