c++ crc16-ccitt 带输入反转输出反转代码

以下是C++中计算CRC16-CCITT校验码，带输入反转和输出反转的代码实现：

#include <iostream>
#include <cstdint>

uint16_t crc16_ccitt(const uint8_t* data, size_t length) {
    const uint16_t polynomial = 0x1021;
    uint16_t crc = 0xFFFF;
    for (size_t i = 0; i < length; ++i) {
        crc ^= (uint16_t)data[i] << 8;
        for (size_t j = 0; j < 8; ++j) {
            if (crc & 0x8000) {
                crc = (crc << 1) ^ polynomial;
            } else {
                crc <<= 1;
            }
        }
    }
    return crc;
}

uint16_t crc16_ccitt_input_reversed(const uint8_t* data, size_t length) {
    uint8_t reversed_data[length];
    for (size_t i = 0; i < length; ++i) {
        reversed_data[length - i - 1] = data[i];
    }
    return crc16_ccitt(reversed_data, length);
}

uint16_t crc16_ccitt_output_reversed(const uint8_t* data, size_t length) {
    uint16_t crc = crc16_ccitt(data, length);
    uint16_t reversed_crc = 0;
    for (size_t i = 0; i < 16; ++i) {
        reversed_crc <<= 1;
        reversed_crc |= crc & 1;
        crc >>= 1;
    }
    return reversed_crc;
}

uint16_t crc16_ccitt_input_output_reversed(const uint8_t* data, size_t length) {
    uint8_t reversed_data[length];
    for (size_t i = 0; i < length; ++i) {
        reversed_data[length - i - 1] = data[i];
    }
    uint16_t crc = crc16_ccitt(reversed_data, length);
    uint16_t reversed_crc = 0;
    for (size_t i = 0; i < 16; ++i) {
        reversed_crc <<= 1;
        reversed_crc |= crc & 1;
        crc >>= 1;
    }
    return reversed_crc;
}

int main() {
    uint8_t data[] = {0x01, 0x02, 0x03};
    size_t length = sizeof(data) / sizeof(data[0]);
    std::cout << std::hex << crc16_ccitt_input_reversed(data, length) << '\n';
    std::cout << std::hex << crc16_ccitt_output_reversed(data, length) << '\n';
    std::cout << std::hex << crc16_ccitt_input_output_reversed(data, length) << '\n';
    return 0;
}

其中，`crc16_ccitt()`函数是计算CRC16-CCITT校验码的核心函数，`crc16_ccitt_input_reversed()`函数是带输入反转的计算函数，`crc16_ccitt_output_reversed()`函数是带输出反转的计算函数，`crc16_ccitt_input_output_reversed()`函数是同时带输入反转和输出反转的计算函数。在实际使用时，根据需要选择相应的函数进行计算即可。