rand.c revision 1.1.1.1 
1/* Implementation of the IRAND, RAND, and SRAND intrinsics.
2   Copyright (C) 2004-2019 Free Software Foundation, Inc.
3   Contributed by Steven G. Kargl <kargls@comcast.net>.
4
5This file is part of the GNU Fortran 95 runtime library (libgfortran).
6
7Libgfortran is free software; you can redistribute it and/or
8modify it under the terms of the GNU General Public
9License as published by the Free Software Foundation; either
10version 3 of the License, or (at your option) any later version.
11
12Libgfortran is distributed in the hope that it will be useful,
13but WITHOUT ANY WARRANTY; without even the implied warranty of
14MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15GNU General Public License for more details.
16
17Under Section 7 of GPL version 3, you are granted additional
18permissions described in the GCC Runtime Library Exception, version
193.1, as published by the Free Software Foundation.
20
21You should have received a copy of the GNU General Public License and
22a copy of the GCC Runtime Library Exception along with this program;
23see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
24<http://www.gnu.org/licenses/>.  */
25
26/* Simple multiplicative congruent algorithm.
27   The period of this generator is approximately 2^31-1, which means that
28   it should not be used for anything serious.  The implementation here
29   is based of an algorithm from  S.K. Park and K.W. Miller, Comm. ACM,
30   31, 1192-1201 (1988).  It is also provided solely for compatibility
31   with G77.  */
32
33#include "libgfortran.h"
34#include <gthr.h>
35
36#define GFC_RAND_A	16807
37#define GFC_RAND_M	2147483647
38#define GFC_RAND_M1	(GFC_RAND_M - 1)
39
40static GFC_UINTEGER_8 rand_seed = 1;
41#ifdef __GTHREAD_MUTEX_INIT
42static __gthread_mutex_t rand_seed_lock = __GTHREAD_MUTEX_INIT;
43#else
44static __gthread_mutex_t rand_seed_lock;
45#endif
46
47
48/* Set the seed of the irand generator.  Note 0 is a bad seed.  */
49
50static void
51srand_internal (GFC_INTEGER_8 i)
52{
53  rand_seed = i ? i : 123459876;
54}
55
56extern void PREFIX(srand) (GFC_INTEGER_4 *i);
57export_proto_np(PREFIX(srand));
58
59void
60PREFIX(srand) (GFC_INTEGER_4 *i)
61{
62  __gthread_mutex_lock (&rand_seed_lock);
63  srand_internal (*i);
64  __gthread_mutex_unlock (&rand_seed_lock);
65}
66
67/* Return an INTEGER in the range [1,GFC_RAND_M-1].  */
68
69extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);
70iexport_proto(irand);
71
72GFC_INTEGER_4
73irand (GFC_INTEGER_4 *i)
74{
75  GFC_INTEGER_4 j;
76  if (i)
77    j = *i;
78  else
79    j = 0;
80
81  __gthread_mutex_lock (&rand_seed_lock);
82
83  switch (j)
84  {
85    /* Return the next RN. */
86    case 0:
87      break;
88
89    /* Reset the RN sequence to system-dependent sequence and return the
90       first value.  */
91    case 1:
92      srand_internal (0);
93      break;
94
95    /* Seed the RN sequence with j and return the first value.  */
96    default:
97      srand_internal (j);
98      break;
99   }
100
101   rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
102   j = (GFC_INTEGER_4) rand_seed;
103
104  __gthread_mutex_unlock (&rand_seed_lock);
105
106   return j;
107}
108iexport(irand);
109
110
111/*  Return a random REAL in the range [0,1).  */
112
113extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);
114export_proto_np(PREFIX(rand));
115
116GFC_REAL_4
117PREFIX(rand) (GFC_INTEGER_4 *i)
118{
119  GFC_UINTEGER_4 mask;
120#if GFC_REAL_4_RADIX == 2
121  mask = ~ (GFC_UINTEGER_4) 0u << (32 - GFC_REAL_4_DIGITS + 1);
122#elif GFC_REAL_4_RADIX == 16
123  mask = ~ (GFC_UINTEGER_4) 0u << ((8 - GFC_REAL_4_DIGITS) * 4 + 1);
124#else
125#error "GFC_REAL_4_RADIX has unknown value"
126#endif
127  return ((GFC_UINTEGER_4) (irand(i) -1) & mask) * (GFC_REAL_4) 0x1.p-31f;
128}
129
130#ifndef __GTHREAD_MUTEX_INIT
131static void __attribute__((constructor))
132init (void)
133{
134  __GTHREAD_MUTEX_INIT_FUNCTION (&rand_seed_lock);
135}
136#endif
137