stdlib/random_r.c

   1 /*
   2    Copyright (C) 1995-2023 Free Software Foundation, Inc.
   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, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 /*
  19    Copyright (C) 1983 Regents of the University of California.
  20    All rights reserved.
  21
  22    Redistribution and use in source and binary forms, with or without
  23    modification, are permitted provided that the following conditions
  24    are met:
  25
  26    1. Redistributions of source code must retain the above copyright
  27       notice, this list of conditions and the following disclaimer.
  28    2. Redistributions in binary form must reproduce the above copyright
  29       notice, this list of conditions and the following disclaimer in the
  30       documentation and/or other materials provided with the distribution.
  31    4. Neither the name of the University nor the names of its contributors
  32       may be used to endorse or promote products derived from this software
  33       without specific prior written permission.
  34
  35    THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  36    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  37    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  38    ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  39    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  40    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  41    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  42    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  43    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  44    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  45    SUCH DAMAGE.*/
  46
  47 /*
  48  * This is derived from the Berkeley source:
  49  *      @(#)random.c    5.5 (Berkeley) 7/6/88
  50  * It was reworked for the GNU C Library by Roland McGrath.
  51  * Rewritten to be reentrant by Ulrich Drepper, 1995
  52  */
  53
  54 #include <errno.h>
  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
  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
 137 struct random_poly_info
 138 {
 139   int seps[MAX_TYPES];
 140   int degrees[MAX_TYPES];
 141 };
 142
 143 static 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 \f
 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.  */
 160 int
 161 __srandom_r (unsigned int seed, struct random_data *buf)
 162 {
 163   int type;
 164   int32_t *state;
 165   long int i;
 166   int32_t word;
 167   int32_t *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       int32_t discard;
 206       (void) __random_r (buf, &discard);
 207     }
 208
 209  done:
 210   return 0;
 211
 212  fail:
 213   return -1;
 214 }
 215
 216 weak_alias (__srandom_r, srandom_r)
 217 \f
 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 0 on success, non-zero on failure.  */
 229 int
 230 __initstate_r (unsigned int seed, char *arg_state, size_t n,
 231                struct random_data *buf)
 232 {
 233   if (buf == NULL)
 234     goto fail;
 235
 236   int32_t *old_state = buf->state;
 237   if (old_state != NULL)
 238     {
 239       int old_type = buf->rand_type;
 240       if (old_type == TYPE_0)
 241         old_state[-1] = TYPE_0;
 242       else
 243         old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
 244     }
 245
 246   int type;
 247   if (n >= BREAK_3)
 248     type = n < BREAK_4 ? TYPE_3 : TYPE_4;
 249   else if (n < BREAK_1)
 250     {
 251       if (n < BREAK_0)
 252         goto fail;
 253
 254       type = TYPE_0;
 255     }
 256   else
 257     type = n < BREAK_2 ? TYPE_1 : TYPE_2;
 258
 259   int degree = random_poly_info.degrees[type];
 260   int separation = random_poly_info.seps[type];
 261
 262   buf->rand_type = type;
 263   buf->rand_sep = separation;
 264   buf->rand_deg = degree;
 265   int32_t *state = &((int32_t *) arg_state)[1]; /* First location.  */
 266   /* Must set END_PTR before srandom.  */
 267   buf->end_ptr = &state[degree];
 268
 269   buf->state = state;
 270
 271   __srandom_r (seed, buf);
 272
 273   state[-1] = TYPE_0;
 274   if (type != TYPE_0)
 275     state[-1] = (buf->rptr - state) * MAX_TYPES + type;
 276
 277   return 0;
 278
 279  fail:
 280   __set_errno (EINVAL);
 281   return -1;
 282 }
 283
 284 weak_alias (__initstate_r, initstate_r)
 285 \f
 286 /* Restore the state from the given state array.
 287    Note: It is important that we also remember the locations of the pointers
 288    in the current state information, and restore the locations of the pointers
 289    from the old state information.  This is done by multiplexing the pointer
 290    location into the zeroth word of the state information. Note that due
 291    to the order in which things are done, it is OK to call setstate with the
 292    same state as the current state
 293    Returns 0 on success, non-zero on failure.  */
 294 int
 295 __setstate_r (char *arg_state, struct random_data *buf)
 296 {
 297   int32_t *new_state = 1 + (int32_t *) arg_state;
 298   int type;
 299   int old_type;
 300   int32_t *old_state;
 301   int degree;
 302   int separation;
 303
 304   if (arg_state == NULL || buf == NULL)
 305     goto fail;
 306
 307   old_type = buf->rand_type;
 308   old_state = buf->state;
 309   if (old_type == TYPE_0)
 310     old_state[-1] = TYPE_0;
 311   else
 312     old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
 313
 314   type = new_state[-1] % MAX_TYPES;
 315   if (type < TYPE_0 || type > TYPE_4)
 316     goto fail;
 317
 318   buf->rand_deg = degree = random_poly_info.degrees[type];
 319   buf->rand_sep = separation = random_poly_info.seps[type];
 320   buf->rand_type = type;
 321
 322   if (type != TYPE_0)
 323     {
 324       int rear = new_state[-1] / MAX_TYPES;
 325       buf->rptr = &new_state[rear];
 326       buf->fptr = &new_state[(rear + separation) % degree];
 327     }
 328   buf->state = new_state;
 329   /* Set end_ptr too.  */
 330   buf->end_ptr = &new_state[degree];
 331
 332   return 0;
 333
 334  fail:
 335   __set_errno (EINVAL);
 336   return -1;
 337 }
 338
 339 weak_alias (__setstate_r, setstate_r)
 340 \f
 341 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
 342    congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
 343    same in all the other cases due to all the global variables that have been
 344    set up.  The basic operation is to add the number at the rear pointer into
 345    the one at the front pointer.  Then both pointers are advanced to the next
 346    location cyclically in the table.  The value returned is the sum generated,
 347    reduced to 31 bits by throwing away the "least random" low bit.
 348    Note: The code takes advantage of the fact that both the front and
 349    rear pointers can't wrap on the same call by not testing the rear
 350    pointer if the front one has wrapped.  Returns a 31-bit random number.  */
 351
 352 int
 353 __random_r (struct random_data *buf, int32_t *result)
 354 {
 355   int32_t *state;
 356
 357   if (buf == NULL || result == NULL)
 358     goto fail;
 359
 360   state = buf->state;
 361
 362   if (buf->rand_type == TYPE_0)
 363     {
 364       int32_t val = ((state[0] * 1103515245U) + 12345U) & 0x7fffffff;
 365       state[0] = val;
 366       *result = val;
 367     }
 368   else
 369     {
 370       int32_t *fptr = buf->fptr;
 371       int32_t *rptr = buf->rptr;
 372       int32_t *end_ptr = buf->end_ptr;
 373       uint32_t val;
 374
 375       val = *fptr += (uint32_t) *rptr;
 376       /* Chucking least random bit.  */
 377       *result = val >> 1;
 378       ++fptr;
 379       if (fptr >= end_ptr)
 380         {
 381           fptr = state;
 382           ++rptr;
 383         }
 384       else
 385         {
 386           ++rptr;
 387           if (rptr >= end_ptr)
 388             rptr = state;
 389         }
 390       buf->fptr = fptr;
 391       buf->rptr = rptr;
 392     }
 393   return 0;
 394
 395  fail:
 396   __set_errno (EINVAL);
 397   return -1;
 398 }
 399
 400 weak_alias (__random_r, random_r)