CRC 计算模板适用于除 CRC8 之外的所有类型

Question

我不知道在这里问这个问题是否合适，还是应该在 codereview 上问。不管怎样，我写了下面的代码来计算各种类型的CRC。它的 CRC16、CRC32 和 CRC64 结果与在线实现匹配（例如 here and here). But for CRC8, the results don't match no matter have I set the parameters. I am not an expert in details of cyclic redundancy check, and just have read a part of the wikipedia article. Can anyone tell me what is wrong with my code?

#include <cstdio>
#include <string>
#include <stdint.h>

namespace crc
{
    namespace templates
    {
        template <typename T> struct crcdata
        {
            T number = 0;
            std::string toHex(void)
            {
                std::string s(2 * sizeof(T), '0');
                for (T n = number, i = s.size(); n; n >>= 4)
                    s[--i] += (n & 0xF) > 9 ? (n % 16 - 9) | 16 : n % 16;

                return s;
            }
        };

        template <typename T, T polynomial, T init_cr, T final_cr>
        class general_crc
        {
        public:
            inline general_crc()
            {
                static T table[256];

                /// build CRC lookup table. Skip the loop if already evaluated
                for (int i = 0, b = 0; i < 256 && !table[255]; b = 8, i++)
                {
                    table[i] = i;
                    while (b--) table[i] = (table[i] >> 1) ^ (table[i] & 1 ? polynomial : 0);
                }

                this->result.number = init_cr;
                this->crc_table = (T const*)(void*)&table[0];
            }

            virtual ~general_crc(){}

        private:
            T const* crc_table;
            crcdata <T> result;

            void crc_calc(const void* buf, size_t size)
            {
                uint8_t* p = (uint8_t*)buf;

                while (size--)
                    this->result.number = this->crc_table[(this->result.number ^ *p++) & 0xFF] ^ (this->result.number >> 8);
            }

        public:
            /// crc of string
            static crcdata <T> calculate(const std::string& s)
            {
                general_crc cr;
                cr.crc_calc(s.c_str(), s.size());
                cr.result.number ^= final_cr;
                return cr.result;
            }
        };
    }

    typedef templates::general_crc <uint8_t,    0xAB, 0, 0> CRC8;
    typedef templates::general_crc <uint16_t,   0xA001, 0, 0>   CRC16;
    typedef templates::general_crc <uint32_t,   0xEDB88320U, 0xFFFFFFFFU, 0xFFFFFFFFU>  CRC32;
    typedef templates::general_crc <uint64_t,   0xC96C5795D7870F42LLU, ~0LLU, ~0LLU>    CRC64;
}

#include <iostream>
int main()
{
    std::string test = "This is a test!!";
    std::cout << crc::CRC8::calculate(test).toHex() << '\n';
    std::cout << crc::CRC16::calculate(test).toHex() << '\n';
    std::cout << crc::CRC32::calculate(test).toHex() << '\n';
    std::cout << crc::CRC64::calculate(test).toHex() << '\n';
    return 0;
}

Answer 1

代码和结果都没有问题。您认为您应该得到什么，为什么？

CRC 计算模板适用于除 CRC8 之外的所有类型

CRC calculation template works for all types except CRC8

c++

templates

crc