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+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_CONTAINER_BTREE_TEST_H_
+#define ABSL_CONTAINER_BTREE_TEST_H_
+
+#include <algorithm>
+#include <cassert>
+#include <random>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/container/btree_map.h"
+#include "absl/container/btree_set.h"
+#include "absl/container/flat_hash_set.h"
+#include "absl/time/time.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace container_internal {
+
+// Like remove_const but propagates the removal through std::pair.
+template <typename T>
+struct remove_pair_const {
+  using type = typename std::remove_const<T>::type;
+};
+template <typename T, typename U>
+struct remove_pair_const<std::pair<T, U> > {
+  using type = std::pair<typename remove_pair_const<T>::type,
+                         typename remove_pair_const<U>::type>;
+};
+
+// Utility class to provide an accessor for a key given a value. The default
+// behavior is to treat the value as a pair and return the first element.
+template <typename K, typename V>
+struct KeyOfValue {
+  struct type {
+    const K& operator()(const V& p) const { return p.first; }
+  };
+};
+
+// Partial specialization of KeyOfValue class for when the key and value are
+// the same type such as in set<> and btree_set<>.
+template <typename K>
+struct KeyOfValue<K, K> {
+  struct type {
+    const K& operator()(const K& k) const { return k; }
+  };
+};
+
+inline char* GenerateDigits(char buf[16], unsigned val, unsigned maxval) {
+  assert(val <= maxval);
+  constexpr unsigned kBase = 64;  // avoid integer division.
+  unsigned p = 15;
+  buf[p--] = 0;
+  while (maxval > 0) {
+    buf[p--] = ' ' + (val % kBase);
+    val /= kBase;
+    maxval /= kBase;
+  }
+  return buf + p + 1;
+}
+
+template <typename K>
+struct Generator {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  K operator()(int i) const {
+    assert(i <= maxval);
+    return K(i);
+  }
+};
+
+template <>
+struct Generator<absl::Time> {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  absl::Time operator()(int i) const { return absl::FromUnixMillis(i); }
+};
+
+template <>
+struct Generator<std::string> {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  std::string operator()(int i) const {
+    char buf[16];
+    return GenerateDigits(buf, i, maxval);
+  }
+};
+
+template <typename T, typename U>
+struct Generator<std::pair<T, U> > {
+  Generator<typename remove_pair_const<T>::type> tgen;
+  Generator<typename remove_pair_const<U>::type> ugen;
+
+  explicit Generator(int m) : tgen(m), ugen(m) {}
+  std::pair<T, U> operator()(int i) const {
+    return std::make_pair(tgen(i), ugen(i));
+  }
+};
+
+// Generate n values for our tests and benchmarks. Value range is [0, maxval].
+inline std::vector<int> GenerateNumbersWithSeed(int n, int maxval, int seed) {
+  // NOTE: Some tests rely on generated numbers not changing between test runs.
+  // We use std::minstd_rand0 because it is well-defined, but don't use
+  // std::uniform_int_distribution because platforms use different algorithms.
+  std::minstd_rand0 rng(seed);
+
+  std::vector<int> values;
+  absl::flat_hash_set<int> unique_values;
+  if (values.size() < n) {
+    for (int i = values.size(); i < n; i++) {
+      int value;
+      do {
+        value = static_cast<int>(rng()) % (maxval + 1);
+      } while (!unique_values.insert(value).second);
+
+      values.push_back(value);
+    }
+  }
+  return values;
+}
+
+// Generates n values in the range [0, maxval].
+template <typename V>
+std::vector<V> GenerateValuesWithSeed(int n, int maxval, int seed) {
+  const std::vector<int> nums = GenerateNumbersWithSeed(n, maxval, seed);
+  Generator<V> gen(maxval);
+  std::vector<V> vec;
+
+  vec.reserve(n);
+  for (int i = 0; i < n; i++) {
+    vec.push_back(gen(nums[i]));
+  }
+
+  return vec;
+}
+
+}  // namespace container_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_BTREE_TEST_H_