1 #include "config.h"
2 /* Avoid conflict with random in Xbsd 24/03/94 [007]
3 *
4 */
5 #if defined(HAVE_RANDOM)
6 #define random rrandom
7 #define srandom ssrandom
8 #endif
9
10 /*
11 * Copyright (c) 1983, 1993
12 * The Regents of the University of California. All rights reserved.
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 * 1. Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 * 2. Redistributions in binary form must reproduce the above copyright
20 * notice, this list of conditions and the following disclaimer in the
21 * documentation and/or other materials provided with the distribution.
22 * 3. All advertising materials mentioning features or use of this software
23 * must display the following acknowledgement:
24 * This product includes software developed by the University of
25 * California, Berkeley and its contributors.
26 * 4. Neither the name of the University nor the names of its contributors
27 * may be used to endorse or promote products derived from this software
28 * without specific prior written permission.
29 *
30 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
31 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
32 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
34 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
35 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
36 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
38 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
39 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
40 * SUCH DAMAGE.
41 */
42
43 #if defined(LIBC_SCCS) && !defined(lint)
44 static char sccsid[] = "@(#)random.c 8.1 (Berkeley) 6/4/93";
45 #endif /* LIBC_SCCS and not lint */
46
47 #include <stdio.h>
48 #include <stdlib.h>
49
50 long random();
51 void srandom();
52
53 /*
54 * random.c:
55 *
56 * An improved random number generation package. In addition to the standard
57 * rand()/srand() like interface, this package also has a special state info
58 * interface. The initstate() routine is called with a seed, an array of
59 * bytes, and a count of how many bytes are being passed in; this array is
60 * then initialized to contain information for random number generation with
61 * that much state information. Good sizes for the amount of state
62 * information are 32, 64, 128, and 256 bytes. The state can be switched by
63 * calling the setstate() routine with the same array as was initiallized
64 * with initstate(). By default, the package runs with 128 bytes of state
65 * information and generates far better random numbers than a linear
66 * congruential generator. If the amount of state information is less than
67 * 32 bytes, a simple linear congruential R.N.G. is used.
68 *
69 * Internally, the state information is treated as an array of longs; the
70 * zeroeth element of the array is the type of R.N.G. being used (small
71 * integer); the remainder of the array is the state information for the
72 * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of
73 * state information, which will allow a degree seven polynomial. (Note:
74 * the zeroeth word of state information also has some other information
75 * stored in it -- see setstate() for details).
76 *
77 * The random number generation technique is a linear feedback shift register
78 * approach, employing trinomials (since there are fewer terms to sum up that
79 * way). In this approach, the least significant bit of all the numbers in
80 * the state table will act as a linear feedback shift register, and will
81 * have period 2^deg - 1 (where deg is the degree of the polynomial being
82 * used, assuming that the polynomial is irreducible and primitive). The
83 * higher order bits will have longer periods, since their values are also
84 * influenced by pseudo-random carries out of the lower bits. The total
85 * period of the generator is approximately deg*(2**deg - 1); thus doubling
86 * the amount of state information has a vast influence on the period of the
87 * generator. Note: the deg*(2**deg - 1) is an approximation only good for
88 * large deg, when the period of the shift register is the dominant factor.
89 * With deg equal to seven, the period is actually much longer than the
90 * 7*(2**7 - 1) predicted by this formula.
91 */
92
93 /*
94 * For each of the currently supported random number generators, we have a
95 * break value on the amount of state information (you need at least this
96 * many bytes of state info to support this random number generator), a degree
97 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
98 * the separation between the two lower order coefficients of the trinomial.
99 */
100 #define TYPE_0 0 /* linear congruential */
101 #define BREAK_0 8
102 #define DEG_0 0
103 #define SEP_0 0
104
105 #define TYPE_1 1 /* x**7 + x**3 + 1 */
106 #define BREAK_1 32
107 #define DEG_1 7
108 #define SEP_1 3
109
110 #define TYPE_2 2 /* x**15 + x + 1 */
111 #define BREAK_2 64
112 #define DEG_2 15
113 #define SEP_2 1
114
115 #define TYPE_3 3 /* x**31 + x**3 + 1 */
116 #define BREAK_3 128
117 #define DEG_3 31
118 #define SEP_3 3
119
120 #define TYPE_4 4 /* x**63 + x + 1 */
121 #define BREAK_4 256
122 #define DEG_4 63
123 #define SEP_4 1
124
125 /*
126 * Array versions of the above information to make code run faster --
127 * relies on fact that TYPE_i == i.
