1 /*
2 Copyright (C) 1995, 2004 Free Software Foundation
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, write to the Free
16 Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
17 02110-1301 USA. */
18
19 /*
20 Copyright (C) 1983 Regents of the University of California.
21 All rights reserved.
22
23 Redistribution and use in source and binary forms, with or without
24 modification, are permitted provided that the following conditions
25 are met:
26
27 1. Redistributions of source code must retain the above copyright
28 notice, this list of conditions and the following disclaimer.
29 2. Redistributions in binary form must reproduce the above copyright
30 notice, this list of conditions and the following disclaimer in the
31 documentation and/or other materials provided with the distribution.
32 4. Neither the name of the University nor the names of its contributors
33 may be used to endorse or promote products derived from this software
34 without specific prior written permission.
35
36 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
37 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
38 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
39 ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
40 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
41 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
42 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
43 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
44 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
45 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
46 SUCH DAMAGE.*/
47
48 /*
49 * This is derived from the Berkeley source:
50 * @(#)random.c 5.5 (Berkeley) 7/6/88
51 * It was reworked for the GNU C Library by Roland McGrath.
52 * Rewritten to be reentrant by Ulrich Drepper, 1995
53 */
54
55 #include <limits.h>
56 #include <stdlib.h>
57 #include "generate-random.h"
58
59
60 /* An improved random number generation package. In addition to the standard
61 rand()/srand() like interface, this package also has a special state info
62 interface. The initstate() routine is called with a seed, an array of
63 bytes, and a count of how many bytes are being passed in; this array is
64 then initialized to contain information for random number generation with
65 that much state information. Good sizes for the amount of state
66 information are 32, 64, 128, and 256 bytes. The state can be switched by
67 calling the setstate() function with the same array as was initialized
68 with initstate(). By default, the package runs with 128 bytes of state
69 information and generates far better random numbers than a linear
70 congruential generator. If the amount of state information is less than
71 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
72 state information is treated as an array of longs; the zeroth element of
73 the array is the type of R.N.G. being used (small integer); the remainder
74 of the array is the state information for the R.N.G. Thus, 32 bytes of
75 state information will give 7 longs worth of state information, which will
76 allow a degree seven polynomial. (Note: The zeroth word of state
77 information also has some other information stored in it; see setstate
78 for details). The random number generation technique is a linear feedback
79 shift register approach, employing trinomials (since there are fewer terms
80 to sum up that way). In this approach, the least significant bit of all
81 the numbers in the state table will act as a linear feedback shift register,
82 and will have period 2^deg - 1 (where deg is the degree of the polynomial
83 being used, assuming that the polynomial is irreducible and primitive).
84 The higher order bits will have longer periods, since their values are
85 also influenced by pseudo-random carries out of the lower bits. The
86 total period of the generator is approximately deg*(2**deg - 1); thus
87 doubling the amount of state information has a vast influence on the
88 period of the generator. Note: The deg*(2**deg - 1) is an approximation
89 only good for large deg, when the period of the shift register is the
90 dominant factor. With deg equal to seven, the period is actually much
91 longer than the 7*(2**7 - 1) predicted by this formula. */
92
93
94
95 /* For each of the currently supported random number generators, we have a
96 break value on the amount of state information (you need at least this many
97 bytes of state info to support this random number generator), a degree for
98 the polynomial (actually a trinomial) that the R.N.G. is based on, and
99 separation between the two lower order coefficients of the trinomial. */
100
101 /* Linear congruential. */
102 #define TYPE_0 0
103 #define BREAK_0 8
104 #define DEG_0 0
105 #define SEP_0 0
106
107 /* x**7 + x**3 + 1. */
108 #define TYPE_1 1
109 #define BREAK_1 32
110 #define DEG_1 7
111 #define SEP_1 3
112
113 /* x**15 + x + 1. */
114 #define TYPE_2 2
115 #define BREAK_2 64
116 #define DEG_2 15
117 #define SEP_2 1
118
119 /* x**31 + x**3 + 1. */
120 #define TYPE_3 3
121 #define BREAK_3 128
122 #define DEG_3 31
123 #define SEP_3 3
124
125 /* x**63 + x + 1. */
126 #define TYPE_4 4
127 #define BREAK_4 256
128 #define DEG_4 63
129 #define SEP_4 1
130
131
132 /* Array versions of the above information to make code run faster.
