Implement std::experimental::sample.

Following specification in "C++ Extensions for Library Fundamentals":
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4480.html#alg.random.sample



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@237264 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/experimental/algorithms/alg.random.sample/sample.fail.cpp

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// template <class PopulationIterator, class SampleIterator, class Distance,
+//           class UniformRandomNumberGenerator>
+// SampleIterator sample(PopulationIterator first, PopulationIterator last,
+//                       SampleIterator out, Distance n,
+//                       UniformRandomNumberGenerator &&g);
+
+#include <experimental/algorithm>
+#include <random>
+#include <cassert>
+
+#include "test_iterators.h"
+
+template <class PopulationIterator, class SampleIterator> void test() {
+  int ia[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+  const unsigned is = sizeof(ia) / sizeof(ia[0]);
+  const unsigned os = 4;
+  int oa[os];
+  std::minstd_rand g;
+  std::experimental::sample(PopulationIterator(ia), PopulationIterator(ia + is),
+                            SampleIterator(oa), os, g);
+}
+
+int main() {
+  test<input_iterator<int *>, output_iterator<int *> >();
+}

test/std/experimental/algorithms/alg.random.sample/sample.pass.cpp

@@ -0,0 +1,146 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// template <class PopulationIterator, class SampleIterator, class Distance,
+//           class UniformRandomNumberGenerator>
+// SampleIterator sample(PopulationIterator first, PopulationIterator last,
+//                       SampleIterator out, Distance n,
+//                       UniformRandomNumberGenerator &&g);
+
+#include <experimental/algorithm>
+#include <random>
+#include <cassert>
+
+#include "test_iterators.h"
+
+struct ReservoirSampleExpectations {
+  enum { os = 4 };
+  static int oa1[os];
+  static int oa2[os];
+};
+
+int ReservoirSampleExpectations::oa1[] = {10, 5, 9, 4};
+int ReservoirSampleExpectations::oa2[] = {5, 2, 10, 4};
+
+struct SelectionSampleExpectations {
+  enum { os = 4 };
+  static int oa1[os];
+  static int oa2[os];
+};
+
+int SelectionSampleExpectations::oa1[] = {1, 4, 6, 7};
+int SelectionSampleExpectations::oa2[] = {1, 2, 6, 8};
+
+template <class IteratorCategory> struct TestExpectations
+    : public SelectionSampleExpectations {};
+
+template <>
+struct TestExpectations<std::input_iterator_tag>
+    : public ReservoirSampleExpectations {};
+
+template <template<class> class PopulationIteratorType, class PopulationItem,
+          template<class> class SampleIteratorType, class SampleItem>
+void test() {
+  typedef PopulationIteratorType<PopulationItem *> PopulationIterator;
+  typedef SampleIteratorType<SampleItem *> SampleIterator;
+  PopulationItem ia[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+  const unsigned is = sizeof(ia) / sizeof(ia[0]);
+  typedef TestExpectations<typename std::iterator_traits<
+      PopulationIterator>::iterator_category> Expectations;
+  const unsigned os = Expectations::os;
+  SampleItem oa[os];
+  const int *oa1 = Expectations::oa1;
+  const int *oa2 = Expectations::oa2;
+  std::minstd_rand g;
+  SampleIterator end;
+  end = std::experimental::sample(PopulationIterator(ia),
+                                  PopulationIterator(ia + is),
+                                  SampleIterator(oa), os, g);
+  assert(&*end - oa == std::min(os, is));
+  assert(std::equal(oa, oa + os, oa1));
+  end = std::experimental::sample(PopulationIterator(ia),
+                                  PopulationIterator(ia + is),
+                                  SampleIterator(oa), os, g);
+  assert(&*end - oa == std::min(os, is));
+  assert(std::equal(oa, oa + os, oa2));
+}
+
+template <template<class> class PopulationIteratorType, class PopulationItem,
+          template<class> class SampleIteratorType, class SampleItem>
+void test_empty_population() {
+  typedef PopulationIteratorType<PopulationItem *> PopulationIterator;
+  typedef SampleIteratorType<SampleItem *> SampleIterator;
+  PopulationItem ia[] = {42};
+  const unsigned os = 4;
+  SampleItem oa[os];
+  std::minstd_rand g;
+  SampleIterator end =
+      std::experimental::sample(PopulationIterator(ia), PopulationIterator(ia),
+                                SampleIterator(oa), os, g);
+  assert(&*end == oa);
+}
+
+template <template<class> class PopulationIteratorType, class PopulationItem,
+          template<class> class SampleIteratorType, class SampleItem>
+void test_empty_sample() {
+  typedef PopulationIteratorType<PopulationItem *> PopulationIterator;
+  typedef SampleIteratorType<SampleItem *> SampleIterator;
+  PopulationItem ia[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+  const unsigned is = sizeof(ia) / sizeof(ia[0]);
+  SampleItem oa[1];
+  std::minstd_rand g;
+  SampleIterator end =
+      std::experimental::sample(PopulationIterator(ia), PopulationIterator(ia + is),
+                                SampleIterator(oa), 0, g);
+  assert(&*end == oa);
+}
+
+template <template<class> class PopulationIteratorType, class PopulationItem,
+          template<class> class SampleIteratorType, class SampleItem>
+void test_small_population() {
+  // The population size is less than the sample size.
+  typedef PopulationIteratorType<PopulationItem *> PopulationIterator;
+  typedef SampleIteratorType<SampleItem *> SampleIterator;
+  PopulationItem ia[] = {1, 2, 3, 4, 5};
+  const unsigned is = sizeof(ia) / sizeof(ia[0]);
+  const unsigned os = 8;
+  SampleItem oa[os];
+  const SampleItem oa1[] = {1, 2, 3, 4, 5};
+  std::minstd_rand g;
+  SampleIterator end;
+  end = std::experimental::sample(PopulationIterator(ia),
+                                  PopulationIterator(ia + is),
+                                  SampleIterator(oa), os, g);
+  assert(&*end - oa == std::min(os, is));
+  assert(std::equal(oa, &*end, oa1));
+}
+
+int main() {
+  test<input_iterator, int, random_access_iterator, int>();
+  test<forward_iterator, int, output_iterator, int>();
+  test<forward_iterator, int, random_access_iterator, int>();
+
+  test<input_iterator, int, random_access_iterator, double>();
+  test<forward_iterator, int, output_iterator, double>();
+  test<forward_iterator, int, random_access_iterator, double>();
+
+  test_empty_population<input_iterator, int, random_access_iterator, int>();
+  test_empty_population<forward_iterator, int, output_iterator, int>();
+  test_empty_population<forward_iterator, int, random_access_iterator, int>();
+
+  test_empty_sample<input_iterator, int, random_access_iterator, int>();
+  test_empty_sample<forward_iterator, int, output_iterator, int>();
+  test_empty_sample<forward_iterator, int, random_access_iterator, int>();
+
+  test_small_population<input_iterator, int, random_access_iterator, int>();
+  test_small_population<forward_iterator, int, output_iterator, int>();
+  test_small_population<forward_iterator, int, random_access_iterator, int>();
+}

