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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: lcrand.c,v 1.3 2000/06/17 11:29:03 mdw Exp $ |
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4 | * |
5 | * Simple linear congruential generator |
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: lcrand.c,v $ |
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33 | * Revision 1.3 2000/06/17 11:29:03 mdw |
34 | * Add the flags word to the generic generator. |
35 | * |
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36 | * Revision 1.2 1999/12/13 15:34:01 mdw |
37 | * Add support for seeding from a generic pseudorandom source. |
38 | * |
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39 | * Revision 1.1 1999/12/10 23:15:27 mdw |
40 | * Noncryptographic random number generator. |
41 | * |
42 | */ |
43 | |
44 | /*----- Header files ------------------------------------------------------*/ |
45 | |
46 | #include <stdarg.h> |
47 | #include <stdio.h> |
48 | #include <stdlib.h> |
49 | #include <string.h> |
50 | |
51 | #include <mLib/bits.h> |
52 | #include <mLib/sub.h> |
53 | |
54 | #include "grand.h" |
55 | #include "lcrand.h" |
56 | |
57 | /*----- Magic numbers -----------------------------------------------------*/ |
58 | |
59 | /* --- The generator parameters --- */ |
60 | |
61 | #define P LCRAND_P /* Modulus */ |
62 | #define A LCRAND_A /* Multiplier (primitive mod @p@) */ |
63 | #define C LCRAND_C /* Additive constant */ |
64 | |
65 | /* --- Precomputed values for modular reduction --- */ |
66 | |
67 | #define D 5 /* %$p = 2^{32} - d$% */ |
68 | |
69 | /* --- Other useful bits --- */ |
70 | |
71 | #define P256 4294967040u /* Highest multiple of 256 < %$p$% */ |
72 | |
73 | /*----- Main code ---------------------------------------------------------*/ |
74 | |
75 | /* --- @lcrand@ --- * |
76 | * |
77 | * Arguments: @uint32 x@ = seed value |
78 | * |
79 | * Returns: New state of the generator. |
80 | * |
81 | * Use: Steps the generator. Returns %$ax + c \bmod p$%. |
82 | */ |
83 | |
84 | uint32 lcrand(uint32 x) |
85 | { |
86 | uint32 a[2], xx[2]; |
87 | uint32 yy[2]; |
88 | |
89 | /* --- Unpack things into the arrays --- */ |
90 | |
91 | a[0] = U16(A); a[1] = U16(A >> 16); |
92 | xx[0] = U16(x); xx[1] = U16(x >> 16); |
93 | |
94 | /* --- Multiply everything together --- * |
95 | * |
96 | * This is plain old long multiplication, although it looks a bit strange. |
97 | * I set up the top and bottom partial products directly where they're |
98 | * supposed to be. The cross terms I add together, with the low 16 bits in |
99 | * @q@ and the high 32 bits in @p@. These I then add into the product. |
100 | */ |
101 | |
102 | { |
103 | uint32 p, q; |
104 | |
105 | yy[0] = a[0] * xx[0]; |
106 | yy[1] = a[1] * xx[1]; |
107 | |
108 | p = a[0] * xx[1]; |
109 | q = p + a[1] * xx[0]; |
110 | p = ((q < p) << 16) + (q >> 16); |
111 | q = U16(q) << 16; |
112 | |
113 | q += yy[0]; |
114 | if (q < yy[0]) |
115 | p++; |
116 | else |
117 | p += (q >> 16) >> 16; |
118 | yy[0] = q; |
119 | |
120 | yy[1] += p; |
121 | } |
122 | |
123 | /* --- Now reduce mod p --- * |
124 | * |
125 | * I'm using shifts and adds to do the multiply step here. This needs to |
126 | * be changed if @D@ ever becomes something other than 5. |
127 | */ |
128 | |
129 | #if D != 5 |
130 | # error "Change shift sequence!" |
131 | #endif |
132 | |
133 | { |
134 | uint32 q; |
135 | |
136 | q = yy[1]; |
137 | x = yy[0]; |
138 | |
139 | while (q) { |
140 | uint32 y, z; |
141 | y = q >> 30; |
142 | z = q << 2; |
143 | z += q; |
144 | if (z < q) |
145 | y++; |
146 | else |
147 | y += (q >> 16) >> 16; |
148 | q = y; |
149 | x += z; |
150 | if (x < z || x > P) |
151 | x -= P; |
152 | } |
153 | } |
154 | |
155 | /* --- Now add on the constant --- */ |
156 | |
157 | x += C; |
158 | if (x < C || x >= P) |
159 | x -= P; |
160 | |
161 | /* --- Done --- */ |
162 | |
163 | return (x); |
164 | } |
165 | |
166 | /* --- @lcrand_range@ --- * |
167 | * |
168 | * Arguments: @uint32 *x@ = pointer to seed value (updated) |
169 | * @uint32 m@ = limit allowable |
