crc校验

u16 GetCheckCode(unsigned char *ptr, unsigned char len)
{
u16 Code;
u8 i,j;

Code = 0xffff;
for(i=0;i<len;i++)
{
Code ^= ptr[i];
for(j=0;j<8;j++)
{
if(Code&0x0001)
{
Code >>= 1;
Code ^= 0xa001;
}
else
{
Code >>= 1;
}
}
}
return (Code);
}