/* Table of CRCs of all 8-bit messages. */
unsigned long crc_table[256];
/* Flag: has the table been computed? Initially false. */
int crc_table_computed = 0;
/* Make the table for a fast CRC. */
void make_crc_table(void)
{
unsigned long c;
int n, k;
for (n=0; n<256; n++)
{
c = (unsigned long) n;
for (k=0; k<8; k++)
{
if (c & 1)
c = 0xedb88320L ^ (c >> 1);
else
c = c >> 1;
}
crc_table[n] = c;
}
crc_table_computed = 1;
}
/* Update a running CRC with the bytes buf[0..len-1]--the CRC
should be initialized to all 1's, and the transmitted value
is the 1's complement of the final running CRC (see the
crc() routine below)). */
unsigned long update_crc(unsigned long crc, unsigned char *buf,
int len)
{
unsigned long c = crc;
int n;
if (!crc_table_computed)
make_crc_table(); //如果crc表还没有生成则生成
for (n=0; n<len; n++)
{
c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
}
return c;
}
/* Return the CRC of the bytes buf[0..len-1]. */
unsigned long crc(unsigned char *buf, int len)
{
return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
}
//要CRC的数据
unsigned char data[43] = {
0x50, 0x4C, 0x54, 0x45, 0xFF, 0xFF, 0x00, 0xFF, 0xED, 0x00, 0xFF, 0xC1, 0x00, 0xFF, 0x99, 0x00,
0xFF, 0x66, 0x00, 0xFF, 0x3B, 0x00, 0xFF, 0x0F, 0x00, 0xE2, 0x00, 0x15, 0xB7, 0x00, 0x34, 0x8B,
0x00, 0x54, 0x60, 0x00, 0x73, 0x33, 0x00, 0x99, 0x09, 0x00, 0xB2
};
void main()
{
//开始crc效验
unsigned long val = crc(data, sizeof(data));
}
