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