Re: [boost] CRC Computation Problem (was: Re: Review Request: CRC)

From: Joel Young (jdy_at_[hidden])
Date: 2001-02-23 17:29:25

x^6+x^5+x^3+x^2 / x+1   should give a remainder of zero unless I screwed
up.

So the codeword for transmission to get zero remainder should then be
the original message.

joel
--------
From: Daryle Walker <darylew_at_[hidden]>
Date: Fri, 23 Feb 2001 15:09:12 -0500
  To: <boost_at_[hidden]>
Subj: [boost] CRC Computation Problem (was: Re: Review Request: CRC)

on 2/22/01 11:20 AM, Joel Young at jdy_at_[hidden] wrote:

> Question on the usage of the crc:
> 
> I run the following code:
> 
> {
>   boost::crc_slow<1> crc_1(1,0,0,false,false);
> 
>   std::bitset<7> t = 108; //("1101100");
>   std::cerr << t << std::endl;
>   for (int i=t.size()-1; i>=0; --i)
>       crc_1( t.test(i) );
>   std::bitset<7> s = *crc_1; //("1101100");
>   t |= *crc_1;
>   std::cerr << t << std::endl;
>   std::cerr << s << std::endl;
> }
> 
> And get this result:
> 
> 1101100
> 1111100
> 0010000
> 
> Indicating that the remainder returned by crc_1 is way to big.
> 
> Shouldn't the remainder be only one bit?  Or am I misunderstanding the
> process?

It is one bit, but it's not the lowest bit.  Since you specified only an
one-bit CRC, the answer should be one or zero.  I'll take a look.  By the
way, what is the CRC supposed to be?

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com
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