ImplicitSurfaceNetwork/shared_module/container/detail/static_bitset/array_access.hpp

// 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"

namespace detail
{

/// \brief array_access is used for getting bunches of 4 bits, which is
/// needed when creating hex-strings
template <size_t N, class T>
struct array_access {
    using base_t  = T;
    using b_chars = bit_chars<N, T>;

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

    enum : size_t { div_four = N / 4, mod_four = N % 4 };

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

    constexpr base_t get_four_bits(array_t const &arr, size_t offset) const noexcept
    {
        return get_four_bits_impl(arr, offset / base_t_n_bits, offset % base_t_n_bits);
    }

    constexpr base_t get_four_bits_impl(array_t const &arr, size_t idx, size_t bit_idx) const noexcept
    {
        return (bit_idx >= 3) ? h1_get_four_bits(arr[idx], bit_idx) : h2_get_four_bits(arr, idx, bit_idx);
    }

    constexpr base_t h1_get_four_bits(base_t v, size_t bit_idx) const noexcept { return (v >> (bit_idx - 3)) & base_t(0xF); }

    constexpr base_t h2_get_four_bits(array_t const &arr, size_t idx, size_t bit_idx) const noexcept
    {
        return ((arr[idx] & ((base_t(1) << (bit_idx + 1)) - 1)) << (3 - bit_idx))
               + ((idx == 0) ? base_t(0) : (arr[idx - 1] >> (base_t_n_bits - (3 - bit_idx))));
    }
}; // struct array_access


} // namespace detail