1 /* $NetBSD: ntp_random.c,v 1.5 2020/05/25 20:47:24 christos Exp $ */
2
3 /*
4 * Copyright (c) 1983, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. All advertising materials mentioning features or use of this software
16 * must display the following acknowledgement:
17 * This product includes software developed by the University of
18 * California, Berkeley and its contributors.
19 * 4. Neither the name of the University nor the names of its contributors
20 * may be used to endorse or promote products derived from this software
21 * without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 *
35 * $FreeBSD: src/lib/libc/stdlib/random.c,v 1.4.2.2 1999/09/05 11:16:45 peter Exp $
36 *
37 */
38
39 #if defined(LIBC_SCCS) && !defined(lint)
40 static char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95";
41 #endif /* LIBC_SCCS and not lint */
42
43 #include "config.h"
44 #include <sys/types.h>
45 #ifdef HAVE_UNISTD_H
46 # include <unistd.h>
47 #endif
48 #include <stdio.h>
49
50 #include <l_stdlib.h>
51 #include <ntp_random.h>
52 #include <ntp_unixtime.h>
53
54 /*
55 * random.c:
56 *
57 * An improved random number generation package. In addition to the standard
58 * rand()/srand() like interface, this package also has a special state info
59 * interface. The initstate() routine is called with a seed, an array of
60 * bytes, and a count of how many bytes are being passed in; this array is
61 * then initialized to contain information for random number generation with
62 * that much state information. Good sizes for the amount of state
63 * information are 32, 64, 128, and 256 bytes. The state can be switched by
64 * calling the setstate() routine with the same array as was initiallized
65 * with initstate(). By default, the package runs with 128 bytes of state
66 * information and generates far better random numbers than a linear
67 * congruential generator. If the amount of state information is less than
68 * 32 bytes, a simple linear congruential R.N.G. is used.
69 *
70 * Internally, the state information is treated as an array of longs; the
71 * zeroeth element of the array is the type of R.N.G. being used (small
72 * integer); the remainder of the array is the state information for the
73 * R.N.G. Thus, 32 bytes of state information will give 7 longs worth of
74 * state information, which will allow a degree seven polynomial. (Note:
75 * the zeroeth word of state information also has some other information
76 * stored in it -- see setstate() for details).
77 *
78 * The random number generation technique is a linear feedback shift register
79 * approach, employing trinomials (since there are fewer terms to sum up that
80 * way). In this approach, the least significant bit of all the numbers in
81 * the state table will act as a linear feedback shift register, and will
82 * have period 2^deg - 1 (where deg is the degree of the polynomial being
83 * used, assuming that the polynomial is irreducible and primitive). The
84 * higher order bits will have longer periods, since their values are also
85 * influenced by pseudo-random carries out of the lower bits. The total
86 * period of the generator is approximately deg*(2**deg - 1); thus doubling
87 * the amount of state information has a vast influence on the period of the
88 * generator. Note: the deg*(2**deg - 1) is an approximation only good for
89 * large deg, when the period of the shift register is the dominant factor.
90 * With deg equal to seven, the period is actually much longer than the
91 * 7*(2**7 - 1) predicted by this formula.
92 *
93 * Modified 28 December 1994 by Jacob S. Rosenberg.
94 * The following changes have been made:
95 * All references to the type u_int have been changed to unsigned long.
96 * All references to type int have been changed to type long. Other
97 * cleanups have been made as well. A warning for both initstate and
98 * setstate has been inserted to the effect that on Sparc platforms
99 * the 'arg_state' variable must be forced to begin on word boundaries.
100 * This can be easily done by casting a long integer array to char *.
101 * The overall logic has been left STRICTLY alone. This software was
102 * tested on both a VAX and Sun SpacsStation with exactly the same
103 * results. The new version and the original give IDENTICAL results.
104 * The new version is somewhat faster than the original. As the
105 * documentation says: "By default, the package runs with 128 bytes of
106 * state information and generates far better random numbers than a linear
107 * congruential generator. If the amount of state information is less than
108 * 32 bytes, a simple linear congruential R.N.G. is used." For a buffer of
109 * 128 bytes, this new version runs about 19 percent faster and for a 16
110 * byte buffer it is about 5 percent faster.
111 */
112
113 /*
114 * For each of the currently supported random number generators, we have a
115 * break value on the amount of state information (you need at least this
116 * many bytes of state info to support this random number generator), a degree
117 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
118 * the separation between the two lower order coefficients of the trinomial.
