stdlib/random_r.c

   1 /*
   2    Copyright (C) 1995, 2005, 2009 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, see
  16    <http://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 (seed, buf)
 162      unsigned int seed;
 163      struct random_data *buf;
 164 {
 165   int type;
 166   int32_t *state;
 167   long int i;
 168   int32_t word;
 169   int32_t *dst;
 170   int kc;
 171
 172   if (buf == NULL)
 173     goto fail;
 174   type = buf->rand_type;
 175   if ((unsigned int) type >= MAX_TYPES)
 176     goto fail;
 177
 178   state = buf->state;
 179   /* We must make sure the seed is not 0.  Take arbitrarily 1 in this case.  */
 180   if (seed == 0)
 181     seed = 1;
 182   state[0] = seed;
 183   if (type == TYPE_0)
 184     goto done;
 185
 186   dst = state;
 187   word = seed;
 188   kc = buf->rand_deg;
 189   for (i = 1; i < kc; ++i)
 190     {
 191       /* This does:
 192            state[i] = (16807 * state[i - 1]) % 2147483647;
 193          but avoids overflowing 31 bits.  */
 194       long int hi = word / 127773;
 195       long int lo = word % 127773;
 196       word = 16807 * lo - 2836 * hi;
 197       if (word < 0)
 198         word += 2147483647;
 199       *++dst = word;
 200     }
 201
 202   buf->fptr = &state[buf->rand_sep];
 203   buf->rptr = &state[0];
 204   kc *= 10;
 205   while (--kc >= 0)
 206     {
 207       int32_t discard;
 208       (void) __random_r (buf, &discard);
 209     }
 210
 211  done:
 212   return 0;
 213
 214  fail:
 215   return -1;
 216 }
 217
 218 weak_alias (__srandom_r, srandom_r)
 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 0 on success, non-zero on failure.  */
 231 int
 232 __initstate_r (seed, arg_state, n, buf)
 233      unsigned int seed;
 234      char *arg_state;
 235      size_t n;
 236      struct random_data *buf;
 237 {
 238   if (buf == NULL)
 239     goto fail;
 240
 241   int32_t *old_state = buf->state;
 242   if (old_state != NULL)
 243     {
 244       int old_type = buf->rand_type;
 245       if (old_type == TYPE_0)
 246         old_state[-1] = TYPE_0;
 247       else
 248         old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
 249     }
 250
 251   int type;
 252   if (n >= BREAK_3)
 253     type = n < BREAK_4 ? TYPE_3 : TYPE_4;
 254   else if (n < BREAK_1)
 255     {
 256       if (n < BREAK_0)
 257         goto fail;
 258
 259       type = TYPE_0;
 260     }
 261   else
 262     type = n < BREAK_2 ? TYPE_1 : TYPE_2;
 263
 264   int degree = random_poly_info.degrees[type];
 265   int separation = random_poly_info.seps[type];
 266
 267   buf->rand_type = type;
 268   buf->rand_sep = separation;
 269   buf->rand_deg = degree;
 270   int32_t *state = &((int32_t *) arg_state)[1]; /* First location.  */
 271   /* Must set END_PTR before srandom.  */
 272   buf->end_ptr = &state[degree];
 273
 274   buf->state = state;
 275
 276   __srandom_r (seed, buf);
 277
 278   state[-1] = TYPE_0;
 279   if (type != TYPE_0)
 280     state[-1] = (buf->rptr - state) * MAX_TYPES + type;
 281
 282   return 0;
 283
 284  fail:
 285   __set_errno (EINVAL);
 286   return -1;
 287 }
 288
 289 weak_alias (__initstate_r, initstate_r)
 290 \f
 291 /* Restore the state from the given state array.
 292    Note: It is important that we also remember the locations of the pointers
 293    in the current state information, and restore the locations of the pointers
 294    from the old state information.  This is done by multiplexing the pointer
 295    location into the zeroth word of the state information. Note that due
 296    to the order in which things are done, it is OK to call setstate with the
 297    same state as the current state
 298    Returns 0 on success, non-zero on failure.  */
 299 int
 300 __setstate_r (arg_state, buf)
 301      char *arg_state;
 302      struct random_data *buf;
 303 {
 304   int32_t *new_state = 1 + (int32_t *) arg_state;
 305   int type;
 306   int old_type;
 307   int32_t *old_state;
 308   int degree;
 309   int separation;
 310
 311   if (arg_state == NULL || buf == NULL)
 312     goto fail;
 313
 314   old_type = buf->rand_type;
 315   old_state = buf->state;
 316   if (old_type == TYPE_0)
 317     old_state[-1] = TYPE_0;
 318   else
 319     old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
 320
 321   type = new_state[-1] % MAX_TYPES;
 322   if (type < TYPE_0 || type > TYPE_4)
 323     goto fail;
 324
 325   buf->rand_deg = degree = random_poly_info.degrees[type];
 326   buf->rand_sep = separation = random_poly_info.seps[type];
 327   buf->rand_type = type;
 328
 329   if (type != TYPE_0)
 330     {
 331       int rear = new_state[-1] / MAX_TYPES;
 332       buf->rptr = &new_state[rear];
 333       buf->fptr = &new_state[(rear + separation) % degree];
 334     }
 335   buf->state = new_state;
 336   /* Set end_ptr too.  */
 337   buf->end_ptr = &new_state[degree];
 338
 339   return 0;
 340
 341  fail:
 342   __set_errno (EINVAL);
 343   return -1;
 344 }
 345
 346 weak_alias (__setstate_r, setstate_r)
 347 \f
 348 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
 349    congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
 350    same in all the other cases due to all the global variables that have been
 351    set up.  The basic operation is to add the number at the rear pointer into
 352    the one at the front pointer.  Then both pointers are advanced to the next
 353    location cyclically in the table.  The value returned is the sum generated,
 354    reduced to 31 bits by throwing away the "least random" low bit.
 355    Note: The code takes advantage of the fact that both the front and
 356    rear pointers can't wrap on the same call by not testing the rear
 357    pointer if the front one has wrapped.  Returns a 31-bit random number.  */
 358
 359 int
 360 __random_r (buf, result)
 361      struct random_data *buf;
 362      int32_t *result;
 363 {
 364   int32_t *state;
 365
 366   if (buf == NULL || result == NULL)
 367     goto fail;
 368
 369   state = buf->state;
 370
 371   if (buf->rand_type == TYPE_0)
 372     {
 373       int32_t val = state[0];
 374       val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
 375       state[0] = val;
 376       *result = val;
 377     }
 378   else
 379     {
 380       int32_t *fptr = buf->fptr;
 381       int32_t *rptr = buf->rptr;
 382       int32_t *end_ptr = buf->end_ptr;
 383       int32_t val;
 384
 385       val = *fptr += *rptr;
 386       /* Chucking least random bit.  */
 387       *result = (val >> 1) & 0x7fffffff;
 388       ++fptr;
 389       if (fptr >= end_ptr)
 390         {
 391           fptr = state;
 392           ++rptr;
 393         }
 394       else
 395         {
 396           ++rptr;
 397           if (rptr >= end_ptr)
 398             rptr = state;
 399         }
 400       buf->fptr = fptr;
 401       buf->rptr = rptr;
 402     }
 403   return 0;
 404
 405  fail:
 406   __set_errno (EINVAL);
 407   return -1;
 408 }
 409
 410 weak_alias (__random_r, random_r)