CRC8 Slice-by-4算法
CRC8 Slice-by-4 algorithm
我需要一个高度优化的 CRC8 算法。我的目标是开发一个从 CRC16 / CRC32 已知的 Slice-by-4 解决方案。我想让代码尽可能接近我在下面发布的用于 CRC16 的解决方案。
生成CRC LookUp的函数-Table:
void crcspeed16_genTable(crcfn16 crcfn, uint16_t table[8][256]) {
uint16_t crc;
/* generate CRCs for all single byte sequences */
for (int n = 0; n < 256; n++) {
table[0][n] = crcfn(0, &n, 1);
}
/* generate nested CRC table for future slice-by-8 lookup */
for (int n = 0; n < 256; n++) {
crc = table[0][n];
for (int k = 1; k < 8; k++) {
crc = table[0][(crc >> 8) & 0xff] ^ (crc << 8);
table[k][n] = crc;
}
}
}
uint16_t crc16(uint16_t crc, const void *in_data, uint64_t len) {
const uint8_t *data = (const uint8_t*) in_data;
for (uint64_t i = 0; i < len; i++) {
crc = crc ^ (data[i] << 8);
for (int j = 0; j < 8; j++) {
if (crc & 0x8000) {
crc = (crc << 1) ^ CRC16_POLYNOMINAL;
} else {
crc = (crc << 1);
}
}
}
return crc;
}
调用生成 table:
crcspeed16_genTable(crc16, crc16_LUT);
基于Slice-by-4解生成CRC16的函数：
uint16_t crc16_slice4(const void *buf, size_t len, uint16_t initialValue, uint16_t XOR_OUT) {
uint16_t crc = initialValue;
unsigned char *next = (unsigned char *)buf;
// process individual bytes until we reach an 8-byte aligned pointer
while (len && ((uintptr_t)next & 7) != 0) {
crc = crc16_LUT[0][((crc >> 8) ^ *next++) & 0xff] ^ (crc << 8);
len--;
}
// fast middle processing, 4 bytes (aligned!) per loop */
while (len >= 4) {
uint32_t n = *(uint32_t *)next;
crc = crc16_LUT[3][(n & 0xff) ^ ((crc >> 8) & 0xff)] ^
crc16_LUT[2][((n >> 8) & 0xff) ^ (crc & 0xff)] ^
crc16_LUT[1][(n >> 16) & 0xff] ^
crc16_LUT[0][n >> 24];
next += 4;
len -= 4;
}
// process remaining bytes (can't be larger than 8)
while (len) {
crc = crc16_LUT[0][((crc >> 8) ^ *next++) & 0xff] ^ (crc << 8);
len--;
}
return crc ^ XOR_OUT;
}
我的目标是使算法适用于 CRC8 和 CRC4。到目前为止，我所做的是将 LUT 生成器更改为生成 LUT 的有效第一行，并根据此 LUT 数据处理有效的 CRC。我未能调整中间部分来计算和利用 CRC 的全部潜力 table。
针对 CRC8 的适配函数（未完全发挥作用）：
Table代数：
void crcspeed8_genTable(crcfn8 crcfn, uint8_t table[8][256]) {
uint16_t crc;
/* generate CRCs for all single byte sequences */
for (int n = 0; n < 256; n++) {
table[0][n] = crcfn(0, &n, 1);
}
/* generate nested CRC table for future slice-by-8 lookup */
for (int n = 0; n < 256; n++) {
crc = table[0][n];
for (int k = 1; k < 8; k++) {
//crc = table[0][crc] ^ crc;
crc = table[0][(crc >> 4) & 0x0f] ^ (crc << 4);
table[k][n] = crc;
}
}
}
uint8_t crc8(uint8_t crc, const void *in_data, uint64_t len) {
const uint8_t *data = (const uint8_t*) in_data;
for (uint64_t i = 0; i < len; i++) {
//crc = crc ^ (data[i] << 8);
crc = crc ^ data[i];
for (int j = 0; j < 8; j++) {
if (crc & 0x80) {
