1 /*
2 * Copyright (c) 1983 Regents of the University of California.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are permitted
6 * provided that the above copyright notice and this paragraph are
7 * duplicated in all such forms and that any documentation,
8 * advertising materials, and other materials related to such
9 * distribution and use acknowledge that the software was developed
10 * by the University of California, Berkeley. The name of the
11 * University may not be used to endorse or promote products derived
12 * from this software without specific prior written permission.
13 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
15 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
16 */
17
18 /*
19 * This is derived from the Berkeley source:
20 * @(#)random.c 5.5 (Berkeley) 7/6/88
21 * It was reworked for the GNU C Library by Roland McGrath.
22 * Rewritten to be reentrant by Ulrich Drepper, 1995
23 */
24
25 #include <features.h>
26 #include <errno.h>
27 #include <limits.h>
28 #include <stddef.h>
29 #include <stdlib.h>
30 #include <unistd.h>
31
32 /* An improved random number generation package. In addition to the standard
33 rand()/srand() like interface, this package also has a special state info
34 interface. The initstate() routine is called with a seed, an array of
35 bytes, and a count of how many bytes are being passed in; this array is
36 then initialized to contain information for random number generation with
37 that much state information. Good sizes for the amount of state
38 information are 32, 64, 128, and 256 bytes. The state can be switched by
39 calling the setstate() function with the same array as was initialized
40 with initstate(). By default, the package runs with 128 bytes of state
41 information and generates far better random numbers than a linear
42 congruential generator. If the amount of state information is less than
43 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
44 state information is treated as an array of longs; the zeroth element of
45 the array is the type of R.N.G. being used (small integer); the remainder
46 of the array is the state information for the R.N.G. Thus, 32 bytes of
47 state information will give 7 longs worth of state information, which will
48 allow a degree seven polynomial. (Note: The zeroth word of state
49 information also has some other information stored in it; see setstate
50 for details). The random number generation technique is a linear feedback
51 shift register approach, employing trinomials (since there are fewer terms
52 to sum up that way). In this approach, the least significant bit of all
53 the numbers in the state table will act as a linear feedback shift register,
54 and will have period 2^deg - 1 (where deg is the degree of the polynomial
55 being used, assuming that the polynomial is irreducible and primitive).
56 The higher order bits will have longer periods, since their values are
57 also influenced by pseudo-random carries out of the lower bits. The
58 total period of the generator is approximately deg*(2**deg - 1); thus
59 doubling the amount of state information has a vast influence on the
60 period of the generator. Note: The deg*(2**deg - 1) is an approximation
61 only good for large deg, when the period of the shift register is the
62 dominant factor. With deg equal to seven, the period is actually much
63 longer than the 7*(2**7 - 1) predicted by this formula. */
64
65
66
67 /* For each of the currently supported random number generators, we have a
68 break value on the amount of state information (you need at least this many
69 bytes of state info to support this random number generator), a degree for
70 the polynomial (actually a trinomial) that the R.N.G. is based on, and
71 separation between the two lower order coefficients of the trinomial. */
72
73 /* Linear congruential. */
74 #define TYPE_0 0
75 #define BREAK_0 8
76 #define DEG_0 0
77 #define SEP_0 0
78
79 /* x**7 + x**3 + 1. */
80 #define TYPE_1 1
81 #define BREAK_1 32
82 #define DEG_1 7
83 #define SEP_1 3
84
85 /* x**15 + x + 1. */
86 #define TYPE_2 2
87 #define BREAK_2 64
88 #define DEG_2 15
89 #define SEP_2 1
90
91 /* x**31 + x**3 + 1. */
92 #define TYPE_3 3
93 #define BREAK_3 128
94 #define DEG_3 31
95 #define SEP_3 3
96
97 /* x**63 + x + 1. */
98 #define TYPE_4 4
99 #define BREAK_4 256
100 #define DEG_4 63
101 #define SEP_4 1
102
103
104 /* Array versions of the above information to make code run faster.
