crc32-ref.h

/// @file
/// @brief	arkana::crc32
///			- An implementation of CRC32
/// @author Copyright(c) 2020 ttsuki
/// 
/// This software is released under the MIT License.
/// https://opensource.org/licenses/MIT

#pragma once

#include "../ark/types.h"
#include "../ark/lutgen.h"

namespace arkana::crc32
{
    using crc32_value_t = uint32_t;
    using crc32_lookup_table_t = lutgen::lookup_table<uint32_t, 256>;

    namespace tables
    {
        template <uint32_t polynomial>
        static inline constexpr crc32_lookup_table_t crc32_table0 = lutgen::generate_table<uint32_t, 256>(
            [](auto i)
            {
                uint32_t v = static_cast<uint32_t>(i);
                for (uint32_t j = 0; j < 8; j++)
                    v = (v >> 1) ^ ((v & 1) * polynomial);
                return v;
            });

        template <uint32_t polynomial, size_t n>
        static inline constexpr crc32_lookup_table_t crc32_table_n = lutgen::generate_table<uint32_t, 256>(
            [](auto i)
            {
                auto& table = crc32_table0<polynomial>;
                auto v = crc32_table_n<polynomial, n - 1>[i];
                return (v >> 8) ^ table[(v & 0xFF)];
            });

        template <uint32_t polynomial>
        static inline constexpr crc32_lookup_table_t crc32_table_n<polynomial, 0> = crc32_table0<polynomial>;
    }

    namespace ref
    {
        template <uint32_t polynomial>
        static inline constexpr crc32_value_t calculate_crc32(const void* data, size_t length, crc32_value_t current = 0)
        {
            constexpr auto& table = tables::crc32_table0<polynomial>;
            const byte_t* p = static_cast<const byte_t*>(data);
            const byte_t* q = p + length;

            crc32_value_t crc = ~current;
            while (p != q)
            {
                crc = (crc >> 8) ^ table[(crc & 0xFF) ^ static_cast<uint8_t>(*p++)];
            }

            return ~crc;
        }
    }

    using namespace ref;
}