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1 | /* Copyright (C) 1995 Free Software Foundation |
2 | ||
3 | The GNU C Library is free software; you can redistribute it and/or | |
4 | modify it under the terms of the GNU Lesser General Public | |
5 | License as published by the Free Software Foundation; either | |
6 | version 2.1 of the License, or (at your option) any later version. | |
7 | ||
8 | The GNU C Library 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 GNU | |
11 | Lesser General Public License for more details. | |
12 | ||
13 | You should have received a copy of the GNU Lesser General Public | |
14 | License along with the GNU C Library; if not, write to the Free | |
15 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |
16 | 02111-1307 USA. */ | |
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17 | |
18 | /* | |
19 | * This is derived from the Berkeley source: | |
20 | * @(#)random.c 5.5 (Berkeley) 7/6/88 | |
21 | * It was reworked for the GNU C Library by Roland McGrath. | |
845dcb57 | 22 | * Rewritten to use reentrant functions by Ulrich Drepper, 1995. |
28f540f4 RM |
23 | */ |
24 | ||
aeb25823 AJ |
25 | /* |
26 | Copyright (C) 1983 Regents of the University of California. | |
27 | All rights reserved. | |
28 | ||
29 | Redistribution and use in source and binary forms, with or without | |
30 | modification, are permitted provided that the following conditions | |
31 | are met: | |
32 | ||
33 | 1. Redistributions of source code must retain the above copyright | |
34 | notice, this list of conditions and the following disclaimer. | |
35 | 2. Redistributions in binary form must reproduce the above copyright | |
36 | notice, this list of conditions and the following disclaimer in the | |
37 | documentation and/or other materials provided with the distribution. | |
38 | 4. Neither the name of the University nor the names of its contributors | |
39 | may be used to endorse or promote products derived from this software | |
40 | without specific prior written permission. | |
41 | ||
42 | THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
43 | ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
44 | IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
45 | ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
46 | FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
47 | DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
48 | OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
49 | HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
50 | LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
51 | OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
52 | SUCH DAMAGE.*/ | |
53 | ||
5107cf1d | 54 | #include <bits/libc-lock.h> |
28f540f4 RM |
55 | #include <limits.h> |
56 | #include <stddef.h> | |
57 | #include <stdlib.h> | |
58 | ||
59 | ||
60 | /* An improved random number generation package. In addition to the standard | |
61 | rand()/srand() like interface, this package also has a special state info | |
62 | interface. The initstate() routine is called with a seed, an array of | |
63 | bytes, and a count of how many bytes are being passed in; this array is | |
64 | then initialized to contain information for random number generation with | |
65 | that much state information. Good sizes for the amount of state | |
66 | information are 32, 64, 128, and 256 bytes. The state can be switched by | |
6d52618b | 67 | calling the setstate() function with the same array as was initialized |
28f540f4 RM |
68 | with initstate(). By default, the package runs with 128 bytes of state |
69 | information and generates far better random numbers than a linear | |
70 | congruential generator. If the amount of state information is less than | |
71 | 32 bytes, a simple linear congruential R.N.G. is used. Internally, the | |
6d52618b | 72 | state information is treated as an array of longs; the zeroth element of |
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73 | the array is the type of R.N.G. being used (small integer); the remainder |
74 | of the array is the state information for the R.N.G. Thus, 32 bytes of | |
75 | state information will give 7 longs worth of state information, which will | |
6d52618b | 76 | allow a degree seven polynomial. (Note: The zeroth word of state |
28f540f4 RM |
77 | information also has some other information stored in it; see setstate |
78 | for details). The random number generation technique is a linear feedback | |
79 | shift register approach, employing trinomials (since there are fewer terms | |
80 | to sum up that way). In this approach, the least significant bit of all | |
81 | the numbers in the state table will act as a linear feedback shift register, | |
82 | and will have period 2^deg - 1 (where deg is the degree of the polynomial | |
83 | being used, assuming that the polynomial is irreducible and primitive). | |
84 | The higher order bits will have longer periods, since their values are | |
85 | also influenced by pseudo-random carries out of the lower bits. The | |
86 | total period of the generator is approximately deg*(2**deg - 1); thus | |
