跨平台 CRC8 函数：C++ 和 Python 奇偶校验

Question

循环冗余校验 (CRC) 可用于检查在传输过程中是否保持数据质量。这对于串行传输和无线电传输都有帮助。

通常，只需使用一个库来计算 CRC8 值，就可以消除这种复杂性。例如，OneWire 库可以在 Python 中非常有效地做到这一点。然而，一旦跨平台工作，例如将数据从 Raspberry Pi 传输到 Arduino，事情就会变得困难。

与其依赖库和包来计算 CRC 值，不如编写您自己的函数来执行此操作更容易。这样的函数在 Arduino (C++) 和 Raspberry Pi (Python 3.5) 上使用会是什么样子？

Answer 1

上下文

奇偶校验用于确保传输时保持数据的完整性。奇偶校验的最简单形式是 1 位循环冗余校验 (CRC-1)，也称为奇偶校验位。这会将所有被检查的二进制代码和 returns 奇数或偶数相加。然后将其附加到传输的数据中，并在接收时进行检查。这提供了一个基本检查，通过它可以突出显示数据传输是否存在问题。

更复杂的检查依赖于多项式函数使用二元运算符对一串二进制数进行重复除法。位数越高，CRC校验越严格，但是复杂度也随着CRC位数的增加而显着增加。常见的变体包括 CRC4、CRC8、CRC16 和 CRC32。这些通常可以使用库来实现，因为涉及的按位处理很快就会变得复杂。

Arduino CRC8 函数

uint8_t crc8( uint8_t *addr, uint8_t len) {
      uint8_t crc=0;
      for (uint8_t i=0; i<len;i++) {
         uint8_t inbyte = addr[i];
         for (uint8_t j=0;j<8;j++) {
             uint8_t mix = (crc ^ inbyte) & 0x01;
             crc >>= 1;
             if (mix) 
                crc ^= 0x8C;
         inbyte >>= 1;
      }
    }
   return crc;
}

Python CRC8 函数

def crc8(data):
crc = 0
for i in range(len(data)):
    byte = data[i]
    for b in range(8):
        fb_bit = (crc ^ byte) & 0x01
        if fb_bit == 0x01:
            crc = crc ^ 0x18
        crc = (crc >> 1) & 0x7f
        if fb_bit == 0x01:
            crc = crc | 0x80
        byte = byte >> 1
return crc

请注意，此代码改编自 Arduino 的 OneWire 库和 Python 的等效包。

欢迎任何其他解决方案、有关在 Arduino 和 Python 上计算 CRC8 值的相关贡献！

Answer 2

// 8-bit CRC using the polynomial x^8+x^6+x^3+x^2+1, 0x14D.
// Chosen based on Koopman, et al. (0xA6 in his notation = 0x14D >> 1):
// http://www.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf
//
// This implementation is reflected, processing the least-significant bit of the
// input first, has an initial CRC register value of 0xff, and exclusive-or's
// the final register value with 0xff. As a result the CRC of an empty string,
// and therefore the initial CRC value, is zero.
//
// The standard description of this CRC is:
// width=8 poly=0x4d init=0xff refin=true refout=true xorout=0xff check=0xd8
// name="CRC-8/KOOP"

