1/* 2 Copyright (C) 1995, 2004 Free Software Foundation 3 4 The GNU C Library is free software; you can redistribute it and/or 5 modify it under the terms of the GNU Lesser General Public 6 License as published by the Free Software Foundation; either 7 version 2.1 of the License, or (at your option) any later version. 8 9 The GNU C Library 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 GNU 12 Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public 15 License along with the GNU C Library; if not, write to the Free 16 Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 17 02110-1301 USA. */ 18 19/* 20 Copyright (C) 1983 Regents of the University of California. 21 All rights reserved. 22 23 Redistribution and use in source and binary forms, with or without 24 modification, are permitted provided that the following conditions 25 are met: 26 27 1. Redistributions of source code must retain the above copyright 28 notice, this list of conditions and the following disclaimer. 29 2. Redistributions in binary form must reproduce the above copyright 30 notice, this list of conditions and the following disclaimer in the 31 documentation and/or other materials provided with the distribution. 32 4. Neither the name of the University nor the names of its contributors 33 may be used to endorse or promote products derived from this software 34 without specific prior written permission. 35 36 THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 37 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 38 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 39 ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 40 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 41 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 42 OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 43 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 44 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 45 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 46 SUCH DAMAGE.*/ 47 48/* 49 * This is derived from the Berkeley source: 50 * @(#)random.c 5.5 (Berkeley) 7/6/88 51 * It was reworked for the GNU C Library by Roland McGrath. 52 * Rewritten to be reentrant by Ulrich Drepper, 1995 53 */ 54 55#include <limits.h> 56#include <stdlib.h> 57#include "generate-random.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 67 calling the setstate() function with the same array as was initialized 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 72 state information is treated as an array of longs; the zeroth element of 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 76 allow a degree seven polynomial. (Note: The zeroth word of state 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 96 break value on the amount of state information (you need at least this many 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 137struct random_poly_info 138{ 139 int seps[MAX_TYPES]; 140 int degrees[MAX_TYPES]; 141}; 142 143static const struct random_poly_info random_poly_info = 144{ 145 { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 }, 146 { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 } 147}; 148 149 150 151 152/* Initialize the random number generator based on the given seed. If the 153 type is the trivial no-state-information type, just remember the seed. 154 Otherwise, initializes state[] based on the given "seed" via a linear 155 congruential generator. Then, the pointers are set to known locations 156 that are exactly rand_sep places apart. Lastly, it cycles the state 157 information a given number of times to get rid of any initial dependencies 158 introduced by the L.C.R.N.G. Note that the initialization of randtbl[] 159 for default usage relies on values produced by this routine. */ 160int 161generate_srandom_r (unsigned int seed, struct generate_random_data *buf) 162{ 163 int type; 164 int *state; 165 long int i; 166 long int word; 167 int *dst; 168 int kc; 169 170 if (buf == NULL) 171 goto fail; 172 type = buf->rand_type; 173 if ((unsigned int) type >= MAX_TYPES) 174 goto fail; 175 176 state = buf->state; 177 /* We must make sure the seed is not 0. Take arbitrarily 1 in this case. */ 178 if (seed == 0) 179 seed = 1; 180 state[0] = seed; 181 if (type == TYPE_0) 182 goto done; 183 184 dst = state; 185 word = seed; 186 kc = buf->rand_deg; 187 for (i = 1; i < kc; ++i) 188 { 189 /* This does: 190 state[i] = (16807 * state[i - 1]) % 2147483647; 191 but avoids overflowing 31 bits. */ 192 long int hi = word / 127773; 193 long int lo = word % 127773; 194 word = 16807 * lo - 2836 * hi; 195 if (word < 0) 196 word += 2147483647; 197 *++dst = word; 198 } 199 200 buf->fptr = &state[buf->rand_sep]; 201 buf->rptr = &state[0]; 202 kc *= 10; 203 while (--kc >= 0) 204 { 205 int discard; 206 (void) generate_random_r (buf, &discard); 207 } 208 209 done: 210 return 0; 211 212 fail: 213 return -1; 214} 215 216/* Initialize the state information in the given array of N bytes for 217 future random number generation. Based on the number of bytes we 218 are given, and the break values for the different R.N.G.'s, we choose 219 the best (largest) one we can and set things up for it. srandom is 220 then called to initialize the state information. Note that on return 221 from srandom, we set state[-1] to be the type multiplexed with the current 222 value of the rear pointer; this is so successive calls to initstate won't 223 lose this information and will be able to restart with setstate. 