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31 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
34 #if defined(LIBC_SCCS) && !defined(lint)
35 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93";
36 #endif /* LIBC_SCCS and not lint */
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD$");
40 #include "namespace.h"
41 #include <sys/param.h>
42 #include <sys/sysctl.h>
48 #include "un-namespace.h"
50 #include "libc_private.h"
54 * Implement rand(3), the standard C PRNG API, using the non-standard but
55 * higher quality random(3) implementation and the same size 128-byte state
56 * LFSR as the random(3) default.
58 * It turns out there are portable applications that want a PRNG but are too
59 * lazy to use better-but-nonstandard interfaces like random(3), when
60 * available, and too lazy to import higher-quality and faster PRNGs into their
61 * codebase (such as any of SFC, JSF, 128-bit LCGs, PCG, or Splitmix64).
63 * Since we're stuck with rand(3) due to the C standard, we can at least have
64 * it produce a relatively good PRNG sequence using our existing random(3)
65 * LFSR. The random(3) design is not particularly fast nor compact, but it has
66 * the advantage of being the one already in the tree.
68 static struct __random_state *rand3_state;
69 static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT;
72 initialize_rand3(void)
76 rand3_state = allocatestate(TYPE_3);
77 error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3);
84 _once(&rand3_state_once, initialize_rand3);
85 return ((int)random_r(rand3_state));
91 _once(&rand3_state_once, initialize_rand3);
92 srandom_r(rand3_state, seed);
96 * FreeBSD 12 and prior compatibility implementation of rand(3).
99 do_rand(unsigned long *ctx)
102 * Compute x = (7^5 * x) mod (2^31 - 1)
103 * without overflowing 31 bits:
104 * (2^31 - 1) = 127773 * (7^5) + 2836
105 * From "Random number generators: good ones are hard to find",
106 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
107 * October 1988, p. 1195.
111 /* Transform to [1, 0x7ffffffe] range. */
112 x = (*ctx % 0x7ffffffe) + 1;
115 x = 16807 * lo - 2836 * hi;
118 /* Transform to [0, 0x7ffffffd] range. */
125 * Can't fix this garbage; too little state.
128 rand_r(unsigned *ctx)
135 *ctx = (unsigned)val;
139 static u_long next = 1;
141 int __rand_fbsd12(void);
145 return (do_rand(&next));
147 __sym_compat(rand, __rand_fbsd12, FBSD_1.0);
149 void __srand_fbsd12(unsigned seed);
151 __srand_fbsd12(unsigned seed)
155 __sym_compat(srand, __srand_fbsd12, FBSD_1.0);
157 void __sranddev_fbsd12(void);
159 __sranddev_fbsd12(void)
161 static bool warned = false;
164 syslog(LOG_DEBUG, "Deprecated function sranddev() called");
168 __sym_compat(sranddev, __sranddev_fbsd12, FBSD_1.0);