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/* Implementation of the IRAND, RAND, and SRAND intrinsics.
Copyright (C) 2004 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 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.
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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with libgfor; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
/* 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 "config.h"
#include "libgfortran.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;
/* Set the seed of the irand generator. Note 0 is a bad seed. */
void
prefix(srand) (GFC_INTEGER_4 *i)
{
rand_seed = (GFC_UINTEGER_8) (*i != 0) ? *i : 123459876;
}
/* Return an INTEGER in the range [1,GFC_RAND_M-1]. */
GFC_INTEGER_4
prefix(irand) (GFC_INTEGER_4 *i)
{
GFC_INTEGER_4 j = *i;
switch (j)
{
/* Return the next RN. */
case 0:
break;
/* Reset the RN sequence to system-dependent sequence and return the
first value. */
case 1:
j = 0;
prefix(srand) (&j);
break;
/* Seed the RN sequence with j and return the first value. */
default:
prefix(srand) (&j);
}
rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
return (GFC_INTEGER_4) rand_seed;
}
/* Return a random REAL in the range [0,1). */
GFC_REAL_4
prefix(rand) (GFC_INTEGER_4 *i)
{
return normalize_r4_i4 (irand (i) - 1, GFC_RAND_M1 - 1);
}
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