// MassBuilderSaveTool
// Copyright (C) 2021-2024 Guillaume Jacquemin
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

#include "Crc32.h"

namespace mbst { namespace Crc32 {

std::uint32_t
update(std::uint32_t initial, Containers::ArrayView<const void> data) {
    static const auto table = []{
        std::uint32_t polynomial = 0xEDB88320u;
        Containers::StaticArray<256, std::uint32_t> temp{ValueInit};

        for(std::uint32_t i = 0; i < 256; i++) {
            std::uint32_t c = i;

            for(std::size_t j = 0; j < 8; j++) {
                if(c & 1) {
                    c = polynomial ^ (c >> 1);
                }
                else {
                    c >>= 1;
                }
            }

            temp[i] = c;
        }

        return temp;
    }();

    std::uint32_t c = initial ^ 0xFFFFFFFF;

    auto u = Containers::arrayCast<const std::uint8_t>(data);

    for(std::size_t i = 0; i < data.size(); ++i) {
        c = table[(c ^ u[i]) & 0xFF] ^ (c >> 8);
    }

    return c ^ 0xFFFFFFFF;
}

}}