2 Copyright (C) 1995, 2005, 2008-2012 Free Software Foundation, Inc.
4 This program is free software: you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 3 of the License, or
7 (at your option) any later version.
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 Copyright (C) 1983 Regents of the University of California.
21 Redistribution and use in source and binary forms, with or without
22 modification, are permitted provided that the following conditions
25 1. Redistributions of source code must retain the above copyright
26 notice, this list of conditions and the following disclaimer.
27 2. Redistributions in binary form must reproduce the above copyright
28 notice, this list of conditions and the following disclaimer in the
29 documentation and/or other materials provided with the distribution.
30 4. Neither the name of the University nor the names of its contributors
31 may be used to endorse or promote products derived from this software
32 without specific prior written permission.
34 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS" AND
35 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
36 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
37 ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
38 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
39 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
40 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
41 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
42 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
43 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
47 * This is derived from the Berkeley source:
48 * @(#)random.c 5.5 (Berkeley) 7/6/88
49 * It was reworked for the GNU C Library by Roland McGrath.
50 * Rewritten to be reentrant by Ulrich Drepper, 1995
55 /* Don't use __attribute__ __nonnull__ in this compilation unit. Otherwise gcc
56 optimizes away the buf == NULL, arg_state == NULL, result == NULL tests
58 #define _GL_ARG_NONNULL(params)
69 /* An improved random number generation package. In addition to the standard
70 rand()/srand() like interface, this package also has a special state info
71 interface. The initstate() routine is called with a seed, an array of
72 bytes, and a count of how many bytes are being passed in; this array is
73 then initialized to contain information for random number generation with
74 that much state information. Good sizes for the amount of state
75 information are 32, 64, 128, and 256 bytes. The state can be switched by
76 calling the setstate() function with the same array as was initialized
77 with initstate(). By default, the package runs with 128 bytes of state
78 information and generates far better random numbers than a linear
79 congruential generator. If the amount of state information is less than
80 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
81 state information is treated as an array of longs; the zeroth element of
82 the array is the type of R.N.G. being used (small integer); the remainder
83 of the array is the state information for the R.N.G. Thus, 32 bytes of
84 state information will give 7 longs worth of state information, which will
85 allow a degree seven polynomial. (Note: The zeroth word of state
86 information also has some other information stored in it; see setstate
87 for details). The random number generation technique is a linear feedback
88 shift register approach, employing trinomials (since there are fewer terms
89 to sum up that way). In this approach, the least significant bit of all
90 the numbers in the state table will act as a linear feedback shift register,
91 and will have period 2^deg - 1 (where deg is the degree of the polynomial
92 being used, assuming that the polynomial is irreducible and primitive).
93 The higher order bits will have longer periods, since their values are
94 also influenced by pseudo-random carries out of the lower bits. The
95 total period of the generator is approximately deg*(2**deg - 1); thus
96 doubling the amount of state information has a vast influence on the
97 period of the generator. Note: The deg*(2**deg - 1) is an approximation
98 only good for large deg, when the period of the shift register is the
99 dominant factor. With deg equal to seven, the period is actually much
100 longer than the 7*(2**7 - 1) predicted by this formula. */
104 /* For each of the currently supported random number generators, we have a
105 break value on the amount of state information (you need at least this many
106 bytes of state info to support this random number generator), a degree for
107 the polynomial (actually a trinomial) that the R.N.G. is based on, and
108 separation between the two lower order coefficients of the trinomial. */
110 /* Linear congruential. */
116 /* x**7 + x**3 + 1. */
128 /* x**31 + x**3 + 1. */
141 /* Array versions of the above information to make code run faster.
142 Relies on fact that TYPE_i == i. */
144 #define MAX_TYPES 5 /* Max number of types above. */
146 struct random_poly_info
149 int degrees[MAX_TYPES];
152 static const struct random_poly_info random_poly_info =
154 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
155 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
159 # define weak_alias(local, symbol)
160 # define __set_errno(e) errno = (e)
161 # define __srandom_r srandom_r
162 # define __initstate_r initstate_r
163 # define __setstate_r setstate_r
164 # define __random_r random_r
169 /* Initialize the random number generator based on the given seed. If the
170 type is the trivial no-state-information type, just remember the seed.
