FD.io VPP  v18.07.1-19-g511ce25
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:
6  *
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
27  included in all copies or substantial portions of the Software.
28 
29  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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34  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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
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.