CRC alogrithism for AC3, What's the difference between generic CRC and ac3's Options

[kevin.wang]

Hi all

I want to unstandard how ac3's CRC work, because it seems the CRC for AC3 is different from the generic one.

AC3 use X^16+X^15+X^2+1 as its poly (0x8005)

the generic alogrithism is:

unsigned short syndrom=0;

for(i=0;i<words; i++){
syndrom = ((syndrom << 8) & 0xff00) ^ crctab[((syndrom>>8)&0xff)^( (data[i]>>8)&0xff) ];
syndrom = ((syndrom << 8) & 0xff00) ^ crctab[((syndrom>>8)&0xff)^( (data[i])&0xff) ];
}

for ac3:
unsigned short syndrom=0;

for(i=0;i<words; i++){
syndrom = ((syndrom << 8) & 0xff00) ^ ((data[i]>>8)&0xff) ^ crctab[(syndrom>>8)&0xff];
syndrom = ((syndrom << 8) & 0xff00) ^ ((data[i])&0xff) ^crctab[(syndrom>>8)&0xff];
}

Who can tell me how to apply generic crc to ac3?