gcc/testsuite/gcc.dg/compat/generate-random.c

   1 /* Copyright (C) 1995, 2004 Free Software Foundation
   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, write to the Free
  15    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  16    02111-1307 USA.  */
  17
  18 /*
  19  * This is derived from the Berkeley source:
  20  *      @(#)random.c    5.5 (Berkeley) 7/6/88
  21  * It was reworked for the GNU C Library by Roland McGrath.
  22  * Rewritten to use reentrant functions by Ulrich Drepper, 1995.
  23  */
  24
  25 /*
  26    Copyright (C) 1983 Regents of the University of California.
  27    All rights reserved.
  28
  29    Redistribution and use in source and binary forms, with or without
  30    modification, are permitted provided that the following conditions
  31    are met:
  32
  33    1. Redistributions of source code must retain the above copyright
  34       notice, this list of conditions and the following disclaimer.
  35    2. Redistributions in binary form must reproduce the above copyright
  36       notice, this list of conditions and the following disclaimer in the
  37       documentation and/or other materials provided with the distribution.
  38    4. Neither the name of the University nor the names of its contributors
  39       may be used to endorse or promote products derived from this software
  40       without specific prior written permission.
  41
  42    THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  43    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  44    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  45    ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  46    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  47    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  48    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  49    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  50    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  51    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  52    SUCH DAMAGE.*/
  53
  54 #include "config.h"
  55 #ifdef HAVE_LIMITS_H
  56 #include <limits.h>
  57 #endif
  58 #include "libiberty.h"
  59 #ifdef HAVE_STDLIB_H
  60 #include <stdlib.h>
  61 #endif
  62 #include "generate-random.h"
  63
  64
  65 /* An improved random number generation package.  In addition to the standard
  66    rand()/srand() like interface, this package also has a special state info
  67    interface.  The initstate() routine is called with a seed, an array of
  68    bytes, and a count of how many bytes are being passed in; this array is
  69    then initialized to contain information for random number generation with
  70    that much state information.  Good sizes for the amount of state
  71    information are 32, 64, 128, and 256 bytes.  The state can be switched by
  72    calling the setstate() function with the same array as was initialized
  73    with initstate().  By default, the package runs with 128 bytes of state
  74    information and generates far better random numbers than a linear
  75    congruential generator.  If the amount of state information is less than
  76    32 bytes, a simple linear congruential R.N.G. is used.  Internally, the
  77    state information is treated as an array of longs; the zeroth element of
  78    the array is the type of R.N.G. being used (small integer); the remainder
  79    of the array is the state information for the R.N.G.  Thus, 32 bytes of
  80    state information will give 7 longs worth of state information, which will
  81    allow a degree seven polynomial.  (Note: The zeroth word of state
  82    information also has some other information stored in it; see setstate
  83    for details).  The random number generation technique is a linear feedback
  84    shift register approach, employing trinomials (since there are fewer terms
  85    to sum up that way).  In this approach, the least significant bit of all
  86    the numbers in the state table will act as a linear feedback shift register,
  87    and will have period 2^deg - 1 (where deg is the degree of the polynomial
  88    being used, assuming that the polynomial is irreducible and primitive).
  89    The higher order bits will have longer periods, since their values are
  90    also influenced by pseudo-random carries out of the lower bits.  The
  91    total period of the generator is approximately deg*(2**deg - 1); thus
  92    doubling the amount of state information has a vast influence on the
  93    period of the generator.  Note: The deg*(2**deg - 1) is an approximation
  94    only good for large deg, when the period of the shift register is the
  95    dominant factor.  With deg equal to seven, the period is actually much
  96    longer than the 7*(2**7 - 1) predicted by this formula.  */
  97
  98
  99
 100 /* For each of the currently supported random number generators, we have a
 101    break value on the amount of state information (you need at least this many
 102    bytes of state info to support this random number generator), a degree for
 103    the polynomial (actually a trinomial) that the R.N.G. is based on, and
 104    separation between the two lower order coefficients of the trinomial.  */
 105
 106 /* Linear congruential.  */
 107 #define TYPE_0          0
 108 #define BREAK_0         8
 109 #define DEG_0           0
 110 #define SEP_0           0
 111
 112 /* x**7 + x**3 + 1.  */
 113 #define TYPE_1          1
 114 #define BREAK_1         32
 115 #define DEG_1           7
 116 #define SEP_1           3
 117
 118 /* x**15 + x + 1.  */
 119 #define TYPE_2          2
 120 #define BREAK_2         64
 121 #define DEG_2           15
 122 #define SEP_2           1
 123
 124 /* x**31 + x**3 + 1.  */
 125 #define TYPE_3          3
 126 #define BREAK_3         128
 127 #define DEG_3           31
 128 #define SEP_3           3
 129
 130 /* x**63 + x + 1.  */
 131 #define TYPE_4          4
 132 #define BREAK_4         256
 133 #define DEG_4           63
 134 #define SEP_4           1
 135
 136
 137 /* Array versions of the above information to make code run faster.
