Index: include/experimental/algorithm
===================================================================
--- include/experimental/algorithm
+++ include/experimental/algorithm
@@ -0,0 +1,97 @@
+// -*- C++ -*-
+//===-------------------------- algorithm ---------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_EXPERIMENTAL_ALGORITHM
+#define _LIBCPP_EXPERIMENTAL_ALGORITHM
+
+/*
+   experimental/algorithm synopsis
+
+#include <algorithm>
+
+namespace std {
+namespace experimental {
+inline namespace fundamentals_v1 {
+
+template <class ForwardIterator, class Searcher>
+ForwardIterator search(ForwardIterator first, ForwardIterator last,
+                       const Searcher &searcher);
+template <class PopulationIterator, class SampleIterator, class Distance,
+          class UniformRandomNumberGenerator>
+SampleIterator sample(PopulationIterator first, PopulationIterator last,
+                      SampleIterator out, Distance n,
+                      UniformRandomNumberGenerator &&g);
+
+} // namespace fundamentals_v1
+} // namespace experimental
+} // namespace std
+
+*/
+
+#include <experimental/__config>
+#include <algorithm>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_LFTS
+
+template <class _PopulationIterator, class _SampleIterator, class _Distance,
+          class _UniformRandomNumberGenerator>
+_SampleIterator __sample(_PopulationIterator __first,
+                         _PopulationIterator __last, _SampleIterator __out,
+                         _Distance __n, _UniformRandomNumberGenerator &&__g,
+                         input_iterator_tag, random_access_iterator_tag) {
+  _Distance __k = 0;
+  for (; __first != __last && __k < __n; ++__first, (void)++__k)
+    __out[__k] = *__first;
+  _Distance __sz = __k;
+  for (; __first != __last; ++__first, (void)++__k) {
+    _Distance __r = _VSTD::uniform_int_distribution<_Distance>(0, __k)(__g);
+    if (__r < __sz)
+      __out[__r] = *__first;
+  }
+  return __out + _VSTD::min(__n, __k);
+}
+
+template <class _PopulationIterator, class _SampleIterator, class _Distance,
+          class _UniformRandomNumberGenerator>
+_SampleIterator __sample(_PopulationIterator __first,
+                         _PopulationIterator __last, _SampleIterator __out,
+                         _Distance __n, _UniformRandomNumberGenerator &&__g,
+                         forward_iterator_tag, output_iterator_tag) {
+  _Distance __unsampled_sz = _VSTD::distance(__first, __last);
+  for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) {
+    _Distance __r =
+        _VSTD::uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
+    if (__r < __n) {
+      *__out++ = *__first;
+      --__n;
+    }
+  }
+  return __out;
+}
+
+template <class _PopulationIterator, class _SampleIterator, class _Distance,
+          class _UniformRandomNumberGenerator>
+_SampleIterator sample(_PopulationIterator __first,
+                         _PopulationIterator __last, _SampleIterator __out,
+                         _Distance __n, _UniformRandomNumberGenerator &&__g) {
+  return _VSTD_LFTS::__sample(
+      __first, __last, __out, __n,
+      _VSTD::forward<_UniformRandomNumberGenerator>(__g),
+      typename iterator_traits<_PopulationIterator>::iterator_category(),
+      typename iterator_traits<_SampleIterator>::iterator_category());
+}
+
+_LIBCPP_END_NAMESPACE_LFTS
+
+#endif /* _LIBCPP_EXPERIMENTAL_ALGORITHM */
Index: test/std/experimental/algorithms/alg.random.sample/sample.fail.cpp
===================================================================
--- test/std/experimental/algorithms/alg.random.sample/sample.fail.cpp
+++ 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 *>>();
+}
Index: test/std/experimental/algorithms/alg.random.sample/sample.pass.cpp
===================================================================
--- test/std/experimental/algorithms/alg.random.sample/sample.pass.cpp
+++ test/std/experimental/algorithms/alg.random.sample/sample.pass.cpp
@@ -0,0 +1,147 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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 {
+  static constexpr unsigned os = 4;
+  static constexpr int oa1[os] = {10, 5, 9, 4};
+  static constexpr int oa2[os] = {5, 2, 10, 4};
+};
+
+constexpr int ReservoirSampleExpectations::oa1[];
+constexpr int ReservoirSampleExpectations::oa2[];
+
+struct SelectionSampleExpectations {
+  static constexpr unsigned os = 4;
+  static constexpr int oa1[os] = {1, 4, 6, 7};
+  static constexpr int oa2[os] = {1, 2, 6, 8};
+};
+
+constexpr int SelectionSampleExpectations::oa1[];
+constexpr int SelectionSampleExpectations::oa2[];
+
+template <class IteratorCategory> struct TestExpectations;
+template <>
+struct TestExpectations<std::random_access_iterator_tag>
+    : public ReservoirSampleExpectations {};
+template <>
+struct TestExpectations<std::output_iterator_tag>
+    : public SelectionSampleExpectations {};
+
+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<
+      SampleIterator>::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>();
+}
Index: test/std/experimental/algorithms/alg.random.sample/sample.stable.pass.cpp
===================================================================
--- test/std/experimental/algorithms/alg.random.sample/sample.stable.pass.cpp
+++ 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);
+}