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/* Copyright (C) 1995, 2004 Free Software Foundation

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, write to the Free

   Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

   02110-1301 USA.  */

/*

 * This is derived from the Berkeley source:

 *      @(#)random.c    5.5 (Berkeley) 7/6/88

 * It was reworked for the GNU C Library by Roland McGrath.

 * Rewritten to use reentrant functions by Ulrich Drepper, 1995.

 */

/*

   Copyright (C) 1983 Regents of the University of California.

   All rights reserved.

   Redistribution and use in source and binary forms, with or without

   modification, are permitted provided that the following conditions

   are met:

   1. Redistributions of source code must retain the above copyright

      notice, this list of conditions and the following disclaimer.

   2. Redistributions in binary form must reproduce the above copyright

      notice, this list of conditions and the following disclaimer in the

      documentation and/or other materials provided with the distribution.

   4. Neither the name of the University nor the names of its contributors

      may be used to endorse or promote products derived from this software

      without specific prior written permission.

   THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

   ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

   ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

   FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

   OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

   HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

   LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

   OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

   SUCH DAMAGE.*/

#include <limits.h>

#include <stdlib.h>

#include "generate-random.h"

/* An improved random number generation package.  In addition to the standard

   rand()/srand() like interface, this package also has a special state info

   interface.  The initstate() routine is called with a seed, an array of

   bytes, and a count of how many bytes are being passed in; this array is

   then initialized to contain information for random number generation with

   that much state information.  Good sizes for the amount of state

   information are 32, 64, 128, and 256 bytes.  The state can be switched by

   calling the setstate() function with the same array as was initialized

   with initstate().  By default, the package runs with 128 bytes of state

   information and generates far better random numbers than a linear

   congruential generator.  If the amount of state information is less than

   32 bytes, a simple linear congruential R.N.G. is used.  Internally, the

   state information is treated as an array of longs; the zeroth element of

   the array is the type of R.N.G. being used (small integer); the remainder

   of the array is the state information for the R.N.G.  Thus, 32 bytes of

   state information will give 7 longs worth of state information, which will

   allow a degree seven polynomial.  (Note: The zeroth word of state

   information also has some other information stored in it; see setstate

   for details).  The random number generation technique is a linear feedback

   shift register approach, employing trinomials (since there are fewer terms

   to sum up that way).  In this approach, the least significant bit of all

   the numbers in the state table will act as a linear feedback shift register,

   and will have period 2^deg - 1 (where deg is the degree of the polynomial

   being used, assuming that the polynomial is irreducible and primitive).

   The higher order bits will have longer periods, since their values are

   also influenced by pseudo-random carries out of the lower bits.  The

   total period of the generator is approximately deg*(2**deg - 1); thus

   doubling the amount of state information has a vast influence on the

   period of the generator.  Note: The deg*(2**deg - 1) is an approximation

   only good for large deg, when the period of the shift register is the

   dominant factor.  With deg equal to seven, the period is actually much

   longer than the 7*(2**7 - 1) predicted by this formula.  */

/* For each of the currently supported random number generators, we have a

   break value on the amount of state information (you need at least this many

   bytes of state info to support this random number generator), a degree for

   the polynomial (actually a trinomial) that the R.N.G. is based on, and

   separation between the two lower order coefficients of the trinomial.  */

/* Linear congruential.  */

#define TYPE_0          0

#define BREAK_0         8

#define DEG_0           0

#define SEP_0           0

/* x**7 + x**3 + 1.  */

#define TYPE_1          1

#define BREAK_1         32

#define DEG_1           7

#define SEP_1           3

/* x**15 + x + 1.  */

#define TYPE_2          2

#define BREAK_2         64

#define DEG_2           15

#define SEP_2           1

/* x**31 + x**3 + 1.  */

#define TYPE_3          3

#define BREAK_3         128

#define DEG_3           31

#define SEP_3           3

/* x**63 + x + 1.  */

#define TYPE_4          4

#define BREAK_4         256

#define DEG_4           63

#define SEP_4           1

/* Array versions of the above information to make code run faster.