crc = (crc << 1) ^ CRC8_POLYNOMINAL;
} else {
crc = (crc << 1);
}
}
}
return crc;
}
CRC计算：
uint8_t crc8_slice4(const void *buf, size_t len, uint8_t initialValue, uint8_t XOR_OUT) {
uint8_t crc = initialValue;
unsigned char *next = (unsigned char *)buf;
// process individual bytes until we reach an 8-byte aligned pointer
while (len && ((uintptr_t)next & 7) != 0) {
printf("\nAlign processing");
crc = crc8_LUT[0][crc ^ *next++];
len--;
}
//fast middle processing, 4 bytes (aligned!) per loop
while (len >= 4) {
printf("\nSlice processing");
uint32_t n = *(uint32_t *)next;
//This part should be adopted to work for CRC8
/*crc = crc8_LUT[3][(n & 0xff) ^ crc] ^
crc8_LUT[2][(n >> 8) & 0xff] ^
crc8_LUT[1][(n >> 16) & 0xff] ^
crc8_LUT[0][n >> 24]; */
uint32_t n0 = (n & 0xFF) ^ crc;
uint32_t n1 = (n >> 8) & 0xFF;
uint32_t n2 = (n >> 16) & 0xFF;
uint32_t n3 = (n >> 24);
//Working multi step for CRC 4 only using first row of LUT
uint8_t crc0 = crc8_LUT[0][crc ^ n0];
uint8_t crc1 = crc8_LUT[0][crc0 ^ n1];
uint8_t crc2 = crc8_LUT[0][crc1 ^ n2];
uint8_t crc3 = crc8_LUT[0][crc2 ^ n3];
crc = crc3;
next += 4;
len -= 4;
}
// process remaining bytes (can't be larger than 8)
while (len) {
printf("\nRemain processing");
crc = crc8_LUT[0][crc ^ *next++];
len--;
}
return crc ^ XOR_OUT;
}
我试图将函数更改为适用于 CRC8，但我无法弄清楚中间部分。解释为各种 CRC (4/8/16/24/32...) 生成 Look-Up-Tables 的一般方法的解决方案也将受到高度赞赏。
感谢您给我指明正确的方向。
您没有提供您的多项式、初始值或最终异或。有了这些（并且你的情况下的 CRC 没有反映出来），你可以使用 crcany 为你生成代码。
这里有一个 little-endian slice-by-4 的例子：
#include <stddef.h>
#include <stdint.h>
#define table_byte table_word[0]
static uint8_t const table_word[][256] = {
{0xbd, 0x92, 0xe3, 0xcc, 0x01, 0x2e, 0x5f, 0x70, 0xea, 0xc5, 0xb4, 0x9b, 0x56,
0x79, 0x08, 0x27, 0x13, 0x3c, 0x4d, 0x62, 0xaf, 0x80, 0xf1, 0xde, 0x44, 0x6b,
0x1a, 0x35, 0xf8, 0xd7, 0xa6, 0x89, 0xce, 0xe1, 0x90, 0xbf, 0x72, 0x5d, 0x2c,
0x03, 0x99, 0xb6, 0xc7, 0xe8, 0x25, 0x0a, 0x7b, 0x54, 0x60, 0x4f, 0x3e, 0x11,
0xdc, 0xf3, 0x82, 0xad, 0x37, 0x18, 0x69, 0x46, 0x8b, 0xa4, 0xd5, 0xfa, 0x5b,
0x74, 0x05, 0x2a, 0xe7, 0xc8, 0xb9, 0x96, 0x0c, 0x23, 0x52, 0x7d, 0xb0, 0x9f,
0xee, 0xc1, 0xf5, 0xda, 0xab, 0x84, 0x49, 0x66, 0x17, 0x38, 0xa2, 0x8d, 0xfc,
0xd3, 0x1e, 0x31, 0x40, 0x6f, 0x28, 0x07, 0x76, 0x59, 0x94, 0xbb, 0xca, 0xe5,
0x7f, 0x50, 0x21, 0x0e, 0xc3, 0xec, 0x9d, 0xb2, 0x86, 0xa9, 0xd8, 0xf7, 0x3a,
0x15, 0x64, 0x4b, 0xd1, 0xfe, 0x8f, 0xa0, 0x6d, 0x42, 0x33, 0x1c, 0x5e, 0x71,
0x00, 0x2f, 0xe2, 0xcd, 0xbc, 0x93, 0x09, 0x26, 0x57, 0x78, 0xb5, 0x9a, 0xeb,
0xc4, 0xf0, 0xdf, 0xae, 0x81, 0x4c, 0x63, 0x12, 0x3d, 0xa7, 0x88, 0xf9, 0xd6,
0x1b, 0x34, 0x45, 0x6a, 0x2d, 0x02, 0x73, 0x5c, 0x91, 0xbe, 0xcf, 0xe0, 0x7a,
