// BITSET2
//
//  Copyright Claas Bontus
//
//  Use, modification and distribution is subject to the
//  Boost Software License, Version 1.0. (See accompanying
//  file LICENSE.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
// Project home: https://github.com/ClaasBontus/bitset2
//

#pragma once

#include "bit_chars.hpp"
#include "array_ops.hpp"

namespace detail
{

/// Allows to add two std::array's in a constexpr
template <size_t N, class T>
struct array_add {
    using base_t  = T;
    using b_chars = bit_chars<N, T>;

    enum : base_t { hgh_bit_pattern = b_chars::hgh_bit_pattern, all_one = b_chars::all_one };

    enum : size_t { n_array = b_chars::n_array };

    using array_t = typename h_types<T>::template array_t<n_array>;

    constexpr array_t add(array_t arr1, array_t const &arr2) const noexcept
    {
        add_assgn(arr1, arr2);
        return arr1;
    }

    constexpr void add_assgn(array_t &arr1, array_t const &arr2, base_t carry = base_t(0)) const noexcept
    {
        for (size_t c = 0; c < n_array; ++c) {
            auto const sm1 = base_t(arr2[c] + carry);
            auto const sm  = base_t(arr1[c] + sm1);
            carry          = sm < arr1[c] || sm1 < arr2[c];
            arr1[c]        = sm;
        }
        arr1[n_array - 1] &= hgh_bit_pattern;
    } // add_assgn

    constexpr array_t midpoint(array_t const &arr1, array_t const &arr2, bool round_down) const noexcept
    {
        // https://devblogs.microsoft.com/oldnewthing/20220207-00/?p=106223
        T val0_1 = arr1[0];
        T val0_2 = arr2[0];
        T carry  = val0_1 & val0_2 & 1;
        if (!round_down && carry == 0) carry = val0_1 & 1;
        array_t ret_val = array_ops<N, T>(1).shift_right(arr1);
        array_t bs2_h   = array_ops<N, T>(1).shift_right(arr2);
        add_assgn(ret_val, bs2_h, carry);
        return ret_val;
    } // midpoint
};    // struct array_add

} // namespace detail