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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 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 <errno.h>
  56 #include <limits.h>
  57 #include <stddef.h>
  58 #include <stdlib.h>
  59
  60
  61 /* An improved random number generation package.  In addition to the standard
  62    rand()/srand() like interface, this package also has a special state info
  63    interface.  The initstate() routine is called with a seed, an array of
  64    bytes, and a count of how many bytes are being passed in; this array is
  65    then initialized to contain information for random number generation with
  66    that much state information.  Good sizes for the amount of state
  67    information are 32, 64, 128, and 256 bytes.  The state can be switched by
  68    calling the setstate() function with the same array as was initialized
  69    with initstate().  By default, the package runs with 128 bytes of state
  70    information and generates far better random numbers than a linear
  71    congruential generator.  If the amount of state information is less than
  72    32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
  73    state information is treated as an array of longs; the zeroth element of
  74    the array is the type of R.N.G. being used (small integer); the remainder
  75    of the array is the state information for the R.N.G.  Thus, 32 bytes of
  76    state information will give 7 longs worth of state information, which will
  77    allow a degree seven polynomial.  (Note: The zeroth word of state
  78    information also has some other information stored in it; see setstate
  79    for details).  The random number generation technique is a linear feedback
  80    shift register approach, employing trinomials (since there are fewer terms
  81    to sum up that way).  In this approach, the least significant bit of all
  82    the numbers in the state table will act as a linear feedback shift register,
  83    and will have period 2^deg - 1 (where deg is the degree of the polynomial
  84    being used, assuming that the polynomial is irreducible and primitive).
  85    The higher order bits will have longer periods, since their values are
  86    also influenced by pseudo-random carries out of the lower bits.  The
  87    total period of the generator is approximately deg*(2**deg - 1); thus
  88    doubling the amount of state information has a vast influence on the
  89    period of the generator.  Note: The deg*(2**deg - 1) is an approximation
  90    only good for large deg, when the period of the shift register is the
  91    dominant factor.  With deg equal to seven, the period is actually much
  92    longer than the 7*(2**7 - 1) predicted by this formula.  */
  93
  94
  95
  96 /* For each of the currently supported random number generators, we have a
  97    break value on the amount of state information (you need at least this many
  98    bytes of state info to support this random number generator), a degree for
  99    the polynomial (actually a trinomial) that the R.N.G. is based on, and
 100    separation between the two lower order coefficients of the trinomial.  */
 101
 102 /* Linear congruential.  */
 103 #define TYPE_0          0
 104 #define BREAK_0         8
 105 #define DEG_0           0
 106 #define SEP_0           0
 107
 108 /* x**7 + x**3 + 1.  */
 109 #define TYPE_1          1
 110 #define BREAK_1         32
 111 #define DEG_1           7
 112 #define SEP_1           3
 113
 114 /* x**15 + x + 1.  */
 115 #define TYPE_2          2
 116 #define BREAK_2         64
 117 #define DEG_2           15
 118 #define SEP_2           1
 119
 120 /* x**31 + x**3 + 1.  */
 121 #define TYPE_3          3
 122 #define BREAK_3         128
 123 #define DEG_3           31
 124 #define SEP_3           3
 125
 126 /* x**63 + x + 1.  */
 127 #define TYPE_4          4
 128 #define BREAK_4         256
 129 #define DEG_4           63
 130 #define SEP_4           1
 131
 132
 133 /* Array versions of the above information to make code run faster.
 134    Relies on fact that TYPE_i == i.  */
 135
 136 #define MAX_TYPES       5       /* Max number of types above.  */
 137
 138 struct random_poly_info
 139 {
 140   int seps[MAX_TYPES];
 141   int degrees[MAX_TYPES];
 142 };
 143
 144 static const struct random_poly_info random_poly_info =
 145 {
 146   { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 },
 147   { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 }
 148 };
 149
 150
 151
 152 \f
 153 /* Initialize the random number generator based on the given seed.  If the
 154    type is the trivial no-state-information type, just remember the seed.