0x55, 0x24, 0x0b, 0xc6, 0xe9, 0x98, 0xb7, 0x83, 0xac, 0xdd, 0xf2, 0x3f, 0x10,
0x61, 0x4e, 0xd4, 0xfb, 0x8a, 0xa5, 0x68, 0x47, 0x36, 0x19, 0xb8, 0x97, 0xe6,
0xc9, 0x04, 0x2b, 0x5a, 0x75, 0xef, 0xc0, 0xb1, 0x9e, 0x53, 0x7c, 0x0d, 0x22,
0x16, 0x39, 0x48, 0x67, 0xaa, 0x85, 0xf4, 0xdb, 0x41, 0x6e, 0x1f, 0x30, 0xfd,
0xd2, 0xa3, 0x8c, 0xcb, 0xe4, 0x95, 0xba, 0x77, 0x58, 0x29, 0x06, 0x9c, 0xb3,
0xc2, 0xed, 0x20, 0x0f, 0x7e, 0x51, 0x65, 0x4a, 0x3b, 0x14, 0xd9, 0xf6, 0x87,
0xa8, 0x32, 0x1d, 0x6c, 0x43, 0x8e, 0xa1, 0xd0, 0xff},
{0xfa, 0x13, 0x07, 0xee, 0x2f, 0xc6, 0xd2, 0x3b, 0x7f, 0x96, 0x82, 0x6b, 0xaa,
0x43, 0x57, 0xbe, 0xdf, 0x36, 0x22, 0xcb, 0x0a, 0xe3, 0xf7, 0x1e, 0x5a, 0xb3,
0xa7, 0x4e, 0x8f, 0x66, 0x72, 0x9b, 0xb0, 0x59, 0x4d, 0xa4, 0x65, 0x8c, 0x98,
0x71, 0x35, 0xdc, 0xc8, 0x21, 0xe0, 0x09, 0x1d, 0xf4, 0x95, 0x7c, 0x68, 0x81,
0x40, 0xa9, 0xbd, 0x54, 0x10, 0xf9, 0xed, 0x04, 0xc5, 0x2c, 0x38, 0xd1, 0x6e,
0x87, 0x93, 0x7a, 0xbb, 0x52, 0x46, 0xaf, 0xeb, 0x02, 0x16, 0xff, 0x3e, 0xd7,
0xc3, 0x2a, 0x4b, 0xa2, 0xb6, 0x5f, 0x9e, 0x77, 0x63, 0x8a, 0xce, 0x27, 0x33,
0xda, 0x1b, 0xf2, 0xe6, 0x0f, 0x24, 0xcd, 0xd9, 0x30, 0xf1, 0x18, 0x0c, 0xe5,
0xa1, 0x48, 0x5c, 0xb5, 0x74, 0x9d, 0x89, 0x60, 0x01, 0xe8, 0xfc, 0x15, 0xd4,
0x3d, 0x29, 0xc0, 0x84, 0x6d, 0x79, 0x90, 0x51, 0xb8, 0xac, 0x45, 0xfd, 0x14,
0x00, 0xe9, 0x28, 0xc1, 0xd5, 0x3c, 0x78, 0x91, 0x85, 0x6c, 0xad, 0x44, 0x50,
0xb9, 0xd8, 0x31, 0x25, 0xcc, 0x0d, 0xe4, 0xf0, 0x19, 0x5d, 0xb4, 0xa0, 0x49,
0x88, 0x61, 0x75, 0x9c, 0xb7, 0x5e, 0x4a, 0xa3, 0x62, 0x8b, 0x9f, 0x76, 0x32,
0xdb, 0xcf, 0x26, 0xe7, 0x0e, 0x1a, 0xf3, 0x92, 0x7b, 0x6f, 0x86, 0x47, 0xae,
0xba, 0x53, 0x17, 0xfe, 0xea, 0x03, 0xc2, 0x2b, 0x3f, 0xd6, 0x69, 0x80, 0x94,
0x7d, 0xbc, 0x55, 0x41, 0xa8, 0xec, 0x05, 0x11, 0xf8, 0x39, 0xd0, 0xc4, 0x2d,
0x4c, 0xa5, 0xb1, 0x58, 0x99, 0x70, 0x64, 0x8d, 0xc9, 0x20, 0x34, 0xdd, 0x1c,
0xf5, 0xe1, 0x08, 0x23, 0xca, 0xde, 0x37, 0xf6, 0x1f, 0x0b, 0xe2, 0xa6, 0x4f,
0x5b, 0xb2, 0x73, 0x9a, 0x8e, 0x67, 0x06, 0xef, 0xfb, 0x12, 0xd3, 0x3a, 0x2e,
0xc7, 0x83, 0x6a, 0x7e, 0x97, 0x56, 0xbf, 0xab, 0x42},
{0xd1, 0xdf, 0xcd, 0xc3, 0xe9, 0xe7, 0xf5, 0xfb, 0xa1, 0xaf, 0xbd, 0xb3, 0x99,
0x97, 0x85, 0x8b, 0x31, 0x3f, 0x2d, 0x23, 0x09, 0x07, 0x15, 0x1b, 0x41, 0x4f,
0x5d, 0x53, 0x79, 0x77, 0x65, 0x6b, 0x3e, 0x30, 0x22, 0x2c, 0x06, 0x08, 0x1a,
0x14, 0x4e, 0x40, 0x52, 0x5c, 0x76, 0x78, 0x6a, 0x64, 0xde, 0xd0, 0xc2, 0xcc,
0xe6, 0xe8, 0xfa, 0xf4, 0xae, 0xa0, 0xb2, 0xbc, 0x96, 0x98, 0x8a, 0x84, 0x20,
0x2e, 0x3c, 0x32, 0x18, 0x16, 0x04, 0x0a, 0x50, 0x5e, 0x4c, 0x42, 0x68, 0x66,
0x74, 0x7a, 0xc0, 0xce, 0xdc, 0xd2, 0xf8, 0xf6, 0xe4, 0xea, 0xb0, 0xbe, 0xac,
