/contrib/ntp/libntp/ntp_random.c

https://bitbucket.org/freebsd/freebsd-head/ · C · 485 lines · 215 code · 29 blank · 241 comment · 31 complexity · 7a8b124fe9be46f8924dadcabd120282 MD5 · raw file

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