2 Copyright (C) 1995, 2005, 2008-2011 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
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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
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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)
67 /* An improved random number generation package. In addition to the standard
68 rand()/srand() like interface, this package also has a special state info
69 interface. The initstate() routine is called with a seed, an array of
70 bytes, and a count of how many bytes are being passed in; this array is
71 then initialized to contain information for random number generation with
72 that much state information. Good sizes for the amount of state
73 information are 32, 64, 128, and 256 bytes. The state can be switched by
74 calling the setstate() function with the same array as was initialized
75 with initstate(). By default, the package runs with 128 bytes of state
76 information and generates far better random numbers than a linear
77 congruential generator. If the amount of state information is less than
78 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
79 state information is treated as an array of longs; the zeroth element of
80 the array is the type of R.N.G. being used (small integer); the remainder
81 of the array is the state information for the R.N.G. Thus, 32 bytes of
82 state information will give 7 longs worth of state information, which will
83 allow a degree seven polynomial. (Note: The zeroth word of state
84 information also has some other information stored in it; see setstate
85 for details). The random number generation technique is a linear feedback
86 shift register approach, employing trinomials (since there are fewer terms
87 to sum up that way). In this approach, the least significant bit of all
88 the numbers in the state table will act as a linear feedback shift register,
89 and will have period 2^deg - 1 (where deg is the degree of the polynomial
90 being used, assuming that the polynomial is irreducible and primitive).
91 The higher order bits will have longer periods, since their values are
92 also influenced by pseudo-random carries out of the lower bits. The
93 total period of the generator is approximately deg*(2**deg - 1); thus
94 doubling the amount of state information has a vast influence on the
95 period of the generator. Note: The deg*(2**deg - 1) is an approximation
96 only good for large deg, when the period of the shift register is the
97 dominant factor. With deg equal to seven, the period is actually much
98 longer than the 7*(2**7 - 1) predicted by this formula. */
102 /* For each of the currently supported random number generators, we have a
103 break value on the amount of state information (you need at least this many
104 bytes of state info to support this random number generator), a degree for
105 the polynomial (actually a trinomial) that the R.N.G. is based on, and
106 separation between the two lower order coefficients of the trinomial. */
108 /* Linear congruential. */
114 /* x**7 + x**3 + 1. */
126 /* x**31 + x**3 + 1. */
139 /* Array versions of the above information to make code run faster.
140 Relies on fact that TYPE_i == i. */
142 #define MAX_TYPES 5 /* Max number of types above. */
144 struct random_poly_info
147 int degrees[MAX_TYPES];
150 static const struct random_poly_info random_poly_info =
152 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
153 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
157 # define weak_alias(local, symbol)
158 # define __set_errno(e) errno = (e)
159 # define __srandom_r srandom_r
160 # define __initstate_r initstate_r
161 # define __setstate_r setstate_r
162 # define __random_r random_r
167 /* Initialize the random number generator based on the given seed. If the
168 type is the trivial no-state-information type, just remember the seed.
169 Otherwise, initializes state[] based on the given "seed" via a linear
170 congruential generator. Then, the pointers are set to known locations
171 that are exactly rand_sep places apart. Lastly, it cycles the state
172 information a given number of times to get rid of any initial dependencies
173 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
174 for default usage relies on values produced by this routine. */
176 __srandom_r (unsigned int seed, struct random_data *buf)
187 type = buf->rand_type;
188 if ((unsigned int) type >= MAX_TYPES)
192 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */
202 for (i = 1; i < kc; ++i)
205 state[i] = (16807 * state[i - 1]) % 2147483647;
206 but avoids overflowing 31 bits. */
207 long int hi = word / 127773;
208 long int lo = word % 127773;
209 word = 16807 * lo - 2836 * hi;
215 buf->fptr = &state[buf->rand_sep];
216 buf->rptr = &state[0];
221 (void) __random_r (buf, &discard);
231 weak_alias (__srandom_r, srandom_r)
233 /* Initialize the state information in the given array of N bytes for
234 future random number generation. Based on the number of bytes we
235 are given, and the break values for the different R.N.G.'s, we choose
236 the best (largest) one we can and set things up for it. srandom is
237 then called to initialize the state information. Note that on return
238 from srandom, we set state[-1] to be the type multiplexed with the current
239 value of the rear pointer; this is so successive calls to initstate won't
240 lose this information and will be able to restart with setstate.