0xa2, 0x88, 0x86, 0x94, 0x9a, 0xcf, 0xc1, 0xd3, 0xdd, 0xf7, 0xf9, 0xeb, 0xe5,
0xbf, 0xb1, 0xa3, 0xad, 0x87, 0x89, 0x9b, 0x95, 0x2f, 0x21, 0x33, 0x3d, 0x17,
0x19, 0x0b, 0x05, 0x5f, 0x51, 0x43, 0x4d, 0x67, 0x69, 0x7b, 0x75, 0x1c, 0x12,
0x00, 0x0e, 0x24, 0x2a, 0x38, 0x36, 0x6c, 0x62, 0x70, 0x7e, 0x54, 0x5a, 0x48,
0x46, 0xfc, 0xf2, 0xe0, 0xee, 0xc4, 0xca, 0xd8, 0xd6, 0x8c, 0x82, 0x90, 0x9e,
0xb4, 0xba, 0xa8, 0xa6, 0xf3, 0xfd, 0xef, 0xe1, 0xcb, 0xc5, 0xd7, 0xd9, 0x83,
0x8d, 0x9f, 0x91, 0xbb, 0xb5, 0xa7, 0xa9, 0x13, 0x1d, 0x0f, 0x01, 0x2b, 0x25,
0x37, 0x39, 0x63, 0x6d, 0x7f, 0x71, 0x5b, 0x55, 0x47, 0x49, 0xed, 0xe3, 0xf1,
0xff, 0xd5, 0xdb, 0xc9, 0xc7, 0x9d, 0x93, 0x81, 0x8f, 0xa5, 0xab, 0xb9, 0xb7,
0x0d, 0x03, 0x11, 0x1f, 0x35, 0x3b, 0x29, 0x27, 0x7d, 0x73, 0x61, 0x6f, 0x45,
0x4b, 0x59, 0x57, 0x02, 0x0c, 0x1e, 0x10, 0x3a, 0x34, 0x26, 0x28, 0x72, 0x7c,
0x6e, 0x60, 0x4a, 0x44, 0x56, 0x58, 0xe2, 0xec, 0xfe, 0xf0, 0xda, 0xd4, 0xc6,
0xc8, 0x92, 0x9c, 0x8e, 0x80, 0xaa, 0xa4, 0xb6, 0xb8},
{0x84, 0x31, 0xc1, 0x74, 0x0e, 0xbb, 0x4b, 0xfe, 0xbf, 0x0a, 0xfa, 0x4f, 0x35,
0x80, 0x70, 0xc5, 0xf2, 0x47, 0xb7, 0x02, 0x78, 0xcd, 0x3d, 0x88, 0xc9, 0x7c,
0x8c, 0x39, 0x43, 0xf6, 0x06, 0xb3, 0x68, 0xdd, 0x2d, 0x98, 0xe2, 0x57, 0xa7,
0x12, 0x53, 0xe6, 0x16, 0xa3, 0xd9, 0x6c, 0x9c, 0x29, 0x1e, 0xab, 0x5b, 0xee,
0x94, 0x21, 0xd1, 0x64, 0x25, 0x90, 0x60, 0xd5, 0xaf, 0x1a, 0xea, 0x5f, 0x73,
0xc6, 0x36, 0x83, 0xf9, 0x4c, 0xbc, 0x09, 0x48, 0xfd, 0x0d, 0xb8, 0xc2, 0x77,
0x87, 0x32, 0x05, 0xb0, 0x40, 0xf5, 0x8f, 0x3a, 0xca, 0x7f, 0x3e, 0x8b, 0x7b,
0xce, 0xb4, 0x01, 0xf1, 0x44, 0x9f, 0x2a, 0xda, 0x6f, 0x15, 0xa0, 0x50, 0xe5,
0xa4, 0x11, 0xe1, 0x54, 0x2e, 0x9b, 0x6b, 0xde, 0xe9, 0x5c, 0xac, 0x19, 0x63,
0xd6, 0x26, 0x93, 0xd2, 0x67, 0x97, 0x22, 0x58, 0xed, 0x1d, 0xa8, 0x45, 0xf0,
0x00, 0xb5, 0xcf, 0x7a, 0x8a, 0x3f, 0x7e, 0xcb, 0x3b, 0x8e, 0xf4, 0x41, 0xb1,
0x04, 0x33, 0x86, 0x76, 0xc3, 0xb9, 0x0c, 0xfc, 0x49, 0x08, 0xbd, 0x4d, 0xf8,
0x82, 0x37, 0xc7, 0x72, 0xa9, 0x1c, 0xec, 0x59, 0x23, 0x96, 0x66, 0xd3, 0x92,
0x27, 0xd7, 0x62, 0x18, 0xad, 0x5d, 0xe8, 0xdf, 0x6a, 0x9a, 0x2f, 0x55, 0xe0,
0x10, 0xa5, 0xe4, 0x51, 0xa1, 0x14, 0x6e, 0xdb, 0x2b, 0x9e, 0xb2, 0x07, 0xf7,
0x42, 0x38, 0x8d, 0x7d, 0xc8, 0x89, 0x3c, 0xcc, 0x79, 0x03, 0xb6, 0x46, 0xf3,
0xc4, 0x71, 0x81, 0x34, 0x4e, 0xfb, 0x0b, 0xbe, 0xff, 0x4a, 0xba, 0x0f, 0x75,
0xc0, 0x30, 0x85, 0x5e, 0xeb, 0x1b, 0xae, 0xd4, 0x61, 0x91, 0x24, 0x65, 0xd0,
0x20, 0x95, 0xef, 0x5a, 0xaa, 0x1f, 0x28, 0x9d, 0x6d, 0xd8, 0xa2, 0x17, 0xe7,
0x52, 0x13, 0xa6, 0x56, 0xe3, 0x99, 0x2c, 0xdc, 0x69}
};
// This code assumes that integers are stored little-endian.