119 */
120 #define TYPE_0 0 /* linear congruential */
121 #define BREAK_0 8
122 #define DEG_0 0
123 #define SEP_0 0
124
125 #define TYPE_1 1 /* x**7 + x**3 + 1 */
126 #define BREAK_1 32
127 #define DEG_1 7
128 #define SEP_1 3
129
130 #define TYPE_2 2 /* x**15 + x + 1 */
131 #define BREAK_2 64
132 #define DEG_2 15
133 #define SEP_2 1
134
135 #define TYPE_3 3 /* x**31 + x**3 + 1 */
136 #define BREAK_3 128
137 #define DEG_3 31
138 #define SEP_3 3
139
140 #define TYPE_4 4 /* x**63 + x + 1 */
141 #define BREAK_4 256
142 #define DEG_4 63
143 #define SEP_4 1
144
145 #define MAX_TYPES 5 /* max number of types above */
146
147 /*
148 * Initially, everything is set up as if from:
149 *
150 * initstate(1, randtbl, 128);
151 *
152 * Note that this initialization takes advantage of the fact that srandom()
153 * advances the front and rear pointers 10*rand_deg times, and hence the
154 * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
155 * element of the state information, which contains info about the current
156 * position of the rear pointer is just
157 *
158 * MAX_TYPES * (rptr - state) + TYPE_3 == TYPE_3.
159 */
160
161 static unsigned long randtbl[DEG_3 + 1] = {
162 TYPE_3,
163 #ifdef USE_WEAK_SEEDING
164 /* Historic implementation compatibility */
165 /* The random sequences do not vary much with the seed */
166 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
167 0xf103bc02, 0x48f340fb, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
168 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88,
169 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
170 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
171 0x27fb47b9,
172 #else /* !USE_WEAK_SEEDING */
173 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,
174 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,
175 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,
176 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
177 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
178 0xf3bec5da
179 #endif /* !USE_WEAK_SEEDING */
180 };
181
182 /*
183 * fptr and rptr are two pointers into the state info, a front and a rear
184 * pointer. These two pointers are always rand_sep places aparts, as they
185 * cycle cyclically through the state information. (Yes, this does mean we
186 * could get away with just one pointer, but the code for random() is more
187 * efficient this way). The pointers are left positioned as they would be
188 * from the call
189 *
190 * initstate(1, randtbl, 128);
191 *
192 * (The position of the rear pointer, rptr, is really 0 (as explained above
193 * in the initialization of randtbl) because the state table pointer is set
194 * to point to randtbl[1] (as explained below).
195 */
196 static unsigned long *fptr = &randtbl[SEP_3 + 1];
197 static unsigned long *rptr = &randtbl[1];
198
199 /*
200 * The following things are the pointer to the state information table, the
201 * type of the current generator, the degree of the current polynomial being
202 * used, and the separation between the two pointers. Note that for efficiency
203 * of random(), we remember the first location of the state information, not
204 * the zeroeth. Hence it is valid to access state[-1], which is used to
205 * store the type of the R.N.G. Also, we remember the last location, since
206 * this is more efficient than indexing every time to find the address of
207 * the last element to see if the front and rear pointers have wrapped.
208 */
209 static unsigned long *state = &randtbl[1];
210 static long rand_type = TYPE_3;
211 static long rand_deg = DEG_3;
212 static long rand_sep = SEP_3;
213 static unsigned long *end_ptr = &randtbl[DEG_3 + 1];
214
215 static inline long good_rand (long);
216
217 static inline long
good_rand(register long x)218 good_rand (
219 register long x
220 )
221 {
222 #ifdef USE_WEAK_SEEDING
223 /*
224 * Historic implementation compatibility.
225 * The random sequences do not vary much with the seed,
226 * even with overflowing.
227 */
228 return (1103515245 * x + 12345);
229 #else /* !USE_WEAK_SEEDING */
230 /*
231 * Compute x = (7^5 * x) mod (2^31 - 1)
232 * wihout overflowing 31 bits:
233 * (2^31 - 1) = 127773 * (7^5) + 2836
234 * From "Random number generators: good ones are hard to find",
235 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
236 * October 1988, p. 1195.
237 */
238 register long hi, lo;
239
240 hi = x / 127773;
241 lo = x % 127773;
242 x = 16807 * lo - 2836 * hi;
243 if (x <= 0)
244 x += 0x7fffffff;
245 return (x);
246 #endif /* !USE_WEAK_SEEDING */
247 }
248
249 /*
250 * srandom:
251 *
252 * Initialize the random number generator based on the given seed. If the
253 * type is the trivial no-state-information type, just remember the seed.
