/* glprng01.c */

/***********************************************************************

*  This code is part of GLPK (GNU Linear Programming Kit).

*

*  This code is a modified version of the module GB_FLIP, a portable

*  pseudo-random number generator. The original version of GB_FLIP is

*  a part of The Stanford GraphBase developed by Donald E. Knuth (see

*  http://www-cs-staff.stanford.edu/~knuth/sgb.html).

*

*  Note that all changes concern only external names, so this modified

*  version produces exactly the same results as the original version.

*

*  Changes were made by Andrew Makhorin <mao@gnu.org>.

*

*  GLPK is free software: you can redistribute it and/or modify it

*  under the terms of the GNU General Public License as published by

*  the Free Software Foundation, either version 3 of the License, or

*  (at your option) any later version.

*

*  GLPK 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 General Public

*  License for more details.

*

*  You should have received a copy of the GNU General Public License

*  along with GLPK. If not, see <http://www.gnu.org/licenses/>.

***********************************************************************/

#include "glpenv.h"

#include "glprng.h"

#if 0

int A[56] = { -1 };

#else

#define A (rand->A)

#endif

/* pseudo-random values */

#if 0

int *fptr = A;

#else

#define fptr (rand->fptr)

#endif

/* the next A value to be exported */

#define mod_diff(x, y) (((x) - (y)) & 0x7FFFFFFF)

/* difference modulo 2^31 */

static int flip_cycle(RNG *rand)

{     /* this is an auxiliary routine to do 55 more steps of the basic

         recurrence, at high speed, and to reset fptr */

      int *ii, *jj;

      for (ii = &A[1], jj = &A[32]; jj <= &A[55]; ii++, jj++)

         *ii = mod_diff(*ii, *jj);

      for (jj = &A[1]; ii <= &A[55]; ii++, jj++)

         *ii = mod_diff(*ii, *jj);

      fptr = &A[54];

      return A[55];

}

/***********************************************************************

*  NAME

*

*  rng_create_rand - create pseudo-random number generator

*

*  SYNOPSIS

*

*  #include "glprng.h"

*  RNG *rng_create_rand(void);

*

*  DESCRIPTION

*

*  The routine rng_create_rand creates and initializes a pseudo-random

*  number generator.

*

*  RETURNS

*

*  The routine returns a pointer to the generator created. */

RNG *rng_create_rand(void)

{     RNG *rand;

      int i;

      rand = xmalloc(sizeof(RNG));

      A[0] = -1;

      for (i = 1; i <= 55; i++) A[i] = 0;

      fptr = A;

      rng_init_rand(rand, 1);

      return rand;

}

/***********************************************************************

*  NAME

*

*  rng_init_rand - initialize pseudo-random number generator

*

*  SYNOPSIS

*

*  #include "glprng.h"

*  void rng_init_rand(RNG *rand, int seed);

*

*  DESCRIPTION

*

*  The routine rng_init_rand initializes the pseudo-random number

*  generator. The parameter seed may be any integer number. Note that

*  on creating the generator this routine is called with the parameter

*  seed equal to 1. */

void rng_init_rand(RNG *rand, int seed)

{     int i;

      int prev = seed, next = 1;

      seed = prev = mod_diff(prev, 0);

      A[55] = prev;

      for (i = 21; i; i = (i + 21) % 55)

      {  A[i] = next;

         next = mod_diff(prev, next);

         if (seed & 1)

            seed = 0x40000000 + (seed >> 1);

         else

            seed >>= 1;

         next = mod_diff(next, seed);

         prev = A[i];

      }

      flip_cycle(rand);

      flip_cycle(rand);

      flip_cycle(rand);

      flip_cycle(rand);

      flip_cycle(rand);

      return;

}

/***********************************************************************

*  NAME

*

*  rng_next_rand - obtain pseudo-random integer in the range [0, 2^31-1]

*

*  SYNOPSIS

*

*  #include "glprng.h"

*  int rng_next_rand(RNG *rand);

*

*  RETURNS

*

*  The routine rng_next_rand returns a next pseudo-random integer which

*  is uniformly distributed between 0 and 2^31-1, inclusive. The period

*  length of the generated numbers is 2^85 - 2^30. The low order bits of

*  the generated numbers are just as random as the high-order bits. */

int rng_next_rand(RNG *rand)

{     return

         *fptr >= 0 ? *fptr-- : flip_cycle(rand);

}

/***********************************************************************

*  NAME

*

*  rng_unif_rand - obtain pseudo-random integer in the range [0, m-1]

*

*  SYNOPSIS

*

*  #include "glprng.h"

*  int rng_unif_rand(RNG *rand, int m);

*

*  RETURNS

*

*  The routine rng_unif_rand returns a next pseudo-random integer which

*  is uniformly distributed between 0 and m-1, inclusive, where m is any

*  positive integer less than 2^31. */

#define two_to_the_31 ((unsigned int)0x80000000)

int rng_unif_rand(RNG *rand, int m)

{     unsigned int t = two_to_the_31 - (two_to_the_31 % m);

      int r;

      xassert(m > 0);

      do { r = rng_next_rand(rand); } while (t <= (unsigned int)r);

      return r % m;

}

/***********************************************************************

*  NAME

*

*  rng_delete_rand - delete pseudo-random number generator

*

*  SYNOPSIS

*

*  #include "glprng.h"

*  void rng_delete_rand(RNG *rand);

*

*  DESCRIPTION

*

*  The routine rng_delete_rand frees all the memory allocated to the

*  specified pseudo-random number generator. */

void rng_delete_rand(RNG *rand)

{     xfree(rand);

      return;

}

/**********************************************************************/

#if 0

/* To be sure that this modified version produces the same results as

   the original version, run this validation program. */

int main(void)

{     RNG *rand;

      int j;

      rand = rng_create_rand();

      rng_init_rand(rand, -314159);

      if (rng_next_rand(rand) != 119318998)

      {  fprintf(stderr, "Failure on the first try!\n");

         return -1;

      }

      for (j = 1; j <= 133; j++) rng_next_rand(rand);

      if (rng_unif_rand(rand, 0x55555555) != 748103812)

      {  fprintf(stderr, "Failure on the second try!\n");

         return -2;

      }

      fprintf(stderr, "OK, the random-number generator routines seem to"

         " work!\n");

      rng_delete_rand(rand);

      return 0;

}

#endif

/* eof */