xf.li | bdd93d5 | 2023-05-12 07:10:14 -0700 | [diff] [blame] | 1 | /* Copyright (C) 1995-2016 Free Software Foundation, Inc. |
| 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, see |
| 15 | <http://www.gnu.org/licenses/>. */ |
| 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 use reentrant functions by Ulrich Drepper, 1995. |
| 22 | */ |
| 23 | |
| 24 | /* |
| 25 | Copyright (C) 1983 Regents of the University of California. |
| 26 | All rights reserved. |
| 27 | |
| 28 | Redistribution and use in source and binary forms, with or without |
| 29 | modification, are permitted provided that the following conditions |
| 30 | are met: |
| 31 | |
| 32 | 1. Redistributions of source code must retain the above copyright |
| 33 | notice, this list of conditions and the following disclaimer. |
| 34 | 2. Redistributions in binary form must reproduce the above copyright |
| 35 | notice, this list of conditions and the following disclaimer in the |
| 36 | documentation and/or other materials provided with the distribution. |
| 37 | 4. Neither the name of the University nor the names of its contributors |
| 38 | may be used to endorse or promote products derived from this software |
| 39 | without specific prior written permission. |
| 40 | |
| 41 | THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| 42 | ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 43 | IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 44 | ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| 45 | FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| 46 | DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| 47 | OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| 48 | HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| 49 | LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| 50 | OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| 51 | SUCH DAMAGE.*/ |
| 52 | |
| 53 | #include <libc-lock.h> |
| 54 | #include <limits.h> |
| 55 | #include <stddef.h> |
| 56 | #include <stdlib.h> |
| 57 | |
| 58 | |
| 59 | /* An improved random number generation package. In addition to the standard |
| 60 | rand()/srand() like interface, this package also has a special state info |
| 61 | interface. The initstate() routine is called with a seed, an array of |
| 62 | bytes, and a count of how many bytes are being passed in; this array is |
| 63 | then initialized to contain information for random number generation with |
| 64 | that much state information. Good sizes for the amount of state |
| 65 | information are 32, 64, 128, and 256 bytes. The state can be switched by |
| 66 | calling the setstate() function with the same array as was initialized |
| 67 | with initstate(). By default, the package runs with 128 bytes of state |
| 68 | information and generates far better random numbers than a linear |
| 69 | congruential generator. If the amount of state information is less than |
| 70 | 32 bytes, a simple linear congruential R.N.G. is used. Internally, the |
| 71 | state information is treated as an array of longs; the zeroth element of |
| 72 | the array is the type of R.N.G. being used (small integer); the remainder |
| 73 | of the array is the state information for the R.N.G. Thus, 32 bytes of |
| 74 | state information will give 7 longs worth of state information, which will |
| 75 | allow a degree seven polynomial. (Note: The zeroth word of state |
| 76 | information also has some other information stored in it; see setstate |
| 77 | for details). The random number generation technique is a linear feedback |
| 78 | shift register approach, employing trinomials (since there are fewer terms |
| 79 | to sum up that way). In this approach, the least significant bit of all |
| 80 | the numbers in the state table will act as a linear feedback shift register, |
| 81 | and will have period 2^deg - 1 (where deg is the degree of the polynomial |
| 82 | being used, assuming that the polynomial is irreducible and primitive). |
| 83 | The higher order bits will have longer periods, since their values are |
| 84 | also influenced by pseudo-random carries out of the lower bits. The |
| 85 | total period of the generator is approximately deg*(2**deg - 1); thus |
| 86 | doubling the amount of state information has a vast influence on the |
| 87 | period of the generator. Note: The deg*(2**deg - 1) is an approximation |
| 88 | only good for large deg, when the period of the shift register is the |
| 89 | dominant factor. With deg equal to seven, the period is actually much |
