分段CRC SAE-J1850

原创已于 2023-05-02 21:36:03 修改 · 518 阅读

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于 2023-05-02 10:35:00 首次发布

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文章提供了两种计算CRC8（sae-j1850协议）的方法：一种是不使用查表的直接计算函数，另一种是使用查表的分段更新函数。同时，文章包含了一段测试代码，展示了如何使用这些函数并验证了它们的计算结果。

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分段CRC SAE-J1850

sae-j1850的多项式是0x1d(0x11d)，查找表如下：

uint8_t crc8_ploy1d[] = {
  0x00, 0x1D, 0x3A, 0x27, 0x74, 0x69, 0x4E, 0x53,
  0xE8, 0xF5, 0xD2, 0xCF, 0x9C, 0x81, 0xA6, 0xBB,
  0xCD, 0xD0, 0xF7, 0xEA, 0xB9, 0xA4, 0x83, 0x9E,
  0x25, 0x38, 0x1F, 0x02, 0x51, 0x4C, 0x6B, 0x76,
  0x87, 0x9A, 0xBD, 0xA0, 0xF3, 0xEE, 0xC9, 0xD4,
  0x6F, 0x72, 0x55, 0x48, 0x1B, 0x06, 0x21, 0x3C,
  0x4A, 0x57, 0x70, 0x6D, 0x3E, 0x23, 0x04, 0x19,
  0xA2, 0xBF, 0x98, 0x85, 0xD6, 0xCB, 0xEC, 0xF1,
  0x13, 0x0E, 0x29, 0x34, 0x67, 0x7A, 0x5D, 0x40,
  0xFB, 0xE6, 0xC1, 0xDC, 0x8F, 0x92, 0xB5, 0xA8,
  0xDE, 0xC3, 0xE4, 0xF9, 0xAA, 0xB7, 0x90, 0x8D,
  0x36, 0x2B, 0x0C, 0x11, 0x42, 0x5F, 0x78, 0x65,
  0x94, 0x89, 0xAE, 0xB3, 0xE0, 0xFD, 0xDA, 0xC7,
  0x7C, 0x61, 0x46, 0x5B, 0x08, 0x15, 0x32, 0x2F,
  0x59, 0x44, 0x63, 0x7E, 0x2D, 0x30, 0x17, 0x0A,
  0xB1, 0xAC, 0x8B, 0x96, 0xC5, 0xD8, 0xFF, 0xE2,
  0x26, 0x3B, 0x1C, 0x01, 0x52, 0x4F, 0x68, 0x75,
  0xCE, 0xD3, 0xF4, 0xE9, 0xBA, 0xA7, 0x80, 0x9D,
  0xEB, 0xF6, 0xD1, 0xCC, 0x9F, 0x82, 0xA5, 0xB8,
  0x03, 0x1E, 0x39, 0x24, 0x77, 0x6A, 0x4D, 0x50,
  0xA1, 0xBC, 0x9B, 0x86, 0xD5, 0xC8, 0xEF, 0xF2,
  0x49, 0x54, 0x73, 0x6E, 0x3D, 0x20, 0x07, 0x1A,
  0x6C, 0x71, 0x56, 0x4B, 0x18, 0x05, 0x22, 0x3F,
  0x84, 0x99, 0xBE, 0xA3, 0xF0, 0xED, 0xCA, 0xD7,
  0x35, 0x28, 0x0F, 0x12, 0x41, 0x5C, 0x7B, 0x66,
  0xDD, 0xC0, 0xE7, 0xFA, 0xA9, 0xB4, 0x93, 0x8E,
  0xF8, 0xE5, 0xC2, 0xDF, 0x8C, 0x91, 0xB6, 0xAB,
  0x10, 0x0D, 0x2A, 0x37, 0x64, 0x79, 0x5E, 0x43,
  0xB2, 0xAF, 0x88, 0x95, 0xC6, 0xDB, 0xFC, 0xE1,
  0x5A, 0x47, 0x60, 0x7D, 0x2E, 0x33, 0x14, 0x09,
  0x7F, 0x62, 0x45, 0x58, 0x0B, 0x16, 0x31, 0x2C,
  0x97, 0x8A, 0xAD, 0xB0, 0xE3, 0xFE, 0xD9, 0xC4
};

不查表，直接算的函数如下

uint8_t getCRCsaej1850(uint8_t *pdata, uint8_t len)
{
	if (pdata == NULL)
	{
		return 0;
	}
  uint8_t u8crc = 0;
  uint8_t i;
  uint8_t j;
  for (i = 0; i < len; i++)
  { 
    u8crc ^= pdata[i];
    for (j = 0; j < 8; j++)
    {
      if (u8crc & 0x80)
      {
        u8crc <<= 1;
        u8crc ^= 0x1D; //Autosar profile 1.
      }
      else
      {
        u8crc <<= 1;
      }
    }
  }
  u8crc ^= 0;
  return u8crc ;
}

分段查表的数据结构和函数如下：

typedef struct {
  uint8_t crc;
} crc8_ctx;

void crc8_init(crc8_ctx *ctx)
{
	if (ctx != NULL)
	{
		ctx->crc = 0x00;
	}
}

void crc8_update(crc8_ctx *ctx, uint8_t *data, size_t len, uint8_t *table)
{
	if ((ctx != NULL) && (data != NULL) && (table != NULL))
	{
		for (size_t i = 0; i < len; i++)
	  {
	    ctx->crc = (ctx->crc >> 8) ^ table[(ctx->crc & 0xff) ^ data[i]];
	  }
	}
}

void crc8_final(crc8_ctx *ctx, uint8_t *md)
{
	if ((ctx != NULL) && (md != NULL))
	{
		ctx->crc ^= 0x00;
		*md = (ctx->crc & 0xff);
	}
}

测试代码如下：

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

uint8_t getCRC8table(uint8_t *p, uint8_t counter, uint8_t *table)
{
  uint8_t res = 0x00;
  if ((p != NULL) && (table != NULL))
  {
  	for (; counter > 0 ; counter--)
	  {
	    res = table[res ^ *p];
	    p++;
	  }
  }
  return res;
}



int main(int argc, char const *argv[])
{
  uint8_t res = 0x00;
  uint8_t num[] = {1, 2, 3, 4, 5, 6, 7, 8};
  uint8_t nnn[] = {1, 2, 3, 4};
  uint8_t mmm[] = {5, 6, 7, 8};
  res = getCRC8table(num, sizeof(num), crc8_ploy1d);
  printf("res = 0x%.2x\n",res);
  res = getCRC8table(nnn, sizeof(nnn), crc8_ploy1d);
  printf("res = 0x%.2x\n",res);
  res = getCRC8table(mmm, sizeof(mmm), crc8_ploy1d);
  printf("res = 0x%.2x\n",res);

  printf("crc1 = 0x%.2x\n", getCRCsaej1850(nnn, sizeof(nnn)));
  printf("crc2 = 0x%.2x\n", getCRCsaej1850(mmm, sizeof(mmm)));
  crc8_ctx ctx;
  crc8_init(&ctx);
  crc8_update(&ctx, nnn, sizeof(nnn), crc8_ploy1d);
  crc8_update(&ctx, mmm, sizeof(mmm), crc8_ploy1d);
  crc8_final(&ctx, &res);
  printf("res = 0x%.2x\n", res);
  return 0;
}