crc.h

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#pragma once
 
#include <array>
#include <cstdint>
#include <cstring>
 
namespace bitstream::utility
{
    inline constexpr auto CHECKSUM_TABLE = []()
    {
        constexpr uint32_t POLYNOMIAL = 0xEDB88320;
 
        std::array<uint32_t, 0x100> table{};
 
        for (uint32_t i = 0; i < 0x100; ++i)
        {
            uint32_t item = i;
            for (uint32_t bit = 0; bit < 8; ++bit)
                item = ((item & 1) != 0) ? (POLYNOMIAL ^ (item >> 1)) : (item >> 1);
            table[i] = item;
        }
 
        return table;
    }();
 
    inline uint32_t crc_uint32(uint32_t checksum, const uint8_t* bytes, uint32_t size)
    {
        uint32_t result = 0xFFFFFFFF;
 
        uint8_t checksum_table[4]{};
        std::memcpy(&checksum_table, &checksum, sizeof(uint32_t));
 
        for (uint32_t i = 0; i < 4; i++)
            result = CHECKSUM_TABLE[(result & 0xFF) ^ *(checksum_table + i)] ^ (result >> 8);
 
        for (uint32_t i = 0; i < size; i++)
            result = CHECKSUM_TABLE[(result & 0xFF) ^ *(bytes + i)] ^ (result >> 8);
 
        return ~result;
    }
}