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16 Copyright (c) 2001, 2002, 2003 Eliot Dresselhaus
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38 #ifndef included_random_h
39 #define included_random_h
41 #include <vppinfra/clib.h>
42 #include <vppinfra/vec.h> /* for vec_resize */
43 #include <vppinfra/format.h> /* for unformat_input_t */
46 Linear Congruential Random Number Generator
48 This specific random number generator is described in
49 "Numerical Recipes in C", 2nd edition, page 284. If you need
50 random numbers with really excellent statistics, take a look
53 By definition, a linear congruential random number generator
54 is of the form: rand[i+1] = a*rand[i] + c (mod m) for specific
57 In this case, choose m = 2**32 and use the low-order 32-bits of
58 the 64-bit product a*N[i]. Knuth suggests the use of a=1664525,
59 H.W. Lewis has tested C=1013904223 extensively. This routine is
60 reputedly as good as any 32-bit LCRN, and costs only a single
63 Several variants: 32/64-bit, machine word width,
64 f64 on the closed interval [0,1].
67 /** \brief 32-bit random number generator */
69 random_u32 (u32 * seed)
71 *seed = (1664525 * *seed) + 1013904223;
75 /* External test routine. */
76 int test_random_main (unformat_input_t * input);
78 /** \brief Maximum value returned by random_u32() */
87 #include <unistd.h> /* for getpid */
89 /** \brief Default random seed (unix/linux user-mode) */
91 random_default_seed (void)
98 #ifdef CLIB_LINUX_KERNEL
100 #include <linux/sched.h> /* for jiffies */
102 /** \brief Default random seed (Linux kernel) */
104 random_default_seed (void)
111 #ifdef CLIB_STANDALONE
112 extern u32 standalone_random_default_seed;
115 random_default_seed (void)
117 return standalone_random_default_seed;
121 /** \brief 64-bit random number generator
122 * Again, constants courtesy of Donald Knuth.
126 random_u64 (u64 * seed)
128 *seed = 6364136223846793005ULL * *seed + 1442695040888963407ULL;
132 /** \brief machine word size random number generator */
135 random_uword (u32 * seed)
137 if (sizeof (uword) == sizeof (u64))
138 return random_u64 ((u64 *) seed);
140 return random_u32 (seed);
143 /** \brief Generate f64 random number in the interval [0,1] */
145 random_f64 (u32 * seed)
147 return (f64) random_u32 (seed) / (f64) random_u32_max ();
150 /** \brief Generate random character vector
152 From the alphabet a-z, lower case.
153 Returns a vector of the supplied length which is NOT guaranteed to be
154 NULL-terminated. FIXME?
157 random_string (u32 * seed, uword len)
159 u8 *alphabet = (u8 *) "abcdefghijklmnopqrstuvwxyz";
164 for (i = 0; i < len; i++)
165 s[i] = alphabet[random_u32 (seed) % 26];
170 f64 clib_chisquare (u64 * values);
172 #endif /* included_random_h */
175 * fd.io coding-style-patch-verification: ON
178 * eval: (c-set-style "gnu")