libcxx/test/std/algorithms/alg.modifying.operations/alg.random.sample/sample.stable.pass.cpp

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 // UNSUPPORTED: c++03, c++11, c++14
  10
  11 // <algorithm>
  12
  13 // template <class PopulationIterator, class SampleIterator, class Distance,
  14 //           class UniformRandomNumberGenerator>
  15 // SampleIterator sample(PopulationIterator first, PopulationIterator last,
  16 //                       SampleIterator out, Distance n,
  17 //                       UniformRandomNumberGenerator &&g);
  18
  19 #include <algorithm>
  20 #include <random>
  21 #include <cassert>
  22
  23 #include "test_macros.h"
  24 #include "test_iterators.h"
  25
  26 // Stable if and only if PopulationIterator meets the requirements of a
  27 // ForwardIterator type.
  28 template <class PopulationIterator, class SampleIterator>
  29 void test_stability(bool expect_stable) {
  30   const unsigned kPopulationSize = 100;
  31   int ia[kPopulationSize];
  32   for (unsigned i = 0; i < kPopulationSize; ++i)
  33     ia[i] = i;
  34   PopulationIterator first(ia);
  35   PopulationIterator last(ia + kPopulationSize);
  36
  37   const unsigned kSampleSize = 20;
  38   int oa[kPopulationSize];
  39   SampleIterator out(oa);
  40
  41   std::minstd_rand g;
  42
  43   const int kIterations = 1000;
  44   bool unstable = false;
  45   for (int i = 0; i < kIterations; ++i) {
  46     std::sample(first, last, out, kSampleSize, g);
  47     unstable |= !std::is_sorted(oa, oa + kSampleSize);
  48   }
  49   assert(expect_stable == !unstable);
  50 }
  51
  52 int main(int, char**) {
  53   test_stability<forward_iterator<int *>, cpp17_output_iterator<int *> >(true);
  54   test_stability<cpp17_input_iterator<int *>, random_access_iterator<int *> >(false);
  55
  56   return 0;
  57 }