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
  //
  //===----------------------------------------------------------------------===//
  
  // UNSUPPORTED: c++03, c++11, c++14
  // UNSUPPORTED: clang-8
  
  // <numeric>
  
  // Became constexpr in C++20
  // template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
  //     OutputIterator
  //     inclusive_scan(InputIterator first, InputIterator last,
  //                    OutputIterator result,
  //                    BinaryOperation binary_op, T init); // C++17
  
  #include <numeric>
  #include <algorithm>
  #include <array>
  #include <cassert>
  #include <functional>
  #include <iterator>
  
  #include "test_macros.h"
  #include "test_iterators.h"
  
  template <class Iter1, class T, class Op>
  TEST_CONSTEXPR_CXX20 void
  test(Iter1 first, Iter1 last, Op op, T init, const T *rFirst, const T *rLast)
  {
      assert((rLast - rFirst) <= 5);  // or else increase the size of "out"
      T out[5];
  
      // Not in place
      T *end = std::inclusive_scan(first, last, out, op, init);
      assert(std::equal(out, end, rFirst, rLast));
  
      // In place
      std::copy(first, last, out);
      end = std::inclusive_scan(out, end, out, op, init);
      assert(std::equal(out, end, rFirst, rLast));
  }
  
  
  template <class Iter>
  TEST_CONSTEXPR_CXX20 void
  test()
  {
      int ia[]         = {1, 3,  5,   7,   9};
      const int pRes[] = {1, 4,  9,  16,  25};
      const int mRes[] = {1, 3, 15, 105, 945};
      const unsigned sa = sizeof(ia) / sizeof(ia[0]);
      static_assert(sa == sizeof(pRes) / sizeof(pRes[0]));       // just to be sure
      static_assert(sa == sizeof(mRes) / sizeof(mRes[0]));       // just to be sure
  
      for (unsigned int i = 0; i < sa; ++i ) {
          test(Iter(ia), Iter(ia + i), std::plus<>(),       0, pRes, pRes + i);
          test(Iter(ia), Iter(ia + i), std::multiplies<>(), 1, mRes, mRes + i);
      }
  }
  
  constexpr size_t triangle(size_t n) { return n*(n+1)/2; }
  
  //  Basic sanity
  TEST_CONSTEXPR_CXX20 void
  basic_tests()
  {
      {
      std::array<size_t, 10> v;
      std::fill(v.begin(), v.end(), 3);
      std::inclusive_scan(v.begin(), v.end(), v.begin(), std::plus<>(), size_t{50});
      for (size_t i = 0; i < v.size(); ++i)
          assert(v[i] == 50 + (i+1) * 3);
      }
  
      {
      std::array<size_t, 10> v;
      std::iota(v.begin(), v.end(), 0);
      std::inclusive_scan(v.begin(), v.end(), v.begin(), std::plus<>(), size_t{40});
      for (size_t i = 0; i < v.size(); ++i)
          assert(v[i] == 40 + triangle(i));
      }
  
      {
      std::array<size_t, 10> v;
      std::iota(v.begin(), v.end(), 1);
      std::inclusive_scan(v.begin(), v.end(), v.begin(), std::plus<>(), size_t{30});
      for (size_t i = 0; i < v.size(); ++i)
          assert(v[i] == 30 + triangle(i + 1));
      }
  
      {
      std::array<size_t, 0> v, res;
      std::inclusive_scan(v.begin(), v.end(), res.begin(), std::plus<>(), size_t{40});
      assert(res.empty());
      }
  
  //  Make sure that the calculations are done using the init typedef
      {
      std::array<unsigned char, 10> v;
      std::iota(v.begin(), v.end(), static_cast<unsigned char>(1));
      std::array<size_t, 10> res;
      std::inclusive_scan(v.begin(), v.end(), res.begin(), std::multiplies<>(), size_t{1});
  
      assert(res.size() == 10);
      size_t j = 1;
      assert(res[0] == 1);
      for (size_t i = 1; i < v.size(); ++i)
      {
          j *= i + 1;
          assert(res[i] == j);
      }
      }
  }
  
  TEST_CONSTEXPR_CXX20 bool
  test()
  {
      basic_tests();
  
  //  All the iterator categories
      test<cpp17_input_iterator        <const int*> >();
      test<forward_iterator      <const int*> >();
      test<bidirectional_iterator<const int*> >();
      test<random_access_iterator<const int*> >();
      test<const int*>();
      test<      int*>();
  
      return true;
  }
  
  int main(int, char**)
  {
      test();
  #if TEST_STD_VER > 17
      static_assert(test());
  #endif
      return 0;
  }
  