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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/param.h>
40 #include <sys/sysctl.h>
41 #include <sys/types.h>
43 #include "un-namespace.h"
50 do_rand(unsigned long *ctx)
52 #ifdef USE_WEAK_SEEDING
54 * Historic implementation compatibility.
55 * The random sequences do not vary much with the seed,
56 * even with overflowing.
58 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
59 #else /* !USE_WEAK_SEEDING */
61 * Compute x = (7^5 * x) mod (2^31 - 1)
62 * without overflowing 31 bits:
63 * (2^31 - 1) = 127773 * (7^5) + 2836
64 * From "Random number generators: good ones are hard to find",
65 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
66 * October 1988, p. 1195.
70 /* Must be in [1, 0x7ffffffe] range at this point. */
73 x = 16807 * lo - 2836 * hi;
77 /* Transform to [0, 0x7ffffffd] range. */
79 #endif /* !USE_WEAK_SEEDING */
84 rand_r(unsigned int *ctx)
89 #ifdef USE_WEAK_SEEDING
92 /* Transform to [1, 0x7ffffffe] range. */
93 val = (*ctx % 0x7ffffffe) + 1;
97 #ifdef USE_WEAK_SEEDING
98 *ctx = (unsigned int)val;
100 *ctx = (unsigned int)(val - 1);
107 #ifdef USE_WEAK_SEEDING
116 return (do_rand(&next));
124 #ifndef USE_WEAK_SEEDING
125 /* Transform to [1, 0x7ffffffe] range. */
126 next = (next % 0x7ffffffe) + 1;
134 * Many programs choose the seed value in a totally predictable manner.
135 * This often causes problems. We seed the generator using pseudo-random
136 * data from the kernel.
148 sysctl(mib, 2, (void *)&next, &len, NULL, 0);
149 #ifndef USE_WEAK_SEEDING
150 /* Transform to [1, 0x7ffffffe] range. */
151 next = (next % 0x7ffffffe) + 1;
163 printf("seeding rand with 0x19610910: \n");
166 printf("generating three pseudo-random numbers:\n");
167 for (i = 0; i < 3; i++)
169 printf("next random number = %d\n", rand());
172 printf("generating the same sequence with rand_r:\n");
174 for (i = 0; i < 3; i++)
176 printf("next random number = %d\n", rand_r(&myseed));