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29 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
32 #if defined(LIBC_SCCS) && !defined(lint)
33 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93";
34 #endif /* LIBC_SCCS and not lint */
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
38 #include "namespace.h"
39 #include <sys/time.h> /* for sranddev() */
40 #include <sys/types.h>
41 #include <fcntl.h> /* for sranddev() */
43 #include <unistd.h> /* for sranddev() */
44 #include "un-namespace.h"
51 do_rand(unsigned long *ctx)
53 #ifdef USE_WEAK_SEEDING
55 * Historic implementation compatibility.
56 * The random sequences do not vary much with the seed,
57 * even with overflowing.
59 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
60 #else /* !USE_WEAK_SEEDING */
62 * Compute x = (7^5 * x) mod (2^31 - 1)
63 * wihout overflowing 31 bits:
64 * (2^31 - 1) = 127773 * (7^5) + 2836
65 * From "Random number generators: good ones are hard to find",
66 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
67 * October 1988, p. 1195.
71 /* Can't be initialized with 0, so use another value. */
76 x = 16807 * lo - 2836 * hi;
79 return ((*ctx = x) % ((u_long)RAND_MAX + 1));
80 #endif /* !USE_WEAK_SEEDING */
85 rand_r(unsigned int *ctx)
87 u_long val = (u_long) *ctx;
88 int r = do_rand(&val);
90 *ctx = (unsigned int) val;
95 static u_long next = 1;
100 return (do_rand(&next));
114 * Many programs choose the seed value in a totally predictable manner.
115 * This often causes problems. We seed the generator using the much more
116 * secure random(4) interface.
124 fd = _open("/dev/random", O_RDONLY, 0);
126 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
135 gettimeofday(&tv, NULL);
136 srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk);
148 printf("seeding rand with 0x19610910: \n");
151 printf("generating three pseudo-random numbers:\n");
152 for (i = 0; i < 3; i++)
154 printf("next random number = %d\n", rand());
157 printf("generating the same sequence with rand_r:\n");
159 for (i = 0; i < 3; i++)
161 printf("next random number = %d\n", rand_r(&myseed));