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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>
47 #include "un-namespace.h"
52 * Implement rand(3), the standard C PRNG API, using the non-standard but
53 * higher quality random(3) implementation and the same size 128-byte state
54 * LFSR as the random(3) default.
56 * It turns out there are portable applications that want a PRNG but are too
57 * lazy to use better-but-nonstandard interfaces like random(3), when
58 * available, and too lazy to import higher-quality and faster PRNGs into their
59 * codebase (such as any of SFC, JSF, 128-bit LCGs, PCG, or Splitmix64).
61 * Since we're stuck with rand(3) due to the C standard, we can at least have
62 * it produce a relatively good PRNG sequence using our existing random(3)
63 * LFSR. The random(3) design is not particularly fast nor compact, but it has
64 * the advantage of being the one already in the tree.
66 static struct __random_state *rand3_state;
69 initialize_rand3(void)
73 rand3_state = allocatestate(TYPE_3);
74 error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3);
81 if (rand3_state == NULL)
83 return ((int)random_r(rand3_state));
89 if (rand3_state == NULL)
91 srandom_r(rand3_state, seed);
95 * FreeBSD 12 and prior compatibility implementation of rand(3).
98 do_rand(unsigned long *ctx)
101 * Compute x = (7^5 * x) mod (2^31 - 1)
102 * without overflowing 31 bits:
103 * (2^31 - 1) = 127773 * (7^5) + 2836
104 * From "Random number generators: good ones are hard to find",
105 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
106 * October 1988, p. 1195.
110 /* Transform to [1, 0x7ffffffe] range. */
111 x = (*ctx % 0x7ffffffe) + 1;
114 x = 16807 * lo - 2836 * hi;
117 /* Transform to [0, 0x7ffffffd] range. */
124 * Can't fix this garbage; too little state.
127 rand_r(unsigned *ctx)
134 *ctx = (unsigned)val;
138 static u_long next = 1;
140 int __rand_fbsd12(void);
144 return (do_rand(&next));
146 __sym_compat(rand, __rand_fbsd12, FBSD_1.0);
148 void __srand_fbsd12(unsigned seed);
150 __srand_fbsd12(unsigned seed)
154 __sym_compat(srand, __srand_fbsd12, FBSD_1.0);
156 void __sranddev_fbsd12(void);
158 __sranddev_fbsd12(void)
160 static bool warned = false;
163 syslog(LOG_DEBUG, "Deprecated function sranddev() called");
167 __sym_compat(sranddev, __sranddev_fbsd12, FBSD_1.0);