 138    Relies on fact that TYPE_i == i.  */
 139
 140 #define MAX_TYPES       5       /* Max number of types above.  */
 141
 142
 143 /* Initially, everything is set up as if from:
 144         initstate(1, randtbl, 128);
 145    Note that this initialization takes advantage of the fact that srandom
 146    advances the front and rear pointers 10*rand_deg times, and hence the
 147    rear pointer which starts at 0 will also end up at zero; thus the zeroth
 148    element of the state information, which contains info about the current
 149    position of the rear pointer is just
 150         (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3.  */
 151
 152 static int randtbl[DEG_3 + 1] =
 153   {
 154     TYPE_3,
 155
 156     -1726662223, 379960547, 1735697613, 1040273694, 1313901226,
 157     1627687941, -179304937, -2073333483, 1780058412, -1989503057,
 158     -615974602, 344556628, 939512070, -1249116260, 1507946756,
 159     -812545463, 154635395, 1388815473, -1926676823, 525320961,
 160     -1009028674, 968117788, -123449607, 1284210865, 435012392,
 161     -2017506339, -911064859, -370259173, 1132637927, 1398500161,
 162     -205601318,
 163   };
 164
 165
 166 static struct generate_random_data unsafe_state =
 167   {
 168 /* FPTR and RPTR are two pointers into the state info, a front and a rear
 169    pointer.  These two pointers are always rand_sep places aparts, as they
 170    cycle through the state information.  (Yes, this does mean we could get
 171    away with just one pointer, but the code for random is more efficient
 172    this way).  The pointers are left positioned as they would be from the call:
 173         initstate(1, randtbl, 128);
 174    (The position of the rear pointer, rptr, is really 0 (as explained above
 175    in the initialization of randtbl) because the state table pointer is set
 176    to point to randtbl[1] (as explained below).)  */
 177
 178    &randtbl[SEP_3 + 1],  /* fptr */
 179    &randtbl[1],          /* rptr */
 180
 181 /* The following things are the pointer to the state information table,
 182    the type of the current generator, the degree of the current polynomial
 183    being used, and the separation between the two pointers.
 184    Note that for efficiency of random, we remember the first location of
 185    the state information, not the zeroth.  Hence it is valid to access
 186    state[-1], which is used to store the type of the R.N.G.
 187    Also, we remember the last location, since this is more efficient than
 188    indexing every time to find the address of the last element to see if
 189    the front and rear pointers have wrapped.  */
 190
 191     &randtbl[1],  /* state */
 192
 193     TYPE_3,  /* rand_type */
 194     DEG_3,   /* rand_deg */
 195     SEP_3,   /* rand_sep */
 196
 197     &randtbl[sizeof (randtbl) / sizeof (randtbl[0])]  /* end_ptr */
 198 };
 199 \f
 200 /* Initialize the random number generator based on the given seed.  If the
 201    type is the trivial no-state-information type, just remember the seed.
 202    Otherwise, initializes state[] based on the given "seed" via a linear
 203    congruential generator.  Then, the pointers are set to known locations
 204    that are exactly rand_sep places apart.  Lastly, it cycles the state
 205    information a given number of times to get rid of any initial dependencies
 206    introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]
 207    for default usage relies on values produced by this routine.  */
 208 void
 209 generate_srandom (unsigned int x)
 210 {
 211   (void) generate_srandom_r (x, &unsafe_state);
 212 }
 213 \f
 214 /* Initialize the state information in the given array of N bytes for
 215    future random number generation.  Based on the number of bytes we
 216    are given, and the break values for the different R.N.G.'s, we choose
 217    the best (largest) one we can and set things up for it.  srandom is
 218    then called to initialize the state information.  Note that on return
 219    from srandom, we set state[-1] to be the type multiplexed with the current
 220    value of the rear pointer; this is so successive calls to initstate won't
 221    lose this information and will be able to restart with setstate.
 222    Note: The first thing we do is save the current state, if any, just like
 223    setstate so that it doesn't matter when initstate is called.
 224    Returns a pointer to the old state.  */
 225 char *
 226 generate_initstate (unsigned int seed, char *arg_state, size_t n)
 227 {
 228   int *ostate;
 229
 230   ostate = &unsafe_state.state[-1];
 231   generate_initstate_r (seed, arg_state, n, &unsafe_state);
 232   return (char *) ostate;
 233 }
 234 \f
 235 /* Restore the state from the given state array.
 236    Note: It is important that we also remember the locations of the pointers
 237    in the current state information, and restore the locations of the pointers
 238    from the old state information.  This is done by multiplexing the pointer
 239    location into the zeroth word of the state information. Note that due
 240    to the order in which things are done, it is OK to call setstate with the
 241    same state as the current state
 242    Returns a pointer to the old state information.  */
 243 char *
 244 generate_setstate (char *arg_state)
 245 {
 246   int *ostate;
 247
 248   ostate = &unsafe_state.state[-1];
 249   if (generate_setstate_r (arg_state, &unsafe_state) < 0)
 250     ostate = NULL;
 251   return (char *) ostate;
 252 }
 253 \f
 254 /* If we are using the trivial TYPE_0 R.N.G., just do the old linear
 255    congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
 256    same in all the other cases due to all the global variables that have been
 257    set up.  The basic operation is to add the number at the rear pointer into
 258    the one at the front pointer.  Then both pointers are advanced to the next
 259    location cyclically in the table.  The value returned is the sum generated,
 260    reduced to 31 bits by throwing away the "least random" low bit.
 261    Note: The code takes advantage of the fact that both the front and
 262    rear pointers can't wrap on the same call by not testing the rear
 263    pointer if the front one has wrapped.  Returns a 31-bit random number.  */
 264
 265 long int
 266 generate_random (void)
 267 {
 268   int retval;
 269   (void) generate_random_r (&unsafe_state, &retval);
 270   return retval;
 271 }