133 Relies on fact that TYPE_i == i. */
134
135 #define MAX_TYPES 5 /* Max number of types above. */
136
137 struct random_poly_info
138 {
139 int seps[MAX_TYPES];
140 int degrees[MAX_TYPES];
141 };
142
143 static const struct random_poly_info random_poly_info =
144 {
145 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
146 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
147 };
148
149
150
151
152 /* Initialize the random number generator based on the given seed. If the
153 type is the trivial no-state-information type, just remember the seed.
154 Otherwise, initializes state[] based on the given "seed" via a linear
155 congruential generator. Then, the pointers are set to known locations
156 that are exactly rand_sep places apart. Lastly, it cycles the state
157 information a given number of times to get rid of any initial dependencies
158 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
159 for default usage relies on values produced by this routine. */
160 int
161 generate_srandom_r (unsigned int seed, struct generate_random_data *buf)
162 {
163 int type;
164 int *state;
165 long int i;
166 long int word;
167 int *dst;
168 int kc;
169
170 if (buf == NULL)
171 goto fail;
172 type = buf->rand_type;
173 if ((unsigned int) type >= MAX_TYPES)
174 goto fail;
175
176 state = buf->state;
177 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
178 if (seed == 0)
179 seed = 1;
180 state[0] = seed;
181 if (type == TYPE_0)
182 goto done;
183
184 dst = state;
185 word = seed;
186 kc = buf->rand_deg;
187 for (i = 1; i < kc; ++i)
188 {
189 /* This does:
190 state[i] = (16807 * state[i - 1]) % 2147483647;
191 but avoids overflowing 31 bits. */
192 long int hi = word / 127773;
193 long int lo = word % 127773;
194 word = 16807 * lo - 2836 * hi;
195 if (word < 0)
196 word += 2147483647;
197 *++dst = word;
198 }
199
200 buf->fptr = &state[buf->rand_sep];
201 buf->rptr = &state[0];
202 kc *= 10;
203 while (--kc >= 0)
204 {
205 int discard;
206 (void) generate_random_r (buf, &discard);
207 }
208
209 done:
210 return 0;
211
212 fail:
213 return -1;
214 }
215
216 /* Initialize the state information in the given array of N bytes for
217 future random number generation. Based on the number of bytes we
218 are given, and the break values for the different R.N.G.'s, we choose
219 the best (largest) one we can and set things up for it. srandom is
220 then called to initialize the state information. Note that on return
221 from srandom, we set state[-1] to be the type multiplexed with the current
222 value of the rear pointer; this is so successive calls to initstate won't
223 lose this information and will be able to restart with setstate.
224 Note: The first thing we do is save the current state, if any, just like
225 setstate so that it doesn't matter when initstate is called.
