/*
 * Copyright (c) 2020-2022, the SerenityOS developers.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Array.h>
#include <AK/Span.h>
#include <AK/Types.h>
#include <LibCrypto/Checksum/CRC32.h>

namespace Crypto::Checksum {

static constexpr auto generate_table()
{
    Array<u32, 256> data {};
    for (auto i = 0u; i < data.size(); i++) {
        u32 value = i;

        for (auto j = 0; j < 8; j++) {
            if (value & 1) {
                value = 0xEDB88320 ^ (value >> 1);
            } else {
                value = value >> 1;
            }
        }

        data[i] = value;
    }
    return data;
}

static constexpr auto table = generate_table();

void CRC32::update(ReadonlyBytes data)
{
    for (size_t i = 0; i < data.size(); i++) {
        m_state = table[(m_state ^ data.at(i)) & 0xFF] ^ (m_state >> 8);
    }
};

u32 CRC32::digest()
{
    return ~m_state;
}

}