105 Relies on fact that TYPE_i == i. */
106
107 #define MAX_TYPES 5 /* Max number of types above. */
108
109 struct random_poly_info
110 {
111 smallint seps[MAX_TYPES];
112 smallint degrees[MAX_TYPES];
113 };
114
115 static const struct random_poly_info random_poly_info =
116 {
117 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
118 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
119 };
120
121
122
123 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
124 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
125 same in all the other cases due to all the global variables that have been
126 set up. The basic operation is to add the number at the rear pointer into
127 the one at the front pointer. Then both pointers are advanced to the next
128 location cyclically in the table. The value returned is the sum generated,
129 reduced to 31 bits by throwing away the "least random" low bit.
130 Note: The code takes advantage of the fact that both the front and
131 rear pointers can't wrap on the same call by not testing the rear
132 pointer if the front one has wrapped. Returns a 31-bit random number. */
133
random_r(struct random_data * buf,int32_t * result)134 int random_r(struct random_data *buf, int32_t *result)
135 {
136 int32_t *state;
137
138 if (buf == NULL || result == NULL)
139 goto fail;
140
141 state = buf->state;
142
143 if (buf->rand_type == TYPE_0)
144 {
145 int32_t val = state[0];
146 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
147 state[0] = val;
148 *result = val;
149 }
150 else
151 {
152 int32_t *fptr = buf->fptr;
153 int32_t *rptr = buf->rptr;
154 int32_t *end_ptr = buf->end_ptr;
155 int32_t val;
156
157 val = *fptr += *rptr;
158 /* Chucking least random bit. */
159 *result = (val >> 1) & 0x7fffffff;
160 ++fptr;
161 if (fptr >= end_ptr)
162 {
163 fptr = state;
164 ++rptr;
165 }
166 else
167 {
168 ++rptr;
169 if (rptr >= end_ptr)
170 rptr = state;
171 }
172 buf->fptr = fptr;
173 buf->rptr = rptr;
174 }
175 return 0;
176
177 fail:
178 __set_errno (EINVAL);
179 return -1;
180 }
libc_hidden_def(random_r)181 libc_hidden_def(random_r)
182
183 /* Initialize the random number generator based on the given seed. If the
184 type is the trivial no-state-information type, just remember the seed.
185 Otherwise, initializes state[] based on the given "seed" via a linear
186 congruential generator. Then, the pointers are set to known locations
187 that are exactly rand_sep places apart. Lastly, it cycles the state
188 information a given number of times to get rid of any initial dependencies
189 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
190 for default usage relies on values produced by this routine. */
191 int srandom_r (unsigned int seed, struct random_data *buf)
192 {
193 int type;
194 int32_t *state;
195 long int i;
196 long int word;
197 int32_t *dst;
198 int kc;
199
200 if (buf == NULL)
201 goto fail;
202 type = buf->rand_type;
203 if ((unsigned int) type >= MAX_TYPES)
204 goto fail;
205
206 state = buf->state;
207 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
208 if (seed == 0)
209 seed = 1;
210 state[0] = seed;
211 if (type == TYPE_0)
212 goto done;
213
214 dst = state;
215 word = seed;
216 kc = buf->rand_deg;
217 for (i = 1; i < kc; ++i)
218 {
219 /* This does:
220 state[i] = (16807 * state[i - 1]) % 2147483647;
221 but avoids overflowing 31 bits. */
222 long int hi = word / 127773;
223 long int lo = word % 127773;
224 word = 16807 * lo - 2836 * hi;
225 if (word < 0)
226 word += 2147483647;
227 *++dst = word;
228 }
229
230 buf->fptr = &state[buf->rand_sep];
231 buf->rptr = &state[0];
232 kc *= 10;
233 while (--kc >= 0)
234 {
235 int32_t discard;
236 (void) random_r (buf, &discard);
237 }
238
239 done:
240 return 0;
241
242 fail:
243 return -1;
244 }
libc_hidden_def(srandom_r)245 libc_hidden_def(srandom_r)
246
247 /* Initialize the state information in the given array of N bytes for
248 future random number generation. Based on the number of bytes we
249 are given, and the break values for the different R.N.G.'s, we choose
250 the best (largest) one we can and set things up for it. srandom is
251 then called to initialize the state information. Note that on return
252 from srandom, we set state[-1] to be the type multiplexed with the current
253 value of the rear pointer; this is so successive calls to initstate won't
254 lose this information and will be able to restart with setstate.