226 Returns a pointer to the old state. */
227 int
228 generate_initstate_r (unsigned int seed, char *arg_state, size_t n,
229 struct generate_random_data *buf)
230 {
231 int type;
232 int degree;
233 int separation;
234 int *state;
235
236 if (buf == NULL)
237 goto fail;
238
239 if (n >= BREAK_3)
240 type = n < BREAK_4 ? TYPE_3 : TYPE_4;
241 else if (n < BREAK_1)
242 {
243 if (n < BREAK_0)
244 {
245 goto fail;
246 }
247 type = TYPE_0;
248 }
249 else
250 type = n < BREAK_2 ? TYPE_1 : TYPE_2;
251
252 degree = random_poly_info.degrees[type];
253 separation = random_poly_info.seps[type];
254
255 buf->rand_type = type;
256 buf->rand_sep = separation;
257 buf->rand_deg = degree;
258 state = &((int *) arg_state)[1]; /* First location. */
259 /* Must set END_PTR before srandom. */
260 buf->end_ptr = &state[degree];
261
262 buf->state = state;
263
264 generate_srandom_r (seed, buf);
265
266 state[-1] = TYPE_0;
267 if (type != TYPE_0)
268 state[-1] = (buf->rptr - state) * MAX_TYPES + type;
269
270 return 0;
271
272 fail:
273 return -1;
274 }
275
276 /* Restore the state from the given state array.
277 Note: It is important that we also remember the locations of the pointers
278 in the current state information, and restore the locations of the pointers
279 from the old state information. This is done by multiplexing the pointer
280 location into the zeroth word of the state information. Note that due
281 to the order in which things are done, it is OK to call setstate with the
282 same state as the current state
283 Returns a pointer to the old state information. */
284 int
285 generate_setstate_r (char *arg_state, struct generate_random_data *buf)
286 {
287 int *new_state = 1 + (int *) arg_state;
288 int type;
289 int old_type;
290 int *old_state;
291 int degree;
292 int separation;
293
294 if (arg_state == NULL || buf == NULL)
295 goto fail;
296
297 old_type = buf->rand_type;
298 old_state = buf->state;
299 if (old_type == TYPE_0)
300 old_state[-1] = TYPE_0;
301 else
302 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
303
304 type = new_state[-1] % MAX_TYPES;
305 if (type < TYPE_0 || type > TYPE_4)
306 goto fail;
307
308 buf->rand_deg = degree = random_poly_info.degrees[type];
309 buf->rand_sep = separation = random_poly_info.seps[type];
310 buf->rand_type = type;
311
312 if (type != TYPE_0)
313 {
314 int rear = new_state[-1] / MAX_TYPES;
315 buf->rptr = &new_state[rear];
316 buf->fptr = &new_state[(rear + separation) % degree];
317 }
318 buf->state = new_state;
319 /* Set end_ptr too. */
320 buf->end_ptr = &new_state[degree];
321
322 return 0;
323
324 fail:
325 return -1;
326 }
327
328 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
329 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
330 same in all the other cases due to all the global variables that have been
331 set up. The basic operation is to add the number at the rear pointer into
332 the one at the front pointer. Then both pointers are advanced to the next
333 location cyclically in the table. The value returned is the sum generated,
334 reduced to 31 bits by throwing away the "least random" low bit.
335 Note: The code takes advantage of the fact that both the front and
336 rear pointers can't wrap on the same call by not testing the rear
337 pointer if the front one has wrapped. Returns a 31-bit random number. */
338
339 int
340 generate_random_r (struct generate_random_data *buf, int *result)
341 {
342 int *state;
343
344 if (buf == NULL || result == NULL)
345 goto fail;
346
347 state = buf->state;
348
349 if (buf->rand_type == TYPE_0)
350 {
351 int val = state[0];
352 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
353 state[0] = val;
354 *result = val;
355 }
356 else
357 {
358 int *fptr = buf->fptr;
359 int *rptr = buf->rptr;
360 int *end_ptr = buf->end_ptr;
361 int val;
362
363 val = *fptr += *rptr;
364 /* Chucking least random bit. */
365 *result = (val >> 1) & 0x7fffffff;
366 ++fptr;
367 if (fptr >= end_ptr)
368 {
369 fptr = state;
370 ++rptr;
371 }
372 else
373 {
374 ++rptr;
375 if (rptr >= end_ptr)
376 rptr = state;
377 }
378 buf->fptr = fptr;
379 buf->rptr = rptr;
380 }
381 return 0;
382
383 fail:
384 return -1;
385 }