2 * Copyright (c) 1990, 1993
3 * The Regents of the University of California. All rights reserved.
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6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
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12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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29 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
31 * @(#)rand.c 8.1 (Berkeley) 6/14/93
32 * $FreeBSD: src/lib/libc/stdlib/rand.c,v 1.17 2007/12/11 20:39:32 ache Exp $
35 #include "namespace.h"
36 #include <sys/time.h> /* for sranddev() */
37 #include <sys/types.h>
38 #include <sys/sysctl.h>
39 #include <fcntl.h> /* for sranddev() */
41 #include <unistd.h> /* for sranddev() */
42 #include "un-namespace.h"
49 * Compute x = (7^5 * x) mod (2^31 - 1)
50 * without overflowing 31 bits:
51 * (2^31 - 1) = 127773 * (7^5) + 2836
52 * From "Random number generators: good ones are hard to find",
53 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
54 * October 1988, p. 1195.
57 do_rand(unsigned long *ctx
)
61 /* Can't be initialized with 0, so use another value. */
66 x
= 16807 * lo
- 2836 * hi
;
69 return ((*ctx
= x
) % ((u_long
)RAND_MAX
+ 1));
74 rand_r(unsigned int *ctx
)
76 u_long val
= (u_long
) *ctx
;
77 int r
= do_rand(&val
);
79 *ctx
= (unsigned int) val
;
84 static u_long next
= 1;
89 return (do_rand(&next
));
102 * Many programs choose the seed value in a totally predictable manner.
103 * This often causes problems. We seed the generator using the much more
104 * secure random(4) interface.
112 fd
= _open("/dev/random", O_RDONLY
, 0);
114 if (_read(fd
, (void *) &next
, sizeof(next
)) == sizeof(next
))
120 size_t len
= sizeof(next
);
122 if (sysctlbyname("kern.random", &next
, &len
, NULL
, 0) == 0)
129 gettimeofday(&tv
, NULL
);
130 srand((getpid() << 16) ^ tv
.tv_sec
^ tv
.tv_usec
);
138 main(int argc __unused
, char *argv
[] __unused
)
143 printf("seeding rand with 0x19610910: \n");
146 printf("generating three pseudo-random numbers:\n");
147 for (i
= 0; i
< 3; i
++)
149 printf("next random number = %d\n", rand());
152 printf("generating the same sequence with rand_r:\n");
154 for (i
= 0; i
< 3; i
++)
156 printf("next random number = %d\n", rand_r(&myseed
));