1 /* Implementation of the IRAND, RAND, and SRAND intrinsics.
2 Copyright (C) 2004-2023 Free Software Foundation, Inc.
3 Contributed by Steven G. Kargl <kargls@comcast.net>.
4
5 This file is part of the GNU Fortran 95 runtime library (libgfortran).
6
7 Libgfortran is free software; you can redistribute it and/or
8 modify it under the terms of the GNU General Public
9 License as published by the Free Software Foundation; either
10 version 3 of the License, or (at your option) any later version.
11
12 Libgfortran is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 Under Section 7 of GPL version 3, you are granted additional
18 permissions described in the GCC Runtime Library Exception, version
19 3.1, as published by the Free Software Foundation.
20
21 You should have received a copy of the GNU General Public License and
22 a copy of the GCC Runtime Library Exception along with this program;
23 see 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
40 static GFC_UINTEGER_8 rand_seed = 1;
41 #ifdef __GTHREAD_MUTEX_INIT
42 static __gthread_mutex_t rand_seed_lock = __GTHREAD_MUTEX_INIT;
43 #else
44 static __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
50 static void
51 srand_internal (GFC_INTEGER_8 i)
52 {
53 rand_seed = i ? i : 123459876;
54 }
55
56 extern void PREFIX(srand) (GFC_INTEGER_4 *i);
57 export_proto_np(PREFIX(srand));
58
59 void
60 PREFIX(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
69 extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);
70 iexport_proto(irand);
71
72 GFC_INTEGER_4
73 irand (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 }
108 iexport(irand);
109
110
111 /* Return a random REAL in the range [0,1). */
112
113 extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);
114 export_proto_np(PREFIX(rand));
115
116 GFC_REAL_4
117 PREFIX(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
131 static void __attribute__((constructor))
132 init (void)
133 {
134 __GTHREAD_MUTEX_INIT_FUNCTION (&rand_seed_lock);
135 }
136 #endif