Line data    Source code

       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
      10             :  * distributed under the License is distributed on an "AS IS" BASIS,
      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,
      22             :   distribute, sublicense, and/or sell copies of the Software, and to
      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,
      30             :   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
      31             :   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
      32             :   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
      33             :   LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
      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.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. */
      47             : u32 standalone_random_default_seed = 1;
      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             : __clib_export f64
      65           0 : clib_chisquare (u64 *values)
      66             : {
      67             :   u32 i, len;
      68             :   f64 d, delta_d, actual_frequency, expected_frequency;
      69           0 :   u64 n_observations = 0;
      70             : 
      71           0 :   len = vec_len (values);
      72             :   /*
      73             :    * Shut up coverity. Return a huge number which should always exceed
      74             :    * the X2 critical value.
      75             :    */
      76           0 :   if (len == 0)
      77           0 :     return (f64) 1e70;
      78             : 
      79           0 :   for (i = 0; i < len; i++)
      80           0 :     n_observations += values[i];
      81             : 
      82           0 :   expected_frequency = (1.0 / (f64) len) * (f64) n_observations;
      83             : 
      84           0 :   d = 0.0;
      85             : 
      86           0 :   for (i = 0; i < len; i++)
      87             :     {
      88           0 :       actual_frequency = ((f64) values[i]);
      89           0 :       delta_d = ((actual_frequency - expected_frequency)
      90           0 :                  * (actual_frequency - expected_frequency))
      91             :         / expected_frequency;
      92           0 :       d += delta_d;
      93             :     }
      94           0 :   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             :  */