# crc algorithm

dream4soul at gmail.com dream4soul at gmail.com
Tue Sep 2 19:50:17 CEST 2014

```Dear all,

I have trouble to implement crc algorithm in python 3.3

c version work  perfect. I try to use bytes, int and c_types without any success
can some who help me:

c version:

unsigned short calc_crc(const void *p_dat, int l_dat){
unsigned char *dat_ptr;
int loopc;
unsigned short crc_dat;
unsigned char c_work;

dat_ptr = (unsigned char*)p_dat;
crc_dat = 0x0000;
for (; l_dat > 0; l_dat--)
{
c_work = *(dat_ptr++);
for (loopc = 0; loopc < 8; loopc++)
{
if ((((unsigned char )(crc_dat & 0x0001)) ^ (c_work & 0x01)) == 0x01)
{
crc_dat >>=1 ;
crc_dat ^=0x8408;
} else {
crc_dat >>=1;

}
c_work >>=1;
}
}
return(crc_dat);
}

python tries:

def calc_crc():
crc_dat = c_ushort(0x0001)

data = [0x00,0x00,0x34,0x35,0x38,0x35]
for x in range(len(data)):
pass
c_work = c_ubyte(data[x])
#print(c_work)
for x in range(8):
pass
if (c_ubyte(crc_dat.value & c_ushort(0x0001).value).value ^ c_ubyte(c_work.value & c_ubyte(0x01).value).value) == c_ubyte(0x01):
crc_dat.value >>=1
crc_dat.value ^=0x8408

else:
crc_dat.value >>=1

c_work.value >>=1
print(crc_dat)

print(crc_dat.value)
pass

```