libcxx/test/std/numerics/numeric.ops/reduce/reduce_init_op.pass.cpp

//===----------------------------------------------------------------------===//
//
// 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

// <numeric>

// Became constexpr in C++20
// template<class InputIterator, class T, class BinaryOperation>
//   T reduce(InputIterator first, InputIterator last, T init, BinaryOperation op);

#include <numeric>
#include <cassert>
#include <functional>
#include <initializer_list>
#include <iterator>

#include "test_macros.h"
#include "test_iterators.h"

template <class Iter, class T, class Op>
TEST_CONSTEXPR_CXX20 void
test(Iter first, Iter last, T init, Op op, T x)
{
    static_assert( std::is_same_v<T, decltype(std::reduce(first, last, init, op))>, "" );
    assert(std::reduce(first, last, init, op) == x);
}

template <class Iter>
TEST_CONSTEXPR_CXX20 void
test()
{
    int ia[] = {1, 2, 3, 4, 5, 6};
    unsigned sa = sizeof(ia) / sizeof(ia[0]);
    test(Iter(ia), Iter(ia), 0, std::plus<>(), 0);
    test(Iter(ia), Iter(ia), 1, std::multiplies<>(), 1);
    test(Iter(ia), Iter(ia+1), 0, std::plus<>(), 1);
    test(Iter(ia), Iter(ia+1), 2, std::multiplies<>(), 2);
    test(Iter(ia), Iter(ia+2), 0, std::plus<>(), 3);
    test(Iter(ia), Iter(ia+2), 3, std::multiplies<>(), 6);
    test(Iter(ia), Iter(ia+sa), 0, std::plus<>(), 21);
    test(Iter(ia), Iter(ia+sa), 4, std::multiplies<>(), 2880);
}

template <typename T, typename Init>
TEST_CONSTEXPR_CXX20 void
test_return_type()
{
    T *p = nullptr;
    static_assert( std::is_same_v<Init, decltype(std::reduce(p, p, Init{}, std::plus<>()))>, "" );
}

TEST_CONSTEXPR_CXX20 bool
test()
{
    test_return_type<char, int>();
    test_return_type<int, int>();
    test_return_type<int, unsigned long>();
    test_return_type<float, int>();
    test_return_type<short, float>();
    test_return_type<double, char>();
    test_return_type<char, double>();

    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*>();

//  Make sure the math is done using the correct type
    {
    auto v = {1, 2, 3, 4, 5, 6, 7, 8};
    unsigned res = std::reduce(v.begin(), v.end(), 1U, std::multiplies<>());
    assert(res == 40320);       // 8! will not fit into a char
    }

    return true;
}

int main(int, char**)
{
    test();
#if TEST_STD_VER > 17
    static_assert(test());
#endif
    return 0;
}