On Tuesday, September 2, 2014 9:24:54 PM UTC+3, Peter Otten wrote:
> dream4s...@gmail.com wrote:
>
>
>
> > 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:
>
>
>
> ctypes is for interfacing with C; don't use it in regular code.
>
>
>
> > 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);
>
> > }
>
>
>
> A near-literal translation would be:
>
>
>
> def calc_crc(data):
>
> crc = 0
>
> for work in data:
>
> for i in range(8):
>
> if (crc & 1) ^ (work & 1):
>
> crc >>= 1
>
> crc ^= 0x8408
>
> else:
>
> crc >>= 1
>
> work >>= 1
>
> return crc
>
>
>
> I don't see any operation where the "unboundedness" of Python's integer type
>
> could be a problem -- but no guarantees.
this doesn't work
calc_crc(b'\x00\x00\x34\x35\x38\x35')
rsult 0x9f41 , but c function gives us 0x8c40
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