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

llvm-svn: 237264

1 files changed, 53 insertions, 0 deletions

diff --git a/libcxx/test/std/experimental/algorithms/alg.random.sample/sample.stable.pass.cpp b/libcxx/test/std/experimental/algorithms/alg.random.sample/sample.stable.pass.cpp
new file mode 100644
index 00000000000..c805c66fa5e
--- /dev/null
+++ b/libcxx/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);
+}