text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // REQUIRES: long_tests
  // UNSUPPORTED: c++98, c++03
  
  // Not a portable test
  
  // <__hash_table>
  
  // size_t __next_hash_pow2(size_t n);
  
  // If n <= 1, return n. If n is a power of 2, return n.
  // Otherwise, return the next power of 2.
  
  #include <__hash_table>
  #include <unordered_map>
  #include <cassert>
  
  #include "test_macros.h"
  
  
  bool
  is_power_of_two(unsigned long n)
  {
      return __builtin_popcount(n) == 1;
  }
  
  void test_next_pow2_val(size_t n)
  {
          std::size_t npow2 = std::__next_hash_pow2(n);
          assert(is_power_of_two(npow2) && npow2 > n);
  }
  
  void
  test_next_pow2()
  {
      assert(!is_power_of_two(0));
      assert(is_power_of_two(1));
      assert(is_power_of_two(2));
      assert(!is_power_of_two(3));
  
      assert(std::__next_hash_pow2(0) == 0);
      assert(std::__next_hash_pow2(1) == 1);
  
      for (std::size_t n = 2; n < (sizeof(std::size_t) * 8 - 1); ++n)
      {
          std::size_t pow2 = 1ULL << n;
          assert(std::__next_hash_pow2(pow2) == pow2);
      }
  
      test_next_pow2_val(3);
      test_next_pow2_val(7);
      test_next_pow2_val(9);
      test_next_pow2_val(15);
      test_next_pow2_val(127);
      test_next_pow2_val(129);
  }
  
  // Note: this is only really useful when run with -fsanitize=undefined.
  void
  fuzz_unordered_map_reserve(unsigned num_inserts,
                             unsigned num_reserve1,
                             unsigned num_reserve2)
  {
      std::unordered_map<uint64_t, unsigned long> m;
      m.reserve(num_reserve1);
      for (unsigned I = 0; I < num_inserts; ++I) m[I] = 0;
      m.reserve(num_reserve2);
      assert(m.bucket_count() >= num_reserve2);
  }
  
  int main(int, char**)
  {
      test_next_pow2();
  
      for (unsigned num_inserts = 0; num_inserts <= 64; ++num_inserts)
          for (unsigned num_reserve1 = 1; num_reserve1 <= 64; ++num_reserve1)
              for (unsigned num_reserve2 = 1; num_reserve2 <= 64; ++num_reserve2)
                  fuzz_unordered_map_reserve(num_inserts, num_reserve1, num_reserve2);
  
      return 0;
  }
  