171 Otherwise, initializes state[] based on the given "seed" via a linear
172 congruential generator. Then, the pointers are set to known locations
173 that are exactly rand_sep places apart. Lastly, it cycles the state
174 information a given number of times to get rid of any initial dependencies
175 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
176 for default usage relies on values produced by this routine. */
178 __srandom_r (unsigned int seed, struct random_data *buf)
189 type = buf->rand_type;
190 if ((unsigned int) type >= MAX_TYPES)
194 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
204 for (i = 1; i < kc; ++i)
207 state[i] = (16807 * state[i - 1]) % 2147483647;
208 but avoids overflowing 31 bits. */
209 long int hi = word / 127773;
210 long int lo = word % 127773;
211 word = 16807 * lo - 2836 * hi;
217 buf->fptr = &state[buf->rand_sep];
218 buf->rptr = &state[0];
223 (void) __random_r (buf, &discard);
233 weak_alias (__srandom_r, srandom_r)
235 /* Initialize the state information in the given array of N bytes for
236 future random number generation. Based on the number of bytes we
237 are given, and the break values for the different R.N.G.'s, we choose
238 the best (largest) one we can and set things up for it. srandom is
239 then called to initialize the state information. Note that on return
240 from srandom, we set state[-1] to be the type multiplexed with the current
241 value of the rear pointer; this is so successive calls to initstate won't
242 lose this information and will be able to restart with setstate.
243 Note: The first thing we do is save the current state, if any, just like
244 setstate so that it doesn't matter when initstate is called.
245 Returns a pointer to the old state. */
247 __initstate_r (unsigned int seed, char *arg_state, size_t n,
248 struct random_data *buf)
259 old_state = buf->state;
260 if (old_state != NULL)
262 int old_type = buf->rand_type;
263 if (old_type == TYPE_0)
264 old_state[-1] = TYPE_0;
266 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
270 type = n < BREAK_4 ? TYPE_3 : TYPE_4;
271 else if (n < BREAK_1)
275 __set_errno (EINVAL);
281 type = n < BREAK_2 ? TYPE_1 : TYPE_2;
283 degree = random_poly_info.degrees[type];
284 separation = random_poly_info.seps[type];
286 buf->rand_type = type;
287 buf->rand_sep = separation;
288 buf->rand_deg = degree;
289 state = &((int32_t *) arg_state)[1]; /* First location. */
290 /* Must set END_PTR before srandom. */
291 buf->end_ptr = &state[degree];
295 __srandom_r (seed, buf);
299 state[-1] = (buf->rptr - state) * MAX_TYPES + type;
304 __set_errno (EINVAL);
308 weak_alias (__initstate_r, initstate_r)
310 /* Restore the state from the given state array.
311 Note: It is important that we also remember the locations of the pointers
312 in the current state information, and restore the locations of the pointers
313 from the old state information. This is done by multiplexing the pointer
314 location into the zeroth word of the state information. Note that due
315 to the order in which things are done, it is OK to call setstate with the
316 same state as the current state
317 Returns a pointer to the old state information. */
319 __setstate_r (char *arg_state, struct random_data *buf)
321 int32_t *new_state = 1 + (int32_t *) arg_state;
328 if (arg_state == NULL || buf == NULL)
331 old_type = buf->rand_type;
332 old_state = buf->state;
333 if (old_type == TYPE_0)
334 old_state[-1] = TYPE_0;
336 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
338 type = new_state[-1] % MAX_TYPES;
339 if (type < TYPE_0 || type > TYPE_4)
342 buf->rand_deg = degree = random_poly_info.degrees[type];
343 buf->rand_sep = separation = random_poly_info.seps[type];
344 buf->rand_type = type;
348 int rear = new_state[-1] / MAX_TYPES;
349 buf->rptr = &new_state[rear];
350 buf->fptr = &new_state[(rear + separation) % degree];
352 buf->state = new_state;
353 /* Set end_ptr too. */
354 buf->end_ptr = &new_state[degree];
359 __set_errno (EINVAL);
363 weak_alias (__setstate_r, setstate_r)
365 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
366 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
367 same in all the other cases due to all the global variables that have been
368 set up. The basic operation is to add the number at the rear pointer into
369 the one at the front pointer. Then both pointers are advanced to the next
370 location cyclically in the table. The value returned is the sum generated,
371 reduced to 31 bits by throwing away the "least random" low bit.
372 Note: The code takes advantage of the fact that both the front and
373 rear pointers can't wrap on the same call by not testing the rear
374 pointer if the front one has wrapped. Returns a 31-bit random number. */
377 __random_r (struct random_data *buf, int32_t *result)
381 if (buf == NULL || result == NULL)
386 if (buf->rand_type == TYPE_0)
388 int32_t val = state[0];
389 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
395 int32_t *fptr = buf->fptr;
396 int32_t *rptr = buf->rptr;
397 int32_t *end_ptr = buf->end_ptr;
400 val = *fptr += *rptr;
401 /* Chucking least random bit. */
402 *result = (val >> 1) & 0x7fffffff;
421 __set_errno (EINVAL);
425 weak_alias (__random_r, random_r)