| 90 | longer than the 7*(2**7 - 1) predicted by this formula. */ |
| 91 | |
| 92 | |
| 93 | |
| 94 | /* For each of the currently supported random number generators, we have a |
| 95 | break value on the amount of state information (you need at least this many |
| 96 | bytes of state info to support this random number generator), a degree for |
| 97 | the polynomial (actually a trinomial) that the R.N.G. is based on, and |
| 98 | separation between the two lower order coefficients of the trinomial. */ |
| 99 | |
| 100 | /* Linear congruential. */ |
| 101 | #define TYPE_0 0 |
| 102 | #define BREAK_0 8 |
| 103 | #define DEG_0 0 |
| 104 | #define SEP_0 0 |
| 105 | |
| 106 | /* x**7 + x**3 + 1. */ |
| 107 | #define TYPE_1 1 |
| 108 | #define BREAK_1 32 |
| 109 | #define DEG_1 7 |
| 110 | #define SEP_1 3 |
| 111 | |
| 112 | /* x**15 + x + 1. */ |
| 113 | #define TYPE_2 2 |
| 114 | #define BREAK_2 64 |
| 115 | #define DEG_2 15 |
| 116 | #define SEP_2 1 |
| 117 | |
| 118 | /* x**31 + x**3 + 1. */ |
| 119 | #define TYPE_3 3 |
| 120 | #define BREAK_3 128 |
| 121 | #define DEG_3 31 |
| 122 | #define SEP_3 3 |
| 123 | |
| 124 | /* x**63 + x + 1. */ |
| 125 | #define TYPE_4 4 |
| 126 | #define BREAK_4 256 |
| 127 | #define DEG_4 63 |
| 128 | #define SEP_4 1 |
| 129 | |
| 130 | |
| 131 | /* Array versions of the above information to make code run faster. |
| 132 | Relies on fact that TYPE_i == i. */ |
| 133 | |
| 134 | #define MAX_TYPES 5 /* Max number of types above. */ |
| 135 | |
| 136 | |
| 137 | /* Initially, everything is set up as if from: |
| 138 | initstate(1, randtbl, 128); |
| 139 | Note that this initialization takes advantage of the fact that srandom |
| 140 | advances the front and rear pointers 10*rand_deg times, and hence the |
| 141 | rear pointer which starts at 0 will also end up at zero; thus the zeroth |
| 142 | element of the state information, which contains info about the current |
| 143 | position of the rear pointer is just |
| 144 | (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3. */ |
| 145 | |
| 146 | static int32_t randtbl[DEG_3 + 1] = |
| 147 | { |
| 148 | TYPE_3, |
| 149 | |
| 150 | -1726662223, 379960547, 1735697613, 1040273694, 1313901226, |
| 151 | 1627687941, -179304937, -2073333483, 1780058412, -1989503057, |
| 152 | -615974602, 344556628, 939512070, -1249116260, 1507946756, |
| 153 | -812545463, 154635395, 1388815473, -1926676823, 525320961, |
| 154 | -1009028674, 968117788, -123449607, 1284210865, 435012392, |
| 155 | -2017506339, -911064859, -370259173, 1132637927, 1398500161, |
| 156 | -205601318, |
| 157 | }; |
| 158 | |
| 159 | |
| 160 | static struct random_data unsafe_state = |
| 161 | { |
| 162 | /* FPTR and RPTR are two pointers into the state info, a front and a rear |
| 163 | pointer. These two pointers are always rand_sep places apart, as they |
| 164 | cycle through the state information. (Yes, this does mean we could get |
| 165 | away with just one pointer, but the code for random is more efficient |
| 166 | this way). The pointers are left positioned as they would be from the call: |
| 167 | initstate(1, randtbl, 128); |
| 168 | (The position of the rear pointer, rptr, is really 0 (as explained above |
| 169 | in the initialization of randtbl) because the state table pointer is set |
| 170 | to point to randtbl[1] (as explained below).) */ |
| 171 | |
| 172 | .fptr = &randtbl[SEP_3 + 1], |
| 173 | .rptr = &randtbl[1], |
| 174 | |
| 175 | /* The following things are the pointer to the state information table, |
| 176 | the type of the current generator, the degree of the current polynomial |
| 177 | being used, and the separation between the two pointers. |
| 178 | Note that for efficiency of random, we remember the first location of |
| 179 | the state information, not the zeroth. Hence it is valid to access |
| 180 | state[-1], which is used to store the type of the R.N.G. |
| 181 | Also, we remember the last location, since this is more efficient than |
| 182 | indexing every time to find the address of the last element to see if |
| 183 | the front and rear pointers have wrapped. */ |
| 184 | |
| 185 | .state = &randtbl[1], |
| 186 | |
| 187 | .rand_type = TYPE_3, |
| 188 | .rand_deg = DEG_3, |
| 189 | .rand_sep = SEP_3, |
| 190 | |
| 191 | .end_ptr = &randtbl[sizeof (randtbl) / sizeof (randtbl[0])] |
| 192 | }; |
| 193 | |
| 194 | /* POSIX.1c requires that there is mutual exclusion for the `rand' and |
| 195 | `srand' functions to prevent concurrent calls from modifying common |
| 196 | data. */ |
