GRASS GIS 8 Programmer's Manual 8.2.0(2022)-exported
lrand48.c
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1/*!
2 * \file lib/gis/lrand48.c
3 *
4 * \brief GIS Library - Pseudo-random number generation
5 *
6 * (C) 2014 by the GRASS Development Team
7 *
8 * This program is free software under the GNU General Public License
9 * (>=v2). Read the file COPYING that comes with GRASS for details.
10 *
11 * \author Glynn Clements
12 */
13
14#include <stdio.h>
15#include <stdlib.h>
16#include <string.h>
17#include <errno.h>
18
19#include <grass/gis.h>
20#include <grass/glocale.h>
21
22#ifdef HAVE_GETTIMEOFDAY
23#include <sys/time.h>
24#else
25#include <time.h>
26#endif
27
28#include <sys/types.h>
29#include <unistd.h>
30
31typedef unsigned short uint16;
32typedef unsigned int uint32;
33typedef signed int int32;
34
35static uint16 x0, x1, x2;
36static const uint32 a0 = 0xE66D;
37static const uint32 a1 = 0xDEEC;
38static const uint32 a2 = 0x5;
39
40static const uint32 b0 = 0xB;
41
42static int seeded;
43
44#define LO(x) ((x) & 0xFFFFU)
45#define HI(x) ((x) >> 16)
46
47/*!
48 * \brief Seed the pseudo-random number generator
49 *
50 * \param seedval 32-bit integer used to seed the PRNG
51 */
52
53void G_srand48(long seedval)
54{
55 uint32 x = (uint32) *(unsigned long *)&seedval;
56 x2 = (uint16) HI(x);
57 x1 = (uint16) LO(x);
58 x0 = (uint16) 0x330E;
59 seeded = 1;
60}
61
62/*!
63 * \brief Seed the pseudo-random number generator from the time and PID
64 *
65 * A weak hash of the current time and PID is generated and used to
66 * seed the PRNG
67 *
68 * \return generated seed value passed to G_srand48()
69 */
70
72{
73 unsigned long seed;
74 char *grass_random_seed = getenv("GRASS_RANDOM_SEED");
75 if(!grass_random_seed) grass_random_seed = getenv("SOURCE_DATE_EPOCH");
76 if(grass_random_seed) {
77 seed = strtoull(grass_random_seed, NULL, 10);
78 } else {
79 seed = (unsigned long) getpid();
80
81#ifdef HAVE_GETTIMEOFDAY
82 {
83 struct timeval tv;
84 if (gettimeofday(&tv, NULL) < 0)
85 G_fatal_error(_("gettimeofday failed: %s"), strerror(errno));
86 seed += (unsigned long) tv.tv_sec;
87 seed += (unsigned long) tv.tv_usec;
88 }
89#else
90 {
91 time_t t = time(NULL);
92 seed += (unsigned long) t;
93 }
94#endif
95 }
96
97 G_srand48((long) seed);
98 return (long) seed;
99}
100
101static void G__next(void)
102{
103 uint32 a0x0 = a0 * x0;
104 uint32 a0x1 = a0 * x1;
105 uint32 a0x2 = a0 * x2;
106 uint32 a1x0 = a1 * x0;
107 uint32 a1x1 = a1 * x1;
108 uint32 a2x0 = a2 * x0;
109
110 uint32 y0 = LO(a0x0) + b0;
111 uint32 y1 = LO(a0x1) + LO(a1x0) + HI(a0x0);
112 uint32 y2 = LO(a0x2) + LO(a1x1) + LO(a2x0) + HI(a0x1) + HI(a1x0);
113
114 if (!seeded)
115 G_fatal_error(_("Pseudo-random number generator not seeded"));
116
117 x0 = (uint16) LO(y0);
118 y1 += HI(y0);
119 x1 = (uint16) LO(y1);
120 y2 += HI(y1);
121 x2 = (uint16) LO(y2);
122}
123
124/*!
125 * \brief Generate an integer in the range [0, 2^31)
126 *
127 * \return the generated value
128 */
129
130long G_lrand48(void)
131{
132 uint32 r;
133 G__next();
134 r = ((uint32) x2 << 15) | ((uint32) x1 >> 1);
135 return (long) r;
136}
137
138/*!
139 * \brief Generate an integer in the range [-2^31, 2^31)
140 *
141 * \return the generated value
142 */
143
144long G_mrand48(void)
145{
146 uint32 r;
147 G__next();
148 r = ((uint32) x2 << 16) | ((uint32) x1);
149 return (long) (int32) r;
150}
151
152/*!
153 * \brief Generate a floating-point value in the range [0,1)
154 *
155 * \return the generated value
156 */
157
158double G_drand48(void)
159{
160 double r = 0.0;
161 G__next();
162 r += x2;
163 r *= 0x10000;
164 r += x1;
165 r *= 0x10000;
166 r += x0;
167 r /= 281474976710656.0; /* 2^48 */
168 return r;
169}
170
171/*
172
173Test program
174
175int main(int argc, char **argv)
176{
177 long s = (argc > 1) ? atol(argv[1]) : 0;
178 int i;
179
180 srand48(s);
181 G_srand48(s);
182
183 for (i = 0; i < 100; i++) {
184 printf("%.50f %.50f\n", drand48(), G_drand48());
185 printf("%lu %lu\n", lrand48(), G_lrand48());
186 printf("%ld %ld\n", mrand48(), G_mrand48());
187 }
188
189 return 0;
190}
191
192*/
#define NULL
Definition: ccmath.h:32
double t
double r
void G_fatal_error(const char *msg,...)
Print a fatal error message to stderr.
Definition: gis/error.c:160
unsigned short uint16
Definition: lrand48.c:31
unsigned int uint32
Definition: lrand48.c:32
long G_mrand48(void)
Generate an integer in the range [-2^31, 2^31)
Definition: lrand48.c:144
long G_lrand48(void)
Generate an integer in the range [0, 2^31)
Definition: lrand48.c:130
long G_srand48_auto(void)
Seed the pseudo-random number generator from the time and PID.
Definition: lrand48.c:71
signed int int32
Definition: lrand48.c:33
#define HI(x)
Definition: lrand48.c:45
void G_srand48(long seedval)
Seed the pseudo-random number generator.
Definition: lrand48.c:53
#define LO(x)
Definition: lrand48.c:44
double G_drand48(void)
Generate a floating-point value in the range [0,1)
Definition: lrand48.c:158
#define x