uint8_t crc8autosar_word(uint8_t crc, void const *mem, size_t len) {
unsigned char const *data = mem;
if (data == NULL)
return 0;
while (len && ((ptrdiff_t)data & 0x3)) {
len--;
crc = table_byte[crc ^ *data++];
}
size_t n = len >> 2;
for (size_t i = 0; i < n; i++) {
uint32_t word = crc ^ ((uint32_t const *)data)[i];
crc = table_word[3][word & 0xff] ^
table_word[2][(word >> 8) & 0xff] ^
table_word[1][(word >> 16) & 0xff] ^
table_word[0][word >> 24];
}
data += n << 2;
len &= 3;
while (len) {
len--;
crc = table_byte[crc ^ *data++];
}
return crc;
}
此代码的惯例是，当使用 mem == NULL 调用时，crc 将被忽略并返回初始 CRC，即空消息的 CRC。
我需要一个高度优化的 CRC8 算法。我的目标是开发一个从 CRC16 / CRC32 已知的 Slice-by-4 解决方案。我想让代码尽可能接近我在下面发布的用于 CRC16 的解决方案。
生成CRC LookUp的函数-Table:
void crcspeed16_genTable(crcfn16 crcfn, uint16_t table[8][256]) {
uint16_t crc;
/* generate CRCs for all single byte sequences */
for (int n = 0; n < 256; n++) {
table[0][n] = crcfn(0, &n, 1);
}
/* generate nested CRC table for future slice-by-8 lookup */
for (int n = 0; n < 256; n++) {
crc = table[0][n];
for (int k = 1; k < 8; k++) {
crc = table[0][(crc >> 8) & 0xff] ^ (crc << 8);
table[k][n] = crc;
}
}
}
uint16_t crc16(uint16_t crc, const void *in_data, uint64_t len) {
const uint8_t *data = (const uint8_t*) in_data;
for (uint64_t i = 0; i < len; i++) {
crc = crc ^ (data[i] << 8);
for (int j = 0; j < 8; j++) {
if (crc & 0x8000) {
crc = (crc << 1) ^ CRC16_POLYNOMINAL;
} else {
crc = (crc << 1);
}
}
}
return crc;
}
调用生成 table:
crcspeed16_genTable(crc16, crc16_LUT);
基于Slice-by-4解生成CRC16的函数：
uint16_t crc16_slice4(const void *buf, size_t len, uint16_t initialValue, uint16_t XOR_OUT) {
uint16_t crc = initialValue;
unsigned char *next = (unsigned char *)buf;
// process individual bytes until we reach an 8-byte aligned pointer
while (len && ((uintptr_t)next & 7) != 0) {
crc = crc16_LUT[0][((crc >> 8) ^ *next++) & 0xff] ^ (crc << 8);
len--;
}
// fast middle processing, 4 bytes (aligned!) per loop */
while (len >= 4) {
uint32_t n = *(uint32_t *)next;
crc = crc16_LUT[3][(n & 0xff) ^ ((crc >> 8) & 0xff)] ^
crc16_LUT[2][((n >> 8) & 0xff) ^ (crc & 0xff)] ^
crc16_LUT[1][(n >> 16) & 0xff] ^
crc16_LUT[0][n >> 24];
next += 4;
len -= 4;
}
// process remaining bytes (can't be larger than 8)
while (len) {
crc = crc16_LUT[0][((crc >> 8) ^ *next++) & 0xff] ^ (crc << 8);
len--;
}
return crc ^ XOR_OUT;
}
我的目标是使算法适用于 CRC8 和 CRC4。到目前为止，我所做的是将 LUT 生成器更改为生成 LUT 的有效第一行，并根据此 LUT 数据处理有效的 CRC。我未能调整中间部分来计算和利用 CRC 的全部潜力 table。
针对 CRC8 的适配函数（未完全发挥作用）： Table代数：
void crcspeed8_genTable(crcfn8 crcfn, uint8_t table[8][256]) {
uint16_t crc;
/* generate CRCs for all single byte sequences */
for (int n = 0; n < 256; n++) {
table[0][n] = crcfn(0, &n, 1);
}
/* generate nested CRC table for future slice-by-8 lookup */
for (int n = 0; n < 256; n++) {
crc = table[0][n];
for (int k = 1; k < 8; k++) {
//crc = table[0][crc] ^ crc;
crc = table[0][(crc >> 4) & 0x0f] ^ (crc << 4);