170 | * |
171 | * Returns: A uniformly distributed pseudorandom integer in the interval |
172 | * %$[0, m)$%. |
173 | */ |
174 | |
175 | uint32 lcrand_range(uint32 *x, uint32 m) |
176 | { |
177 | uint32 xx = *x; |
178 | uint32 r = P - P % m; |
179 | do xx = lcrand(xx); while (xx >= r); |
180 | *x = xx; |
181 | return (xx / (r / m)); |
182 | } |
183 | |
184 | /*----- Generic interface -------------------------------------------------*/ |
185 | |
186 | typedef struct gctx { |
187 | grand r; |
188 | uint32 x; |
189 | } gctx; |
190 | |
191 | static void gdestroy(grand *r) |
192 | { |
193 | gctx *g = (gctx *)r; |
194 | DESTROY(g); |
195 | } |
196 | |
197 | static int gmisc(grand *r, unsigned op, ...) |
198 | { |
199 | gctx *g = (gctx *)r; |
200 | va_list ap; |
201 | int rc = 0; |
202 | va_start(ap, op); |
203 | |
204 | switch (op) { |
205 | case GRAND_CHECK: |
206 | switch (va_arg(ap, unsigned)) { |
207 | case GRAND_CHECK: |
208 | case GRAND_SEEDINT: |
209 | case GRAND_SEEDUINT32: |
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210 | case GRAND_SEEDRAND: |
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211 | rc = 1; |
212 | break; |
213 | default: |
214 | rc = 0; |
215 | break; |
216 | } |
217 | break; |
218 | case GRAND_SEEDINT: |
219 | g->x = va_arg(ap, unsigned); |
220 | break; |
221 | case GRAND_SEEDUINT32: |
222 | g->x = va_arg(ap, uint32); |
223 | break; |
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224 | case GRAND_SEEDRAND: { |
225 | grand *rr = va_arg(ap, grand *); |
226 | uint32 x; |
227 | do x = rr->ops->word(rr); while (x >= P || x == LCRAND_FIXEDPT); |
228 | g->x = x; |
229 | } break; |
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230 | default: |
231 | GRAND_BADOP; |
232 | break; |
233 | } |
234 | |
235 | va_end(ap); |
236 | return (rc); |
237 | } |
238 | |
239 | static uint32 graw(grand *r) |
240 | { |
241 | gctx *g = (gctx *)r; |
242 | g->x = lcrand(g->x); |
243 | return (g->x); |
244 | } |
245 | |
246 | static octet gbyte(grand *r) |
247 | { |
248 | gctx *g = (gctx *)r; |
249 | uint32 x = g->x; |
250 | do x = lcrand(x); while (x >= P256); |
251 | g->x = x; |
252 | return (x / (P256 / 256)); |
253 | } |
254 | |
255 | static uint32 grange(grand *r, uint32 l) |
256 | { |
257 | gctx *g = (gctx *)r; |
258 | return (lcrand_range(&g->x, l)); |
259 | } |
260 | |
261 | static const grand_ops gops = { |
262 | "lcrand", |
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263 | LCRAND_P, 0, |
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264 | gmisc, gdestroy, |
265 | graw, gbyte, grand_word, grange, grand_fill |
266 | }; |
267 | |
268 | /* --- @lcrand_create@ --- * |
269 | * |
270 | * Arguments: @uint32 x@ = initial seed |
271 | * |
272 | * Returns: Pointer to a generic generator. |
273 | * |
274 | * Use: Constructs a generic generator interface over a linear |
275 | * congruential generator. |
276 | */ |
277 | |
278 | grand *lcrand_create(uint32 x) |
279 | { |
280 | gctx *g = CREATE(gctx); |
281 | g->r.ops = &gops; |
282 | g->x = x; |
283 | return (&g->r); |
284 | } |
285 | |
286 | /*----- Test rig ----------------------------------------------------------*/ |
287 | |
288 | #ifdef TEST_RIG |
289 | |
290 | #include <mLib/testrig.h> |
291 | |
292 | static int verify(dstr *v) |
293 | { |
294 | uint32 x = *(uint32 *)v[0].buf; |
295 | uint32 y = *(uint32 *)v[1].buf; |
296 | uint32 z = lcrand(x); |
297 | int ok = 1; |
298 | if (y != z) { |
299 | fprintf(stderr, |
300 | "\n*** lcrand failed. lcrand(%lu) = %lu, expected %lu\n", |
301 | (unsigned long)x, (unsigned long)z, (unsigned long)y); |
302 | ok = 0; |
303 | } |
304 | return (ok); |
305 | } |
306 | |
307 | static test_chunk tests[] = { |
308 | { "lcrand", verify, { &type_uint32, &type_uint32, 0 } }, |
309 | { 0, 0, { 0 } } |
310 | }; |
311 | |
312 | int main(int argc, char *argv[]) |
313 | { |
314 | test_run(argc, argv, tests, SRCDIR"/tests/lcrand"); |
315 | return (0); |
316 | } |
317 | |
318 | #endif |
319 | |
320 | /*----- That's all, folks -------------------------------------------------*/ |