FD.io VPP  v20.09-64-g4f7b92f0a
Vector Packet Processing
random.c
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1 /*
2  * Copyright (c) 2015 Cisco and/or its affiliates.
3  * Licensed under the Apache License, Version 2.0 (the "License");
4  * you may not use this file except in compliance with the License.
5  * You may obtain a copy of the License at:
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12  * See the License for the specific language governing permissions and
13  * limitations under the License.
14  */
15 /*
16  Copyright (c) 2001, 2002, 2003 Eliot Dresselhaus
17 
18  Permission is hereby granted, free of charge, to any person obtaining
19  a copy of this software and associated documentation files (the
20  "Software"), to deal in the Software without restriction, including
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24  the following conditions:
25 
26  The above copyright notice and this permission notice shall be
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29  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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36 */
37 
38 #include <vppinfra/random.h>
39 
40 /** \file random.c
41  Random number support
42  */
43 
44 /** \brief Default random seed for standalone version of library.
45  Value can be overridden by platform code from e.g.
46  machine's clock count register. */
48 
49 /**
50  * \brief Compute the X2 test statistic for a vector of counts.
51  * Each value element corresponds to a histogram bucket.
52  *
53  * Typical use-case: test the hypothesis that a set of octets
54  * are uniformly distributed (aka random).
55  *
56  * In a 1-dimensional use-case, the result should be compared
57  * with the critical value from chi square tables with
58  * vec_len(values) - 1 degrees of freedom.
59  *
60  * @param[in] values vector of histogram bucket values
61  * @return d - Pearson's X2 test statistic
62  */
63 
64 f64
65 clib_chisquare (u64 * values)
66 {
67  u32 i, len;
68  f64 d, delta_d, actual_frequency, expected_frequency;
69  u64 n_observations = 0;
70 
71  len = vec_len (values);
72  /*
73  * Shut up coverity. Return a huge number which should always exceed
74  * the X2 critical value.
75  */
76  if (len == 0)
77  return (f64) 1e70;
78 
79  for (i = 0; i < len; i++)
80  n_observations += values[i];
81 
82  expected_frequency = (1.0 / (f64) len) * (f64) n_observations;
83 
84  d = 0.0;
85 
86  for (i = 0; i < len; i++)
87  {
88  actual_frequency = ((f64) values[i]);
89  delta_d = ((actual_frequency - expected_frequency)
90  * (actual_frequency - expected_frequency))
91  / expected_frequency;
92  d += delta_d;
93  }
94  return d;
95 }
96 
97 /*
98  * fd.io coding-style-patch-verification: ON
99  *
100  * Local Variables:
101  * eval: (c-set-style "gnu")
102  * End:
103  */
unsigned long u64
Definition: types.h:89
double f64
Definition: types.h:142
unsigned int u32
Definition: types.h:88
u8 len
Definition: ip_types.api:92
sll srl srl sll sra u16x4 i
Definition: vector_sse42.h:317
u32 standalone_random_default_seed
Default random seed for standalone version of library.
Definition: random.c:47
f64 clib_chisquare(u64 *values)
Compute the X2 test statistic for a vector of counts.
Definition: random.c:65
#define vec_len(v)
Number of elements in vector (rvalue-only, NULL tolerant)
Linear Congruential Random Number Generator.