table[k][n] = crc;
}
}
}
uint8_t crc8(uint8_t crc, const void *in_data, uint64_t len) {
const uint8_t *data = (const uint8_t*) in_data;
for (uint64_t i = 0; i < len; i++) {
//crc = crc ^ (data[i] << 8);
crc = crc ^ data[i];
for (int j = 0; j < 8; j++) {
if (crc & 0x80) {
crc = (crc << 1) ^ CRC8_POLYNOMINAL;
} else {
crc = (crc << 1);
}
}
}
return crc;
}
CRC计算：
uint8_t crc8_slice4(const void *buf, size_t len, uint8_t initialValue, uint8_t XOR_OUT) {
uint8_t crc = initialValue;
unsigned char *next = (unsigned char *)buf;
// process individual bytes until we reach an 8-byte aligned pointer
while (len && ((uintptr_t)next & 7) != 0) {
printf("\nAlign processing");
crc = crc8_LUT[0][crc ^ *next++];
len--;
}
//fast middle processing, 4 bytes (aligned!) per loop
while (len >= 4) {
printf("\nSlice processing");
uint32_t n = *(uint32_t *)next;
//This part should be adopted to work for CRC8
/*crc = crc8_LUT[3][(n & 0xff) ^ crc] ^
crc8_LUT[2][(n >> 8) & 0xff] ^
crc8_LUT[1][(n >> 16) & 0xff] ^
crc8_LUT[0][n >> 24]; */
uint32_t n0 = (n & 0xFF) ^ crc;
uint32_t n1 = (n >> 8) & 0xFF;
uint32_t n2 = (n >> 16) & 0xFF;
uint32_t n3 = (n >> 24);
//Working multi step for CRC 4 only using first row of LUT
uint8_t crc0 = crc8_LUT[0][crc ^ n0];
uint8_t crc1 = crc8_LUT[0][crc0 ^ n1];
uint8_t crc2 = crc8_LUT[0][crc1 ^ n2];
uint8_t crc3 = crc8_LUT[0][crc2 ^ n3];
crc = crc3;
next += 4;
len -= 4;
}
// process remaining bytes (can't be larger than 8)
while (len) {
printf("\nRemain processing");
crc = crc8_LUT[0][crc ^ *next++];
len--;
}
return crc ^ XOR_OUT;
}
我试图将函数更改为适用于 CRC8，但我无法弄清楚中间部分。解释为各种 CRC (4/8/16/24/32...) 生成 Look-Up-Tables 的一般方法的解决方案也将受到高度赞赏。 感谢您给我指明正确的方向。
您没有提供您的多项式、初始值或最终异或。有了这些（并且你的情况下的 CRC 没有反映出来），你可以使用 crcany 为你生成代码。
这里有一个 little-endian slice-by-4 的例子：
#include <stddef.h>
#include <stdint.h>
#define table_byte table_word[0]
static uint8_t const table_word[][256] = {
{0xbd, 0x92, 0xe3, 0xcc, 0x01, 0x2e, 0x5f, 0x70, 0xea, 0xc5, 0xb4, 0x9b, 0x56,
0x79, 0x08, 0x27, 0x13, 0x3c, 0x4d, 0x62, 0xaf, 0x80, 0xf1, 0xde, 0x44, 0x6b,
0x1a, 0x35, 0xf8, 0xd7, 0xa6, 0x89, 0xce, 0xe1, 0x90, 0xbf, 0x72, 0x5d, 0x2c,
0x03, 0x99, 0xb6, 0xc7, 0xe8, 0x25, 0x0a, 0x7b, 0x54, 0x60, 0x4f, 0x3e, 0x11,
0xdc, 0xf3, 0x82, 0xad, 0x37, 0x18, 0x69, 0x46, 0x8b, 0xa4, 0xd5, 0xfa, 0x5b,
0x74, 0x05, 0x2a, 0xe7, 0xc8, 0xb9, 0x96, 0x0c, 0x23, 0x52, 0x7d, 0xb0, 0x9f,
0xee, 0xc1, 0xf5, 0xda, 0xab, 0x84, 0x49, 0x66, 0x17, 0x38, 0xa2, 0x8d, 0xfc,
0xd3, 0x1e, 0x31, 0x40, 0x6f, 0x28, 0x07, 0x76, 0x59, 0x94, 0xbb, 0xca, 0xe5,
0x7f, 0x50, 0x21, 0x0e, 0xc3, 0xec, 0x9d, 0xb2, 0x86, 0xa9, 0xd8, 0xf7, 0x3a,
0x15, 0x64, 0x4b, 0xd1, 0xfe, 0x8f, 0xa0, 0x6d, 0x42, 0x33, 0x1c, 0x5e, 0x71,
0x00, 0x2f, 0xe2, 0xcd, 0xbc, 0x93, 0x09, 0x26, 0x57, 0x78, 0xb5, 0x9a, 0xeb,
0xc4, 0xf0, 0xdf, 0xae, 0x81, 0x4c, 0x63, 0x12, 0x3d, 0xa7, 0x88, 0xf9, 0xd6,
0x1b, 0x34, 0x45, 0x6a, 0x2d, 0x02, 0x73, 0x5c, 0x91, 0xbe, 0xcf, 0xe0, 0x7a,
