07871354 |
1 | /* -*-c-*- |
2 | * |
3 | * $Id: lcrand.c,v 1.1 1999/12/10 23:15:27 mdw Exp $ |
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 $ |
33 | * Revision 1.1 1999/12/10 23:15:27 mdw |
34 | * Noncryptographic random number generator. |
35 | * |
36 | */ |
37 | |
38 | /*----- Header files ------------------------------------------------------*/ |
39 | |
40 | #include <stdarg.h> |
41 | #include <stdio.h> |
42 | #include <stdlib.h> |
43 | #include <string.h> |
44 | |
45 | #include <mLib/bits.h> |
46 | #include <mLib/sub.h> |
47 | |
48 | #include "grand.h" |
49 | #include "lcrand.h" |
50 | |
51 | /*----- Magic numbers -----------------------------------------------------*/ |
52 | |
53 | /* --- The generator parameters --- */ |
54 | |
55 | #define P LCRAND_P /* Modulus */ |
56 | #define A LCRAND_A /* Multiplier (primitive mod @p@) */ |
57 | #define C LCRAND_C /* Additive constant */ |
58 | |
59 | /* --- Precomputed values for modular reduction --- */ |
60 | |
61 | #define D 5 /* %$p = 2^{32} - d$% */ |
62 | |
63 | /* --- Other useful bits --- */ |
64 | |
65 | #define P256 4294967040u /* Highest multiple of 256 < %$p$% */ |
66 | |
67 | /*----- Main code ---------------------------------------------------------*/ |
68 | |
69 | /* --- @lcrand@ --- * |
70 | * |
71 | * Arguments: @uint32 x@ = seed value |
72 | * |
73 | * Returns: New state of the generator. |
74 | * |
75 | * Use: Steps the generator. Returns %$ax + c \bmod p$%. |
76 | */ |
77 | |
78 | uint32 lcrand(uint32 x) |
79 | { |
80 | uint32 a[2], xx[2]; |
81 | uint32 yy[2]; |
82 | |
83 | /* --- Unpack things into the arrays --- */ |
84 | |
85 | a[0] = U16(A); a[1] = U16(A >> 16); |
86 | xx[0] = U16(x); xx[1] = U16(x >> 16); |
87 | |
88 | /* --- Multiply everything together --- * |
89 | * |
90 | * This is plain old long multiplication, although it looks a bit strange. |
91 | * I set up the top and bottom partial products directly where they're |
92 | * supposed to be. The cross terms I add together, with the low 16 bits in |
93 | * @q@ and the high 32 bits in @p@. These I then add into the product. |
94 | */ |
95 | |
96 | { |
97 | uint32 p, q; |
98 | |
99 | yy[0] = a[0] * xx[0]; |
100 | yy[1] = a[1] * xx[1]; |
101 | |
102 | p = a[0] * xx[1]; |
103 | q = p + a[1] * xx[0]; |
104 | p = ((q < p) << 16) + (q >> 16); |
105 | q = U16(q) << 16; |
106 | |
107 | q += yy[0]; |
108 | if (q < yy[0]) |
109 | p++; |
110 | else |
111 | p += (q >> 16) >> 16; |
112 | yy[0] = q; |
113 | |
114 | yy[1] += p; |
115 | } |
116 | |
117 | /* --- Now reduce mod p --- * |
118 | * |
119 | * I'm using shifts and adds to do the multiply step here. This needs to |
120 | * be changed if @D@ ever becomes something other than 5. |
121 | */ |
122 | |
123 | #if D != 5 |
124 | # error "Change shift sequence!" |
125 | #endif |
126 | |
127 | { |
128 | uint32 q; |
129 | |
130 | q = yy[1]; |
131 | x = yy[0]; |
132 | |
133 | while (q) { |
134 | uint32 y, z; |
135 | y = q >> 30; |
136 | z = q << 2; |
137 | z += q; |
138 | if (z < q) |
139 | y++; |
140 | else |
141 | y += (q >> 16) >> 16; |
142 | q = y; |
143 | x += z; |
144 | if (x < z || x > P) |
145 | x -= P; |
146 | } |
147 | } |
148 | |
149 | /* --- Now add on the constant --- */ |
150 | |
151 | x += C; |
152 | if (x < C || x >= P) |
153 | x -= P; |
154 | |
155 | /* --- Done --- */ |
156 | |
157 | return (x); |
158 | } |
159 | |
160 | /* --- @lcrand_range@ --- * |
161 | * |
162 | * Arguments: @uint32 *x@ = pointer to seed value (updated) |
163 | * @uint32 m@ = limit allowable |