254 * Otherwise, initializes state[] based on the given "seed" via a linear
255 * congruential generator. Then, the pointers are set to known locations
256 * that are exactly rand_sep places apart. Lastly, it cycles the state
257 * information a given number of times to get rid of any initial dependencies
258 * introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
259 * for default usage relies on values produced by this routine.
260 */
261 void
ntp_srandom(unsigned long x)262 ntp_srandom(
263 unsigned long x
264 )
265 {
266 long i;
267
268 if (rand_type == TYPE_0) {
269 state[0] = x;
270 } else {
271 state[0] = x;
272 for (i = 1; i < rand_deg; i++)
273 state[i] = good_rand(state[i - 1]);
274 fptr = &state[rand_sep];
275 rptr = &state[0];
276 for (i = 0; i < 10 * rand_deg; i++)
277 x = ntp_random();
278 }
279
280 /* seed the likely faster (and poorer) rand() as well */
281 srand((u_int)x);
282 }
283
284 /*
285 * srandomdev:
286 *
287 * Many programs choose the seed value in a totally predictable manner.
288 * This often causes problems. We seed the generator using the much more
289 * secure urandom(4) interface. Note that this particular seeding
290 * procedure can generate states which are impossible to reproduce by
291 * calling srandom() with any value, since the succeeding terms in the
292 * state buffer are no longer derived from the LC algorithm applied to
293 * a fixed seed.
294 */
295 #ifdef NEED_SRANDOMDEV
296 void
ntp_srandomdev(void)297 ntp_srandomdev( void )
298 {
299 struct timeval tv;
300 unsigned long junk; /* Purposely used uninitialized */
301
302 GETTIMEOFDAY(&tv, NULL);
303 ntp_srandom(getpid() ^ tv.tv_sec ^ tv.tv_usec ^ junk);
304 return;
305 }
306 #endif
307
308
309 /*
310 * ntp_initstate() and ntp_setstate() are unused in our codebase and
311 * trigger warnings due to casting to a more-strictly-aligned pointer
312 * on alignment-sensitive platforms. #ifdef them away to save noise,
313 * build time, and binary space, but retain the code in case we find a
314 * use.
315 */
316 #ifdef COMPILE_UNUSED_FUNCTIONS
317 /*
318 * Array versions of the above information to make code run faster --
319 * relies on fact that TYPE_i == i.
320 */
321 #define MAX_TYPES 5 /* max number of types above */
322
323 static long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
324 static long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
325
326 /*
327 * initstate:
328 *
329 * Initialize the state information in the given array of n bytes for future
330 * random number generation. Based on the number of bytes we are given, and
331 * the break values for the different R.N.G.'s, we choose the best (largest)
332 * one we can and set things up for it. srandom() is then called to
333 * initialize the state information.
334 *
335 * Note that on return from srandom(), we set state[-1] to be the type
336 * multiplexed with the current value of the rear pointer; this is so
337 * successive calls to initstate() won't lose this information and will be
338 * able to restart with setstate().
339 *
340 * Note: the first thing we do is save the current state, if any, just like
341 * setstate() so that it doesn't matter when initstate is called.
342 *
343 * Returns a pointer to the old state.
344 *
345 * Note: The Sparc platform requires that arg_state begin on a long
346 * word boundary; otherwise a bus error will occur. Even so, lint will
347 * complain about mis-alignment, but you should disregard these messages.
