FD.io VPP  v19.04.4-rc0-5-ge88582fac
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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7  * http://www.apache.org/licenses/LICENSE-2.0
8  *
9  * Unless required by applicable law or agreed to in writing, software
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11  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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
21  without limitation the rights to use, copy, modify, merge, publish,
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23  permit persons to whom the Software is furnished to do so, subject to
24  the following conditions:
25 
26  The above copyright notice and this permission notice shall be
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28 
29  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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35  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
36 */
37 
38 #include <vppinfra/random.h>
39 
40 /** \file Random number support
41  */
42 
43 /** \brief Default random seed for standalone version of library.
44  Value can be overridden by platform code from e.g.
45  machine's clock count register. */
47 
48 /**
49  * \brief Compute the X2 test statistic for a vector of counts.
50  * Each value element corresponds to a histogram bucket.
51  *
52  * Typical use-case: test the hypothesis that a set of octets
53  * are uniformly distributed (aka random).
54  *
55  * In a 1-dimensional use-case, the result should be compared
56  * with the critical value from chi square tables with
57  * vec_len(values) - 1 degrees of freedom.
58  *
59  * @param[in] values vector of histogram bucket values
60  * @return d - Pearson's X2 test statistic
61  */
62 
63 f64
64 clib_chisquare (u64 * values)
65 {
66  u32 i, len;
67  f64 d, delta_d, actual_frequency, expected_frequency;
68  u64 n_observations = 0;
69 
70  len = vec_len (values);
71  /*
72  * Shut up coverity. Return a huge number which should always exceed
73  * the X2 critical value.
74  */
75  if (len == 0)
76  return (f64) 1e70;
77 
78  for (i = 0; i < len; i++)
79  n_observations += values[i];
80 
81  expected_frequency = (1.0 / (f64) len) * (f64) n_observations;
82 
83  d = 0.0;
84 
85  for (i = 0; i < len; i++)
86  {
87  actual_frequency = ((f64) values[i]);
88  delta_d = ((actual_frequency - expected_frequency)
89  * (actual_frequency - expected_frequency))
90  / expected_frequency;
91  d += delta_d;
92  }
93  return d;
94 }
95 
96 /*
97  * fd.io coding-style-patch-verification: ON
98  *
99  * Local Variables:
100  * eval: (c-set-style "gnu")
101  * End:
102  */
unsigned long u64
Definition: types.h:89
int i
double f64
Definition: types.h:142
unsigned int u32
Definition: types.h:88
u8 len
Definition: ip_types.api:49
u32 standalone_random_default_seed
Default random seed for standalone version of library.
Definition: random.c:46
f64 clib_chisquare(u64 *values)
Compute the X2 test statistic for a vector of counts.
Definition: random.c:64
#define vec_len(v)
Number of elements in vector (rvalue-only, NULL tolerant)
Linear Congruential Random Number Generator.