87 | doubling the amount of state information has a vast influence on the | |
88 | period of the generator. Note: The deg*(2**deg - 1) is an approximation | |
89 | only good for large deg, when the period of the shift register is the | |
90 | dominant factor. With deg equal to seven, the period is actually much | |
91 | longer than the 7*(2**7 - 1) predicted by this formula. */ | |
92 | ||
93 | ||
94 | ||
95 | /* For each of the currently supported random number generators, we have a | |
6d52618b | 96 | break value on the amount of state information (you need at least this many |
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97 | bytes of state info to support this random number generator), a degree for |
98 | the polynomial (actually a trinomial) that the R.N.G. is based on, and | |
99 | separation between the two lower order coefficients of the trinomial. */ | |
100 | ||
101 | /* Linear congruential. */ | |
102 | #define TYPE_0 0 | |
103 | #define BREAK_0 8 | |
104 | #define DEG_0 0 | |
105 | #define SEP_0 0 | |
106 | ||
107 | /* x**7 + x**3 + 1. */ | |
108 | #define TYPE_1 1 | |
109 | #define BREAK_1 32 | |
110 | #define DEG_1 7 | |
111 | #define SEP_1 3 | |
112 | ||
113 | /* x**15 + x + 1. */ | |
114 | #define TYPE_2 2 | |
115 | #define BREAK_2 64 | |
116 | #define DEG_2 15 | |
117 | #define SEP_2 1 | |
118 | ||
119 | /* x**31 + x**3 + 1. */ | |
120 | #define TYPE_3 3 | |
121 | #define BREAK_3 128 | |
122 | #define DEG_3 31 | |
123 | #define SEP_3 3 | |
124 | ||
125 | /* x**63 + x + 1. */ | |
126 | #define TYPE_4 4 | |
127 | #define BREAK_4 256 | |
128 | #define DEG_4 63 | |
129 | #define SEP_4 1 | |
130 | ||
131 | ||
132 | /* Array versions of the above information to make code run faster. | |
133 | Relies on fact that TYPE_i == i. */ | |
134 | ||
135 | #define MAX_TYPES 5 /* Max number of types above. */ | |
136 | ||
28f540f4 RM |
137 | |
138 | /* Initially, everything is set up as if from: | |
139 | initstate(1, randtbl, 128); | |
140 | Note that this initialization takes advantage of the fact that srandom | |
141 | advances the front and rear pointers 10*rand_deg times, and hence the | |
6d52618b | 142 | rear pointer which starts at 0 will also end up at zero; thus the zeroth |
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143 | element of the state information, which contains info about the current |
144 | position of the rear pointer is just | |
145 | (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3. */ | |
146 | ||
b20e47cb | 147 | static int32_t randtbl[DEG_3 + 1] = |
28f540f4 RM |
148 | { |
149 | TYPE_3, | |
50843ff0 | 150 | |
845dcb57 UD |
151 | -1726662223, 379960547, 1735697613, 1040273694, 1313901226, |
152 | 1627687941, -179304937, -2073333483, 1780058412, -1989503057, | |
153 | -615974602, 344556628, 939512070, -1249116260, 1507946756, | |
154 | -812545463, 154635395, 1388815473, -1926676823, 525320961, | |
155 | -1009028674, 968117788, -123449607, 1284210865, 435012392, | |
156 | -2017506339, -911064859, -370259173, 1132637927, 1398500161, | |
157 | -205601318, | |
28f540f4 RM |
158 | }; |
159 | ||
60478656 RM |
160 | |
161 | static struct random_data unsafe_state = | |
162 | { | |
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163 | /* FPTR and RPTR are two pointers into the state info, a front and a rear |
164 | pointer. These two pointers are always rand_sep places aparts, as they | |
165 | cycle through the state information. (Yes, this does mean we could get | |
166 | away with just one pointer, but the code for random is more efficient | |
167 | this way). The pointers are left positioned as they would be from the call: | |
168 | initstate(1, randtbl, 128); | |
169 | (The position of the rear pointer, rptr, is really 0 (as explained above | |
170 | in the initialization of randtbl) because the state table pointer is set | |
171 | to point to randtbl[1] (as explained below).) */ | |
172 | ||
0274d73c RM |
173 | .fptr = &randtbl[SEP_3 + 1], |
174 | .rptr = &randtbl[1], | |
28f540f4 RM |
175 | |
176 | /* The following things are the pointer to the state information table, | |
177 | the type of the current generator, the degree of the current polynomial | |
178 | being used, and the separation between the two pointers. | |
179 | Note that for efficiency of random, we remember the first location of | |
6d52618b | 180 | the state information, not the zeroth. Hence it is valid to access |
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181 | state[-1], which is used to store the type of the R.N.G. |
182 | Also, we remember the last location, since this is more efficient than | |
183 | indexing every time to find the address of the last element to see if | |
184 | the front and rear pointers have wrapped. */ | |
185 | ||
0274d73c | 186 | .state = &randtbl[1], |
28f540f4 | 187 | |
0274d73c RM |
188 | .rand_type = TYPE_3, |
189 | .rand_deg = DEG_3, | |
190 | .rand_sep = SEP_3, | |
28f540f4 | 191 | |
0274d73c | 192 | .end_ptr = &randtbl[sizeof (randtbl) / sizeof (randtbl[0])] |
60478656 | 193 | }; |
28f540f4 | 194 | \f |
ba1ffaa1 UD |
195 | /* POSIX.1c requires that there is mutual exclusion for the `rand' and |
196 | `srand' functions to prevent concurrent calls from modifying common | |