224 Note: The first thing we do is save the current state, if any, just like 225 setstate so that it doesn't matter when initstate is called. 226 Returns a pointer to the old state. */ 227int 228generate_initstate_r (unsigned int seed, char *arg_state, size_t n, 229 struct generate_random_data *buf) 230{ 231 int type; 232 int degree; 233 int separation; 234 int *state; 235 236 if (buf == NULL) 237 goto fail; 238 239 if (n >= BREAK_3) 240 type = n < BREAK_4 ? TYPE_3 : TYPE_4; 241 else if (n < BREAK_1) 242 { 243 if (n < BREAK_0) 244 { 245 goto fail; 246 } 247 type = TYPE_0; 248 } 249 else 250 type = n < BREAK_2 ? TYPE_1 : TYPE_2; 251 252 degree = random_poly_info.degrees[type]; 253 separation = random_poly_info.seps[type]; 254 255 buf->rand_type = type; 256 buf->rand_sep = separation; 257 buf->rand_deg = degree; 258 state = &((int *) arg_state)[1]; /* First location. */ 259 /* Must set END_PTR before srandom. */ 260 buf->end_ptr = &state[degree]; 261 262 buf->state = state; 263 264 generate_srandom_r (seed, buf); 265 266 state[-1] = TYPE_0; 267 if (type != TYPE_0) 268 state[-1] = (buf->rptr - state) * MAX_TYPES + type; 269 270 return 0; 271 272 fail: 273 return -1; 274} 275 276/* Restore the state from the given state array. 277 Note: It is important that we also remember the locations of the pointers 278 in the current state information, and restore the locations of the pointers 279 from the old state information. This is done by multiplexing the pointer 280 location into the zeroth word of the state information. Note that due 281 to the order in which things are done, it is OK to call setstate with the 282 same state as the current state 283 Returns a pointer to the old state information. */ 284int 285generate_setstate_r (char *arg_state, struct generate_random_data *buf) 286{ 287 int *new_state = 1 + (int *) arg_state; 288 int type; 289 int old_type; 290 int *old_state; 291 int degree; 292 int separation; 293 294 if (arg_state == NULL || buf == NULL) 295 goto fail; 296 297 old_type = buf->rand_type; 298 old_state = buf->state; 299 if (old_type == TYPE_0) 300 old_state[-1] = TYPE_0; 301 else 302 old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type; 303 304 type = new_state[-1] % MAX_TYPES; 305 if (type < TYPE_0 || type > TYPE_4) 306 goto fail; 307 308 buf->rand_deg = degree = random_poly_info.degrees[type]; 309 buf->rand_sep = separation = random_poly_info.seps[type]; 310 buf->rand_type = type; 311 312 if (type != TYPE_0) 313 { 314 int rear = new_state[-1] / MAX_TYPES; 315 buf->rptr = &new_state[rear]; 316 buf->fptr = &new_state[(rear + separation) % degree]; 317 } 318 buf->state = new_state; 319 /* Set end_ptr too. */ 320 buf->end_ptr = &new_state[degree]; 321 322 return 0; 323 324 fail: 325 return -1; 326} 327 328/* If we are using the trivial TYPE_0 R.N.G., just do the old linear 329 congruential bit. Otherwise, we do our fancy trinomial stuff, which is the 330 same in all the other cases due to all the global variables that have been 331 set up. The basic operation is to add the number at the rear pointer into 332 the one at the front pointer. Then both pointers are advanced to the next 333 location cyclically in the table. The value returned is the sum generated, 334 reduced to 31 bits by throwing away the "least random" low bit. 335 Note: The code takes advantage of the fact that both the front and 336 rear pointers can't wrap on the same call by not testing the rear 337 pointer if the front one has wrapped. Returns a 31-bit random number. */ 338 339int 340generate_random_r (struct generate_random_data *buf, int *result) 341{ 342 int *state; 343 344 if (buf == NULL || result == NULL) 345 goto fail; 346 347 state = buf->state; 348 349 if (buf->rand_type == TYPE_0) 350 { 351 int val = state[0]; 352 val = ((state[0] * 1103515245) + 12345) & 0x7fffffff; 353 state[0] = val; 354 *result = val; 355 } 356 else 357 { 358 int *fptr = buf->fptr; 359 int *rptr = buf->rptr; 360 int *end_ptr = buf->end_ptr; 361 int val; 362 363 val = *fptr += *rptr; 364 /* Chucking least random bit. */ 365 *result = (val >> 1) & 0x7fffffff; 366 ++fptr; 367 if (fptr >= end_ptr) 368 { 369 fptr = state; 370 ++rptr; 371 } 372 else 373 { 374 ++rptr; 375 if (rptr >= end_ptr) 376 rptr = state; 377 } 378 buf->fptr = fptr; 379 buf->rptr = rptr; 380 } 381 return 0; 382 383 fail: 384 return -1; 385} 386