128 */
129 #define MAX_TYPES 5 /* max number of types above */
130
131 static int degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
132 static int seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
133
134 /*
135 * Initially, everything is set up as if from:
136 *
137 * initstate(1, &randtbl, 128);
138 *
139 * Note that this initialization takes advantage of the fact that srandom()
140 * advances the front and rear pointers 10*rand_deg times, and hence the
141 * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
142 * element of the state information, which contains info about the current
143 * position of the rear pointer is just
144 *
145 * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3.
146 */
147
148 static long randtbl[DEG_3 + 1] = {
149 TYPE_3,
150 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
151 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
152 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
153 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
154 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
155 0x27fb47b9,
156 };
157
158 /*
159 * fptr and rptr are two pointers into the state info, a front and a rear
160 * pointer. These two pointers are always rand_sep places aparts, as they
161 * cycle cyclically through the state information. (Yes, this does mean we
162 * could get away with just one pointer, but the code for random() is more
163 * efficient this way). The pointers are left positioned as they would be
164 * from the call
165 *
166 * initstate(1, randtbl, 128);
167 *
168 * (The position of the rear pointer, rptr, is really 0 (as explained above
169 * in the initialization of randtbl) because the state table pointer is set
170 * to point to randtbl[1] (as explained below).
171 */
172 static long *fptr = &randtbl[SEP_3 + 1];
173 static long *rptr = &randtbl[1];
174
175 /*
176 * The following things are the pointer to the state information table, the
177 * type of the current generator, the degree of the current polynomial being
178 * used, and the separation between the two pointers. Note that for efficiency
179 * of random(), we remember the first location of the state information, not
180 * the zeroeth. Hence it is valid to access state[-1], which is used to
181 * store the type of the R.N.G. Also, we remember the last location, since
182 * this is more efficient than indexing every time to find the address of
183 * the last element to see if the front and rear pointers have wrapped.
184 */
185 static long *state = &randtbl[1];
186 static int rand_type = TYPE_3;
187 static int rand_deg = DEG_3;
188 static int rand_sep = SEP_3;
189 static long *end_ptr = &randtbl[DEG_3 + 1];
190
191 /*
192 * srandom:
193 *
194 * Initialize the random number generator based on the given seed. If the
195 * type is the trivial no-state-information type, just remember the seed.
196 * Otherwise, initializes state[] based on the given "seed" via a linear
197 * congruential generator. Then, the pointers are set to known locations
198 * that are exactly rand_sep places apart. Lastly, it cycles the state
199 * information a given number of times to get rid of any initial dependencies
200 * introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
201 * for default usage relies on values produced by this routine.
202 */
203 void
srandom(x)204 srandom (x)
205 unsigned int x;
206 {
207 register int i, j;
208
209 if (rand_type == TYPE_0)
210 state[0] = x;
211 else {
212 j = 1;
213 state[0] = x;
214 for (i = 1; i < rand_deg; i++)
215 state[i] = 1103515245 * state[i - 1] + 12345;
216 fptr = &state[rand_sep];
217 rptr = &state[0];
218 for (i = 0; i < 10 * rand_deg; i++)
219 (void) random ();
220 }
221 }
222
223 /*
224 * initstate:
225 *
226 * Initialize the state information in the given array of n bytes for future
227 * random number generation. Based on the number of bytes we are given, and
228 * the break values for the different R.N.G.'s, we choose the best (largest)
229 * one we can and set things up for it. srandom() is then called to
230 * initialize the state information.
231 *
232 * Note that on return from srandom(), we set state[-1] to be the type
233 * multiplexed with the current value of the rear pointer; this is so
234 * successive calls to initstate() won't lose this information and will be
235 * able to restart with setstate().
236 *
237 * Note: the first thing we do is save the current state, if any, just like
238 * setstate() so that it doesn't matter when initstate is called.
239 *
240 * Returns a pointer to the old state.