 155    Otherwise, initializes state[] based on the given "seed" via a linear
 156    congruential generator.  Then, the pointers are set to known locations
 157    that are exactly rand_sep places apart.  Lastly, it cycles the state
 158    information a given number of times to get rid of any initial dependencies
 159    introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
 160    for default usage relies on values produced by this routine.  */
 161 int
 162 __srandom_r (seed, buf)
 163      unsigned int seed;
 164      struct random_data *buf;
 165 {
 166   int type;
 167   int32_t *state;
 168   long int i;
 169   int32_t word;
 170   int32_t *dst;
 171   int kc;
 172
 173   if (buf == NULL)
 174     goto fail;
 175   type = buf->rand_type;
 176   if ((unsigned int) type >= MAX_TYPES)
 177     goto fail;
 178
 179   state = buf->state;
 180   /* We must make sure the seed is not 0.  Take arbitrarily 1 in this case.  */
 181   if (seed == 0)
 182     seed = 1;
 183   state[0] = seed;
 184   if (type == TYPE_0)
 185     goto done;
 186
 187   dst = state;
 188   word = seed;
 189   kc = buf->rand_deg;
 190   for (i = 1; i < kc; ++i)
 191     {
 192       /* This does:
 193            state[i] = (16807 * state[i - 1]) % 2147483647;
 194          but avoids overflowing 31 bits.  */
 195       long int hi = word / 127773;
 196       long int lo = word % 127773;
 197       word = 16807 * lo - 2836 * hi;
 198       if (word < 0)
 199         word += 2147483647;
 200       *++dst = word;
 201     }
 202
 203   buf->fptr = &state[buf->rand_sep];
 204   buf->rptr = &state[0];
 205   kc *= 10;
 206   while (--kc >= 0)
 207     {
 208       int32_t discard;
 209       (void) __random_r (buf, &discard);
 210     }
 211
 212  done:
 213   return 0;
 214
 215  fail:
 216   return -1;
 217 }
 218
 219 weak_alias (__srandom_r, srandom_r)
 220 \f
 221 /* Initialize the state information in the given array of N bytes for
 222    future random number generation.  Based on the number of bytes we
 223    are given, and the break values for the different R.N.G.'s, we choose
 224    the best (largest) one we can and set things up for it.  srandom is
 225    then called to initialize the state information.  Note that on return
 226    from srandom, we set state[-1] to be the type multiplexed with the current
 227    value of the rear pointer; this is so successive calls to initstate won't
 228    lose this information and will be able to restart with setstate.
 229    Note: The first thing we do is save the current state, if any, just like
 230    setstate so that it doesn't matter when initstate is called.
 231    Returns a pointer to the old state.  */
 232 int
 233 __initstate_r (seed, arg_state, n, buf)
 234      unsigned int seed;
 235      char *arg_state;
 236      size_t n;
 237      struct random_data *buf;
 238 {
 239   if (buf == NULL)
 240     goto fail;
 241
 242   int32_t *old_state = buf->state;
 243   if (old_state != NULL)
 244     {
 245       int old_type = buf->rand_type;
 246       if (old_type == TYPE_0)
 247         old_state[-1] = TYPE_0;
 248       else
 249         old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
 250     }
 251
 252   int type;
 253   if (n >= BREAK_3)
 254     type = n < BREAK_4 ? TYPE_3 : TYPE_4;
 255   else if (n < BREAK_1)
 256     {
 257       if (n < BREAK_0)
 258         {
 259           __set_errno (EINVAL);
 260           goto fail;
 261         }
 262       type = TYPE_0;
 263     }
 264   else
 265     type = n < BREAK_2 ? TYPE_1 : TYPE_2;
 266
 267   int degree = random_poly_info.degrees[type];
 268   int separation = random_poly_info.seps[type];
 269
 270   buf->rand_type = type;
 271   buf->rand_sep = separation;
 272   buf->rand_deg = degree;
 273   int32_t *state = &((int32_t *) arg_state)[1]; /* First location.  */
 274   /* Must set END_PTR before srandom.  */
 275   buf->end_ptr = &state[degree];
 276
 277   buf->state = state;
 278
 279   __srandom_r (seed, buf);
 280
 281   state[-1] = TYPE_0;
 282   if (type != TYPE_0)
 283     state[-1] = (buf->rptr - state) * MAX_TYPES + type;
 284
 285   return 0;
 286
 287  fail:
 288   __set_errno (EINVAL);
 289   return -1;
 290 }
 291
 292 weak_alias (__initstate_r, initstate_r)
 293 \f
 294 /* Restore the state from the given state array.