   Relies on fact that TYPE_i == i.  */

#define MAX_TYPES       5       /* Max number of types above.  */

/* Initially, everything is set up as if from:

        initstate(1, randtbl, 128);

   Note that this initialization takes advantage of the fact that srandom

   advances the front and rear pointers 10*rand_deg times, and hence the

   rear pointer which starts at 0 will also end up at zero; thus the zeroth

   element of the state information, which contains info about the current

   position of the rear pointer is just

        (MAX_TYPES * (rptr - state)) + TYPE_3 == TYPE_3.  */

static int randtbl[DEG_3 + 1] =

  {

    TYPE_3,

    -1726662223, 379960547, 1735697613, 1040273694, 1313901226,

    1627687941, -179304937, -2073333483, 1780058412, -1989503057,

    -615974602, 344556628, 939512070, -1249116260, 1507946756,

    -812545463, 154635395, 1388815473, -1926676823, 525320961,

    -1009028674, 968117788, -123449607, 1284210865, 435012392,

    -2017506339, -911064859, -370259173, 1132637927, 1398500161,

    -205601318,

  };

static struct generate_random_data unsafe_state =

  {

/* FPTR and RPTR are two pointers into the state info, a front and a rear

   pointer.  These two pointers are always rand_sep places aparts, as they

   cycle through the state information.  (Yes, this does mean we could get

   away with just one pointer, but the code for random is more efficient

   this way).  The pointers are left positioned as they would be from the call:

        initstate(1, randtbl, 128);

   (The position of the rear pointer, rptr, is really 0 (as explained above

   in the initialization of randtbl) because the state table pointer is set

   to point to randtbl[1] (as explained below).)  */

   &randtbl[SEP_3 + 1],  /* fptr */

   &randtbl[1],          /* rptr */

/* The following things are the pointer to the state information table,

   the type of the current generator, the degree of the current polynomial

   being used, and the separation between the two pointers.

   Note that for efficiency of random, we remember the first location of

   the state information, not the zeroth.  Hence it is valid to access

   state[-1], which is used to store the type of the R.N.G.

   Also, we remember the last location, since this is more efficient than

   indexing every time to find the address of the last element to see if

   the front and rear pointers have wrapped.  */

    &randtbl[1],  /* state */

    TYPE_3,  /* rand_type */

    DEG_3,   /* rand_deg */

    SEP_3,   /* rand_sep */

    &randtbl[sizeof (randtbl) / sizeof (randtbl[0])]  /* end_ptr */

};

/* Initialize the random number generator based on the given seed.  If the

   type is the trivial no-state-information type, just remember the seed.

   Otherwise, initializes state[] based on the given "seed" via a linear

   congruential generator.  Then, the pointers are set to known locations

   that are exactly rand_sep places apart.  Lastly, it cycles the state

   information a given number of times to get rid of any initial dependencies

   introduced by the L.C.R.N.G.  Note that the initialization of randtbl[]

   for default usage relies on values produced by this routine.  */

void

generate_srandom (unsigned int x)

{

  (void) generate_srandom_r (x, &unsafe_state);

}

/* Initialize the state information in the given array of N bytes for

   future random number generation.  Based on the number of bytes we

   are given, and the break values for the different R.N.G.'s, we choose

   the best (largest) one we can and set things up for it.  srandom is

   then called to initialize the state information.  Note that on return

   from srandom, we set state[-1] to be the type multiplexed with the current

   value of the rear pointer; this is so successive calls to initstate won't

   lose this information and will be able to restart with setstate.

   Note: The first thing we do is save the current state, if any, just like

   setstate so that it doesn't matter when initstate is called.

   Returns a pointer to the old state.  */

char *

generate_initstate (unsigned int seed, char *arg_state, size_t n)

{

  int *ostate;

  ostate = &unsafe_state.state[-1];

  generate_initstate_r (seed, arg_state, n, &unsafe_state);

  return (char *) ostate;

}

/* Restore the state from the given state array.

   Note: It is important that we also remember the locations of the pointers

   in the current state information, and restore the locations of the pointers

   from the old state information.  This is done by multiplexing the pointer

   location into the zeroth word of the state information. Note that due

   to the order in which things are done, it is OK to call setstate with the

   same state as the current state

   Returns a pointer to the old state information.  */

char *

generate_setstate (char *arg_state)

{

  int *ostate;

  ostate = &unsafe_state.state[-1];

  if (generate_setstate_r (arg_state, &unsafe_state) < 0)

    ostate = NULL;

  return (char *) ostate;

}

/* If we are using the trivial TYPE_0 R.N.G., just do the old linear

   congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the

   same in all the other cases due to all the global variables that have been

   set up.  The basic operation is to add the number at the rear pointer into

   the one at the front pointer.  Then both pointers are advanced to the next

   location cyclically in the table.  The value returned is the sum generated,

   reduced to 31 bits by throwing away the "least random" low bit.

   Note: The code takes advantage of the fact that both the front and

   rear pointers can't wrap on the same call by not testing the rear

   pointer if the front one has wrapped.  Returns a 31-bit random number.  */

long int

generate_random (void)

{

  int retval;

  (void) generate_random_r (&unsafe_state, &retval);

  return retval;

}