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1 /* Copyright (C) 1995-2021 Free Software Foundation, Inc.
2
3 This file is free software: you can redistribute it and/or modify
4 it under the terms of the GNU Lesser General Public License as
5 published by the Free Software Foundation; either version 3 of the
6 License, or (at your option) any later version.
7
8 This file is distributed in the hope that it will be useful,
9 but WITHOUT ANY WARRANTY; without even the implied warranty of
10 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 GNU Lesser General Public License for more details.
12
13 You should have received a copy of the GNU Lesser General Public License
14 along with this program. If not, see <https://www.gnu.org/licenses/>. */
15
16 /*
17 * This is derived from the Berkeley source:
18 * @(#)random.c 5.5 (Berkeley) 7/6/88
19 * It was reworked for the GNU C Library by Roland McGrath.
20 * Rewritten to use reentrant functions by Ulrich Drepper, 1995.
21 */
22
23 /*
24 Copyright (C) 1983 Regents of the University of California.
25 All rights reserved.
26
27 Redistribution and use in source and binary forms, with or without
28 modification, are permitted provided that the following conditions
29 are met:
30
31 1. Redistributions of source code must retain the above copyright
32 notice, this list of conditions and the following disclaimer.
33 2. Redistributions in binary form must reproduce the above copyright
34 notice, this list of conditions and the following disclaimer in the
35 documentation and/or other materials provided with the distribution.
36 4. Neither the name of the University nor the names of its contributors
37 may be used to endorse or promote products derived from this software
38 without specific prior written permission.
39
40 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS" AND
41 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
42 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
43 ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
44 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
45 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
46 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
47 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
48 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
49 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
50 SUCH DAMAGE.*/
51
52 #ifndef _LIBC
53 # include <libc-config.h>
54 # define __srandom srandom
55 # define __initstate initstate
56 # define __setstate setstate
57 # define __random random
58 # define __srandom_r srandom_r
59 # define __initstate_r initstate_r
60 # define __setstate_r setstate_r
61 # define __random_r random_r
62 #endif
63
64 /* Specification. */
65 #include <stdlib.h>
66
67 #ifdef _LIBC
68 # include <libc-lock.h>
69 #else
70 /* Allow memory races; that's random enough. */
71 # define __libc_lock_define_initialized(class, name)
72 # define __libc_lock_lock(name) ((void) 0)
73 # define __libc_lock_unlock(name) ((void) 0)
74 #endif
75
76 /* An improved random number generation package. In addition to the standard
77 rand()/srand() like interface, this package also has a special state info
78 interface. The initstate() routine is called with a seed, an array of
79 bytes, and a count of how many bytes are being passed in; this array is
80 then initialized to contain information for random number generation with
81 that much state information. Good sizes for the amount of state
82 information are 32, 64, 128, and 256 bytes. The state can be switched by
83 calling the setstate() function with the same array as was initialized
84 with initstate(). By default, the package runs with 128 bytes of state
85 information and generates far better random numbers than a linear
86 congruential generator. If the amount of state information is less than
87 32 bytes, a simple linear congruential R.N.G. is used. Internally, the
88 state information is treated as an array of longs; the zeroth element of
89 the array is the type of R.N.G. being used (small integer); the remainder
90 of the array is the state information for the R.N.G. Thus, 32 bytes of
91 state information will give 7 longs worth of state information, which will
92 allow a degree seven polynomial. (Note: The zeroth word of state
93 information also has some other information stored in it; see setstate
94 for details). The random number generation technique is a linear feedback
95 shift register approach, employing trinomials (since there are fewer terms
96 to sum up that way). In this approach, the least significant bit of all
97 the numbers in the state table will act as a linear feedback shift register,
98 and will have period 2^deg - 1 (where deg is the degree of the polynomial
99 being used, assuming that the polynomial is irreducible and primitive).
100 The higher order bits will have longer periods, since their values are
101 also influenced by pseudo-random carries out of the lower bits. The
102 total period of the generator is approximately deg*(2**deg - 1); thus
103 doubling the amount of state information has a vast influence on the
104 period of the generator. Note: The deg*(2**deg - 1) is an approximation
105 only good for large deg, when the period of the shift register is the
106 dominant factor. With deg equal to seven, the period is actually much
107 longer than the 7*(2**7 - 1) predicted by this formula. */
108
109
110
111 /* For each of the currently supported random number generators, we have a
112 break value on the amount of state information (you need at least this many
113 bytes of state info to support this random number generator), a degree for
114 the polynomial (actually a trinomial) that the R.N.G. is based on, and
115 separation between the two lower order coefficients of the trinomial. */
116
117 /* Linear congruential. */
118 #define TYPE_0 0
119 #define BREAK_0 8
120 #define DEG_0 0
121 #define SEP_0 0
122
123 /* x**7 + x**3 + 1. */
124 #define TYPE_1 1
125 #define BREAK_1 32
126 #define DEG_1 7
127 #define SEP_1 3
128
129 /* x**15 + x + 1. */
130 #define TYPE_2 2
131 #define BREAK_2 64
132 #define DEG_2 15
133 #define SEP_2 1
134
135 /* x**31 + x**3 + 1. */
136 #define TYPE_3 3
137 #define BREAK_3 128
138 #define DEG_3 31
139 #define SEP_3 3
140
141 /* x**63 + x + 1. */
142 #define TYPE_4 4
143 #define BREAK_4 256
144 #define DEG_4 63
145 #define SEP_4 1
146
147
148 /* Array versions of the above information to make code run faster.