241 */
242 char *
initstate(seed,arg_state,n)243 initstate(seed, arg_state, n)
244 unsigned int seed; /* seed for R.N.G. */
245 char *arg_state; /* pointer to state array */
246 int n; /* # bytes of state info */
247 {
248 register char *ostate = (char *)(&state[-1]);
249
250 if (rand_type == TYPE_0)
251 state[-1] = rand_type;
252 else
253 state[-1] = MAX_TYPES * (rptr - state) + rand_type;
254 if (n < BREAK_0) {
255 (void)fprintf(stderr,
256 "random: not enough state (%d bytes); ignored.\n", n);
257 return(0);
258 }
259 if (n < BREAK_1) {
260 rand_type = TYPE_0;
261 rand_deg = DEG_0;
262 rand_sep = SEP_0;
263 } else if (n < BREAK_2) {
264 rand_type = TYPE_1;
265 rand_deg = DEG_1;
266 rand_sep = SEP_1;
267 } else if (n < BREAK_3) {
268 rand_type = TYPE_2;
269 rand_deg = DEG_2;
270 rand_sep = SEP_2;
271 } else if (n < BREAK_4) {
272 rand_type = TYPE_3;
273 rand_deg = DEG_3;
274 rand_sep = SEP_3;
275 } else {
276 rand_type = TYPE_4;
277 rand_deg = DEG_4;
278 rand_sep = SEP_4;
279 }
280 state = &(((long *)arg_state)[1]); /* first location */
281 end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */
282 srandom(seed);
283 if (rand_type == TYPE_0)
284 state[-1] = rand_type;
285 else
286 state[-1] = MAX_TYPES*(rptr - state) + rand_type;
287 return(ostate);
288 }
289
290 /*
291 * setstate:
292 *
293 * Restore the state from the given state array.
294 *
295 * Note: it is important that we also remember the locations of the pointers
296 * in the current state information, and restore the locations of the pointers
297 * from the old state information. This is done by multiplexing the pointer
298 * location into the zeroeth word of the state information.
299 *
300 * Note that due to the order in which things are done, it is OK to call
301 * setstate() with the same state as the current state.
302 *
303 * Returns a pointer to the old state information.
304 */
305 char *
setstate(arg_state)306 setstate(arg_state)
307 char *arg_state;
308 {
309 register long *new_state = (long *)arg_state;
310 register int type = new_state[0] % MAX_TYPES;
311 register int rear = new_state[0] / MAX_TYPES;
312 char *ostate = (char *)(&state[-1]);
313
314 if (rand_type == TYPE_0)
315 state[-1] = rand_type;
316 else
317 state[-1] = MAX_TYPES * (rptr - state) + rand_type;
318 switch(type) {
319 case TYPE_0:
320 case TYPE_1:
321 case TYPE_2:
322 case TYPE_3:
323 case TYPE_4:
324 rand_type = type;
325 rand_deg = degrees[type];
326 rand_sep = seps[type];
327 break;
328 default:
329 (void)fprintf(stderr,
330 "random: state info corrupted; not changed.\n");
331 }
332 state = &new_state[1];
333 if (rand_type != TYPE_0) {
334 rptr = &state[rear];
335 fptr = &state[(rear + rand_sep) % rand_deg];
336 }
337 end_ptr = &state[rand_deg]; /* set end_ptr too */
338 return(ostate);
339 }
340
341 /*
342 * random:
343 *
344 * If we are using the trivial TYPE_0 R.N.G., just do the old linear
345 * congruential bit. Otherwise, we do our fancy trinomial stuff, which is
346 * the same in all the other cases due to all the global variables that have
347 * been set up. The basic operation is to add the number at the rear pointer
348 * into the one at the front pointer. Then both pointers are advanced to
349 * the next location cyclically in the table. The value returned is the sum
350 * generated, reduced to 31 bits by throwing away the "least random" low bit.
351 *
352 * Note: the code takes advantage of the fact that both the front and
353 * rear pointers can't wrap on the same call by not testing the rear
354 * pointer if the front one has wrapped.
355 *
356 * Returns a 31-bit random number.
357 */
358 long
random()359 random ()
360 {
361 long i;
362
363 if (rand_type == TYPE_0)
364 i = state[0] = (state[0] * 1103515245 + 12345) & 0x7fffffff;
365 else {
366 *fptr += *rptr;
367 i = (*fptr >> 1) & 0x7fffffff; /* chucking least random bit */
368 if (++fptr >= end_ptr) {
369 fptr = state;
370 ++rptr;
371 } else if (++rptr >= end_ptr)
372 rptr = state;
373 }
374 return (i);
375 }
376