348 */
349 char *
ntp_initstate(unsigned long seed,char * arg_state,long n)350 ntp_initstate(
351 unsigned long seed, /* seed for R.N.G. */
352 char *arg_state, /* pointer to state array */
353 long n /* # bytes of state info */
354 )
355 {
356 register char *ostate = (char *)(&state[-1]);
357 register long *long_arg_state = (long *) arg_state;
358
359 if (rand_type == TYPE_0)
360 state[-1] = rand_type;
361 else
362 state[-1] = MAX_TYPES * (rptr - state) + rand_type;
363 if (n < BREAK_0) {
364 (void)fprintf(stderr,
365 "random: not enough state (%ld bytes); ignored.\n", n);
366 return(0);
367 }
368 if (n < BREAK_1) {
369 rand_type = TYPE_0;
370 rand_deg = DEG_0;
371 rand_sep = SEP_0;
372 } else if (n < BREAK_2) {
373 rand_type = TYPE_1;
374 rand_deg = DEG_1;
375 rand_sep = SEP_1;
376 } else if (n < BREAK_3) {
377 rand_type = TYPE_2;
378 rand_deg = DEG_2;
379 rand_sep = SEP_2;
380 } else if (n < BREAK_4) {
381 rand_type = TYPE_3;
382 rand_deg = DEG_3;
383 rand_sep = SEP_3;
384 } else {
385 rand_type = TYPE_4;
386 rand_deg = DEG_4;
387 rand_sep = SEP_4;
388 }
389 state = (unsigned long *) (long_arg_state + 1); /* first location */
390 end_ptr = &state[rand_deg]; /* must set end_ptr before srandom */
391 ntp_srandom(seed);
392 if (rand_type == TYPE_0)
393 long_arg_state[0] = rand_type;
394 else
395 long_arg_state[0] = MAX_TYPES * (rptr - state) + rand_type;
396 return(ostate);
397 }
398
399 /*
400 * setstate:
401 *
402 * Restore the state from the given state array.
403 *
404 * Note: it is important that we also remember the locations of the pointers
405 * in the current state information, and restore the locations of the pointers
406 * from the old state information. This is done by multiplexing the pointer
407 * location into the zeroeth word of the state information.
408 *
409 * Note that due to the order in which things are done, it is OK to call
410 * setstate() with the same state as the current state.
411 *
412 * Returns a pointer to the old state information.
413 *
414 * Note: The Sparc platform requires that arg_state begin on a long
415 * word boundary; otherwise a bus error will occur. Even so, lint will
416 * complain about mis-alignment, but you should disregard these messages.
417 */
418 char *
ntp_setstate(char * arg_state)419 ntp_setstate(
420 char *arg_state /* pointer to state array */
421 )
422 {
423 register unsigned long *new_state = (unsigned long *) arg_state;
424 register long type = new_state[0] % MAX_TYPES;
425 register long rear = new_state[0] / MAX_TYPES;
426 char *ostate = (char *)(&state[-1]);
427
428 if (rand_type == TYPE_0)
429 state[-1] = rand_type;
430 else
431 state[-1] = MAX_TYPES * (rptr - state) + rand_type;
432 switch(type) {
433 case TYPE_0:
434 case TYPE_1:
435 case TYPE_2:
436 case TYPE_3:
437 case TYPE_4:
438 rand_type = type;
439 rand_deg = degrees[type];
440 rand_sep = seps[type];
441 break;
442 default:
443 (void)fprintf(stderr,
444 "random: state info corrupted; not changed.\n");
445 }
446 state = (new_state + 1);
447 if (rand_type != TYPE_0) {
448 rptr = &state[rear];
449 fptr = &state[(rear + rand_sep) % rand_deg];
450 }
451 end_ptr = &state[rand_deg]; /* set end_ptr too */
452 return(ostate);
453 }
454 #endif /* COMPILE_UNUSED_FUNCTIONS */
455
456
457 /*
458 * random:
459 *
460 * If we are using the trivial TYPE_0 R.N.G., just do the old linear
461 * congruential bit. Otherwise, we do our fancy trinomial stuff, which is
462 * the same in all the other cases due to all the global variables that have
463 * been set up. The basic operation is to add the number at the rear pointer
464 * into the one at the front pointer. Then both pointers are advanced to
465 * the next location cyclically in the table. The value returned is the sum
466 * generated, reduced to 31 bits by throwing away the "least random" low bit.
467 *
468 * Note: the code takes advantage of the fact that both the front and
469 * rear pointers can't wrap on the same call by not testing the rear
470 * pointer if the front one has wrapped.
471 *
472 * Returns a 31-bit random number.
473 */
474 long
ntp_random(void)475 ntp_random( void )
476 {
477 register long i;
478 register unsigned long *f, *r;
479
480 if (rand_type == TYPE_0) {
481 i = state[0];
482 state[0] = i = (good_rand(i)) & 0x7fffffff;
483 } else {
484 /*
485 * Use local variables rather than static variables for speed.
486 */
487 f = fptr; r = rptr;
488 *f += *r;
489 i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */
490 if (++f >= end_ptr) {
491 f = state;
492 ++r;
493 }
494 else if (++r >= end_ptr) {
495 r = state;
496 }
497
498 fptr = f; rptr = r;
499 }
500 return(i);
501 }
502