 295    Note: It is important that we also remember the locations of the pointers
 296    in the current state information, and restore the locations of the pointers
 297    from the old state information.  This is done by multiplexing the pointer
 298    location into the zeroth word of the state information. Note that due
 299    to the order in which things are done, it is OK to call setstate with the
 300    same state as the current state
 301    Returns a pointer to the old state information.  */
 302 int
 303 __setstate_r (arg_state, buf)
 304      char *arg_state;
 305      struct random_data *buf;
 306 {
 307   int32_t *new_state = 1 + (int32_t *) arg_state;
 308   int type;
 309   int old_type;
 310   int32_t *old_state;
 311   int degree;
 312   int separation;
 313
 314   if (arg_state == NULL || buf == NULL)
 315     goto fail;
 316
 317   old_type = buf->rand_type;
 318   old_state = buf->state;
 319   if (old_type == TYPE_0)
 320     old_state[-1] = TYPE_0;
 321   else
 322     old_state[-1] = (MAX_TYPES * (buf->rptr - old_state)) + old_type;
 323
 324   type = new_state[-1] % MAX_TYPES;
 325   if (type < TYPE_0 || type > TYPE_4)
 326     goto fail;
 327
 328   buf->rand_deg = degree = random_poly_info.degrees[type];
 329   buf->rand_sep = separation = random_poly_info.seps[type];
 330   buf->rand_type = type;
 331
 332   if (type != TYPE_0)
 333     {
 334       int rear = new_state[-1] / MAX_TYPES;
 335       buf->rptr = &new_state[rear];
 336       buf->fptr = &new_state[(rear + separation) % degree];
 337     }
 338   buf->state = new_state;
 339   /* Set end_ptr too.  */
 340   buf->end_ptr = &new_state[degree];
 341
 342   return 0;
 343
 344  fail:
 345   __set_errno (EINVAL);
 346   return -1;
 347 }
 348
 349 weak_alias (__setstate_r, setstate_r)
 350 \f
 351 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
 352    congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
 353    same in all the other cases due to all the global variables that have been
 354    set up.  The basic operation is to add the number at the rear pointer into
 355    the one at the front pointer.  Then both pointers are advanced to the next
 356    location cyclically in the table.  The value returned is the sum generated,
 357    reduced to 31 bits by throwing away the "least random" low bit.
 358    Note: The code takes advantage of the fact that both the front and
 359    rear pointers can't wrap on the same call by not testing the rear
 360    pointer if the front one has wrapped.  Returns a 31-bit random number.  */
 361
 362 int
 363 __random_r (buf, result)
 364      struct random_data *buf;
 365      int32_t *result;
 366 {
 367   int32_t *state;
 368
 369   if (buf == NULL || result == NULL)
 370     goto fail;
 371
 372   state = buf->state;
 373
 374   if (buf->rand_type == TYPE_0)
 375     {
 376       int32_t val = state[0];
 377       val = ((state[0] * 1103515245) + 12345) & 0x7fffffff;
 378       state[0] = val;
 379       *result = val;
 380     }
 381   else
 382     {
 383       int32_t *fptr = buf->fptr;
 384       int32_t *rptr = buf->rptr;
 385       int32_t *end_ptr = buf->end_ptr;
 386       int32_t val;
 387
 388       val = *fptr += *rptr;
 389       /* Chucking least random bit.  */
 390       *result = (val >> 1) & 0x7fffffff;
 391       ++fptr;
 392       if (fptr >= end_ptr)
 393         {
 394           fptr = state;
 395           ++rptr;
 396         }
 397       else
 398         {
 399           ++rptr;
 400           if (rptr >= end_ptr)
 401             rptr = state;
 402         }
 403       buf->fptr = fptr;
 404       buf->rptr = rptr;
 405     }
 406   return 0;
 407
 408  fail:
 409   __set_errno (EINVAL);
 410   return -1;
 411 }
 412
 413 weak_alias (__random_r, random_r)