static unsigned char const crc8_table[] = {
    0xea, 0xd4, 0x96, 0xa8, 0x12, 0x2c, 0x6e, 0x50, 0x7f, 0x41, 0x03, 0x3d,
    0x87, 0xb9, 0xfb, 0xc5, 0xa5, 0x9b, 0xd9, 0xe7, 0x5d, 0x63, 0x21, 0x1f,
    0x30, 0x0e, 0x4c, 0x72, 0xc8, 0xf6, 0xb4, 0x8a, 0x74, 0x4a, 0x08, 0x36,
    0x8c, 0xb2, 0xf0, 0xce, 0xe1, 0xdf, 0x9d, 0xa3, 0x19, 0x27, 0x65, 0x5b,
    0x3b, 0x05, 0x47, 0x79, 0xc3, 0xfd, 0xbf, 0x81, 0xae, 0x90, 0xd2, 0xec,
    0x56, 0x68, 0x2a, 0x14, 0xb3, 0x8d, 0xcf, 0xf1, 0x4b, 0x75, 0x37, 0x09,
    0x26, 0x18, 0x5a, 0x64, 0xde, 0xe0, 0xa2, 0x9c, 0xfc, 0xc2, 0x80, 0xbe,
    0x04, 0x3a, 0x78, 0x46, 0x69, 0x57, 0x15, 0x2b, 0x91, 0xaf, 0xed, 0xd3,
    0x2d, 0x13, 0x51, 0x6f, 0xd5, 0xeb, 0xa9, 0x97, 0xb8, 0x86, 0xc4, 0xfa,
    0x40, 0x7e, 0x3c, 0x02, 0x62, 0x5c, 0x1e, 0x20, 0x9a, 0xa4, 0xe6, 0xd8,
    0xf7, 0xc9, 0x8b, 0xb5, 0x0f, 0x31, 0x73, 0x4d, 0x58, 0x66, 0x24, 0x1a,
    0xa0, 0x9e, 0xdc, 0xe2, 0xcd, 0xf3, 0xb1, 0x8f, 0x35, 0x0b, 0x49, 0x77,
    0x17, 0x29, 0x6b, 0x55, 0xef, 0xd1, 0x93, 0xad, 0x82, 0xbc, 0xfe, 0xc0,
    0x7a, 0x44, 0x06, 0x38, 0xc6, 0xf8, 0xba, 0x84, 0x3e, 0x00, 0x42, 0x7c,
    0x53, 0x6d, 0x2f, 0x11, 0xab, 0x95, 0xd7, 0xe9, 0x89, 0xb7, 0xf5, 0xcb,
    0x71, 0x4f, 0x0d, 0x33, 0x1c, 0x22, 0x60, 0x5e, 0xe4, 0xda, 0x98, 0xa6,
    0x01, 0x3f, 0x7d, 0x43, 0xf9, 0xc7, 0x85, 0xbb, 0x94, 0xaa, 0xe8, 0xd6,
    0x6c, 0x52, 0x10, 0x2e, 0x4e, 0x70, 0x32, 0x0c, 0xb6, 0x88, 0xca, 0xf4,
    0xdb, 0xe5, 0xa7, 0x99, 0x23, 0x1d, 0x5f, 0x61, 0x9f, 0xa1, 0xe3, 0xdd,
    0x67, 0x59, 0x1b, 0x25, 0x0a, 0x34, 0x76, 0x48, 0xf2, 0xcc, 0x8e, 0xb0,
    0xd0, 0xee, 0xac, 0x92, 0x28, 0x16, 0x54, 0x6a, 0x45, 0x7b, 0x39, 0x07,
    0xbd, 0x83, 0xc1, 0xff};

#include <stddef.h>

// Return the CRC-8 of data[0..len-1] applied to the seed crc. This permits the
// calculation of a CRC a chunk at a time, using the previously returned value
// for the next seed. If data is NULL, then return the initial seed. See the
// test code for an example of the proper usage.
unsigned crc8(unsigned crc, unsigned char const *data, size_t len)
{
    if (data == NULL)
        return 0;
    crc &= 0xff;
    unsigned char const *end = data + len;
    while (data < end)
        crc = crc8_table[crc ^ *data++];
    return crc;
}

// crc8_slow() is an equivalent bit-wise implementation of crc8() that does not
// need a table, and which can be used to generate crc8_table[]. Entry k in the
// table is the CRC-8 of the single byte k, with an initial crc value of zero.
// 0xb2 is the bit reflection of 0x4d, the polynomial coefficients below x^8.
unsigned crc8_slow(unsigned crc, unsigned char const *data, size_t len)
{
    if (data == NULL)
        return 0;
    crc = ~crc & 0xff;
    while (len--) {
        crc ^= *data++;
        for (unsigned k = 0; k < 8; k++)
            crc = crc & 1 ? (crc >> 1) ^ 0xb2 : crc >> 1;
    }
    return crc ^ 0xff;
}

#ifdef TEST
#include <stdio.h>
#define CHUNK 16384

int main(void) {
    unsigned char buf[CHUNK];
    unsigned crc = crc8(0, NULL, 0);
    size_t len;
    do {
        len = fread(buf, 1, CHUNK, stdin);
        crc = crc8(crc, buf, len);
    } while (len == CHUNK);
    printf("%#02x\n", crc);
    return 0;
}
#endif

跨平台 CRC8 函数：C++ 和 Python 奇偶校验

Cross Platform CRC8 Function: C++ and Python Parity Check

python

arduino

crc

parity

raspberry-pi

上下文

Arduino CRC8 函数

Python CRC8 函数