241 Note: The first thing we do is save the current state, if any, just like
242 setstate so that it doesn't matter when initstate is called.
243 Returns a pointer to the old state. */
245 __initstate_r (unsigned int seed, char *arg_state, size_t n,
246 struct random_data *buf)
257 old_state = buf->state;
258 if (old_state != NULL)
260 int old_type = buf->rand_type;
261 if (old_type == TYPE_0)
262 old_state[-1] = TYPE_0;
264 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
268 type = n < BREAK_4 ? TYPE_3 : TYPE_4;
269 else if (n < BREAK_1)
273 __set_errno (EINVAL);
279 type = n < BREAK_2 ? TYPE_1 : TYPE_2;
281 degree = random_poly_info.degrees[type];
282 separation = random_poly_info.seps[type];
284 buf->rand_type = type;
285 buf->rand_sep = separation;
286 buf->rand_deg = degree;
287 state = &((int32_t *) arg_state)[1]; /* First location. */
288 /* Must set END_PTR before srandom. */
289 buf->end_ptr = &state[degree];
293 __srandom_r (seed, buf);
297 state[-1] = (buf->rptr - state) * MAX_TYPES + type;
302 __set_errno (EINVAL);
306 weak_alias (__initstate_r, initstate_r)
308 /* Restore the state from the given state array.
309 Note: It is important that we also remember the locations of the pointers
310 in the current state information, and restore the locations of the pointers
311 from the old state information. This is done by multiplexing the pointer
312 location into the zeroth word of the state information. Note that due
313 to the order in which things are done, it is OK to call setstate with the
314 same state as the current state
315 Returns a pointer to the old state information. */
317 __setstate_r (char *arg_state, struct random_data *buf)
319 int32_t *new_state = 1 + (int32_t *) arg_state;
326 if (arg_state == NULL || buf == NULL)
329 old_type = buf->rand_type;
330 old_state = buf->state;
331 if (old_type == TYPE_0)
332 old_state[-1] = TYPE_0;
334 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
336 type = new_state[-1] % MAX_TYPES;
337 if (type < TYPE_0 || type > TYPE_4)
340 buf->rand_deg = degree = random_poly_info.degrees[type];
341 buf->rand_sep = separation = random_poly_info.seps[type];
342 buf->rand_type = type;
346 int rear = new_state[-1] / MAX_TYPES;
347 buf->rptr = &new_state[rear];
348 buf->fptr = &new_state[(rear + separation) % degree];
350 buf->state = new_state;
351 /* Set end_ptr too. */
352 buf->end_ptr = &new_state[degree];
357 __set_errno (EINVAL);
361 weak_alias (__setstate_r, setstate_r)
363 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
364 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
365 same in all the other cases due to all the global variables that have been
366 set up. The basic operation is to add the number at the rear pointer into
367 the one at the front pointer. Then both pointers are advanced to the next
368 location cyclically in the table. The value returned is the sum generated,
369 reduced to 31 bits by throwing away the "least random" low bit.
370 Note: The code takes advantage of the fact that both the front and
371 rear pointers can't wrap on the same call by not testing the rear
372 pointer if the front one has wrapped. Returns a 31-bit random number. */
375 __random_r (struct random_data *buf, int32_t *result)
379 if (buf == NULL || result == NULL)
384 if (buf->rand_type == TYPE_0)
386 int32_t val = state[0];
387 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
393 int32_t *fptr = buf->fptr;
394 int32_t *rptr = buf->rptr;
395 int32_t *end_ptr = buf->end_ptr;
398 val = *fptr += *rptr;
399 /* Chucking least random bit. */
400 *result = (val >> 1) & 0x7fffffff;
419 __set_errno (EINVAL);
423 weak_alias (__random_r, random_r)