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31 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
34 #include "namespace.h"
35 #include <sys/param.h>
36 #include <sys/sysctl.h>
42 #include "un-namespace.h"
44 #include "libc_private.h"
48 * Implement rand(3), the standard C PRNG API, using the non-standard but
49 * higher quality random(3) implementation and the same size 128-byte state
50 * LFSR as the random(3) default.
52 * It turns out there are portable applications that want a PRNG but are too
53 * lazy to use better-but-nonstandard interfaces like random(3), when
54 * available, and too lazy to import higher-quality and faster PRNGs into their
55 * codebase (such as any of SFC, JSF, 128-bit LCGs, PCG, or Splitmix64).
57 * Since we're stuck with rand(3) due to the C standard, we can at least have
58 * it produce a relatively good PRNG sequence using our existing random(3)
59 * LFSR. The random(3) design is not particularly fast nor compact, but it has
60 * the advantage of being the one already in the tree.
62 static struct __random_state *rand3_state;
63 static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT;
66 initialize_rand3(void)
70 rand3_state = allocatestate(TYPE_3);
71 error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3);
78 _once(&rand3_state_once, initialize_rand3);
79 return ((int)random_r(rand3_state));
85 _once(&rand3_state_once, initialize_rand3);
86 srandom_r(rand3_state, seed);
90 * FreeBSD 12 and prior compatibility implementation of rand(3).
93 do_rand(unsigned long *ctx)
96 * Compute x = (7^5 * x) mod (2^31 - 1)
97 * without overflowing 31 bits:
98 * (2^31 - 1) = 127773 * (7^5) + 2836
99 * From "Random number generators: good ones are hard to find",
100 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
101 * October 1988, p. 1195.
105 /* Transform to [1, 0x7ffffffe] range. */
106 x = (*ctx % 0x7ffffffe) + 1;
109 x = 16807 * lo - 2836 * hi;
112 /* Transform to [0, 0x7ffffffd] range. */
119 * Can't fix this garbage; too little state.
122 rand_r(unsigned *ctx)
129 *ctx = (unsigned)val;
133 static u_long next = 1;
135 int __rand_fbsd12(void);
139 return (do_rand(&next));
141 __sym_compat(rand, __rand_fbsd12, FBSD_1.0);
143 void __srand_fbsd12(unsigned seed);
145 __srand_fbsd12(unsigned seed)
149 __sym_compat(srand, __srand_fbsd12, FBSD_1.0);
151 void __sranddev_fbsd12(void);
153 __sranddev_fbsd12(void)
155 static bool warned = false;
158 syslog(LOG_DEBUG, "Deprecated function sranddev() called");
162 __sym_compat(sranddev, __sranddev_fbsd12, FBSD_1.0);