libstdc++-v3/testsuite/20_util/hash/chi2_q_bit_flip_set.cc

   1 // Use smaller statistics when running on simulators, so it takes less time.
   2 // { dg-options "-DSAMPLES=30000" { target simulator } }
   3 // { dg-do run { target c++11 } }
   4
   5 // Copyright (C) 2010-2024 Free Software Foundation, Inc.
   6 //
   7 // This file is part of the GNU ISO C++ Library.  This library is free
   8 // software; you can redistribute it and/or modify it under the
   9 // terms of the GNU General Public License as published by the
  10 // Free Software Foundation; either version 3, or (at your option)
  11 // any later version.
  12 //
  13 // This library is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17 //
  18 // You should have received a copy of the GNU General Public License
  19 // along with this library; see the file COPYING3.  If not see
  20 // <http://www.gnu.org/licenses/>.
  21
  22 #include "chi2_quality.h"
  23
  24 // Tests chi^2 for a distribution of strings that differ from each
  25 // other by only a few bits. We start with an arbitrary base string, and
  26 // flip three random bits for each member of the set.
  27 void
  28 test_bit_flip_set()
  29 {
  30   const unsigned long N = SAMPLES;
  31   const unsigned long k = N/100;
  32   const unsigned int len = 67;
  33   const unsigned int bitlen = len * 8;
  34   const unsigned int bits_to_flip = 3;
  35   const char base[len+1] = "abcdefghijklmnopqrstuvwxyz"
  36                            "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  37                            "0123456789!@#$%";
  38
  39   std::unordered_set<std::string> set;
  40   while (set.size() < N)
  41     {
  42       std::string s(base, base+len);
  43       for (unsigned int i = 0; i < bits_to_flip; ++i)
  44         {
  45           int bit = rand() % bitlen;
  46           s[bit/8] ^= (1 << (bit%8));
  47         }
  48       set.insert(s);
  49     }
  50
  51   double chi2 = chi2_hash(set, k);
  52   VERIFY( chi2 < k*1.1 );
  53 }
  54
  55 int
  56 main()
  57 {
  58   test_bit_flip_set();
  59   return 0;
  60 }