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/* Implementation of the IRAND, RAND, and SRAND intrinsics.

   Copyright (C) 2004, 2005, 2007, 2009 Free Software Foundation, Inc.

   Contributed by Steven G. Kargl <kargls@comcast.net>.

This file is part of the GNU Fortran 95 runtime library (libgfortran).

Libgfortran 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.

Libgfortran 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.

Under Section 7 of GPL version 3, you are granted additional

permissions described in the GCC Runtime Library Exception, version

3.1, as published by the Free Software Foundation.

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

a copy of the GCC Runtime Library Exception along with this program;

see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

<http://www.gnu.org/licenses/>.  */

/* Simple multiplicative congruent algorithm.

   The period of this generator is approximately 2^31-1, which means that

   it should not be used for anything serious.  The implementation here

   is based of an algorithm from  S.K. Park and K.W. Miller, Comm. ACM,

   31, 1192-1201 (1988).  It is also provided solely for compatibility

   with G77.  */

#include "libgfortran.h"

#include <gthr.h>

#define GFC_RAND_A      16807

#define GFC_RAND_M      2147483647

#define GFC_RAND_M1     (GFC_RAND_M - 1)

static GFC_UINTEGER_8 rand_seed = 1;

#ifdef __GTHREAD_MUTEX_INIT

static __gthread_mutex_t rand_seed_lock = __GTHREAD_MUTEX_INIT;

#else

static __gthread_mutex_t rand_seed_lock;

#endif

/* Set the seed of the irand generator.  Note 0 is a bad seed.  */

static void

srand_internal (GFC_INTEGER_8 i)

{

  rand_seed = i ? i : 123459876;

}

extern void PREFIX(srand) (GFC_INTEGER_4 *i);

export_proto_np(PREFIX(srand));

void

PREFIX(srand) (GFC_INTEGER_4 *i)

{

  __gthread_mutex_lock (&rand_seed_lock);

  srand_internal (*i);

  __gthread_mutex_unlock (&rand_seed_lock);

}

/* Return an INTEGER in the range [1,GFC_RAND_M-1].  */

extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);

iexport_proto(irand);

GFC_INTEGER_4

irand (GFC_INTEGER_4 *i)

{

  GFC_INTEGER_4 j;

  if (i)

    j = *i;

  else

    j = 0;

  __gthread_mutex_lock (&rand_seed_lock);

  switch (j)

  {

    /* Return the next RN. */

    case 0:

      break;

    /* Reset the RN sequence to system-dependent sequence and return the

       first value.  */

    case 1:

      srand_internal (0);

      break;

    /* Seed the RN sequence with j and return the first value.  */

    default:

      srand_internal (j);

      break;

   }

   rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;

   j = (GFC_INTEGER_4) rand_seed;

  __gthread_mutex_unlock (&rand_seed_lock);

   return j;

}

iexport(irand);

/*  Return a random REAL in the range [0,1).  */

extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);

export_proto_np(PREFIX(rand));

GFC_REAL_4

PREFIX(rand) (GFC_INTEGER_4 *i)

{

  GFC_UINTEGER_4 mask;

#if GFC_REAL_4_RADIX == 2

  mask = ~ (GFC_UINTEGER_4) 0u << (32 - GFC_REAL_4_DIGITS + 1);

#elif GFC_REAL_4_RADIX == 16

  mask = ~ (GFC_UINTEGER_4) 0u << ((8 - GFC_REAL_4_DIGITS) * 4 + 1);

#else

#error "GFC_REAL_4_RADIX has unknown value"

#endif

  return ((GFC_UINTEGER_4) (irand(i) -1) & mask) * (GFC_REAL_4) 0x1.p-31f;

}

#ifndef __GTHREAD_MUTEX_INIT

static void __attribute__((constructor))

init (void)

{

  __GTHREAD_MUTEX_INIT_FUNCTION (&rand_seed_lock);

}

#endif