164 | * |
165 | * Returns: A uniformly distributed pseudorandom integer in the interval |
166 | * %$[0, m)$%. |
167 | */ |
168 | |
169 | uint32 lcrand_range(uint32 *x, uint32 m) |
170 | { |
171 | uint32 xx = *x; |
172 | uint32 r = P - P % m; |
173 | do xx = lcrand(xx); while (xx >= r); |
174 | *x = xx; |
175 | return (xx / (r / m)); |
176 | } |
177 | |
178 | /*----- Generic interface -------------------------------------------------*/ |
179 | |
180 | typedef struct gctx { |
181 | grand r; |
182 | uint32 x; |
183 | } gctx; |
184 | |
185 | static void gdestroy(grand *r) |
186 | { |
187 | gctx *g = (gctx *)r; |
188 | DESTROY(g); |
189 | } |
190 | |
191 | static int gmisc(grand *r, unsigned op, ...) |
192 | { |
193 | gctx *g = (gctx *)r; |
194 | va_list ap; |
195 | int rc = 0; |
196 | va_start(ap, op); |
197 | |
198 | switch (op) { |
199 | case GRAND_CHECK: |
200 | switch (va_arg(ap, unsigned)) { |
201 | case GRAND_CHECK: |
202 | case GRAND_SEEDINT: |
203 | case GRAND_SEEDUINT32: |
204 | rc = 1; |
205 | break; |
206 | default: |
207 | rc = 0; |
208 | break; |
209 | } |
210 | break; |
211 | case GRAND_SEEDINT: |
212 | g->x = va_arg(ap, unsigned); |
213 | break; |
214 | case GRAND_SEEDUINT32: |
215 | g->x = va_arg(ap, uint32); |
216 | break; |
217 | default: |
218 | GRAND_BADOP; |
219 | break; |
220 | } |
221 | |
222 | va_end(ap); |
223 | return (rc); |
224 | } |
225 | |
226 | static uint32 graw(grand *r) |
227 | { |
228 | gctx *g = (gctx *)r; |
229 | g->x = lcrand(g->x); |
230 | return (g->x); |
231 | } |
232 | |
233 | static octet gbyte(grand *r) |
234 | { |
235 | gctx *g = (gctx *)r; |
236 | uint32 x = g->x; |
237 | do x = lcrand(x); while (x >= P256); |
238 | g->x = x; |
239 | return (x / (P256 / 256)); |
240 | } |
241 | |
242 | static uint32 grange(grand *r, uint32 l) |
243 | { |
244 | gctx *g = (gctx *)r; |
245 | return (lcrand_range(&g->x, l)); |
246 | } |
247 | |
248 | static const grand_ops gops = { |
249 | "lcrand", |
250 | LCRAND_P, |
251 | gmisc, gdestroy, |
252 | graw, gbyte, grand_word, grange, grand_fill |
253 | }; |
254 | |
255 | /* --- @lcrand_create@ --- * |
256 | * |
257 | * Arguments: @uint32 x@ = initial seed |
258 | * |
259 | * Returns: Pointer to a generic generator. |
260 | * |
261 | * Use: Constructs a generic generator interface over a linear |
262 | * congruential generator. |
263 | */ |
264 | |
265 | grand *lcrand_create(uint32 x) |
266 | { |
267 | gctx *g = CREATE(gctx); |
268 | g->r.ops = &gops; |
269 | g->x = x; |
270 | return (&g->r); |
271 | } |
272 | |
273 | /*----- Test rig ----------------------------------------------------------*/ |
274 | |
275 | #ifdef TEST_RIG |
276 | |
277 | #include <mLib/testrig.h> |
278 | |
279 | static int verify(dstr *v) |
280 | { |
281 | uint32 x = *(uint32 *)v[0].buf; |
282 | uint32 y = *(uint32 *)v[1].buf; |
283 | uint32 z = lcrand(x); |
284 | int ok = 1; |
285 | if (y != z) { |
286 | fprintf(stderr, |
287 | "\n*** lcrand failed. lcrand(%lu) = %lu, expected %lu\n", |
288 | (unsigned long)x, (unsigned long)z, (unsigned long)y); |
289 | ok = 0; |
290 | } |
291 | return (ok); |
292 | } |
293 | |
294 | static test_chunk tests[] = { |
295 | { "lcrand", verify, { &type_uint32, &type_uint32, 0 } }, |
296 | { 0, 0, { 0 } } |
297 | }; |
298 | |
299 | int main(int argc, char *argv[]) |
300 | { |
301 | test_run(argc, argv, tests, SRCDIR"/tests/lcrand"); |
302 | return (0); |
303 | } |
304 | |
305 | #endif |
306 | |
307 | /*----- That's all, folks -------------------------------------------------*/ |