255 Note: The first thing we do is save the current state, if any, just like
256 setstate so that it doesn't matter when initstate is called.
257 Returns a pointer to the old state. */
258 int initstate_r (unsigned int seed, char *arg_state, size_t n, struct random_data *buf)
259 {
260 int type;
261 int degree;
262 int separation;
263 int32_t *state;
264
265 if (buf == NULL)
266 goto fail;
267
268 if (n >= BREAK_3)
269 type = n < BREAK_4 ? TYPE_3 : TYPE_4;
270 else if (n < BREAK_1)
271 {
272 if (n < BREAK_0)
273 {
274 __set_errno (EINVAL);
275 goto fail;
276 }
277 type = TYPE_0;
278 }
279 else
280 type = n < BREAK_2 ? TYPE_1 : TYPE_2;
281
282 degree = random_poly_info.degrees[type];
283 separation = random_poly_info.seps[type];
284
285 buf->rand_type = type;
286 buf->rand_sep = separation;
287 buf->rand_deg = degree;
288 state = &((int32_t *) arg_state)[1]; /* First location. */
289 /* Must set END_PTR before srandom. */
290 buf->end_ptr = &state[degree];
291
292 buf->state = state;
293
294 srandom_r (seed, buf);
295
296 state[-1] = TYPE_0;
297 if (type != TYPE_0)
298 state[-1] = (buf->rptr - state) * MAX_TYPES + type;
299
300 return 0;
301
302 fail:
303 __set_errno (EINVAL);
304 return -1;
305 }
libc_hidden_def(initstate_r)306 libc_hidden_def(initstate_r)
307
308 /* Restore the state from the given state array.
309 Note: It is important that we also remember the locations of the pointers
310 in the current state information, and restore the locations of the pointers
311 from the old state information. This is done by multiplexing the pointer
312 location into the zeroth word of the state information. Note that due
313 to the order in which things are done, it is OK to call setstate with the
314 same state as the current state
315 Returns a pointer to the old state information. */
316 int setstate_r (char *arg_state, struct random_data *buf)
317 {
318 int32_t *new_state = 1 + (int32_t *) arg_state;
319 int type;
320 int old_type;
321 int32_t *old_state;
322 int degree;
323 int separation;
324
325 if (arg_state == NULL || buf == NULL)
326 goto fail;
327
328 old_type = buf->rand_type;
329 old_state = buf->state;
330 if (old_type == TYPE_0)
331 old_state[-1] = TYPE_0;
332 else
333 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
334
335 type = new_state[-1] % MAX_TYPES;
336 if (type < TYPE_0 || type > TYPE_4)
337 goto fail;
338
339 buf->rand_deg = degree = random_poly_info.degrees[type];
340 buf->rand_sep = separation = random_poly_info.seps[type];
341 buf->rand_type = type;
342
343 if (type != TYPE_0)
344 {
345 int rear = new_state[-1] / MAX_TYPES;
346 buf->rptr = &new_state[rear];
347 buf->fptr = &new_state[(rear + separation) % degree];
348 }
349 buf->state = new_state;
350 /* Set end_ptr too. */
351 buf->end_ptr = &new_state[degree];
352
353 return 0;
354
355 fail:
356 __set_errno (EINVAL);
357 return -1;
358 }
359 libc_hidden_def(setstate_r)
360