0x55, 0x24, 0x0b, 0xc6, 0xe9, 0x98, 0xb7, 0x83, 0xac, 0xdd, 0xf2, 0x3f, 0x10,
0x61, 0x4e, 0xd4, 0xfb, 0x8a, 0xa5, 0x68, 0x47, 0x36, 0x19, 0xb8, 0x97, 0xe6,
0xc9, 0x04, 0x2b, 0x5a, 0x75, 0xef, 0xc0, 0xb1, 0x9e, 0x53, 0x7c, 0x0d, 0x22,
0x16, 0x39, 0x48, 0x67, 0xaa, 0x85, 0xf4, 0xdb, 0x41, 0x6e, 0x1f, 0x30, 0xfd,
0xd2, 0xa3, 0x8c, 0xcb, 0xe4, 0x95, 0xba, 0x77, 0x58, 0x29, 0x06, 0x9c, 0xb3,
0xc2, 0xed, 0x20, 0x0f, 0x7e, 0x51, 0x65, 0x4a, 0x3b, 0x14, 0xd9, 0xf6, 0x87,
0xa8, 0x32, 0x1d, 0x6c, 0x43, 0x8e, 0xa1, 0xd0, 0xff},
{0xfa, 0x13, 0x07, 0xee, 0x2f, 0xc6, 0xd2, 0x3b, 0x7f, 0x96, 0x82, 0x6b, 0xaa,
0x43, 0x57, 0xbe, 0xdf, 0x36, 0x22, 0xcb, 0x0a, 0xe3, 0xf7, 0x1e, 0x5a, 0xb3,
0xa7, 0x4e, 0x8f, 0x66, 0x72, 0x9b, 0xb0, 0x59, 0x4d, 0xa4, 0x65, 0x8c, 0x98,
0x71, 0x35, 0xdc, 0xc8, 0x21, 0xe0, 0x09, 0x1d, 0xf4, 0x95, 0x7c, 0x68, 0x81,
0x40, 0xa9, 0xbd, 0x54, 0x10, 0xf9, 0xed, 0x04, 0xc5, 0x2c, 0x38, 0xd1, 0x6e,
0x87, 0x93, 0x7a, 0xbb, 0x52, 0x46, 0xaf, 0xeb, 0x02, 0x16, 0xff, 0x3e, 0xd7,
0xc3, 0x2a, 0x4b, 0xa2, 0xb6, 0x5f, 0x9e, 0x77, 0x63, 0x8a, 0xce, 0x27, 0x33,
0xda, 0x1b, 0xf2, 0xe6, 0x0f, 0x24, 0xcd, 0xd9, 0x30, 0xf1, 0x18, 0x0c, 0xe5,
0xa1, 0x48, 0x5c, 0xb5, 0x74, 0x9d, 0x89, 0x60, 0x01, 0xe8, 0xfc, 0x15, 0xd4,
0x3d, 0x29, 0xc0, 0x84, 0x6d, 0x79, 0x90, 0x51, 0xb8, 0xac, 0x45, 0xfd, 0x14,
0x00, 0xe9, 0x28, 0xc1, 0xd5, 0x3c, 0x78, 0x91, 0x85, 0x6c, 0xad, 0x44, 0x50,
0xb9, 0xd8, 0x31, 0x25, 0xcc, 0x0d, 0xe4, 0xf0, 0x19, 0x5d, 0xb4, 0xa0, 0x49,
0x88, 0x61, 0x75, 0x9c, 0xb7, 0x5e, 0x4a, 0xa3, 0x62, 0x8b, 0x9f, 0x76, 0x32,
0xdb, 0xcf, 0x26, 0xe7, 0x0e, 0x1a, 0xf3, 0x92, 0x7b, 0x6f, 0x86, 0x47, 0xae,
0xba, 0x53, 0x17, 0xfe, 0xea, 0x03, 0xc2, 0x2b, 0x3f, 0xd6, 0x69, 0x80, 0x94,
0x7d, 0xbc, 0x55, 0x41, 0xa8, 0xec, 0x05, 0x11, 0xf8, 0x39, 0xd0, 0xc4, 0x2d,
0x4c, 0xa5, 0xb1, 0x58, 0x99, 0x70, 0x64, 0x8d, 0xc9, 0x20, 0x34, 0xdd, 0x1c,
0xf5, 0xe1, 0x08, 0x23, 0xca, 0xde, 0x37, 0xf6, 0x1f, 0x0b, 0xe2, 0xa6, 0x4f,
0x5b, 0xb2, 0x73, 0x9a, 0x8e, 0x67, 0x06, 0xef, 0xfb, 0x12, 0xd3, 0x3a, 0x2e,
0xc7, 0x83, 0x6a, 0x7e, 0x97, 0x56, 0xbf, 0xab, 0x42},
{0xd1, 0xdf, 0xcd, 0xc3, 0xe9, 0xe7, 0xf5, 0xfb, 0xa1, 0xaf, 0xbd, 0xb3, 0x99,
0x97, 0x85, 0x8b, 0x31, 0x3f, 0x2d, 0x23, 0x09, 0x07, 0x15, 0x1b, 0x41, 0x4f,
0x5d, 0x53, 0x79, 0x77, 0x65, 0x6b, 0x3e, 0x30, 0x22, 0x2c, 0x06, 0x08, 0x1a,
0x14, 0x4e, 0x40, 0x52, 0x5c, 0x76, 0x78, 0x6a, 0x64, 0xde, 0xd0, 0xc2, 0xcc,
0xe6, 0xe8, 0xfa, 0xf4, 0xae, 0xa0, 0xb2, 0xbc, 0x96, 0x98, 0x8a, 0x84, 0x20,
0x2e, 0x3c, 0x32, 0x18, 0x16, 0x04, 0x0a, 0x50, 0x5e, 0x4c, 0x42, 0x68, 0x66,
0x74, 0x7a, 0xc0, 0xce, 0xdc, 0xd2, 0xf8, 0xf6, 0xe4, 0xea, 0xb0, 0xbe, 0xac,
0xa2, 0x88, 0x86, 0x94, 0x9a, 0xcf, 0xc1, 0xd3, 0xdd, 0xf7, 0xf9, 0xeb, 0xe5,
0xbf, 0xb1, 0xa3, 0xad, 0x87, 0x89, 0x9b, 0x95, 0x2f, 0x21, 0x33, 0x3d, 0x17,
0x19, 0x0b, 0x05, 0x5f, 0x51, 0x43, 0x4d, 0x67, 0x69, 0x7b, 0x75, 0x1c, 0x12,
0x00, 0x0e, 0x24, 0x2a, 0x38, 0x36, 0x6c, 0x62, 0x70, 0x7e, 0x54, 0x5a, 0x48,
