random_r.c 11 KB

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