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Vector Packet Processing
random.h
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15 /*
16  Copyright (c) 2001, 2002, 2003 Eliot Dresselhaus
17 
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37 
38 #ifndef included_random_h
39 #define included_random_h
40 
41 #include <vppinfra/clib.h>
42 #include <vppinfra/vec.h> /* for vec_resize */
43 #include <vppinfra/format.h> /* for unformat_input_t */
44 
45 /** \file
46  Linear Congruential Random Number Generator
47 
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
51  at Chapter 7...
52 
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
55  values of (a,c,m).
56 
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
61  multiply-add.
62 
63  Several variants: 32/64-bit, machine word width,
64  f64 on the closed interval [0,1].
65 */
66 
67 /** \brief 32-bit random number generator */
69 random_u32 (u32 * seed)
70 {
71  *seed = (1664525 * *seed) + 1013904223;
72  return *seed;
73 }
74 
75 /* External test routine. */
77 
78 /** \brief Maximum value returned by random_u32() */
81 {
82  return 0xffffffff;
83 }
84 
85 #ifdef CLIB_UNIX
86 
87 #include <unistd.h> /* for getpid */
88 
89 /** \brief Default random seed (unix/linux user-mode) */
92 {
93  return getpid ();
94 }
95 
96 #endif
97 
98 #ifdef CLIB_LINUX_KERNEL
99 
100 #include <linux/sched.h> /* for jiffies */
101 
102 /** \brief Default random seed (Linux kernel) */
104 random_default_seed (void)
105 {
106  return jiffies;
107 }
108 
109 #endif
110 
111 #ifdef CLIB_STANDALONE
113 
115 random_default_seed (void)
116 {
118 }
119 #endif
120 
121 /** \brief 64-bit random number generator
122  * Again, constants courtesy of Donald Knuth.
123  *
124  */
126 random_u64 (u64 * seed)
127 {
128  *seed = 6364136223846793005ULL * *seed + 1442695040888963407ULL;
129  return *seed;
130 }
131 
132 /** \brief machine word size random number generator */
133 
136 {
137  if (sizeof (uword) == sizeof (u64))
138  return random_u64 ((u64 *) seed);
139  else
140  return random_u32 (seed);
141 }
142 
143 /** \brief Generate f64 random number in the interval [0,1] */
145 random_f64 (u32 * seed)
146 {
147  return (f64) random_u32 (seed) / (f64) random_u32_max ();
148 }
149 
150 /** \brief Generate random character vector
151 
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?
155 */
157 random_string (u32 * seed, uword len)
158 {
159  u8 *alphabet = (u8 *) "abcdefghijklmnopqrstuvwxyz";
160  u8 *s = 0;
161  word i;
162 
163  vec_resize (s, len);
164  for (i = 0; i < len; i++)
165  s[i] = alphabet[random_u32 (seed) % 26];
166 
167  return s;
168 }
169 
170 f64 clib_chisquare (u64 * values);
171 
172 #endif /* included_random_h */
173 
174 /*
175  * fd.io coding-style-patch-verification: ON
176  *
177  * Local Variables:
178  * eval: (c-set-style "gnu")
179  * End:
180  */
static uword random_default_seed(void)
Default random seed (unix/linux user-mode)
Definition: random.h:91
unsigned long u64
Definition: types.h:89
int i
static u64 random_u64(u64 *seed)
64-bit random number generator Again, constants courtesy of Donald Knuth.
Definition: random.h:126
unsigned char u8
Definition: types.h:56
double f64
Definition: types.h:142
i64 word
Definition: types.h:111
static u8 * random_string(u32 *seed, uword len)
Generate random character vector.
Definition: random.h:157
#define always_inline
Definition: clib.h:92
#define vec_resize(V, N)
Resize a vector (no header, unspecified alignment) Add N elements to end of given vector V...
Definition: vec.h:240
unsigned int u32
Definition: types.h:88
struct _unformat_input_t unformat_input_t
static uword random_uword(u32 *seed)
machine word size random number generator
Definition: random.h:135
static u32 random_u32_max(void)
Maximum value returned by random_u32()
Definition: random.h:80
static f64 random_f64(u32 *seed)
Generate f64 random number in the interval [0,1].
Definition: random.h:145
u32 standalone_random_default_seed
Default random seed for standalone version of library.
Definition: random.c:46
u64 uword
Definition: types.h:112
f64 clib_chisquare(u64 *values)
Compute the X2 test statistic for a vector of counts.
Definition: random.c:64
int test_random_main(unformat_input_t *input)
static u32 random_u32(u32 *seed)
32-bit random number generator
Definition: random.h:69
CLIB vectors are ubiquitous dynamically resized arrays with by user defined "headers".