ios - 如何计算 NSData 的 CRC-8-Dallas/Maxim？

Question

我需要准确计算

CRC-8-Dallas/Maxim

。有人可以提供算法吗？

感谢任何帮助！

Answer 1

CRC-8-Dallas/Maxim 变体 1（C 型）：

unsigned char dallas_crc8(const unsigned char * data, const unsigned int size)
{
    unsigned char crc = 0;
    for ( unsigned int i = 0; i < size; ++i )
    {
        unsigned char inbyte = data[i];
        for ( unsigned char j = 0; j < 8; ++j )
        {
            unsigned char mix = (crc ^ inbyte) & 0x01;
            crc >>= 1;
            if ( mix ) crc ^= 0x8C;
            inbyte >>= 1;
        }
    }
    return crc;
}

CRC-8-Dallas/Maxim 变体 2（C 型）：

unsigned char crc_bits(unsigned char data)
{
    unsigned char crc = 0;
    if(data & 1)     crc ^= 0x5e;
    if(data & 2)     crc ^= 0xbc;
    if(data & 4)     crc ^= 0x61;
    if(data & 8)     crc ^= 0xc2;
    if(data & 0x10)  crc ^= 0x9d;
    if(data & 0x20)  crc ^= 0x23;
    if(data & 0x40)  crc ^= 0x46;
    if(data & 0x80)  crc ^= 0x8c;
    return crc;
}

unsigned char dallas_crc8(const unsigned char * data, const unsigned int size)
{
    unsigned char crc = 0;
    for ( unsigned int i = 0; i < size; ++i )
    {
         crc = crc_bits(data[i] ^ crc);
    }
    return crc;
}

CRC-8-Dallas/Maxim 变体 3（C 型）：

unsigned char crc_array[256] =
{
    0x00, 0x5e, 0xbc, 0xe2, 0x61, 0x3f, 0xdd, 0x83,
    0xc2, 0x9c, 0x7e, 0x20, 0xa3, 0xfd, 0x1f, 0x41,
    0x9d, 0xc3, 0x21, 0x7f, 0xfc, 0xa2, 0x40, 0x1e,
    0x5f, 0x01, 0xe3, 0xbd, 0x3e, 0x60, 0x82, 0xdc,
    0x23, 0x7d, 0x9f, 0xc1, 0x42, 0x1c, 0xfe, 0xa0,
    0xe1, 0xbf, 0x5d, 0x03, 0x80, 0xde, 0x3c, 0x62,
    0xbe, 0xe0, 0x02, 0x5c, 0xdf, 0x81, 0x63, 0x3d,
    0x7c, 0x22, 0xc0, 0x9e, 0x1d, 0x43, 0xa1, 0xff,
    0x46, 0x18, 0xfa, 0xa4, 0x27, 0x79, 0x9b, 0xc5,
    0x84, 0xda, 0x38, 0x66, 0xe5, 0xbb, 0x59, 0x07,
    0xdb, 0x85, 0x67, 0x39, 0xba, 0xe4, 0x06, 0x58,
    0x19, 0x47, 0xa5, 0xfb, 0x78, 0x26, 0xc4, 0x9a,
    0x65, 0x3b, 0xd9, 0x87, 0x04, 0x5a, 0xb8, 0xe6,
    0xa7, 0xf9, 0x1b, 0x45, 0xc6, 0x98, 0x7a, 0x24,
    0xf8, 0xa6, 0x44, 0x1a, 0x99, 0xc7, 0x25, 0x7b,
    0x3a, 0x64, 0x86, 0xd8, 0x5b, 0x05, 0xe7, 0xb9,
    0x8c, 0xd2, 0x30, 0x6e, 0xed, 0xb3, 0x51, 0x0f,
    0x4e, 0x10, 0xf2, 0xac, 0x2f, 0x71, 0x93, 0xcd,
    0x11, 0x4f, 0xad, 0xf3, 0x70, 0x2e, 0xcc, 0x92,
    0xd3, 0x8d, 0x6f, 0x31, 0xb2, 0xec, 0x0e, 0x50,
    0xaf, 0xf1, 0x13, 0x4d, 0xce, 0x90, 0x72, 0x2c,
    0x6d, 0x33, 0xd1, 0x8f, 0x0c, 0x52, 0xb0, 0xee,
    0x32, 0x6c, 0x8e, 0xd0, 0x53, 0x0d, 0xef, 0xb1,
    0xf0, 0xae, 0x4c, 0x12, 0x91, 0xcf, 0x2d, 0x73,
    0xca, 0x94, 0x76, 0x28, 0xab, 0xf5, 0x17, 0x49,
    0x08, 0x56, 0xb4, 0xea, 0x69, 0x37, 0xd5, 0x8b,
    0x57, 0x09, 0xeb, 0xb5, 0x36, 0x68, 0x8a, 0xd4,
    0x95, 0xcb, 0x29, 0x77, 0xf4, 0xaa, 0x48, 0x16,
    0xe9, 0xb7, 0x55, 0x0b, 0x88, 0xd6, 0x34, 0x6a,
    0x2b, 0x75, 0x97, 0xc9, 0x4a, 0x14, 0xf6, 0xa8,
    0x74, 0x2a, 0xc8, 0x96, 0x15, 0x4b, 0xa9, 0xf7,
    0xb6, 0xe8, 0x0a, 0x54, 0xd7, 0x89, 0x6b, 0x35,
};

unsigned char dallas_crc8(const unsigned char * data, const unsigned int size)
{
    unsigned char crc = 0;
    for ( unsigned int i = 0; i < size; ++i )
    {
         crc = crc_array[data[i] ^ crc];
    }
    return crc;
}

CRC-8-Dallas/Maxim 变体 4（带有 boost 的 C++ 样式）：

#include "boost/crc.hpp"

uint8_t dallas_crc8(const uint8_t * data, const uint32_t size)
{
    boost::crc_optimal <8, 0x31, 0, 0, true, true> crc;
    crc.process_bytes(data, size);
    return crc.checksum();
}

Answer 2

#define CRC8INIT 0x00
#define CRC8POLY 0x31 // = X^8+X^5+X^4+X^0

uint8_t crc8(uint8_t *data, uint16_t size)
{
    uint8_t crc, i;
    crc = CRC8INIT;

    while (size--)
    {
        crc ^= *data++;

        for (i = 0; i < 8; i++)
        {
            if (crc & 0x80) crc = (crc << 1) ^ CRC8POLY;
            else crc <<= 1;
        }
    }

    return crc;
}

Answer 3

基于 Stamen Rakov 的回答，这里是 Go 风格的变体 1 函数：

func dallas_crc8(data []uint8) uint8 {
  var crc uint8 = 0;
  for _, inbyte := range data {
    for j := 0; j < 8; j++ {
        mix := (crc ^ inbyte) & 0x01
        crc >>= 1;
        if mix > 0 {
            crc ^= 0x8C
        }
        inbyte >>= 1
    }
  }
  return crc
}

Answer 4

高速非循环版本：

uint8_t crc_8(uint8_t crc, uint8_t data) {
    uint8_t X, Y;
    
    X = Y = crc ^ data;
    Y <<= 3;
    X ^= Y;
    Y <<= 1;
    X ^= Y;
    Y <<= 2;
    X ^= Y;
    
    Y = X;
    X >>= 4;
    Y ^= X;
    X >>= 1;
    Y ^= X;
    return (uint8_t) Y;
}