Python实现CRC-16校验算法（crcmod python）

什么是CRC校验？
CRC即循环冗余校验码（Cyclic Redundancy Check）：是数据通信领域中最常用的一种查错校验码，其特征是信息字段和校验字段的长度可以任意选定。奇偶校验虽然简单，但是漏检率太高，而CRC则要低的多，所以大多数都是使用CRC来校验。CRC也称为多项式码。

循环冗余检查（CRC）是一种数据传输检错功能，对数据进行多项式计算，并将得到的结果附在帧的后面，接收设备也执行类似的算法，进而可以保证在软件层次上数据传输的正确性和完整性。

CRC-16校验码的应用
根据Modbus协议，常规485通讯的信息发送形式如下：

地址 功能码 数据信息 校验码
1byte 1byte N byte 2byte
其中2 Byte的校验码一般就是采用CRC16。

核心代码如下：

def GetFormattedHex(intNum, lenOfHexString):
    return format(intNum, "0" + str(lenOfHexString) + "x").upper()


def checksumDataFormat(packageList):
    packageChecksum = convertListToString(packageList)  # transforma em uma string o pacote a ser calculado o CRC
    print("Package to be calculated CRC: " + packageChecksum)

    return packageChecksum


def GetCrc16(strHexData):    # Ex: requestData = "0A134004040001000F"     output---> dcee

    crc16tab = (
        0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
        0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
        0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
        0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
        0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
        0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
        0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
        0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
        0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
        0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
        0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
        0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
        0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9,
        0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1,
        0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
        0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70,
        0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7,
        0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
        0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036,
        0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E,
        0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
        0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD,
        0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134,
        0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
        0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3,
        0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB,
        0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
        0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A,
        0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1,
        0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
        0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330,
        0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78,
    )
    fcs = int("FFFF", 16)
    i = 0
    while i < len(strHexData):
        strHexNumber = strHexData[i:i + 2]
        intNumber = int(strHexNumber, 16)
        crc16tabIndex = (fcs ^ intNumber) & int("FF", 16)
        fcs = (fcs >> 8) ^ crc16tab[crc16tabIndex]
        i = i + 2
    return fcs ^ 0xffff


def convertListToString(listBytes):
    return ''.join(map(str, listBytes))  # funcao do python pronta para convert listas em string


packageList = ['1A', '80', '12', '00000000', '54494D45522C36302C3336303023', '0001']

n = 4  # in my case my the return is with 4 characters

checksumData = checksumDataFormat(packageList)  # transformando o package para o modelo de calculo do CRC
checksumCalculated = (GetFormattedHex(GetCrc16(checksumData), n))

print(checksumCalculated)

运行结果：

在线计算对比：

网址：http://www.ip33.com/crc.html