149 Relies on fact that TYPE_i == i. */
150
151 #define MAX_TYPES 5 /* Max number of types above. */
152
153
154 /* Initially, everything is set up as if from:
155 initstate(1, randtbl, 128);
156 Note that this initialization takes advantage of the fact that srandom
157 advances the front and rear pointers 10*rand_deg times, and hence the
158 rear pointer which starts at 0 will also end up at zero; thus the zeroth
159 element of the state information, which contains info about the current
160 position of the rear pointer is just
161 (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3. */
162
163 static int32_t randtbl[DEG_3 + 1] =
164 {
165 TYPE_3,
166
167 -1726662223, 379960547, 1735697613, 1040273694, 1313901226,
168 1627687941, -179304937, -2073333483, 1780058412, -1989503057,
169 -615974602, 344556628, 939512070, -1249116260, 1507946756,
170 -812545463, 154635395, 1388815473, -1926676823, 525320961,
171 -1009028674, 968117788, -123449607, 1284210865, 435012392,
172 -2017506339, -911064859, -370259173, 1132637927, 1398500161,
173 -205601318,
174 };
175
176
177 static struct random_data unsafe_state =
178 {
179 /* FPTR and RPTR are two pointers into the state info, a front and a rear
180 pointer. These two pointers are always rand_sep places apart, as they
181 cycle through the state information. (Yes, this does mean we could get
182 away with just one pointer, but the code for random is more efficient
183 this way). The pointers are left positioned as they would be from the call:
184 initstate(1, randtbl, 128);
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 .fptr = &randtbl[SEP_3 + 1],
190 .rptr = &randtbl[1],
191
192 /* The following things are the pointer to the state information table,
193 the type of the current generator, the degree of the current polynomial
194 being used, and the separation between the two pointers.
195 Note that for efficiency of random, we remember the first location of
196 the state information, not the zeroth. Hence it is valid to access
197 state[-1], which is used to store the type of the R.N.G.
198 Also, we remember the last location, since this is more efficient than
199 indexing every time to find the address of the last element to see if
200 the front and rear pointers have wrapped. */
201
202 .state = &randtbl[1],
203
204 .rand_type = TYPE_3,
205 .rand_deg = DEG_3,
206 .rand_sep = SEP_3,
207
208 .end_ptr = &randtbl[sizeof (randtbl) / sizeof (randtbl[0])]
209 };
210
211 /* POSIX.1c requires that there is mutual exclusion for the 'rand' and
212 'srand' functions to prevent concurrent calls from modifying common
213 data. */
214 __libc_lock_define_initialized (static, lock)
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*/
215
216 /* Initialize the random number generator based on the given seed. If the
217 type is the trivial no-state-information type, just remember the seed.
218 Otherwise, initializes state[] based on the given "seed" via a linear
219 congruential generator. Then, the pointers are set to known locations
220 that are exactly rand_sep places apart. Lastly, it cycles the state
221 information a given number of times to get rid of any initial dependencies
222 introduced by the L.C.R.N.G. Note that the initialization of randtbl[]
223 for default usage relies on values produced by this routine. */
224 void
225 __srandom (unsigned int x)
226 {
227 __libc_lock_lock (lock);
228 (void) __srandom_r (x, &unsafe_state);
229 __libc_lock_unlock (lock);
230 }
231
232 weak_alias (__srandom, srandom)
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*/
233 weak_alias (__srandom, srand)
234
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. */
246 char *
247 __initstate (unsigned int seed, char *arg_state, size_t n)
248 {
249 int32_t *ostate;
250 int ret;
251
252 __libc_lock_lock (lock);
253
254 ostate = &unsafe_state.state[-1];
255
256 ret = __initstate_r (seed, arg_state, n, &unsafe_state);
257
258 __libc_lock_unlock (lock);
259
260 return ret == -1 ? NULL : (char *) ostate;
261 }
262
263 weak_alias (__initstate, initstate)
/* */
264
265 /* Restore the state from the given state array.
266 Note: It is important that we also remember the locations of the pointers
267 in the current state information, and restore the locations of the pointers
268 from the old state information. This is done by multiplexing the pointer
269 location into the zeroth word of the state information. Note that due
270 to the order in which things are done, it is OK to call setstate with the
271 same state as the current state
272 Returns a pointer to the old state information. */
273 char *
274 __setstate (char *arg_state)
275 {
276 int32_t *ostate;
277
278 __libc_lock_lock (lock);
279
280 ostate = &unsafe_state.state[-1];
281
282 if (__setstate_r (arg_state, &unsafe_state) < 0)
283 ostate = NULL;
284
285 __libc_lock_unlock (lock);
286
287 return (char *) ostate;
288 }
289
290 weak_alias (__setstate, setstate)
/* ![[last]](../icons/n_last.png)
*/
291
292 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
293 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the
294 same in all the other cases due to all the global variables that have been
295 set up. The basic operation is to add the number at the rear pointer into
296 the one at the front pointer. Then both pointers are advanced to the next
297 location cyclically in the table. The value returned is the sum generated,
298 reduced to 31 bits by throwing away the "least random" low bit.
299 Note: The code takes advantage of the fact that both the front and
300 rear pointers can't wrap on the same call by not testing the rear
301 pointer if the front one has wrapped. Returns a 31-bit random number. */
302
303 long int
304 __random (void)
305 {
306 int32_t retval;
307
308 __libc_lock_lock (lock);
309
310 (void) __random_r (&unsafe_state, &retval);
311
312 __libc_lock_unlock (lock);
313
314 return retval;
315 }
316
317 weak_alias (__random, random)
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*/