197 | data. */ | |
198 | __libc_lock_define_initialized (static, lock) | |
199 | \f | |
28f540f4 RM |
200 | /* Initialize the random number generator based on the given seed. If the |
201 | type is the trivial no-state-information type, just remember the seed. | |
202 | Otherwise, initializes state[] based on the given "seed" via a linear | |
203 | congruential generator. Then, the pointers are set to known locations | |
204 | that are exactly rand_sep places apart. Lastly, it cycles the state | |
205 | information a given number of times to get rid of any initial dependencies | |
206 | introduced by the L.C.R.N.G. Note that the initialization of randtbl[] | |
207 | for default usage relies on values produced by this routine. */ | |
208 | void | |
60478656 RM |
209 | __srandom (x) |
210 | unsigned int x; | |
28f540f4 | 211 | { |
0f110f41 | 212 | __libc_lock_lock (lock); |
60478656 | 213 | (void) __srandom_r (x, &unsafe_state); |
0f110f41 | 214 | __libc_lock_unlock (lock); |
28f540f4 RM |
215 | } |
216 | ||
217 | weak_alias (__srandom, srandom) | |
218 | weak_alias (__srandom, srand) | |
219 | \f | |
220 | /* Initialize the state information in the given array of N bytes for | |
221 | future random number generation. Based on the number of bytes we | |
222 | are given, and the break values for the different R.N.G.'s, we choose | |
223 | the best (largest) one we can and set things up for it. srandom is | |
224 | then called to initialize the state information. Note that on return | |
225 | from srandom, we set state[-1] to be the type multiplexed with the current | |
226 | value of the rear pointer; this is so successive calls to initstate won't | |
227 | lose this information and will be able to restart with setstate. | |
228 | Note: The first thing we do is save the current state, if any, just like | |
229 | setstate so that it doesn't matter when initstate is called. | |
230 | Returns a pointer to the old state. */ | |
50497a16 | 231 | char * |
60478656 RM |
232 | __initstate (seed, arg_state, n) |
233 | unsigned int seed; | |
50497a16 | 234 | char *arg_state; |
60478656 | 235 | size_t n; |
28f540f4 | 236 | { |
a9e4124c | 237 | int32_t *ostate; |
ba1ffaa1 | 238 | |
0f110f41 | 239 | __libc_lock_lock (lock); |
ba1ffaa1 | 240 | |
a9e4124c | 241 | ostate = &unsafe_state.state[-1]; |
60478656 RM |
242 | |
243 | __initstate_r (seed, arg_state, n, &unsafe_state); | |
28f540f4 | 244 | |
0f110f41 | 245 | __libc_lock_unlock (lock); |
ba1ffaa1 | 246 | |
a9e4124c | 247 | return (char *) ostate; |
28f540f4 RM |
248 | } |
249 | ||
250 | weak_alias (__initstate, initstate) | |
251 | \f | |
252 | /* Restore the state from the given state array. | |
253 | Note: It is important that we also remember the locations of the pointers | |
254 | in the current state information, and restore the locations of the pointers | |
255 | from the old state information. This is done by multiplexing the pointer | |
6d52618b | 256 | location into the zeroth word of the state information. Note that due |
28f540f4 RM |
257 | to the order in which things are done, it is OK to call setstate with the |
258 | same state as the current state | |
259 | Returns a pointer to the old state information. */ | |
50497a16 | 260 | char * |
60478656 | 261 | __setstate (arg_state) |
50497a16 | 262 | char *arg_state; |
28f540f4 | 263 | { |
a9e4124c | 264 | int32_t *ostate; |
ba1ffaa1 | 265 | |
0f110f41 | 266 | __libc_lock_lock (lock); |
ba1ffaa1 | 267 | |
a9e4124c | 268 | ostate = &unsafe_state.state[-1]; |
60478656 RM |
269 | |
270 | if (__setstate_r (arg_state, &unsafe_state) < 0) | |
ba1ffaa1 UD |
271 | ostate = NULL; |
272 | ||
0f110f41 | 273 | __libc_lock_unlock (lock); |
28f540f4 | 274 | |
a9e4124c | 275 | return (char *) ostate; |
28f540f4 RM |
276 | } |
277 | ||
278 | weak_alias (__setstate, setstate) | |
279 | \f | |
280 | /* If we are using the trivial TYPE_0 R.N.G., just do the old linear | |
281 | congruential bit. Otherwise, we do our fancy trinomial stuff, which is the | |
6d52618b | 282 | same in all the other cases due to all the global variables that have been |
28f540f4 RM |
283 | set up. The basic operation is to add the number at the rear pointer into |
284 | the one at the front pointer. Then both pointers are advanced to the next | |
285 | location cyclically in the table. The value returned is the sum generated, | |
286 | reduced to 31 bits by throwing away the "least random" low bit. | |
287 | Note: The code takes advantage of the fact that both the front and | |
288 | rear pointers can't wrap on the same call by not testing the rear | |
289 | pointer if the front one has wrapped. Returns a 31-bit random number. */ | |
290 | ||
61f9d0a3 | 291 | long int |
60478656 | 292 | __random () |
28f540f4 | 293 | { |
b20e47cb | 294 | int32_t retval; |
60478656 | 295 | |
0f110f41 | 296 | __libc_lock_lock (lock); |
ba1ffaa1 | 297 | |
60478656 RM |
298 | (void) __random_r (&unsafe_state, &retval); |
299 | ||
0f110f41 | 300 | __libc_lock_unlock (lock); |
ba1ffaa1 | 301 | |
60478656 | 302 | return retval; |
28f540f4 RM |
303 | } |
304 | ||
305 | weak_alias (__random, random) |