0x46, 0xfc, 0xf2, 0xe0, 0xee, 0xc4, 0xca, 0xd8, 0xd6, 0x8c, 0x82, 0x90, 0x9e,
0xb4, 0xba, 0xa8, 0xa6, 0xf3, 0xfd, 0xef, 0xe1, 0xcb, 0xc5, 0xd7, 0xd9, 0x83,
0x8d, 0x9f, 0x91, 0xbb, 0xb5, 0xa7, 0xa9, 0x13, 0x1d, 0x0f, 0x01, 0x2b, 0x25,
0x37, 0x39, 0x63, 0x6d, 0x7f, 0x71, 0x5b, 0x55, 0x47, 0x49, 0xed, 0xe3, 0xf1,
0xff, 0xd5, 0xdb, 0xc9, 0xc7, 0x9d, 0x93, 0x81, 0x8f, 0xa5, 0xab, 0xb9, 0xb7,
0x0d, 0x03, 0x11, 0x1f, 0x35, 0x3b, 0x29, 0x27, 0x7d, 0x73, 0x61, 0x6f, 0x45,
0x4b, 0x59, 0x57, 0x02, 0x0c, 0x1e, 0x10, 0x3a, 0x34, 0x26, 0x28, 0x72, 0x7c,
0x6e, 0x60, 0x4a, 0x44, 0x56, 0x58, 0xe2, 0xec, 0xfe, 0xf0, 0xda, 0xd4, 0xc6,
0xc8, 0x92, 0x9c, 0x8e, 0x80, 0xaa, 0xa4, 0xb6, 0xb8},
{0x84, 0x31, 0xc1, 0x74, 0x0e, 0xbb, 0x4b, 0xfe, 0xbf, 0x0a, 0xfa, 0x4f, 0x35,
0x80, 0x70, 0xc5, 0xf2, 0x47, 0xb7, 0x02, 0x78, 0xcd, 0x3d, 0x88, 0xc9, 0x7c,
0x8c, 0x39, 0x43, 0xf6, 0x06, 0xb3, 0x68, 0xdd, 0x2d, 0x98, 0xe2, 0x57, 0xa7,
0x12, 0x53, 0xe6, 0x16, 0xa3, 0xd9, 0x6c, 0x9c, 0x29, 0x1e, 0xab, 0x5b, 0xee,
0x94, 0x21, 0xd1, 0x64, 0x25, 0x90, 0x60, 0xd5, 0xaf, 0x1a, 0xea, 0x5f, 0x73,
0xc6, 0x36, 0x83, 0xf9, 0x4c, 0xbc, 0x09, 0x48, 0xfd, 0x0d, 0xb8, 0xc2, 0x77,
0x87, 0x32, 0x05, 0xb0, 0x40, 0xf5, 0x8f, 0x3a, 0xca, 0x7f, 0x3e, 0x8b, 0x7b,
0xce, 0xb4, 0x01, 0xf1, 0x44, 0x9f, 0x2a, 0xda, 0x6f, 0x15, 0xa0, 0x50, 0xe5,
0xa4, 0x11, 0xe1, 0x54, 0x2e, 0x9b, 0x6b, 0xde, 0xe9, 0x5c, 0xac, 0x19, 0x63,
0xd6, 0x26, 0x93, 0xd2, 0x67, 0x97, 0x22, 0x58, 0xed, 0x1d, 0xa8, 0x45, 0xf0,
0x00, 0xb5, 0xcf, 0x7a, 0x8a, 0x3f, 0x7e, 0xcb, 0x3b, 0x8e, 0xf4, 0x41, 0xb1,
0x04, 0x33, 0x86, 0x76, 0xc3, 0xb9, 0x0c, 0xfc, 0x49, 0x08, 0xbd, 0x4d, 0xf8,
0x82, 0x37, 0xc7, 0x72, 0xa9, 0x1c, 0xec, 0x59, 0x23, 0x96, 0x66, 0xd3, 0x92,
0x27, 0xd7, 0x62, 0x18, 0xad, 0x5d, 0xe8, 0xdf, 0x6a, 0x9a, 0x2f, 0x55, 0xe0,
0x10, 0xa5, 0xe4, 0x51, 0xa1, 0x14, 0x6e, 0xdb, 0x2b, 0x9e, 0xb2, 0x07, 0xf7,
0x42, 0x38, 0x8d, 0x7d, 0xc8, 0x89, 0x3c, 0xcc, 0x79, 0x03, 0xb6, 0x46, 0xf3,
0xc4, 0x71, 0x81, 0x34, 0x4e, 0xfb, 0x0b, 0xbe, 0xff, 0x4a, 0xba, 0x0f, 0x75,
0xc0, 0x30, 0x85, 0x5e, 0xeb, 0x1b, 0xae, 0xd4, 0x61, 0x91, 0x24, 0x65, 0xd0,
0x20, 0x95, 0xef, 0x5a, 0xaa, 0x1f, 0x28, 0x9d, 0x6d, 0xd8, 0xa2, 0x17, 0xe7,
0x52, 0x13, 0xa6, 0x56, 0xe3, 0x99, 0x2c, 0xdc, 0x69}
};
// This code assumes that integers are stored little-endian.
uint8_t crc8autosar_word(uint8_t crc, void const *mem, size_t len) {
unsigned char const *data = mem;
if (data == NULL)
return 0;
while (len && ((ptrdiff_t)data & 0x3)) {
len--;
crc = table_byte[crc ^ *data++];
}
size_t n = len >> 2;
for (size_t i = 0; i < n; i++) {
uint32_t word = crc ^ ((uint32_t const *)data)[i];
crc = table_word[3][word & 0xff] ^
table_word[2][(word >> 8) & 0xff] ^
table_word[1][(word >> 16) & 0xff] ^
table_word[0][word >> 24];
}
data += n << 2;
len &= 3;
while (len) {
len--;
crc = table_byte[crc ^ *data++];
}
return crc;
}
此代码的惯例是，当使用 mem == NULL 调用时，crc 将被忽略并返回初始 CRC，即空消息的 CRC。