test/std/experimental/algorithms/alg.random.sample/sample.stable.pass.cpp

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// template <class PopulationIterator, class SampleIterator, class Distance,
+//           class UniformRandomNumberGenerator>
+// SampleIterator sample(PopulationIterator first, PopulationIterator last,
+//                       SampleIterator out, Distance n,
+//                       UniformRandomNumberGenerator &&g);
+
+#include <experimental/algorithm>
+#include <random>
+#include <cassert>
+
+#include "test_iterators.h"
+
+// Stable if and only if PopulationIterator meets the requirements of a
+// ForwardIterator type.
+template <class PopulationIterator, class SampleIterator>
+void test_stability(bool expect_stable) {
+  const unsigned kPopulationSize = 100;
+  int ia[kPopulationSize];
+  for (unsigned i = 0; i < kPopulationSize; ++i)
+    ia[i] = i;
+  PopulationIterator first(ia);
+  PopulationIterator last(ia + kPopulationSize);
+
+  const unsigned kSampleSize = 20;
+  int oa[kPopulationSize];
+  SampleIterator out(oa);
+
+  std::minstd_rand g;
+
+  const int kIterations = 1000;
+  bool unstable = false;
+  for (int i = 0; i < kIterations; ++i) {
+    std::experimental::sample(first, last, out, kSampleSize, g);
+    unstable |= !std::is_sorted(oa, oa + kSampleSize);
+  }
+  assert(expect_stable == !unstable);
+}
+
+int main() {
+  test_stability<forward_iterator<int *>, output_iterator<int *> >(true);
+  test_stability<input_iterator<int *>, random_access_iterator<int *> >(false);
+}