| 197 | __libc_lock_define_initialized (static, lock) |
| 198 | |
| 199 | /* Initialize the random number generator based on the given seed. If the |
| 200 | type is the trivial no-state-information type, just remember the seed. |
| 201 | Otherwise, initializes state[] based on the given "seed" via a linear |
| 202 | congruential generator. Then, the pointers are set to known locations |
| 203 | that are exactly rand_sep places apart. Lastly, it cycles the state |
| 204 | information a given number of times to get rid of any initial dependencies |
| 205 | introduced by the L.C.R.N.G. Note that the initialization of randtbl[] |
| 206 | for default usage relies on values produced by this routine. */ |
| 207 | void |
| 208 | __srandom (unsigned int x) |
| 209 | { |
| 210 | __libc_lock_lock (lock); |
| 211 | (void) __srandom_r (x, &unsafe_state); |
| 212 | __libc_lock_unlock (lock); |
| 213 | } |
| 214 | |
| 215 | weak_alias (__srandom, srandom) |
| 216 | weak_alias (__srandom, srand) |
| 217 | |
| 218 | /* Initialize the state information in the given array of N bytes for |
| 219 | future random number generation. Based on the number of bytes we |
| 220 | are given, and the break values for the different R.N.G.'s, we choose |
| 221 | the best (largest) one we can and set things up for it. srandom is |
| 222 | then called to initialize the state information. Note that on return |
| 223 | from srandom, we set state[-1] to be the type multiplexed with the current |
| 224 | value of the rear pointer; this is so successive calls to initstate won't |
| 225 | lose this information and will be able to restart with setstate. |
| 226 | Note: The first thing we do is save the current state, if any, just like |
| 227 | setstate so that it doesn't matter when initstate is called. |
| 228 | Returns a pointer to the old state. */ |
| 229 | char * |
| 230 | __initstate (unsigned int seed, char *arg_state, size_t n) |
| 231 | { |
| 232 | int32_t *ostate; |
| 233 | int ret; |
| 234 | |
| 235 | __libc_lock_lock (lock); |
| 236 | |
| 237 | ostate = &unsafe_state.state[-1]; |
| 238 | |
| 239 | ret = __initstate_r (seed, arg_state, n, &unsafe_state); |
| 240 | |
| 241 | __libc_lock_unlock (lock); |
| 242 | |
| 243 | return ret == -1 ? NULL : (char *) ostate; |
| 244 | } |
| 245 | |
| 246 | weak_alias (__initstate, initstate) |
| 247 | |
| 248 | /* Restore the state from the given state array. |
| 249 | Note: It is important that we also remember the locations of the pointers |
| 250 | in the current state information, and restore the locations of the pointers |
| 251 | from the old state information. This is done by multiplexing the pointer |
| 252 | location into the zeroth word of the state information. Note that due |
| 253 | to the order in which things are done, it is OK to call setstate with the |
| 254 | same state as the current state |
| 255 | Returns a pointer to the old state information. */ |
| 256 | char * |
| 257 | __setstate (char *arg_state) |
| 258 | { |
| 259 | int32_t *ostate; |
| 260 | |
| 261 | __libc_lock_lock (lock); |
| 262 | |
| 263 | ostate = &unsafe_state.state[-1]; |
| 264 | |
| 265 | if (__setstate_r (arg_state, &unsafe_state) < 0) |
| 266 | ostate = NULL; |
| 267 | |
| 268 | __libc_lock_unlock (lock); |
| 269 | |
| 270 | return (char *) ostate; |
| 271 | } |
| 272 | |
| 273 | weak_alias (__setstate, setstate) |
| 274 | |
| 275 | /* If we are using the trivial TYPE_0 R.N.G., just do the old linear |
| 276 | congruential bit. Otherwise, we do our fancy trinomial stuff, which is the |
| 277 | same in all the other cases due to all the global variables that have been |
| 278 | set up. The basic operation is to add the number at the rear pointer into |
| 279 | the one at the front pointer. Then both pointers are advanced to the next |
| 280 | location cyclically in the table. The value returned is the sum generated, |
| 281 | reduced to 31 bits by throwing away the "least random" low bit. |
| 282 | Note: The code takes advantage of the fact that both the front and |
| 283 | rear pointers can't wrap on the same call by not testing the rear |
| 284 | pointer if the front one has wrapped. Returns a 31-bit random number. */ |
| 285 | |
| 286 | long int |
| 287 | __random (void) |
| 288 | { |
| 289 | int32_t retval; |
| 290 | |
| 291 | __libc_lock_lock (lock); |
| 292 | |
| 293 | (void) __random_r (&unsafe_state, &retval); |
| 294 | |
| 295 | __libc_lock_unlock (lock); |
| 296 | |
| 297 | return retval; |
| 298 | } |
| 299 | |
| 300 | weak_alias (__random, random) |